Refined discrete and empirical horizontal gradients in VLBI analysis

Science.gov (United States)

Landskron, Daniel; Böhm, Johannes

2018-02-01

Missing or incorrect consideration of azimuthal asymmetry of troposphere delays is a considerable error source in space geodetic techniques such as Global Navigation Satellite Systems (GNSS) or Very Long Baseline Interferometry (VLBI). So-called horizontal troposphere gradients are generally utilized for modeling such azimuthal variations and are particularly required for observations at low elevation angles. Apart from estimating the gradients within the data analysis, which has become common practice in space geodetic techniques, there is also the possibility to determine the gradients beforehand from different data sources than the actual observations. Using ray-tracing through Numerical Weather Models (NWMs), we determined discrete gradient values referred to as GRAD for VLBI observations, based on the standard gradient model by Chen and Herring (J Geophys Res 102(B9):20489-20502, 1997. https://doi.org/10.1029/97JB01739) and also for new, higher-order gradient models. These gradients are produced on the same data basis as the Vienna Mapping Functions 3 (VMF3) (Landskron and Böhm in J Geod, 2017.https://doi.org/10.1007/s00190-017-1066-2), so they can also be regarded as the VMF3 gradients as they are fully consistent with each other. From VLBI analyses of the Vienna VLBI and Satellite Software (VieVS), it becomes evident that baseline length repeatabilities (BLRs) are improved on average by 5% when using a priori gradients GRAD instead of estimating the gradients. The reason for this improvement is that the gradient estimation yields poor results for VLBI sessions with a small number of observations, while the GRAD a priori gradients are unaffected from this. We also developed a new empirical gradient model applicable for any time and location on Earth, which is included in the Global Pressure and Temperature 3 (GPT3) model. Although being able to describe only the systematic component of azimuthal asymmetry and no short-term variations at all, even these

Operational production of Geodetic Excitation Functions from EOP estimated values at ASI-CGS

Science.gov (United States)

Sciarretta, C.; Luceri, V.; Bianco, G.

2009-04-01

ASI-CGS is routinely providing geodetic excitation functions from its own estimated EOP values (at present SLR and VLBI; the current use of GPS EOP's is also planned as soon as this product will be fully operational) on the ASI geodetic web site (http://geodaf.mt.asi.it). This product has been generated and monitored (for ASI internal use only) in a long pre-operational phase (more than two years), including validation and testing. The daily geodetic excitation functions are now weekly updated along with the operational ASI SLR and VLBI EOP solutions and compared, whenever possible, with the atmospheric excitation functions available at the IERS SBAAM, under the IB and not-IB assumption, including the "wind" term. The work will present the available estimated geodetic function time series and its comparison with the relevant atmospheric excitation functions, deriving quantitative indicators on the quality of the estimates. The similarities as well as the discrepancies among the atmospheric and geodetic series will be analysed and commented, evaluating in particular the degree of correlation among the two estimated time series and the likelihood of a linear dependence hypothesis.

International VLBI Service for Geodesy and Astrometry 2007 Annual Report

Science.gov (United States)

Behrend, D. (Editor); Baver, K. D. (Editor)

2008-01-01

This volume of reports is the 2007 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2007 Annual Report documents the work of these IVS components over the period January 1, 2007 through December 31, 2007. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2007.

International VLBI Service for Geodesy and Astrometry 2008 Annual Report

Science.gov (United States)

Behrend, Dirk; Baver, Karen D.

2009-01-01

This volume of reports is the 2008 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2008 Annual Report documents the work of these IVS components over the period January 1, 2008 through December 31, 2008. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2008.

International VLBI Service for Geodesy and Astrometry 2011 Annual Report

Science.gov (United States)

Baver, Karen D. (Editor); Behrend, Dirk

2012-01-01

This volume of reports is the 2011 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2011 Annual Report documents the work of these IVS components over the period January 1, 2011 through December 31, 2011. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2011.

International VLBI Service for Geodesy and Astrometry 2005 Annual Report

Science.gov (United States)

Behrend, Dirk (Editor); Baver, Karen D. (Editor)

2006-01-01

This volume of reports is the 2005 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the components of IVS. The 2005 Annual Report documents the work of these IVS components over the period January 1, 2005 through December 31, 2005. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2005.

Earth orientation determinations by short duration VLBI observations

Science.gov (United States)

Nothnagel, Axel; Zhihan, Qian; Nicolson, George D.; Tomasi, Paolo

1994-03-01

In May 1989 and April 1990 the radio telescopes of the Wettzell Geodetic Fundamental Station in Germany and of the Shanghai Observatory near Seshan in China observed two series of daily VLBI experiments of short duration for precise determination of UT1. In 1990 a few experiments were complemented by the Hartebeesthoek Radio Astronomy Observatory in South Africa and the Medicina telescope of the Bologna Istituto di Radioastronomia in Italy. Employing the South African station together with the east-west baseline formed by the observatories of Seshan and Medicina permitted simultaneous determinations of UT1 and polar motion. Here we report on the results of these observations. Comparing the UT1 results with those of the IRIS Intensive series gives a clear indication of the absolute accuracy of such short duration VLBI measurements which is estimated to be of the order of ±60 µs.

NASA Space Geodesy Program: GSFC data analysis, 1992. Crustal Dynamics Project VLBI geodetic results, 1979 - 1991

Science.gov (United States)

Ryan, J. W.; Ma, C.; Caprette, D. S.

1993-01-01

The Goddard VLBI group reports the results of analyzing 1648 Mark 3 data sets acquired from fixed and mobile observing sites through the end of 1991, and available to the Crustal Dynamics Project. Two large solutions were used to obtain Earth rotation parameters, nutation offsets, radio source positions, site positions, site velocities, and baseline evolution. Site positions are tabulated on a yearly basis for 1979 to 1995, inclusive. Site velocities are presented in both geocentric Cartesian and topocentric coordinates. Baseline evolution is plotted for 200 baselines, and individual length determinations are presented for an additional 356 baselines. This report includes 155 quasar radio sources, 96 fixed stations and mobile sites, and 556 baselines.

An Improved Empirical Harmonic Model of the Celestial Intermediate Pole Offsets from a Global VLBI Solution

Science.gov (United States)

Belda, Santiago; Heinkelmann, Robert; Ferrándiz, José M.; Karbon, Maria; Nilsson, Tobias; Schuh, Harald

2017-10-01

Very Long Baseline Interferometry (VLBI) is the only space geodetic technique capable of measuring all the Earth orientation parameters (EOP) accurately and simultaneously. Modeling the Earth's rotational motion in space within the stringent consistency goals of the Global Geodetic Observing System (GGOS) makes VLBI observations essential for constraining the rotation theories. However, the inaccuracy of early VLBI data and the outdated products could cause non-compliance with these goals. In this paper, we perform a global VLBI analysis of sessions with different processing settings to determine a new set of empirical corrections to the precession offsets and rates, and to the amplitudes of a wide set of terms included in the IAU 2006/2000A precession-nutation theory. We discuss the results in terms of consistency, systematic errors, and physics of the Earth. We find that the largest improvements w.r.t. the values from IAU 2006/2000A precession-nutation theory are associated with the longest periods (e.g., 18.6-yr nutation). A statistical analysis of the residuals shows that the provided corrections attain an error reduction at the level of 15 μas. Additionally, including a Free Core Nutation (FCN) model into a priori Celestial Pole Offsets (CPOs) provides the lowest Weighted Root Mean Square (WRMS) of residuals. We show that the CPO estimates are quite insensitive to TRF choice, but slightly sensitive to the a priori EOP and the inclusion of different VLBI sessions. Finally, the remaining residuals reveal two apparent retrograde signals with periods of nearly 2069 and 1034 days.

The impacts of source structure on geodetic parameters demonstrated by the radio source 3C371

Science.gov (United States)

Xu, Ming H.; Heinkelmann, Robert; Anderson, James M.; Mora-Diaz, Julian; Karbon, Maria; Schuh, Harald; Wang, Guang L.

2017-07-01

Closure quantities measured by very-long-baseline interferometry (VLBI) observations are independent of instrumental and propagation instabilities and antenna gain factors, but are sensitive to source structure. A new method is proposed to calculate a structure index based on the median values of closure quantities rather than the brightness distribution of a source. The results are comparable to structure indices based on imaging observations at other epochs and demonstrate the flexibility of deriving structure indices from exactly the same observations as used for geodetic analysis and without imaging analysis. A three-component model for the structure of source 3C371 is developed by model-fitting closure phases. It provides a real case of tracing how the structure effect identified by closure phases in the same observations as the delay observables affects the geodetic analysis, and investigating which geodetic parameters are corrupted to what extent by the structure effect. Using the resulting structure correction based on the three-component model of source 3C371, two solutions, with and without correcting the structure effect, are made. With corrections, the overall rms of this source is reduced by 1 ps, and the impacts of the structure effect introduced by this single source are up to 1.4 mm on station positions and up to 4.4 microarcseconds on Earth orientation parameters. This study is considered as a starting point for handling the source structure effect on geodetic VLBI from geodetic sessions themselves.

The effect of meteorological data on atmospheric pressure loading corrections in VLBI data analysis

Science.gov (United States)

Balidakis, Kyriakos; Glaser, Susanne; Karbon, Maria; Soja, Benedikt; Nilsson, Tobias; Lu, Cuixian; Anderson, James; Liu, Li; Andres Mora-Diaz, Julian; Raposo-Pulido, Virginia; Xu, Minghui; Heinkelmann, Robert; Schuh, Harald

2015-04-01

Earth's crustal deformation is a manifestation of numerous geophysical processes, which entail the atmosphere and ocean general circulation and tidal attraction, climate change, and the hydrological circle. The present study deals with the elastic deformations induced by atmospheric pressure variations. At geodetic sites, APL (Atmospheric Pressure Loading) results in displacements covering a wide range of temporal scales which is undesirable when rigorous geodetic/geophysical analysis is intended. Hence, it is of paramount importance that the APL signal are removed at the observation level in the space geodetic data analysis. In this study, elastic non-tidal components of loading displacements were calculated in the local topocentric frame for all VLBI (Very Long Baseline Interferometry) stations with respect to the center-of-figure of the solid Earth surface and the center-of-mass of the total Earth system. The response of the Earth to the load variation at the surface was computed by convolving Farrell Green's function with the homogenized in situ surface pressure observations (in the time span 1979-2014) after the subtraction of the reference pressure and the S1, S2 and S3 thermal tidal signals. The reference pressure was calculated through a hypsometric adjustment of the absolute pressure level determined from World Meteorological Organization stations in the vicinity of each VLBI observatory. The tidal contribution was calculated following the 2010 International Earth Rotation and Reference Systems Service conventions. Afterwards, this approach was implemented into the VLBI software VieVS@GFZ and the entirety of available VLBI sessions was analyzed. We rationalize our new approach on the basis that the potential error budget is substantially reduced, since several common errors are not applicable in our approach, e.g. those due to the finite resolution of NWM (Numerical Weather Models), the accuracy of the orography model necessary for adjusting the former as

A Fast Radio Burst Search Method for VLBI Observation

Science.gov (United States)

Liu, Lei; Tong, Fengxian; Zheng, Weimin; Zhang, Juan; Tong, Li

2018-02-01

We introduce the cross-spectrum-based fast radio burst (FRB) search method for Very Long Baseline Interferometer (VLBI) observation. This method optimizes the fringe fitting scheme in geodetic VLBI data post-processing, which fully utilizes the cross-spectrum fringe phase information and therefore maximizes the power of single-pulse signals. Working with cross-spectrum greatly reduces the effect of radio frequency interference compared with using auto-power spectrum. Single-pulse detection confidence increases by cross-identifying detections from multiple baselines. By combining the power of multiple baselines, we may improve the detection sensitivity. Our method is similar to that of coherent beam forming, but without the computational expense to form a great number of beams to cover the whole field of view of our telescopes. The data processing pipeline designed for this method is easy to implement and parallelize, which can be deployed in various kinds of VLBI observations. In particular, we point out that VGOS observations are very suitable for FRB search.

Introducing a New Software for Geodetic Analysis

Science.gov (United States)

Hjelle, Geir Arne; Dähnn, Michael; Fausk, Ingrid; Kirkvik, Ann-Silje; Mysen, Eirik

2017-04-01

At the Norwegian Mapping Authority, we are currently developing Where, a new software for geodetic analysis. Where is built on our experiences with the Geosat software, and will be able to analyse and combine data from VLBI, SLR, GNSS and DORIS. The software is mainly written in Python which has proved very fruitful. The code is quick to write and the architecture is easily extendable and maintainable, while at the same time taking advantage of well-tested code like the SOFA and IERS libraries. This presentation will show some of the current capabilities of Where, including benchmarks against other software packages, and outline our plans for further progress. In addition we will report on some investigations we have done experimenting with alternative weighting strategies for VLBI.

Round-Trip System Available to Measure Path Length Variation in Korea VLBI System for Geodesy

Science.gov (United States)

Oh, Hongjong; Kondo, Tetsuro; Lee, Jinoo; Kim, Tuhwan; Kim, Myungho; Kim, Suchul; Park, Jinsik; Ju, Hyunhee

2010-01-01

The construction project of Korea Geodetic VLBI officially started in October 2008. The construction of all systems will be completed by the end of 2011. The project was named Korea VLBI system for Geodesy (KVG), and its main purpose is to maintain the Korea Geodetic Datum. In case of the KVG system, an observation room with an H-maser frequency standard is located in a building separated from the antenna by several tens of meters. Therefore KVG system will adopt a so-called round-trip system to transmit reference signals to the antenna with reduction of the effect of path length variations. KVG s round-trip system is designed not only to use either metal or optical fiber cables, but also to measure path length variations directly. We present this unique round trip system for KVG.

Long-term mass variations from SLR, VLBI and GPS data

Science.gov (United States)

Luceri, Vincenza; Sciarretta, Cecilia; Bianco, Giuseppe

2013-04-01

The second-degree geopotential coefficients reflect the behaviour of the Earth's inertia tensor of order 2 which describes the main mass variations of our planet impacting polar motion and length of day (EOP). SLR, VLBI and GPS allow the estimation of those variations, either directly in the case of SLR through its dynamics, and indirectly, for all the three geodetic techniques, by deriving excitation functions from the EOP estimations. The geodetic estimates include the influence of the Earth's atmosphere and oceans, both from their mass and motion components, which can be modelled using the atmospheric and oceanic angular momenta variations. The different C21, S21 and C20 geodetic time series are compared in order to evaluate their coherence and their response to the mass variations after the removal of the motion terms. Moreover, the residual signal contents of the geodetic values, deprived by the atmospheric and oceanic mass and motion components, will be investigated.

International VLBI Service for Geodesy and Astrometry 2013 Annual Report

Science.gov (United States)

Baver, Karen D.; Behrend, Dirk; Armstrong, Kyla L.

2014-01-01

This volume of reports is the 2013 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the permanent components of IVS. The IVS 2013 Annual Report documents the work of the IVS components for the calendar year 2013, our fifteenth year of existence. The reports describe changes, activities, and progress of the IVS. Many thanks to all IVS components who contributed to this Annual Report. With the exception of the first section and the last section, the contents of this Annual Report also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/ar2013.

Vienna VLBI and Satellite Software (VieVS) for Geodesy and Astrometry

Science.gov (United States)

Böhm, Johannes; Böhm, Sigrid; Boisits, Janina; Girdiuk, Anastasiia; Gruber, Jakob; Hellerschmied, Andreas; Krásná, Hana; Landskron, Daniel; Madzak, Matthias; Mayer, David; McCallum, Jamie; McCallum, Lucia; Schartner, Matthias; Teke, Kamil

2018-04-01

The Vienna VLBI and Satellite Software (VieVS) is state-of-the-art Very Long Baseline Interferometry (VLBI) analysis software for geodesy and astrometry. VieVS has been developed at Technische Universität Wien (TU Wien) since 2008, where it is used for research purposes and for teaching space geodetic techniques. In the past decade, it has been successfully applied on Very Long Baseline Interferometry (VLBI) observations for the determination of celestial and terrestrial reference frames as well as for the estimation of celestial pole offsets, universal Time (UT1-UTC), and polar motion based on least-squares adjustment. Furthermore, VieVS is equipped with tools for scheduling and simulating VLBI observations to extragalactic radio sources as well as to satellites and spacecraft, features which proved to be very useful for a variety of applications. VieVS is now available as version 3.0 and we do provide the software to all interested persons and institutions. A wiki with more information about VieVS is available at http://vievswiki.geo.tuwien.ac.at/.

MARBLE (Multiple Antenna Radio-interferometry for Baseline Length Evaluation): Development of a Compact VLBI System for Calibrating GNSS and Electronic Distance Measurement Devices

Science.gov (United States)

Ichikawa, R.; Ishii, A.; Takiguchi, H.; Kimura, M.; Sekido, M.; Takefuji, K.; Ujihara, H.; Hanado, Y.; Koyama, Y.; Kondo, T.; Kurihara, S.; Kokado, K.; Kawabata, R.; Nozawa, K.; Mukai, Y.; Kuroda, J.; Ishihara, M.; Matsuzaka, S.

2012-12-01

We are developing a compact VLBI system with a 1.6-m diameter aperture dish in order to provide reference baseline lengths for calibration. The reference baselines are used to validate surveying instruments such as GPS and EDM and is maintained by the Geospatial Information Authority of Japan (GSI). The compact VLBI system will be installed at both ends of the reference baseline. Since the system is not sensitive enough to detect fringes between the two small dishes, we have designed a new observation concept including one large dish station. We can detect two group delays between each compact VLBI system and the large dish station based on conventional VLBI measurement. A group delay between the two compact dishes can be indirectly calculated using a simple equation. We named the idea "Multiple Antenna Radio-interferometry for Baseline Length Evaluation", or MARBLE system. The compact VLBI system is easy transportable and consists of the compact dish, a new wide-band front-end system, azimuth and elevation drive units, an IF down-converter unit, an antenna control unit (ACU), a counterweight, and a monument pillar. Each drive unit is equipped with a zero-backlash harmonic drive gearing component. A monument pillar is designed to mount typical geodetic GNSS antennas easily and an offset between the GNSS antenna reference point. The location of the azimuth-elevation crossing point of the VLBI system is precisely determined with an uncertainty of less than 0.2 mm. We have carried out seven geodetic VLBI experiments on the Kashima-Tsukuba baseline (about 54 km) using the two prototypes of the compact VLBI system between December 2009 and December 2010. The average baseline length and repeatability of the experiments is 54184874.0 ± 2.4 mm. The results are well consistent with those obtained by GPS measurements. In addition, we are now planning to use the compact VLBI system for precise time and frequency comparison between separated locations.

Space Geodetic Technique Co-location in Space: Simulation Results for the GRASP Mission

Science.gov (United States)

Kuzmicz-Cieslak, M.; Pavlis, E. C.

2011-12-01

The Global Geodetic Observing System-GGOS, places very stringent requirements in the accuracy and stability of future realizations of the International Terrestrial Reference Frame (ITRF): an origin definition at 1 mm or better at epoch and a temporal stability on the order of 0.1 mm/y, with similar numbers for the scale (0.1 ppb) and orientation components. These goals were derived from the requirements of Earth science problems that are currently the international community's highest priority. None of the geodetic positioning techniques can achieve this goal alone. This is due in part to the non-observability of certain attributes from a single technique. Another limitation is imposed from the extent and uniformity of the tracking network and the schedule of observational availability and number of suitable targets. The final limitation derives from the difficulty to "tie" the reference points of each technique at the same site, to an accuracy that will support the GGOS goals. The future GGOS network will address decisively the ground segment and to certain extent the space segment requirements. The JPL-proposed multi-technique mission GRASP (Geodetic Reference Antenna in Space) attempts to resolve the accurate tie between techniques, using their co-location in space, onboard a well-designed spacecraft equipped with GNSS receivers, a SLR retroreflector array, a VLBI beacon and a DORIS system. Using the anticipated system performance for all four techniques at the time the GGOS network is completed (ca 2020), we generated a number of simulated data sets for the development of a TRF. Our simulation studies examine the degree to which GRASP can improve the inter-technique "tie" issue compared to the classical approach, and the likely modus operandi for such a mission. The success of the examined scenarios is judged by the quality of the origin and scale definition of the resulting TRF.

International VLBI Service for Geodesy and Astrometry 2012 Annual Report

Science.gov (United States)

Baver, Karen D.; Behrend, Dirk; Armstrong, Kyla L.

2013-01-01

This volume of reports is the 2012 Annual Report of the International VLBI Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the permanent components of IVS. The IVS 2012 Annual Report documents the work of the IVS components for the calendar year 2012, our fourteenth year of existence. The reports describe changes, activities, and progress ofthe IVS. Many thanks to all IVS components who contributed to this Annual Report. With the exception of the first section and parts of the last section (described below), the contents of this Annual Report also appear on the IVS Web site athttp:ivscc.gsfc.nasa.gov/publications/ar2012

Co-location of space geodetic techniques carried out at the Geodetic Observatory Wettzell using a closure in time and a multi-technique reference target

Science.gov (United States)

Kodet, J.; Schreiber, K. U.; Eckl, J.; Plötz, C.; Mähler, S.; Schüler, T.; Klügel, T.; Riepl, S.

2018-01-01

The quality of the links between the different space geodetic techniques (VLBI, SLR, GNSS and DORIS) is still one of the major limiting factors for the realization of a unique global terrestrial reference frame that is accurate enough to allow the monitoring of the Earth system, i.e., of processes like sea level change, postglacial rebound and silent earthquakes. According to the specifications of the global geodetic observing system of the International Association of Geodesy, such a reference frame should be accurate to 1 mm over decades, with rates of change stable at the level of 0.1 mm/year. The deficiencies arise from inaccurate or incomplete local ties at many fundamental sites as well as from systematic instrumental biases in the individual space geodetic techniques. Frequently repeated surveys, the continuous monitoring of antenna heights and the geometrical mount stability (Lösler et al. in J Geod 90:467-486, 2016. https://doi.org/10.1007/s00190-016-0887-8) have not provided evidence for insufficient antenna stability. Therefore, we have investigated variations in the respective system delays caused by electronic circuits, which is not adequately captured by the calibration process, either because of subtle differences in the circuitry between geodetic measurement and calibration, high temporal variability or because of lacking resolving bandwidth. The measured system delay variations in the electric chain of both VLBI- and SLR systems reach the order of 100 ps, which is equivalent to 3 cm of path length. Most of this variability is usually removed by the calibrations but by far not all. This paper focuses on the development of new technologies and procedures for co-located geodetic instrumentation in order to identify and remove systematic measurement biases within and between the individual measurement techniques. A closed-loop optical time and frequency distribution system and a common inter-technique reference target provide the possibility to remove

The Tropospheric Products of the International VLBI Service for Geodesy and Astrometry

Science.gov (United States)

Heinkelmann, Robert; Schwatke, Christian

2010-01-01

The IVS runs two tropospheric products: The IVS tropospheric parameter rapid combination monitors the zenith wet delay (ZWD) and zenith total delay (ZTD) of the rapid turnaround sessions R1 and R4. Goal of the combination is the identification and the exclusion of outliers by comparison and the assessment of the precision of current VLBI solutions in terms of tropospheric parameters. The rapid combination is done on a weekly basis four weeks after the observation files are released on IVS Data Centers. Since tropospheric and geodetic parameters, such as vertical station components, can significantly correlate, the consistency of the ZTD can be a measure of the consistency of the corresponding TRF as well. The ZWD mainly rely on accurate atmospheric pressure data. Thus, besides estimation techniques, modeling and analyst s noise, ZWD reflects differences in the atmospheric pressure data applied to the VLBI analysis. The second product, called tropospheric parameter long-term combination, aims for an accurate determination of climatological signals, such as trends of the atmospheric water vapor observed by VLBI. Therefore, the long-term homogeneity of atmospheric pressure data plays a crucial role for this product. The paper reviews the methods applied and results achieved so far and describes the new maintenance through DGFI.

Rigorous Combination of GNSS and VLBI: How it Improves Earth Orientation and Reference Frames

Science.gov (United States)

Lambert, S. B.; Richard, J. Y.; Bizouard, C.; Becker, O.

2017-12-01

Current reference series (C04) of the International Earth Rotation and Reference Systems Service (IERS) are produced by a weighted combination of Earth orientation parameters (EOP) time series built up by combination centers of each technique (VLBI, GNSS, Laser ranging, DORIS). In the future, we plan to derive EOP from a rigorous combination of the normal equation systems of the four techniques.We present here the results of a rigorous combination of VLBI and GNSS pre-reduced, constraint-free, normal equations with the DYNAMO geodetic analysis software package developed and maintained by the French GRGS (Groupe de Recherche en GeÌodeÌsie Spatiale). The used normal equations are those produced separately by the IVS and IGS combination centers to which we apply our own minimal constraints.We address the usefulness of such a method with respect to the classical, a posteriori, combination method, and we show whether EOP determinations are improved.Especially, we implement external validations of the EOP series based on comparison with geophysical excitation and examination of the covariance matrices. Finally, we address the potential of the technique for the next generation celestial reference frames, which are currently determined by VLBI only.

On the Impact of Inhomogeneities in Meteorological Data on VLBI Data Analysis

Science.gov (United States)

Balidakis, Kyriakos; Heinkelmann, Robert; Phogat, Apurva; Soja, Benedikt; Glaser, Susanne; Nilsson, Tobias; Karbon, Maria; Schuh, Harald

2016-12-01

In this study, we address the issue of the quality of meteorological data employed for VLBI data analysis. We use data from six numerical weather models (NWMs) to form references on which the homogenization process is based. We explore the impact of the choice of NWM as well as the way to extract data from it. Among our findings is that data from the surface fields of NWMs are not suitable for either geodetic analysis or homogenization efforts, whether they are in their original form or after they have been compensated for the height difference between the orography of the NWM and the actual elevation. The reason lies in the fact that for 77% of the VLBI stations a height bias larger than 2.5 mm appears, as well as an average bias in the zenith wet delay estimates of 12.2 mm. Should the proposed extraction approach be followed, the difference between operational and reanalysis NWMs is not significant for such an application. Our conclusions are based on the analysis of VLBI data over 13 years.

International VLBI Service for Geodesy and Astrometry: 1999 Annual Report

Science.gov (United States)

Vandenberg, Nancy R. (Editor)

1999-01-01

This volume of reports is the 1999 Annual Report of the International VLBI Service for Geodesy and Astrometry -IVS. The individual reports were contributed by VLBI groups in the international geodetic community who constitute the components of IVS. The 1999 Annual Report documents the work of the IVS components for the year ending March 1, 1999, the official inauguration date of IVS. As the newest of the space technique services, IVS decided to publish this Annual Report as a reference to our organization and its components. The entire contents of this Annual Report also appear on the IVS website at: http://ivscc.gsfc.nasa.gov/pub/arl999. The IVS 1999 Annual Report will be a valuable reference for information about IVS and its components. This Annual Report will serve as a baseline from which we can measure the anticipated progress of IVS in coming years.

Integration of space geodesy: A US National Geodetic Observatory

Science.gov (United States)

Yunck, Thomas P.; Neilan, Ruth E.

2005-11-01

In the interest of improving the performance and efficiency of space geodesy a diverse group in the US, in collaboration with IGGOS, has begun to establish a unified National Geodetic Observatory (NGO). To launch this effort an international team will conduct a multi-year program of research into the technical issues of integrating SLR, VLBI, and GPS geodesy to produce a unified set of global geodetic products. The goal is to improve measurement accuracy by up to an order of magnitude while lowering the cost to current sponsors. A secondary goal is to expand and diversify international sponsorship of space geodesy. Principal benefits will be to open new vistas of research in geodynamics and surface change while freeing scarce NASA funds for scientific studies. NGO will proceed in partnership with, and under the auspices of, the International Association of Geodesy (IAG) as an element of the Integrated Global Geodetic Observation System project. The collaboration will be conducted within, and will make full use of, the IAG's existing international services: the IGS, IVS, ILRS, and IERS. Seed funding for organizational activities and technical analysis will come from NASA's Solid Earth and Natural Hazards Program. Additional funds to develop an integrated geodetic data system known as Inter-service Data Integration for Geodetic Operations (INDIGO), will come from a separate NASA program in Earth science information technology. INDIGO will offer ready access to the full variety of NASA's space geodetic data and will extend the GPS Seamless Archive (GSAC) philosophy to all space geodetic data types.

The Australian Geodetic Observing Program. Current Status and Future Plans

Science.gov (United States)

Johnston, G.; Dawson, J. H.

2015-12-01

Over the last decade, the Australian government has through programs like AuScope, the Asia Pacific Reference Frame (APREF), and the Pacific Sea Level Monitoring (PSLM) Project made a significant contribution to the Global Geodetic Observing Program. In addition to supporting the national research priorities, this contribution is justified by Australia's growing economic dependence on precise positioning to underpin efficient transportation, geospatial data management, and industrial automation (e.g., robotic mining and precision agriculture) and the consequent need for the government to guarantee provision of precise positioning products to the Australian community. It is also well recognised within Australia that there is an opportunity to exploit our near unique position as being one of the few regions in the world to see all new and emerging satellite navigation systems including Galileo (Europe), GPS III (USA), GLONASS (Russia), Beidou (China), QZSS (Japan) and IRNSS (India). It is in this context that the Australian geodetic program will build on earlier efforts and further develop its key geodetic capabilities. This will include the creation of an independent GNSS analysis capability that will enable Australia to contribute to the International GNSS Service (IGS) and an upgrade of key geodetic infrastructure including the national VLBI and GNSS arrays. This presentation will overview the significant geodetic activities undertaken by the Australian government and highlight its future plans.

Multi-technique approach for deriving a VLBI signal extra-path variation model induced by gravity: the example of Medicina

Science.gov (United States)

Sarti, P.; Abbondanza, C.; Negusini, M.; Vittuari, L.

2009-09-01

During the measurement sessions gravity might induce significant deformations in large VLBI telescopes. If neglected or mismodelled, these deformations might bias the phase of the incoming signal thus corrupting the estimate of some crucial geodetic parameters (e.g. the height component of VLBI Reference Point). This paper describes a multi-technique approach implemented for measuring and quantifying the gravity-dependent deformations experienced by the 32-m diameter VLBI antenna of Medicina (Northern Italy). Such an approach integrates three different methods: Terrestrial Triangulations and Trilaterations (TTT), Laser Scanning (LS) and a Finite Element Model (FEM) of the antenna. The combination of the observations performed with these methods allows to accurately define an elevation-dependent model of the signal path variation which appears to be, for the Medicina telescope, non negligible. In the range [0,90] deg the signal path increases monotonically by almost 2 cm. The effect of such a variation has not been introduced in actual VLBI analysis yet; nevertheless this is the task we are going to pursue in the very next future.

Complex demodulation in VLBI estimation of high frequency Earth rotation components

Science.gov (United States)

Böhm, S.; Brzeziński, A.; Schuh, H.

2012-12-01

The spectrum of high frequency Earth rotation variations contains strong harmonic signal components mainly excited by ocean tides along with much weaker non-harmonic fluctuations driven by irregular processes like the diurnal thermal tides in the atmosphere and oceans. In order to properly investigate non-harmonic phenomena a representation in time domain is inevitable. We present a method, operating in time domain, which is easily applicable within Earth rotation estimation from Very Long Baseline Interferometry (VLBI). It enables the determination of diurnal and subdiurnal variations, and is still effective with merely diurnal parameter sampling. The features of complex demodulation are used in an extended parameterization of polar motion and universal time which was implemented into a dedicated version of the Vienna VLBI Software VieVS. The functionality of the approach was evaluated by comparing amplitudes and phases of harmonic variations at tidal periods (diurnal/semidiurnal), derived from demodulated Earth rotation parameters (ERP), estimated from hourly resolved VLBI ERP time series and taken from a recently published VLBI ERP model to the terms of the conventional model for ocean tidal effects in Earth rotation recommended by the International Earth Rotation and Reference System Service (IERS). The three sets of tidal terms derived from VLBI observations extensively agree among each other within the three-sigma level of the demodulation approach, which is below 6 μas for polar motion and universal time. They also coincide in terms of differences to the IERS model, where significant deviations primarily for several major tidal terms are apparent. An additional spectral analysis of the as well estimated demodulated ERP series of the ter- and quarterdiurnal frequency bands did not reveal any significant signal structure. The complex demodulation applied in VLBI parameter estimation could be demonstrated a suitable procedure for the reliable reproduction of

Results from the Geodetic Observatory TIGO due to the Mw 8.8 Earthquake

Science.gov (United States)

Hase, H.; Böer, A.; Sierk, B.; Ihde, J.; Weber, G.; Wilmes, H.; Falk, R.; Hessels, U.; Neumaier, P.; Söhne, W.; Wziontek, H.; Engelhard, G.; Sobarzo, S.; Cifuentes, O.; Guaitiao, C.; Cona, I.; Avendaño, M.; Herrera, C.; Mora, V.; Fernandez, A.; Oñate, E.; Zaror, P.; Pedreros, F.; Zapata, O.

2010-12-01

The Geodetic Observatory TIGO is unique in Latin America. With its sensors and instruments it defines a reference point in the time, space and gravity field domain. Its operation started in 2002, for which reason data series documented the preseismic situation very well. With the Mw 8.8 earthquake on February 27, 2010, the entire observatory was exposed to strong motions due to its closeness to the epicenter. Since then the postseismic behaviour of the subduction zone can be studied and compared with the preseismic situation. TIGO provided continuous GPS/GLONASS data with 1s samples which give an insight to the mechanism of the decoupling of the Nazca and the South-American plate. The displacement of more than 3m had a duration of 30s at the beginning of the 147s duration of the earthquake. The displacement could be confirmed afterwards with VLBI and SLR methods. TIGO used its absolute gravity meter in an unusual way with weekly measurements on the same monument. These data show an irregularity during the last 3 weeks before the earthquake. Finally the postseismic movement to the west triggered by the earthquake and registered by geodetic space techniques indicate that the western expansion of the South-American plate did not stop yet. The pre- and post-seismic displacement vectors differ by less than 180° which might be explained by a fractional strike slip in the mega thrust. The coincidence of the epicenter with one of the keystations for global reference frames showed deficiencies by the linear modelling of tectonical movements in terrestial reference frames. This problem calls for near-real time reference frames.

Contribution of SELENE-2 geodetic measurements to constrain the lunar internal structure

Science.gov (United States)

Matsumoto, K.; Kikuchi, F.; Yamada, R.; Iwata, T.; Kono, Y.; Tsuruta, S.; Hanada, H.; Goossens, S. J.; Ishihara, Y.; Kamata, S.; Sasaki, S.

2012-12-01

Internal structure and composition of the Moon provide important clue and constraints on theories for how the Moon formed and evolved. The Apollo seismic network has contributed to the internal structure modeling. Efforts have been made to detect the lunar core from the noisy Apollo data (e.g., [1], [2]), but there is scant information about the structure below the deepest moonquakes at about 1000 km depth. On the other hand, there have been geodetic studies to infer the deep structure of the Moon. For example, LLR (Lunar Laser Ranging) data analyses detected a displacement of the lunar pole of rotation, indicating that dissipation is acting on the rotation arising from a fluid core [3]. Bayesian inversion using geodetic data (such as mass, moments of inertia, tidal Love numbers k2 and h2, and quality factor Q) also suggests a fluid core and partial melt in the lower mantle region [4]. Further improvements in determining the second-degree gravity coefficients (which will lead to better estimates of moments of inertia) and the Love number k2 will help us to better constrain the lunar internal structure. Differential VLBI (Very Long Baseline Interferometry) technique, which was used in the Japanese lunar exploration mission SELENE (Sept. 2007 - June 2009), is expected to contribute to better determining the second-degree potential Love number k2 and low-degree gravity coefficients. SELENE will be followed by the future lunar mission SELENE-2 which will carry both a lander and an orbiter. We propose to put the SELENE-type radio sources on these spacecraft in order to accurately estimate k2 and the low-degree gravity coefficients. By using the same-beam VLBI tracking technique, these parameters will be retrieved through precision orbit determination of the orbiter with respect to the lander which serves as a reference. The VLBI mission with the radio sources is currently one of the mission candidates for SELENE-2. We have conducted a preliminary simulation study on the

Influence of ocean tides on the diurnal and semidiurnal earth rotation variations from VLBI observations

Science.gov (United States)

Gubanov, V. S.; Kurdubov, S. L.

2015-05-01

The International astrogeodetic standard IERS Conventions (2010) contains a model of the diurnal and semidiurnal variations in Earth rotation parameters (ERPs), the pole coordinates and the Universal Time, arising from lunisolar tides in the world ocean. This model was constructed in the mid-1990s through a global analysis of Topex/Poseidon altimetry. The goal of this study is to try to estimate the parameters of this model by processing all the available VLBI observations on a global network of stations over the last 35 years performed within the framework of IVS (International VLBI Service) geodetic programs. The complexity of the problemlies in the fact that the sought-for corrections to the parameters of this model lie within 1 mm and, thus, are at the limit of their detectability by all currently available methods of ground-based positional measurements. This requires applying universal software packages with a high accuracy of reduction calculations and a well-developed system of controlling the simultaneous adjustment of observational data to analyze long series of VLBI observations. This study has been performed with the QUASAR software package developed at the Institute of Applied Astronomy of the Russian Academy of Sciences. Although the results obtained, on the whole, confirm a high accuracy of the basic model in the IERS Conventions (2010), statistically significant corrections that allow this model to be refined have been detected for some harmonics of the ERP variations.

Geodetic Volcano Monitoring Research in Canary Islands: Recent Results

Science.gov (United States)

Fernandez, J.; Gonzalez, P. J.; Arjona, A.; Camacho, A. G.; Prieto, J. F.; Seco, A.; Tizzani, P.; Manzo, M. R.; Lanari, R.; Blanco, P.; Mallorqui, J. J.

2009-05-01

The Canarian Archipelago is an oceanic island volcanic chain with a long-standing history of volcanic activity (> 40 Ma). It is located off the NW coast of the African continent, lying over a transitional crust of the Atlantic African passive margin. At least 12 eruptions have been occurred on the islands of Lanzarote, Tenerife and La Palma in the last 500 years. Volcanism manifest predominantly as basaltic strombolian monogenetic activity (whole archipelago) and central felsic volcanism (active only in Tenerife Island). We concentrate our studies in the two most active islands, Tenerife and La Palma. In these islands, we tested different methodologies of geodetic monitoring systems. We use a combination of ground- and space-based techniques. At Tenerife Island, a differential interferometric study was performed to detect areas of deformation. DInSAR detected two clear areas of deformation, using this results a survey-based GPS network was designed and optimized to control those deformations and the rest of the island. Finally, using SBAS DInSAR results weak spatial long- wavelength subsidence signals has been detected. At La Palma, the first DInSAR analysis have not shown any clear deformation, so a first time series analysis was performed detecting a clear subsidence signal at Teneguia volcano, as for Tenerife a GPS network was designed and optimized taking into account stable and deforming areas. After several years of activities, geodetic results served to study ground deformations caused by a wide variety of sources, such as changes in groundwater levels, volcanic activity, volcano-tectonics, gravitational loading, etc. These results proof that a combination of ground-based and space-based techniques is suitable tool for geodetic volcano monitoring in Canary Islands. Finally, we would like to strength that those results could have serious implications on the continuous geodetic monitoring system design and implementation for the Canary Islands which is under

Hartebeesthoek Radio Astronomy Observatory (HartRAO)

Science.gov (United States)

Nickola, Marisa; Gaylard, Mike; Quick, Jonathan; Combrinck, Ludwig

2013-01-01

HartRAO provides the only fiducial geodetic site in Africa, and it participates in global networks for VLBI, GNSS, SLR, and DORIS. This report provides an overview of geodetic VLBI activities at HartRAO during 2012, including the conversion of a 15-m alt-az radio telescope to an operational geodetic VLBI antenna.

VLBI Technology Development at SHAO

Science.gov (United States)

Zhang, Xiuzhong; Shu, Fengchun; Xiang, Ying; Zhu, Renjie; Xu, Zhijun; Chen, Zhong; Zheng, Weimin; Luo, Jintao; Wu, Yajun

2010-01-01

VLBI technology development made significant progress at SHAO in the last few years. The development status of the Chinese DBBC, the software and FPGA-based correlators, and the new VLBI antenna, as well as VLBI applications are summarized in this paper.

Supernova research with VLBI

Science.gov (United States)

Bartel, Norbert; Bietenholz, Michael F.

2016-06-01

Core-collapse supernovae have been monitored with VLBI from shortly after the explosion to many years thereafter. Radio emission is produced as the ejecta hit the stellar wind left over from the dyingstar. Images show the details of the interaction as the shock front expands into the circumstellar medium. Measurements of the velocity and deceleration of the expansion provide information on both the ejecta and the circumstellar medium. VLBI observations can also search for the stellar remnant of the explosion, a neutron star or a black hole. Combining the transverse expansion rate with the radial expansion rate from optical spectra allows a geometric determination of the distance to the host galaxy. We will present results from recent VLBI observations, focus on their interpretations, and show updated movies of supernovae from soon after their explosion to the present.

Supernova VLBI

Science.gov (United States)

Bartel, N.

2009-08-01

We review VLBI observations of supernovae over the last quarter century and discuss the prospect of imaging future supernovae with space VLBI in the context of VSOP-2. From thousands of discovered supernovae, most of them at cosmological distances, ˜50 have been detected at radio wavelengths, most of them in relatively nearby galaxies. All of the radio supernovae are Type II or Ib/c, which originate from the explosion of massive progenitor stars. Of these, 12 were observed with VLBI and four of them, SN 1979C, SN 1986J, SN 1993J, and SN 1987A, could be imaged in detail, the former three with VLBI. In addition, supernovae or young supernova remnants were discovered at radio wavelengths in highly dust-obscured galaxies, such as M82, Arp 299, and Arp 220, and some of them could also be imaged in detail. Four of the supernovae so far observed were sufficiently bright to be detectable with VSOP-2. With VSOP-2 the expansion of supernovae can be monitored and investigated with unsurpassed angular resolution, starting as early as the time of the supernova's transition from its opaque to transparent stage. Such studies can reveal, in a movie, the aftermath of a supernova explosion shortly after shock break out.

The "Quasar" Network Observations in e-VLBI Mode Within the Russian Domestic VLBI Programs

Science.gov (United States)

Finkelstein, Andrey; Ipatov, Alexander; Kaidanovsky, Michael; Bezrukov, Ilia; Mikhailov, Andrey; Salnikov, Alexander; Surkis, Igor; Skurikhina, Elena

2010-01-01

The purpose of the Russian VLBI "Quasar" Network is to carry out astrometrical and geodynamical investigations. Since 2006 purely domestic observational programs with data processing at the IAA correlator have been carried out. To maintain these geodynamical programs e-VLBI technology is being developed and tested. This paper describes the IAA activity of developing a real-time VLBI system using high-speed digital communication links.

International VLBI Service for Geodesy and Astrometry 2000 Annual Report

Science.gov (United States)

Vandenberg, N. R. (Editor); Baver, K. D. (Editor); Smith, David E. (Technical Monitor)

2000-01-01

This volume of reports is the 2000 Annual Report of the International Very Long Base Interferometry (VLBI) Service for Geodesy and Astrometry (IVS). The individual reports were contributed by VLBI groups in the international geodetic and astrometric community who constitute the permanent components of IVS. The IVS 2000 Annual Report documents the work of the IVS components for the period March 1, 1999 (the official inauguration date of IVS) through December 31, 2000. The reports document changes, activities, and progress of the IVS. The entire contents of this Annual Report also appear on the IVS web site at http://ivscc.gsfc.nasa.gov/publications/ar2000. This book and the web site are organized as follows: (1) The first section contains general information about IVS, a map showing the location of the components, information about the Directing Board members, and the report of the IVS Chair; (2) The second section of Special Reports contains a status report of the IVS Working Group on GPS phase center mapping, a reproduction of the resolution making IVS a Service of the International Astronomical Union (IAU), and a reprint of the VLBI Standard Interface (VSI); (3) The next seven sections hold the component reports from the Coordinators, Network Stations, Operation Centers, Correlators, Data Centers, Analysis Centers, and Technology Development Centers; and (4) The last section includes reference information about IVS: the Terms of Reference, the lists of Member and Affiliated organizations, the IVS Associate Member list, a complete list of IVS components, the list of institutions contributing to this report, and a list of acronyms. The 2000 Annual Report demonstrates the vitality of the IVS and the outstanding progress we have made during our first 22 months.

IVS Organization

Science.gov (United States)

2004-01-01

International VLBI Service (IVS) is an international collaboration of organizations which operate or support Very Long Baseline Interferometry (VLBI) components. The goals are: To provide a service to support geodetic, geophysical and astrometric research and operational activities. To promote research and development activities in all aspects of the geodetic and astrometric VLBI technique. To interact with the community of users of VLBI products and to integrate VLBI into a global Earth observing system.

Geodetic Control Points - National Geodetic Survey Benchmarks

Data.gov (United States)

NSGIC Local Govt | GIS Inventory — This data contains a set of geodetic control stations maintained by the National Geodetic Survey. Each geodetic control station in this dataset has either a precise...

Two-Component Structure of the Radio Source 0014+813 from VLBI Observations within the CONT14 Program

Science.gov (United States)

Titov, O. A.; Lopez, Yu. R.

2018-03-01

We consider a method of reconstructing the structure delay of extended radio sources without constructing their radio images. The residuals derived after the adjustment of geodetic VLBI observations are used for this purpose. We show that the simplest model of a radio source consisting of two point components can be represented by four parameters (the angular separation of the components, the mutual orientation relative to the poleward direction, the flux-density ratio, and the spectral index difference) that are determined for each baseline of a multi-baseline VLBI network. The efficiency of this approach is demonstrated by estimating the coordinates of the radio source 0014+813 observed during the two-week CONT14 program organized by the International VLBI Service (IVS) in May 2014. Large systematic deviations have been detected in the residuals of the observations for the radio source 0014+813. The averaged characteristics of the radio structure of 0014+813 at a frequency of 8.4 GHz can be calculated from these deviations. Our modeling using four parameters has confirmed that the source consists of two components at an angular separation of 0.5 mas in the north-south direction. Using the structure delay when adjusting the CONT14 observations leads to a correction of the average declination estimate for the radio source 0014+813 by 0.070 mas.

Search for Binary Black Hole Candidates from the VLBI Images of ...

Indian Academy of Sciences (India)

2016-01-27

Jan 27, 2016 ... We have searched the core-jet pairs in the VLBI scales (< 1 kpc), from several VLBI catalogues, and found out 5 possible Binary Black Hole (BBH) candidates. We present here the search results and analyse the candidates preliminarily. We plan to study with multi-band VLBI observation. We also plan to ...

International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings

Science.gov (United States)

Vandenberg, Nancy R. (Editor); Baver, Karen D. (Editor)

2004-01-01

This volume is the proceedings of the third General Meeting of the International VLBI Service for Geodesy and Astromctry IVS), held in Otlawa, Canada, February 9-11,2004. The keynote of the third GM was visions for the next decade following the main theme of "Today's Results and Tomorrow's Vision". with a recognition that the outstanding VLBI results available today are the foundation and motivation for the next generation VLBI system requirements. The goal of the meeting was to provide an interesting and informative program for a wide cross section of IVS members, including station operators, program managers, and analysts.

The Global Geodetic Observing System: Space Geodesy Networks for the Future

Science.gov (United States)

Pearlman, Michael; Pavlis, Erricos; Ma, Chopo; Altamini, Zuheir; Noll, Carey; Stowers, David

2011-01-01

Ground-based networks of co-located space geodetic techniques (VLBI, SLR, GNSS. and DORIS) are the basis for the development and maintenance of the International Terrestrial Reference frame (ITRF), which is our metric of reference for measurements of global change, The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) has established a task to develop a strategy to design, integrate and maintain the fundamental geodetic network and supporting infrastructure in a sustainable way to satisfy the long-term requirements for the reference frame. The GGOS goal is an origin definition at 1 mm or better and a temporal stability on the order of 0.1 mm/y, with similar numbers for the scale and orientation components. These goals are based on scientific requirements to address sea level rise with confidence, but other applications are not far behind. Recent studies including one by the US National Research Council has strongly stated the need and the urgency for the fundamental space geodesy network. Simulations are underway to examining accuracies for origin, scale and orientation of the resulting ITRF based on various network designs and system performance to determine the optimal global network to achieve this goal. To date these simulations indicate that 24 - 32 co-located stations are adequate to define the reference frame and a more dense GNSS and DORIS network will be required to distribute the reference frame to users anywhere on Earth. Stations in the new global network will require geologically stable sites with good weather, established infrastructure, and local support and personnel. GGOS wil seek groups that are interested in participation. GGOS intends to issues a Call for Participation of groups that would like to contribute in the network implementation and operation. Some examples of integrated stations currently in operation or under development will be presented. We will examine necessary conditions and challenges in

VLBI2010 in NASA's Space Geodesy Project

Science.gov (United States)

Ma, Chopo

2012-01-01

In the summer of 20 11 NASA approved the proposal for the Space Geodesy Project (SGP). A major element is developing at the Goddard Geophysical and Astronomical Observatory a prototype of the next generation of integrated stations with co-located VLBI, SLR, GNSS and DORIS instruments as well as a system for monitoring the vector ties. VLBI2010 is a key component of the integrated station. The objectives ofSGP, the role of VLBI20 lOin the context of SGP, near term plans and possible future scenarios will be discussed.

Prospect of Continuous VLBI Measurement of Earth Rotation in Monitoring Geophysical Fluids

Science.gov (United States)

Chao, Benjamin F.; Ma, Chopo; Clark, Thomas

1998-01-01

Large-scale mass transports in the geophysical fluids of the Earth system excite Earth's rotational variations in both length-of-day and polar motion. The excitation process is via the conservation of angular momentum. Therefore Earth rotation observations contain information about the integrated angular momentum (consisting of both the mass term and the motion term) of the geophysical fluids, which include atmosphere, hydrosphere, mantle, and the outer and inner cores. Such global information is often important and otherwise unattainable depending on the nature of the mass transport, its magnitude and time scale. The last few years have seen great advances in VLBI measurement of Earth rotation in precision and temporal resolution. These advances have opened new. areas in geophysical fluid studies, such as oceanic tidal angular momentum, atmospheric tides, Earth librations, and rapid atmospheric angular momentum fluctuations. Precision of 10 microseconds in UTI and 200 microarcseconds in polar motion can now be achieved on hourly basis. Building upon this heritage, the multi-network geodetic VLBI project, Continuous Observation of the Rotation of the Earth (CORE), promises to further these studies and to make possible studies on elusive but tell-tale geophysical processes such as oscillatory modes in the core and in the atmosphere. Currently the early phase of CORE is underway. Within a few years into the new mellinnium, the upcoming space gravity missions (such as GRACE) will measure the temporal variations in Earth's gravitational field, thus providing complementary information to that from Earth rotation study for a better understanding of global geophysical fluid processes.

Applying Kalman filtering to investigate tropospheric effects in VLBI

Science.gov (United States)

Soja, Benedikt; Nilsson, Tobias; Karbon, Maria; Heinkelmann, Robert; Liu, Li; Lu, Cuixian; Andres Mora-Diaz, Julian; Raposo-Pulido, Virginia; Xu, Minghui; Schuh, Harald

2014-05-01

Very Long Baseline Interferometry (VLBI) currently provides results, e.g., estimates of the tropospheric delays, with a delay of more than two weeks. In the future, with the coming VLBI2010 Global Observing System (VGOS) and increased usage of electronic data transfer, it is planned that the time between observations and results is decreased. This may, for instance, allow the integration of VLBI-derived tropospheric delays into numerical weather prediction models. Therefore, future VLBI analysis software packages need to be able to process the observational data autonomously in near real-time. For this purpose, we have extended the Vienna VLBI Software (VieVS) by a Kalman filter module. This presentation describes the filter and discusses its application for tropospheric studies. Instead of estimating zenith wet delays as piece-wise linear functions in a least-squares adjustment, the Kalman filter allows for more sophisticated stochastic modeling. We start with a random walk process to model the time-dependent behavior of the zenith wet delays. Other possible approaches include the stochastic model described by turbulence theory, e.g. the model by Treuhaft and Lanyi (1987). Different variance-covariance matrices of the prediction error, depending on the time of the year and the geographic latitude, have been tested. In winter and closer to the poles, lower variances and covariances are appropriate. The horizontal variations in tropospheric delays have been investigated by comparing three different strategies: assumption of a horizontally stratified troposphere, using north and south gradients modeled, e.g., as Gauss-Markov processes, and applying a turbulence model assuming correlations between observations in different azimuths. By conducting Monte-Carlo simulations of current standard VLBI networks and of future VGOS networks, the different tropospheric modeling strategies are investigated. For this purpose, we use the simulator module of VieVS which takes into

Astrometry VLBI in Space (AVS)

Science.gov (United States)

Cheng, Li-Jen; Reyes, George

1995-01-01

This paper describes a proposal for a new space radio astronomy mission for astrometry using Very Long Baseline Interferometry (VLBI) called Astrometry VLBI in Space (AVS). The ultimate goals of AVS are improving the accuracy of radio astrometry measurements to the microarcsecond level in one epoch of measurements and improving the accuracy of the transformation between the inertial radio and optical coordinate reference frames. This study will also assess the impact of this mission on astrophysics astrometry and geophysics.

Geodesy introduction to geodetic datum and geodetic systems

CERN Document Server

Lu, Zhiping; Qiao, Shubo

2014-01-01

A full introduction to geodetic data and systems written by well-known experts in their respective fields, this book is an ideal text for courses in geodesy and geomatics covering everything from coordinate and gravimetry data to geodetic systems of all types.

Tropospheric Delay from VLBI and GNSS Measurements

Science.gov (United States)

Gubanov, V. S.

2018-02-01

Using an updated version of the QUASAR software package developed at the Institute of Applied Astronomy of the Russian Academy of Sciences, we have processed the VLBI observations within the international CONT14 program (May 6-20, 2014), in which a global network of 17 stations was involved (a total of 250 000 observations). The package update concerned the optimization of data structure and the refinement of stochastic models for the random variations in wet tropospheric delay and atomic clock difference. The main goal of this paper is to compare the VLBI determinations of the tropospheric delay with its independent determinations using global navigation satellite systems (GNSS). We show that both these determinations agree well between themselves only in the case of a global analysis of the VLBI observations, where the VLBI station coordinates are also refined, along with the tropospheric delay and the clock synchronization and Earth orientation parameters. If, alternatively, the station coordinates are insufficiently accurate and are not refined from VLBI observations, then it is appropriate not to determine the tropospheric delay from these observations, but to take it from the publicly accessible independent GNSS data. However, this requires that the VLBI and GNSS techniques operate simultaneously at a common observing site. We have established the shortcomings of the universally accepted method of stabilizing the global solution associated with the absence of a criterion for choosing reference stations and radio sources. Two ways of their elimination are proposed: (i) introducing a coordinated list of weight factors for the errors in the coordinates of such stations and sources into the stabilization algorithm and (ii) adopting a coordinated list of stations and sources the refinement of whose coordinates is not required at all for a certain time.

DETECTING FLARING STRUCTURES IN SAGITTARIUS A* WITH HIGH-FREQUENCY VLBI

International Nuclear Information System (INIS)

Doeleman, Sheperd S.; Fish, Vincent L.; Rogers, Alan E. E.; Broderick, Avery E.; Loeb, Abraham

2009-01-01

The super-massive black hole candidate, Sagittarius A*, exhibits variability from radio to X-ray wavelengths on timescales that correspond to <10 Schwarzschild radii. We survey the potential of millimeter wavelength very long baseline interferometry (VLBI) to detect and constrain time-variable structures that could give rise to such variations, focusing on a model in which an orbiting hot spot is embedded in an accretion disk. Nonimaging algorithms are developed that use interferometric closure quantities to test for periodicity, and applied to an ensemble of hot spot models that sample a range of parameter space. We find that structural periodicity in a wide range of cases can be detected on most potential VLBI arrays using modern VLBI instrumentation. Future enhancements of millimeter/submillimeter VLBI arrays including phased-array processors to aggregate VLBI station collecting area, increased bandwidth recording, and addition of new VLBI sites all significantly aid periodicity detection. The methods described herein can be applied to other models of Sagittarius A*, including jet outflows and magnetohydrodynamic accretion simulations.

CDDIS_VLBI_products_positions

Data.gov (United States)

National Aeronautics and Space Administration — Station positions and velocity solutions in Software INdependent EXchange (SINEX) format derived from analysis of Very Long Baseline Interferometry (VLBI) data....

Design of VLBI Array in South America

Science.gov (United States)

Carrara, E. A.; Abraham, Z.

1990-11-01

RESUMEN. Estudiamos la localizaci6n 6ptima de estaciones de \\ ras' en territorlo brasileno. Con una red VLBI de estaciones reales y ficti- cias simulamos observaciones. Se usan los datos generados de estps ex- perimentos para obtener Ia distribuci6n de brillo de radiofuentes fic- ticias por medlo de tecaicas de mapeo bIbrido. Se concluye que l mejor localizaci6n de estacionee'VLBI futuras, tomando en cuenta las estacio- nes de EUA y de Europa, se encuentra en el Norte-Noreste de razll. El analisis de los datos se hizo con los programas de CALTECH, los cuales estan instalados en una computadora VAX del Departamento de Astronomla del Instituto Astron6mico y Geoflsico de la Universidad de Sa"'o Paulo. ABSTRACT: In this work we study the optimum localization for future VLBI stations in the Brazilian territory. With a VLBI network of real and fictitious stations we make simulations of observations. The data generated in these experiments are used to obtain brightness distribution of a fictitious radio source by the hybrid mapping techniques. We conclude that the best localization of a future VLBI station taking into account the addition of US and European Stations, is roughly in North-Northeast sites in Brazil. The analysis of the data is made with the software of CALTECH, which is installed in the VAX computer of the Astronomy Department of Instituto e Geofisico - USP. Key `{` : INSTRUMENTS - INTERFEROMETRY

The Medicina Station Status Report

Science.gov (United States)

Orfei, Alessandro; Orlati, Andrea; Maccaferri, Giuseppe

2013-01-01

General information about the Medicina Radio Astronomy Station, the 32-m antenna status, and the staff in charge of the VLBI observations is provided. In 2012, the data from geodetic VLBI observations were acquired using the Mark 5A recording system with good results. Updates of the hardware were performed and are briefly described.

Collaborative VLBI experiments with Radioastron

International Nuclear Information System (INIS)

Jones, D.L.; Preston, R.A.; Jordan, J.F.; Linfield, R.P.

1987-01-01

The USSR is planning to launch a 10-m radio telescope into earth orbit for use in VLBI observations. This mission (Radioastron) will be the first opportunity for astronomically important VLBI experiments with baselines much longer than can be obtained between telescopes on the earth. This paper describes the potential scientific advantages of combining data from the orbiting telescope with data from some of the very sensitive radio telescopes in western Europe, Australia, Japan, and the U.S. The advantages of using NASA's Space Network telescopes to track the Radioastron spacecraft when it is not visible from Soviet tracking stations are considered

Uses of the ICRF and implications for future VLBI

Science.gov (United States)

Ma, Chopo

2006-01-01

Since its inception on 1 Jan 1998, the fundamental ICRF has been set by the VLBI positions of 212 "defining" extragalactic radio sources. In all there are approx.3000 sources with usefully accurate (< few mas) positions consistent with the ICRF. The uses of the ICRF include fundamental astrometry, monitoring of Earth orientation, and spacecraft navigation. For fundamental astrometry, stability and accuracy are most important, and realizations at different frequencies must be in proper registration. However, there is no preferred frequency, and the GAIA mission has the potential for an optical ICRF with 500,000 objects at the 50 microarcsec level some time after the planned 2011 launch. The radio ICRF should be properly prepared for a transition to assure long term stability and consistency. Earth orientation monitoring requires objects attached to the solid Earth, and VLBI will continue to be the fundamental technique. For this purpose it is essential that the new VLBI stations contemplated in the VLBI20l0 report be capable of observing a sufficiently large and well-distributed set of stable sources, and identifying these sources is an on-going effort. Spacecraft navigation by differential VLBI is planned using the Ka-band telemetry signal, and work has begun towards an ICRF realization suitable for this purpose. The balancing of different needs related to the VLBI ICRF will be discussed.

Integration of Reference Frames Using VLBI

Science.gov (United States)

Ma, Chopo; Smith, David E. (Technical Monitor)

2001-01-01

Very Long Baseline Interferometry (VLBI) has the unique potential to integrate the terrestrial and celestial reference frames through simultaneous estimation of positions and velocities of approx. 40 active VLBI stations and a similar number of stations/sites with sufficient historical data, the position and position stability of approx. 150 well-observed extragalactic radio sources and another approx. 500 sources distributed fairly uniformly on the sky, and the time series of the five parameters that specify the relative orientation of the two frames. The full realization of this potential is limited by a number of factors including the temporal and spatial distribution of the stations, uneven distribution of observations over the sources and the sky, variations in source structure, modeling of the solid/fluid Earth and troposphere, logistical restrictions on the daily observing network size, and differing strategies for optimizing analysis for TRF, for CRF and for EOP. The current status of separately optimized and integrated VLBI analysis will be discussed.

National Geodetic Survey (NGS) Geodetic Control Stations, (Horizontal and/or Vertical Control), March 2009

Data.gov (United States)

Earth Data Analysis Center, University of New Mexico — This data contains a set of geodetic control stations maintained by the National Geodetic Survey. Each geodetic control station in this dataset has either a precise...

Geodetic Space Weather Monitoring by means of Ionosphere Modelling

Science.gov (United States)

Schmidt, Michael

2017-04-01

The term space weather indicates physical processes and phenomena in space caused by radiation of energy mainly from the Sun. Manifestations of space weather are (1) variations of the Earth's magnetic field, (2) the polar lights in the northern and southern hemisphere, (3) variations within the ionosphere as part of the upper atmosphere characterized by the existence of free electrons and ions, (4) the solar wind, i.e. the permanent emission of electrons and photons, (5) the interplanetary magnetic field, and (6) electric currents, e.g. the van Allen radiation belt. It can be stated that ionosphere disturbances are often caused by so-called solar storms. A solar storm comprises solar events such as solar flares and coronal mass ejections (CMEs) which have different effects on the Earth. Solar flares may cause disturbances in positioning, navigation and communication. CMEs can effect severe disturbances and in extreme cases damages or even destructions of modern infrastructure. Examples are interruptions to satellite services including the global navigation satellite systems (GNSS), communication systems, Earth observation and imaging systems or a potential failure of power networks. Currently the measurements of solar satellite missions such as STEREO and SOHO are used to forecast solar events. Besides these measurements the Earth's ionosphere plays another key role in monitoring the space weather, because it responses to solar storms with an increase of the electron density. Space-geodetic observation techniques, such as terrestrial GNSS, satellite altimetry, space-borne GPS (radio occultation), DORIS and VLBI provide valuable global information about the state of the ionosphere. Additionally geodesy has a long history and large experience in developing and using sophisticated analysis and combination techniques as well as empirical and physical modelling approaches. Consequently, geodesy is predestinated for strongly supporting space weather monitoring via

National Geodetic Control Stations, Geographic NAD83, NGS (2004) [geodetic_ctrl_point_la_NGS_2004

Data.gov (United States)

Louisiana Geographic Information Center — This data contains a set of geodetic control stations maintained by the National Geodetic Survey. Each geodetic control station in this dataset has either a precise...

Effect of horizontal displacements due to ocean tide loading on the determination of polar motion and UT1

Science.gov (United States)

Scherneck, Hans-Georg; Haas, Rüdiger

We show the influence of horizontal displacements due to ocean tide loading on the determination of polar motion and UT1 (PMU) on the daily and subdaily timescale. So called ‘virtual PMU variations’ due to modelling errors of ocean tide loading are predicted for geodetic Very Long Baseline Interferometry (VLBI) networks. This leads to errors of subdaily determination of PMU. The predicted effects are confirmed by the analysis of geodetic VLBI observations.

First Space VLBI Observations and Images Using the VLBA and VSOP

Science.gov (United States)

Romney, J. D.; Benson, J. M.; Claussen, M. J.; Desai, K. M.; Flatters, C.; Mioduszewski, A. J.; Ulvestad, J. S.

1997-12-01

The National Radio Astronomy Observatory (NRAO) is a participant in the VSOP Space VLBI mission, an international collaboration led by Japan's Institute of Space and Astronautical Science. NRAO has committed up to 30% of scheduled observing time on the Very Long Baseline Array (VLBA), and corresponding correlation resources, to Space VLBI observations. The NRAO Space VLBI Project, funded by NASA, has been working for several years to complete the necessary enhancements to the VLBA correlator and the AIPS image processing system. These developments were completed by the time of the successful launch of the VSOP mission's Halca spacecraft on 1997 February 12. As part of the in-orbit checkout phase, the first Space VLBI fringes from a VLBA observation were detected on 1997 June 12, and the VSOP mission's first images, in both the 1.6- and 5-GHz bands, were obtained shortly thereafter. In-orbit test observations continued through early September, with the first General Observing Time (GOT) scientific observations beginning in July. Through mid-October, a total of 20 Space VLBI observations, comprising 190 hours, had been completed at the VLBA correlator. This paper reviews the unique features of correlation and imaging of Space VLBI observations. These include, for correlation, the ephemeris for an orbiting VLBI ``station'' which is not fixed on the surface of the earth, and the requirement to close the loop on the phase-transfer process from a frequency standard on the ground to the spacecraft. Images from a number of early tests and scientific observations are presented. NRAO's user-support program, providing expert assistance in data analysis to Space VLBI observers, is also described.

Possible systematics in the VLBI catalogs as seen from Gaia

Science.gov (United States)

Liu, N.; Zhu, Z.; Liu, J.-C.

2018-01-01

Aims: In order to investigate the systematic errors in the very long baseline interferometry (VLBI) positions of extragalactic sources (quasars) and the global differences between Gaia and VLBI catalogs, we use the first data release of Gaia (Gaia DR1) quasar positions as the reference and study the positional offsets of the second realization of the International Celestial Reference Frame (ICRF2) and the Goddard VLBI solution 2016a (gsf2016a) catalogs. Methods: We select a sample of 1032 common sources among three catalogs and adopt two methods to represent the systematics: considering the differential orientation (offset) and declination bias; analyzing with the vector spherical harmonics (VSH) functions. Results: Between two VLBI catalogs and Gaia DR1, we find that: i) the estimated orientation is consistent with the alignment accuracy of Gaia DR1 to ICRF, of 0.1 mas, but the southern and northern hemispheres show opposite orientations; ii) the declination bias in the southern hemisphere between Gaia DR1 and ICRF2 is estimated to be +152 μas, much larger than that between Gaia DR1 and gsf2016a which is +34 μas. Between two VLBI catalogs, we find that: i) the rotation component shows that ICRF2 and gsf2016a are generally consistent within 30 μas; ii) the glide component and quadrupole component report two declination-dependent offsets: dipolar deformation of +50 μas along the Z-axis, and quadrupolar deformation of -50 μas that would induce a pattern of sin2δ. Conclusions: The significant declination bias between Gaia DR1 and ICRF2 catalogs reported in previous studies is possibly attributed to the systematic errors of ICRF2 in the southern hemisphere. The global differences between ICRF2 and gsf2016a catalogs imply that possible, mainly declination-dependent systematics exit in the VLBI positions and need further investigations in the future Gaia data release and the next generation of ICRF.

An Experiment on Radio Location of Objects in the Near-Earth Space with VLBI in 2012

Directory of Open Access Journals (Sweden)

Nechaeva M.

2013-03-01

Full Text Available An experiment on radar location of space debris objects using of the method of VLBI was carried out in April, 2012. The radar VLBI experiment consisted in irradiation of some space debris objects (4 rocket stages and 5 inactive satellites with a signal of the transmitter with RT-70 in Evpatoria, Ukraine. Reflected signals were received by a complex of radio telescopes in the VLBI mode. The following VLBI stations took part in the observations: Ventspils (RT-32, Urumqi (RT-25, Medicina (RT-32 and Simeiz (RT-22. The experiment included measurements of the Doppler frequency shift and the delay for orbit refining, and measurements of the rotation period and sizes of objects by the amplitudes of output interferometer signals. The cross-correlation of VLBI-data is performed at a correlator NIRFI-4 of Radiophysical Research Institute (Nizhny Novgorod. Preliminary data processing resulted in the series of Doppler frequency shifts, which comprised the information on radial velocities of the objects. Some results of the experiment are presented.

The African VLBI network project

Science.gov (United States)

Loots, Anita

2015-01-01

The AVN is one of the most significant vehicles through which capacity development in Africa for SKA participation will be realized. It is a forerunner to the long baseline Phase 2 component of the mid-frequency SKA. Besides the 26m HartRAO telescope in South Africa, Ghana is expected to be the first to establish a VLBI-capable telescope through conversion of a redundant 32m telecommunications system near Accra. The most widely used receivers in the EVN are L-band and C-band (5 GHz). L-band is divided into a low band around the hydrogen (HI) line frequency of 1420 MHz, and a high band covering the hydroxyl line frequencies of 1612-1720 MHz. The high band is much more commonly used for VLBI as it provides more bandwidth. For the AVN, the methanol maser line at 6668 MHz is a key target for the initial receiver and the related 12178MHz methanol maser line also seen in star-forming regions a potential future Ku-band receiver. In the potential future band around 22GHz(K-band), water masers in star-forming regions and meg-maser galaxies at 22.235 GHz are targets, as are other radio continuum sources such as AGNs. The AVN system will include 5GHz and 6.668GHz receiver systems with recommendation to partner countries that the first upgrade should be L-band receivers. The original satellite telecommunications feed horns cover 3.8 - 6.4 GHz and should work at 5 GHz and operation at 6.668 GHz for the methanol maser is yet to be verified. The first light science will be conducted in the 6.7 GHz methanol maser band. Telescopes developed for the AVN will initially join other global networks for VLBI. When at least four VLBI-capable telescopes are operational on the continent, it will be possible to initiate stand-alone AVN VLBI. Each country where an AVN telescope becomes operational will have its own single-dish observing program. Capacity building to run an observatory includes the establishment of competent core essential observatory staff in partner countries who can train

Status and Prospects for Combined GPS LOD and VLBI UT1 Measurements

Science.gov (United States)

Senior, K.; Kouba, J.; Ray, J.

2010-01-01

A Kalman filter was developed to combine VLBI estimates of UT1-TAI with biased length of day (LOD) estimates from GPS. The VLBI results are the analyses of the NASA Goddard Space Flight Center group from 24-hr multi-station observing sessions several times per week and the nearly daily 1-hr single-baseline sessions. Daily GPS LOD estimates from the International GNSS Service (IGS) are combined with the VLBI UT1-TAI by modeling the natural excitation of LOD as the integral of a white noise process (i.e., as a random walk) and the UT1 variations as the integration of LOD, similar to the method described by Morabito et al. (1988). To account for GPS technique errors, which express themselves mostly as temporally correlated biases in the LOD measurements, a Gauss-Markov model has been added to assimilate the IGS data, together with a fortnightly sinusoidal term to capture errors in the IGS treatments of tidal effects. Evaluated against independent atmospheric and oceanic axial angular momentum (AAM + OAM) excitations and compared to other UT1/LOD combinations, ours performs best overall in terms of lowest RMS residual and highest correlation with (AAM + OAM) over sliding intervals down to 3 d. The IERS 05C04 and Bulletin A combinations show strong high-frequency smoothing and other problems. Until modified, the JPL SPACE series suffered in the high frequencies from not including any GPS-based LODs. We find, surprisingly, that further improvements are possible in the Kalman filter combination by selective rejection of some VLBI data. The best combined results are obtained by excluding all the 1-hr single-baseline UT1 data as well as those 24-hr UT1 measurements with formal errors greater than 5 μs (about 18% of the multi-baseline sessions). A rescaling of the VLBI formal errors, rather than rejection, was not an effective strategy. These results suggest that the UT1 errors of the 1-hr and weaker 24-hr VLBI sessions are non-Gaussian and more heterogeneous than expected

Using TDRSS as an orbiting VLBI observatory

International Nuclear Information System (INIS)

Ulvestad, J.S.

1987-01-01

The procedures and results of experimental VLBI astronomical observations performed using TDRSE, the first deployed satellite of the NASA TDRSS, as one of the network telescopes are reviewed. The other two elements of the VLBI network were the high-sensitivity 64-m antennas of the NASA DSN in Australia and of ISAS in Japan, with a 25-m Japanese antenna used to check their performance. The E configuration of the Mark III recording system at White Sands was used to record seven contiguous 2-MHz channels centered at 2.27799 GHz during five 3-h periods in July-August 1986. Although satellite pointing failures and ground-station problems limited the number of useful observations to six, interferometric fringes of the sources were obtained in all of these observations, demonstrating the feasibility of the approach. 6 references

Plate Motion and Crustal Deformation Estimated with Geodetic Data from the Global Positioning System

Science.gov (United States)

Argus, Donald F.; Heflin, Michael B.

1995-01-01

We use geodetic data taken over four years with the Global Positioning System (GPS) to estimate: (1) motion between six major plates and (2) motion relative to these plates of ten sites in plate boundary zones. The degree of consistency between geodetic velocities and rigid plates requires the (one-dimensional) standard errors in horizontal velocities to be approx. 2 mm/yr. Each of the 15 angular velocities describing motion between plate pairs that we estimate with GPS differs insignificantly from the corresponding angular velocity in global plate motion model NUVEL-1A, which averages motion over the past 3 m.y. The motion of the Pacific plate relative to both the Eurasian and North American plates is observed to be faster than predicted by NUVEL-1A, supporting the inference from Very Long B ase- line Interferometry (VLBI) that motion of the Pacific plate has speed up over the past few m.y. The Eurasia-North America pole of rotation is estimated to be north of NUVEL-1A, consistent with the independent hypothesis that the pole has recently migrated northward across northeast Asia to near the Lena River delta. Victoria, which lies above the main thrust at the Cascadia subduction zone, moves relative to the interior of the overriding plate at 30% of the velocity of the subducting plate, reinforcing the conclusion that the thrust there is locked beneath the continental shelf and slope.

Geodetic Control Information on Passive Marks: Horizontal and Vertical Geodetic Control Data for the United States - National Geospatial Data Asset (NGDA) Geodetic Control Information on Passive Marks

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This data contains a set of geodetic control stations maintained by the National Geodetic Survey. Each geodetic control station in this dataset has either a precise...

Development of a New VLBI Data Analysis Software

Science.gov (United States)

Bolotin, Sergei; Gipson, John M.; MacMillan, Daniel S.

2010-01-01

We present an overview of a new VLBI analysis software under development at NASA GSFC. The new software will replace CALC/SOLVE and many related utility programs. It will have the capabilities of the current system as well as incorporate new models and data analysis techniques. In this paper we give a conceptual overview of the new software. We formulate the main goals of the software. The software should be flexible and modular to implement models and estimation techniques that currently exist or will appear in future. On the other hand it should be reliable and possess production quality for processing standard VLBI sessions. Also, it needs to be capable of processing observations from a fully deployed network of VLBI2010 stations in a reasonable time. We describe the software development process and outline the software architecture.

VLBI observations with the Kunming 40-meter radio telescope

International Nuclear Information System (INIS)

Hao Longfei; Wang Min; Yang Jun

2010-01-01

The Kunming 40-meter radio telescope is situated in the yard of the Yunnan Astronomical Observatory (Longitude: 102.8 0 East, Latitude: 25.0 0 North) and saw its first light in 2006 May. The Kunming station successfully joined the VLBI tracking of China's first lunar probe 'Chang'E-1 together with the other Chinese telescopes: the Beijing Miyun 50-meter radio telescope, Urumqi Nanshan 25-meter radio telescope, and Shanghai Sheshan 25-meter radio telescope, and received the downlinked scientific data together with the Miyun station from October of 2007 to March of 2009. We give an introduction to the new Chinese VLBI facility and investigate its potential applications. Due to its location, the Kunming station can significantly improve the u - v coverage of the European VLBI Network (EVN), in particular, in long baseline observations. We also report the results of the first EVN fringe-test experiment of N09SX1 with the Kunming station. The first fringes in the European telescopes were successfully detected at 2.3 GHz with the ftp-transferred data on 2009 June 17. From scheduling the observations to performing the post correlations, the Kunming station shows its good compatibility to work with the EVN. The imaging result of the extended source 1156+295 further demonstrates that the Kunming station greatly enhances the EVN performance. (research papers)

Monitoring of Earth Rotation by VLBI

Science.gov (United States)

Ma., Chopo; Macmillan, D. S.

2000-01-01

Monitoring Earth rotation with Very Long Baseline Interferometry (VLBI) has unique potential because of direct access to the Celestial Reference System (CRF and Terrestrial Reference System (TRF) and the feasibility of re-analyzing the entire data set. While formal precision of better than 0.045 mas for pole and 0.002 ms for UT 1 has been seen in the best 24-hr data, the accuracy of the Earth Orientation Parameter (EOP) time series as a whole is subject to logistical, operational, analytical and conceptual constraints. The current issues related to the VLBI data set and the CORE program for greater time resolution such as analysis consistency, network jitter and reference frame stability will be discussed.

Meter-wavelength VLBI. III. Pulsars

International Nuclear Information System (INIS)

Vandenberg, N.R.; Clark, T.A.; Clark, W.C.; Erickson, W.C.; Resch, G.M.; Broderick, J.J.

1976-01-01

The results and analysis of observations of pulsars, especially the Crab Nebula pulsar, taken during a series of meter-wavelength very long baseline interferometry (VLBI) experiments are discussed. Based on a crude 144 MHz visibility curve which is consistent with a Gaussian brightness distribution, the measured visibilities at 196, 111, and 74 MHz were interpreted to yield apparent angular diameters (at half-power) of 0 .03 +- 0 .01, 0 .07 +- 0 .01, and 0 .18 +- 0 .01, respectively. These sizes scale approximately as wavelength-squared, and the 74 MHz size agrees with recent observations using interplanetary scintillation techniques.The VLBI-measured total flux densities lie on the extrapolation from higher frequencies of the pulsing flux densities. Variations in the total flux density up to 25 percent were observed. A lack of fine structure other than the pulsar in the nebula is indicated by our simple visibility curves. The pulse shapes observed with the interferometer are similar to single-dish measurements at 196 MHz but reveal a steady, nonpulsing component at 111 MHz. The ratio of pulsing to total power was approximately equal to one-half but varied with time. No pulsing power was detected at 74 MHz. It was found that four strong, low-dispersion pulsars were only slightly resolved

DSN Beowulf Cluster-Based VLBI Correlator

Science.gov (United States)

Rogstad, Stephen P.; Jongeling, Andre P.; Finley, Susan G.; White, Leslie A.; Lanyi, Gabor E.; Clark, John E.; Goodhart, Charles E.

2009-01-01

The NASA Deep Space Network (DSN) requires a broadband VLBI (very long baseline interferometry) correlator to process data routinely taken as part of the VLBI source Catalogue Maintenance and Enhancement task (CAT M&E) and the Time and Earth Motion Precision Observations task (TEMPO). The data provided by these measurements are a crucial ingredient in the formation of precision deep-space navigation models. In addition, a VLBI correlator is needed to provide support for other VLBI related activities for both internal and external customers. The JPL VLBI Correlator (JVC) was designed, developed, and delivered to the DSN as a successor to the legacy Block II Correlator. The JVC is a full-capability VLBI correlator that uses software processes running on multiple computers to cross-correlate two-antenna broadband noise data. Components of this new system (see Figure 1) consist of Linux PCs integrated into a Beowulf Cluster, an existing Mark5 data storage system, a RAID array, an existing software correlator package (SoftC) originally developed for Delta DOR Navigation processing, and various custom- developed software processes and scripts. Parallel processing on the JVC is achieved by assigning slave nodes of the Beowulf cluster to process separate scans in parallel until all scans have been processed. Due to the single stream sequential playback of the Mark5 data, some ramp-up time is required before all nodes can have access to required scan data. Core functions of each processing step are accomplished using optimized C programs. The coordination and execution of these programs across the cluster is accomplished using Pearl scripts, PostgreSQL commands, and a handful of miscellaneous system utilities. Mark5 data modules are loaded on Mark5 Data systems playback units, one per station. Data processing is started when the operator scans the Mark5 systems and runs a script that reads various configuration files and then creates an experiment-dependent status database

Approaching the event horizon: 1.3mmλ VLBI of SgrA*

International Nuclear Information System (INIS)

Doeleman, Sheperd

2008-01-01

Advances in VLBI instrumentation now allow wideband recording that significantly increases the sensitivity of short wavelength VLBI observations. Observations of the super-massive black hole candidate at the center of the Milky Way, SgrA*, with short wavelength VLBI reduces the scattering effects of the intervening interstellar medium, allowing observations with angular resolution comparable to the apparent size of the event horizon of the putative black hole. Observations in April 2007 at a wavelength of 1.3mm on a three station VLBI array have now confirmed structure in SgrA* on scales of just a few Schwarzschild radii. When modeled as a circular Gaussian, the fitted diameter of SgrA* is 37 μas (+16,-10; 3σ), which is smaller than the expected apparent size of the event horizon of the Galactic Center black hole. These observations demonstrate that mm/sub-mm VLBI is poised to open a new window onto the study of black hole physics via high angular resolution observations of the Galactic Center.

Modified geodetic brane cosmology

International Nuclear Information System (INIS)

Cordero, Rubén; Cruz, Miguel; Molgado, Alberto; Rojas, Efraín

2012-01-01

We explore the cosmological implications provided by the geodetic brane gravity action corrected by an extrinsic curvature brane term, describing a codimension-1 brane embedded in a 5D fixed Minkowski spacetime. In the geodetic brane gravity action, we accommodate the correction term through a linear term in the extrinsic curvature swept out by the brane. We study the resulting geodetic-type equation of motion. Within a Friedmann–Robertson–Walker metric, we obtain a generalized Friedmann equation describing the associated cosmological evolution. We observe that, when the radiation-like energy contribution from the extra dimension is vanishing, this effective model leads to a self-(non-self)-accelerated expansion of the brane-like universe in dependence on the nature of the concomitant parameter β associated with the correction, which resembles an analogous behaviour in the DGP brane cosmology. Several possibilities in the description for the cosmic evolution of this model are embodied and characterized by the involved density parameters related in turn to the cosmological constant, the geometry characterizing the model, the introduced β parameter as well as the dark-like energy and the matter content on the brane. (paper)

Positioning Reduction of Deep Space Probes Based on VLBI Tracking

Science.gov (United States)

Qiao, S. B.

2011-11-01

In the background of the Chinese Lunar Exploration Project and the Yinghuo Project, through theoretical analysis, algorithm study, software development, data simulation, real data processing and so on, the positioning reductions of the European lunar satellite Smart-1 and Mars Express (MEX) satellite, as well as the Chinese Chang'e-1 (CE-1) and Chang'e-2 (CE-2) satellites are accomplished by using VLBI and USB tracking data in this dissertation. The progress is made in various aspects including the development of theoretical model, the construction of observation equation, the analysis of the condition of normal equation, the selection and determination of the constraint, the analysis of data simulation, the detection of outliers in observations, the maintenance of the stability of the solution of parameters, the development of the practical software system, the processing of the real tracking data and so on. The details of the research progress in this dissertation are written as follows: (1) The algorithm is analyzed concerning the positioning reduction of the deep spacecraft based on VLBI tracking data. Through data simulation, it is analyzed for the effects of the bias in predicted orbit, the white noises and systematic errors in VLBI delays, and USB ranges on the positioning reduction of spacecraft. Results show that it is preferable to suppress the dispersion of positioning data points by applying the constraint of geocentric distance of spacecraft when there are only VLBI tracking data. The positioning solution is a biased estimate via observations of three VLBI stations. For the case of four tracking stations, the uncertainty of the constraint should be in accordance with the bias in the predicted orbit. White noises in delays and ranges mainly result in dispersion of the sequence of positioning data points. If there is the systematic error of observations, the systematic offset of the positioning results is caused, and there are trend jumps in the shape of

New VLBI Observing System 'OCTAVE-Family' to Support VDIF Specifications with 10 GigE for VERA, JVN, and Japanese e-VLBI (OCTAVE)

Science.gov (United States)

Oyama, T.; Kono, Y.; Suzuki, S.; Mizuno, S.; Bushimata, T.; Jike, T.; Kawaguchi, N.; Kobayashi, H.; Kimura, M.

2012-12-01

The new VLBI observing system (OCTAVE-Family) has been designed and developed based on the VSI-H and VDIF specifications at NAOJ (National Astronomical Observatory of Japan). It consists of 1) a high speed 8-Gsps 3-bit ADC (OCTAD) enabling us to acquire not only wide intermediate frequencies but also radio frequencies up to 50 GHz, 2) a converter (OCTAVIA) between one 10 GigE port and four 2 Gbps input and output ports conformable to VSI-H, 3) new recorders (OCTADISK and OCTADISK2) at rates of 4.5 Gbps and above 8 Gbps, and 4) a high speed software correlator system (OCTACOR) using GICO3 which was developed by NICT. These OCTAVE systems are connected via 10 GigE network with VDIF and VSI specifications. These components are used for VERA, JVN (Japanese VLBI network), and KJJVC (Korea-Japan Joint VLBI Correlator).

Geodetic Survey Water Level Observations

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Over one million images of National Coast & Geodetic Survey (now NOAA's National Geodetic Survey/NGS) forms captured from microfiche. Tabular forms and charts...

SAND: an automated VLBI imaging and analysing pipeline - I. Stripping component trajectories

Science.gov (United States)

Zhang, M.; Collioud, A.; Charlot, P.

2018-02-01

We present our implementation of an automated very long baseline interferometry (VLBI) data-reduction pipeline that is dedicated to interferometric data imaging and analysis. The pipeline can handle massive VLBI data efficiently, which makes it an appropriate tool to investigate multi-epoch multiband VLBI data. Compared to traditional manual data reduction, our pipeline provides more objective results as less human interference is involved. The source extraction is carried out in the image plane, while deconvolution and model fitting are performed in both the image plane and the uv plane for parallel comparison. The output from the pipeline includes catalogues of CLEANed images and reconstructed models, polarization maps, proper motion estimates, core light curves and multiband spectra. We have developed a regression STRIP algorithm to automatically detect linear or non-linear patterns in the jet component trajectories. This algorithm offers an objective method to match jet components at different epochs and to determine their proper motions.

The simulation of lunar gravity field recovery from D-VLBI of Chang’E-1 and SELENE lunar orbiters

Science.gov (United States)

Yan, Jianguo; Ping, Jingsong; Matsumoto, K.; Li, Fei

2008-07-01

The lunar gravity field is a foundation to study the lunar interior structure, and to recover the evolution history of the Moon. It is still an open and key topic for lunar science. For above mentioned reasons, it becomes one of the important scientific objectives of recent lunar missions, such as KAGUYA (SELENE) the Japanese lunar mission and Chang’E-1, the Chinese lunar mission. The Chang’E-1 and the SELENE were successfully launched in 2007. It is estimated that these two missions can fly around the Moon longer than 6 months simultaneously. In these two missions, the Chinese new VLBI (Very Long Baseline Interferometry) network will be applied for precise orbit determination (POD) by using a differential VLBI (D-VLBI) method during the mission period. The same-beam D-VLBI technique will contribute to recover the lunar gravity field together with other conventional observables, i.e. R&RR (Range and Range Rate) and multi-way Doppler. Taking VLBI tracking conditions into consideration and using the GEODYNII/SOVLE software of GSFC/NASA/USA [Rowlands, D.D., Marshall, J.A., Mccarthy, J., et al. GEODYN II System Description, vols. 1 5. Contractor Report, Hughes STX Corp. Greenbelt, MD, 1997; Ullman, R.E. SOLVE program: mathematical formulation and guide to user input, Hughes/STX Contractor Report, Contract NAS5-31760. NASA Goddard Space Flight Center, Greenbelt, Maryland, 1994], we simulated the lunar gravity field recovering ability with and without D-VLBI between the Chang’E-1 and SELENE main satellite. The cases of overlapped flying and tracking period of 30 days, 60 days and 90 days have been analyzed, respectively. The results show that D-VLBI tracking between two lunar satellites can improve the gravity field recovery remarkably. The results and methods introduced in this paper will benefit the actual missions.

Observing atmospheric tides in Earth rotation parameters with VLBI

Science.gov (United States)

Girdiuk, Anastasiia; Böhm, Johannes; Schindelegger, Michael

2015-04-01

In this study, we assess the contribution of diurnal (S1) and semi-diurnal (S2) atmospheric tides to variations in Earth rotation by analyzing Very Long Baseline Interferometry (VLBI) observations. Particular emphasis is placed on the dependency of S1 and S2 estimates on varying settings in the a priori delay model. We use hourly Earth rotation parameters (ERP) of polar motion and UT1 as determined with the Vienna VLBI Software (VieVS) from 25 years of VLBI observations and we adjust diurnal and semi-diurnal amplitudes to the hourly ERP estimates after disregarding the effect of high-frequency ocean tides. Prograde and retrograde polar motion coefficients are obtained for several solutions differing in processing strategies (with/without thermal deformation, time span of observations, choice of a priori ERP model and celestial pole offsets) and we compare the corresponding harmonics with those derived from atmospheric and non-tidal oceanic angular momentum estimates.

VLBI detection of the internal shocks in nova V959 Mon

Science.gov (United States)

Yang, J.; Paragi, Z.; O'Brien, T.; Chomiuk, L.; Linford, J. D.

V959 Mon is a classical nova detected at GeV gamma-ray wavelengths on 2012 June 19. While classical novae are now routinely detected in gamma-rays, the origin of the shocks that produce relativistic particles has remained unknown. We carried out electronic European VLBI Network (e-EVN) observations that revealed a pair of compact synchrotron emission features in V959 Mon on 2012 Sep 18. Since synchrotron emission requires strong shocks as well, we identify these features as the location where the gamma rays were produced. We also detected the extended ejecta in the follow-up EVN observations. They expanded much faster in East-West direction than the compact knots detected in the aforementioned e-EVN measurements. By comparing the VLBI results with lower resolution images obtained using e-MERLIN and the VLA - as reported by Chomiuk et al. (2014) - it appears that 1) influenced by the binary orbit, the nova ejecta was highly asymmetric with a dense and slow outflow in the equatorial plane and low-density and faster ejecta along the poles; and 2) the VLBI knots were related to shocks formed in the interaction region of these outflows.

Application of space geodetic techniques for the determination of intraplate deformations and movements in relation with the postglacial rebound of Fennoscandia

Energy Technology Data Exchange (ETDEWEB)

Scherneck, H G; Johansson, J M; Elgered, G [Chalmers Univ. of Technology, Goeteborg (Sweden). Onsala Space Observatory

1996-04-01

This report introduces into space geodetic measurements of relative positions over distances ranging from tens to thousands of kilometers. Such measurements can routinely be carried out with repeatabilities on the order of a few millimeters. The techniques presented are Very Long Baseline Interferometry (VLBI), employing observations of radio-astronomical objects in the distant universe, and ranging measurements to satellites of the GPS, the Global Positioning System. These techniques have helped to trace plate tectonic motions. More recently, deformations within continents have been detected. We present the SWEPOS system of permanently operating GPS stations as one of the major geoscience investments starting in 1993. BIFROST (Baseline Interference for Fennoscandian Rebound Observations, Sea level, and Tectonics) is a project within SWEPOS with main purpose to detect crustal movements in Fennoscandia. First results are presented, indicating movements which generally support the notion of a dominating displacement pattern due to the postglacial rebound of Fennoscandia. However deviations exist. densification is indicated in those areas which are notable for an increased seismicity. 148 refs.

Application of space geodetic techniques for the determination of intraplate deformations and movements in relation with the postglacial rebound of Fennoscandia

International Nuclear Information System (INIS)

Scherneck, H.G.; Johansson, J.M.; Elgered, G.

1996-04-01

This report introduces into space geodetic measurements of relative positions over distances ranging from tens to thousands of kilometers. Such measurements can routinely be carried out with repeatabilities on the order of a few millimeters. The techniques presented are Very Long Baseline Interferometry (VLBI), employing observations of radio-astronomical objects in the distant universe, and ranging measurements to satellites of the GPS, the Global Positioning System. These techniques have helped to trace plate tectonic motions. More recently, deformations within continents have been detected. We present the SWEPOS system of permanently operating GPS stations as one of the major geoscience investments starting in 1993. BIFROST (Baseline Interference for Fennoscandian Rebound Observations, Sea level, and Tectonics) is a project within SWEPOS with main purpose to detect crustal movements in Fennoscandia. First results are presented, indicating movements which generally support the notion of a dominating displacement pattern due to the postglacial rebound of Fennoscandia. However deviations exist. densification is indicated in those areas which are notable for an increased seismicity. 148 refs

VLBI FOR GRAVITY PROBE B. IV. A NEW ASTROMETRIC ANALYSIS TECHNIQUE AND A COMPARISON WITH RESULTS FROM OTHER TECHNIQUES

International Nuclear Information System (INIS)

Lebach, D. E.; Ratner, M. I.; Shapiro, I. I.; Bartel, N.; Bietenholz, M. F.; Lederman, J. I.; Ransom, R. R.; Campbell, R. M.; Gordon, D.; Lestrade, J.-F.

2012-01-01

When very long baseline interferometry (VLBI) observations are used to determine the position or motion of a radio source relative to reference sources nearby on the sky, the astrometric information is usually obtained via (1) phase-referenced maps or (2) parametric model fits to measured fringe phases or multiband delays. In this paper, we describe a 'merged' analysis technique which combines some of the most important advantages of these other two approaches. In particular, our merged technique combines the superior model-correction capabilities of parametric model fits with the ability of phase-referenced maps to yield astrometric measurements of sources that are too weak to be used in parametric model fits. We compare the results from this merged technique with the results from phase-referenced maps and from parametric model fits in the analysis of astrometric VLBI observations of the radio-bright star IM Pegasi (HR 8703) and the radio source B2252+172 nearby on the sky. In these studies we use central-core components of radio sources 3C 454.3 and B2250+194 as our positional references. We obtain astrometric results for IM Peg with our merged technique even when the source is too weak to be used in parametric model fits, and we find that our merged technique yields astrometric results superior to the phase-referenced mapping technique. We used our merged technique to estimate the proper motion and other astrometric parameters of IM Peg in support of the NASA/Stanford Gravity Probe B mission.

Engineering processes for the African VLBI network

Science.gov (United States)

Thondikulam, Venkatasubramani L.; Loots, Anita; Gaylard, Michael

2013-04-01

The African VLBI Network (AVN) is an initiative by the SKA-SA and HartRAO, business units of the National Research Foundation (NRF), Department of Science and Technology (DST), South Africa. The aim is to fill the existing gap of Very Long Baseline Interferometry (VLBI)-capable radio telescopes in the African continent by a combination of new build as well as conversion of large redundant telecommunication antennas through an Inter-Governmental collaborative programme in Science and Technology. The issue of human capital development in the Continent in the techniques of radio astronomy engineering and science is a strong force to drive the project and is expected to contribute significantly to the success of Square Kilometer Array (SKA) in the Continent.

First Results of the VLBI Experiment on Radar Location of the Asteroid 2012 DA14

Directory of Open Access Journals (Sweden)

Nechaeva M.

2013-12-01

Full Text Available An international VLBI experiment on radio location of the asteroid 2012 DA14 was organized on 2013 February 15–16, during its flyby close to Earth. The purpose of observations was to investigate and specify orbital parameters of the asteroid, as well as to evaluate its rotation period and other characteristics. The irradiation of the asteroid was performed by the RT-70 transmitter at Evpatoria (Crimea, Ukraine, while the reflected signals were successfully accepted by the two 32 m radio telescopes at Medicina (Bologna, Italy and Irbene (Ventspils, Latvia. Processing and interpretation of the data were performed both in the Radiophysical Research Institute at Nizhny Novgorod and in the Ventspils International Radio Astronomy Center. The first results of this experiment are presented and discussed.

Legacy and future of Kilauea's geodetic studies

Science.gov (United States)

Montgomery-Brown, E. D.; Miklius, A.

2011-12-01

Because of its extensive and detailed history of geodetic measurements, Kilauea is one of the best-studied if not also best-understood volcanic systems in the world. Hawaiian volcanoes have a long history of deformation observations. These observations range from native legends of Pele's underground travels, through initial measurements made by the Hawaiian Volcano Observatory, and finally to current ground-based and satellite observations. Many questions still remain, relating to Kilauea's dynamics, where geodetic measurements could offer fundamental insights. For example, new geodetic experiments could lead to a better understanding of the degree of magmatic and tectonic interaction, the geometries of faults at depth, the extent of offshore deformation, and the magmatic plumbing system. While it is possible to design many experiments to address these issues, we focus on three deformation targets where geodetic improvements, including finer sampling in space and time, could yield significant advancements toward understanding Kilauea's dynamics. First, by scrutinizing spatially-dense space-borne geodetic data for signs of upper east rift zone deformation and incorporating gravity and seismic data in a high resolution tomographic model, the hydraulic connection between Kilauea's summit and the rift zone could be imaged, which would provide insight into the pathways that transport magma out to the rift zones. Second, a combination of geodetic and seismic data could be used to determine the nature of possible relationships and interactions between the Hilina fault system and Kilauea's basal decollement. Such a study would have important implications for assessments of future earthquake and sector collapse hazards. Lastly, by adding seafloor geodetic measurements and seismic data to the current geodetic network on Kilauea, we could delimit the offshore extent of transient and episodic decollement deformation. In addition to multidisciplinary approaches, future geodetic

Electron content near the lunar surface using dual-frequency VLBI tracking data in a single lunar orbiter mission

International Nuclear Information System (INIS)

Wang, Zhen; Wang, Na; Ping, Jin-Song

2015-01-01

In VLBI observations of Vstar, a subsatellite of the Japanese lunar mission SELENE, there were opportunities for lunar grazing occultation when Vstar was very close to the limb of the Moon. This kind of chance made it possible to probe the thin plasma layer above the Moon's surface as a meaningful by-product of VLBI, by using the radio occultation method with coherent radio waves from the S/X bands. The dual-frequency measurements were carried out at Earth-based VLBI stations. In the line-of-sight direction between the satellite and the ground-based tracking station where VLBI measurements were made, the effects of the terrestrial ionosphere, interplanetary plasma and the thin lunar ionosphere mixed together in the combined observables of dual-frequency Doppler shift and phase shift. To separate the variation of the ionospheric total electron content (TEC) near the surface of the Moon from the mixed signal, the influences of the terrestrial ionosphere and interplanetary plasma have been removed by using an extrapolation method based on a short-term trend. The lunar TEC is estimated from the dual-frequency observation for Vstar from UT 22:18 to UT 22:20 on 2008 June 28 at several tracking stations. The TEC results obtained from VLBI sites are identical, however, they are not as remarkable as the result obtained at the Usuda deep space tracking station. (paper)

1.3 mm WAVELENGTH VLBI OF SAGITTARIUS A*: DETECTION OF TIME-VARIABLE EMISSION ON EVENT HORIZON SCALES

International Nuclear Information System (INIS)

Fish, Vincent L.; Doeleman, Sheperd S.; Beaudoin, Christopher; Bolin, David E.; Rogers, Alan E. E.; Blundell, Ray; Gurwell, Mark A.; Moran, James M.; Primiani, Rurik; Bower, Geoffrey C.; Plambeck, Richard; Chamberlin, Richard; Freund, Robert; Friberg, Per; Honma, Mareki; Oyama, Tomoaki; Inoue, Makoto; Krichbaum, Thomas P.; Lamb, James; Marrone, Daniel P.

2011-01-01

Sagittarius A*, the ∼4 x 10 6 M sun black hole candidate at the Galactic center, can be studied on Schwarzschild radius scales with (sub)millimeter wavelength very long baseline interferometry (VLBI). We report on 1.3 mm wavelength observations of Sgr A* using a VLBI array consisting of the JCMT on Mauna Kea, the Arizona Radio Observatory's Submillimeter Telescope on Mt. Graham in Arizona, and two telescopes of the CARMA array at Cedar Flat in California. Both Sgr A* and the quasar calibrator 1924-292 were observed over three consecutive nights, and both sources were clearly detected on all baselines. For the first time, we are able to extract 1.3 mm VLBI interferometer phase information on Sgr A* through measurement of closure phase on the triangle of baselines. On the third night of observing, the correlated flux density of Sgr A* on all VLBI baselines increased relative to the first two nights, providing strong evidence for time-variable change on scales of a few Schwarzschild radii. These results suggest that future VLBI observations with greater sensitivity and additional baselines will play a valuable role in determining the structure of emission near the event horizon of Sgr A*.

Italy INAF Analysis Center Report

Science.gov (United States)

Negusini, M.; Sarti, P.

2013-01-01

This report summarizes the activity of the Italian INAF VLBI Analysis Center. Our Analysis Center is located in Bologna, Italy and belongs to the Institute of Radioastronomy, which is part of the National Institute of Astrophysics. IRA runs the observatories of Medicina and Noto, where two 32-m VLBI AZ-EL telescopes are situated. This report contains the AC's VLBI data analysis activities and shortly outlines the investigations into the co-locations of space geodetic instruments.

National Geodetic Survey's Airport Aerial Photography

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The National Geodetic Survey (NGS), formerly part of the U.S. Coast and Geodetic Survey, has been performing Aeronautical surveys since the 1920's. NGS, in...

Postglacial Rebound from VLBI Geodesy: On Establishing Vertical Reference

Science.gov (United States)

Argus, Donald F.

1996-01-01

Difficulty in establishing a reference frame fixed to the earth's interior complicates the measurement of the vertical (radial) motions of the surface. I propose that a useful reference frame for vertical motions is that found by minimizing differences between vertical motions observed with VLBI [Ma and Ryan] and predictions from postglacial rebound predictions [Peltier]. The optimal translation of the geocenter is 1.7mm/year toward 36degN, 111degE when determined from the motions of 10 VLBI sites. This translation gives a better fit of observations to predictions than does the VLBI reference frame used by Ma and Ryan, but the improvement is statistically insignificant. The root mean square of differences decreases 20% to 0.73 mm/yr and the correlation coefficient increases from 0.76 to 0.87. Postglacial rebound is evident in the uplift of points in Sweden and Ontario that were beneath the ancient ice sheets of Fennoscandia and Canada, and in the subsidence of points in the northeastern U.S., Germany, and Alaska that were around the periphery of the ancient ice sheets.

A preliminary geodetic data model for geographic information systems

Science.gov (United States)

Kelly, K. M.

2009-12-01

Our ability to gather and assimilate integrated data collections from multiple disciplines is important for earth system studies. Moreover, geosciences data collection has increased dramatically, with pervasive networks of observational stations on the ground, in the oceans, in the atmosphere and in space. Contemporary geodetic observations from several space and terrestrial technologies contribute to our knowledge of earth system processes and thus are a valuable source of high accuracy information for many global change studies. Assimilation of these geodetic observations and numerical models into models of weather, climate, oceans, hydrology, ice, and solid Earth processes is an important contribution geodesists can make to the earth science community. Clearly, the geodetic observations and models are fundamental to these contributions. ESRI wishes to provide leadership in the geodetic community to collaboratively build an open, freely available content specification that can be used by anyone to structure and manage geodetic data. This Geodetic Data Model will provide important context for all geographic information. The production of a task-specific geodetic data model involves several steps. The goal of the data model is to provide useful data structures and best practices for each step, making it easier for geodesists to organize their data and metadata in a way that will be useful in their data analyses and to their customers. Built on concepts from the successful Arc Marine data model, we introduce common geodetic data types and summarize the main thematic layers of the Geodetic Data Model. These provide a general framework for envisioning the core feature classes required to represent geodetic data in a geographic information system. Like Arc Marine, the framework is generic to allow users to build workflow or product specific geodetic data models tailored to the specific task(s) at hand. This approach allows integration of the data with other existing

Love numbers for the long-period tides estimated by VLBI

Science.gov (United States)

Krásná, Hana; Böhm, Johannes; Haas, Rüdiger; Schuh, Harald

2013-04-01

Love and Shida numbers are proportionality factors characterizing the deformation of the anelastic Earth which arises as a response to external forces from the Moon and Sun. The increasing precision and quality of the Very Long Baseline Interferometry (VLBI) measurements allow determining those parameters. In particular, the long history of the VLBI data enables the estimation of Love and Shida numbers at the low frequencies of the tidal waves including the periods from 14 days to 18.6 years. In this study we analyse 27 years of VLBI measurements (1984.0 - 2011.0) following the recent IERS Conventions 2010. In several global solutions, we estimate the complex Love and Shida numbers of the solid Earth tides for the main long-period tidal waves. Furthermore, we determine the Love and Shida numbers of the rotational deformation due to polar motion, the so-called pole tide. We also focus on station displacement where still some deficiencies in the long-period signal modelling can be seen.

Astrometry VLBI in Space (AVS

Science.gov (United States)

Altunin, V.; Alekseev, V.; Akim, E.; Eubanks, M.; Kingham, K.; Treuhaft, R.; Sukhanov, K.

1995-01-01

A proposed new space radio astronomy mission for astrometry is described. The Astrometry VLBI (very long baseline) in Space (AVS) nominal mission includes two identical spacecraft, each with a 4-m antenna sending data to a 70-m ground station. The goals of AVS are improving astrometry accuracy to the microarcsecond level and improving the accuracy of the transformation between the inertial radio and optical coordinate reference frames.

On an Allan variance approach to classify VLBI radio-sources on the basis of their astrometric stability

Science.gov (United States)

Gattano, C.; Lambert, S.; Bizouard, C.

2017-12-01

In the context of selecting sources defining the celestial reference frame, we compute astrometric time series of all VLBI radio-sources from observations in the International VLBI Service database. The time series are then analyzed with Allan variance in order to estimate the astrometric stability. From results, we establish a new classification that takes into account the whole multi-time scales information. The algorithm is flexible on the definition of ``stable source" through an adjustable threshold.

NASA's Next Generation Space Geodesy Network

Science.gov (United States)

Desai, S. D.; Gross, R. S.; Hilliard, L.; Lemoine, F. G.; Long, J. L.; Ma, C.; McGarry, J. F.; Merkowitz, S. M.; Murphy, D.; Noll, C. E.;

The New Generation Russian VLBI Network

Science.gov (United States)

Finkelstein, Andrey; Ipatov, Alexander; Smolentsev, Sergey; Mardyshkin, Vyacheslav; Fedotov, Leonid; Surkis, Igor; Ivanov, Dmitrij; Gayazov, Iskander

2010-01-01

This paper deals with a new project of the Russian VLBI Network dedicated for Universal Time determinations in quasi on-line mode. The basic principles of the network design and location of antennas are explained. Variants of constructing receiving devices, digital data acquisition system, and phase calibration system are specially considered. The frequency ranges and expected values of noise temperature are given.

Preliminary design work on a DSN VLBI correlator. [Deep Space Network

Science.gov (United States)

Lushbaugh, W. A.; Layland, J. W.

1978-01-01

The Deep Space Network is in the process of fielding high-density digital instrumentation recorders for support of the Pioneer Venus 1978 entry experiment and other related tasks. It has long been obvious that these recorders would also serve well as the recording medium for very long base interferometry (VLBI) experiments with relatively weak radio sources, provided that a suitable correlation processor for these tape recordings could be established. The overall design and current status of a VLBI correlator designed to mate with these tape recorders are described.

THE APPLICATION OF MULTIVIEW METHODS FOR HIGH-PRECISION ASTROMETRIC SPACE VLBI AT LOW FREQUENCIES

Energy Technology Data Exchange (ETDEWEB)

Dodson, R.; Rioja, M.; Imai, H. [International Centre for Radio Astronomy Research, M468, University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia 6009 (Australia); Asaki, Y. [Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Chuou, Sagamihara, Kanagawa 252-5210 (Japan); Hong, X.-Y.; Shen, Z., E-mail: richard.dodson@icrar.org [Shanghai Astronomical Observatory, CAS, 200030 Shanghai (China)

2013-06-15

High-precision astrometric space very long baseline interferometry (S-VLBI) at the low end of the conventional frequency range, i.e., 20 cm, is a requirement for a number of high-priority science goals. These are headlined by obtaining trigonometric parallax distances to pulsars in pulsar-black hole pairs and OH masers anywhere in the Milky Way and the Magellanic Clouds. We propose a solution for the most difficult technical problems in S-VLBI by the MultiView approach where multiple sources, separated by several degrees on the sky, are observed simultaneously. We simulated a number of challenging S-VLBI configurations, with orbit errors up to 8 m in size and with ionospheric atmospheres consistent with poor conditions. In these simulations we performed MultiView analysis to achieve the required science goals. This approach removes the need for beam switching requiring a Control Moment Gyro, and the space and ground infrastructure required for high-quality orbit reconstruction of a space-based radio telescope. This will dramatically reduce the complexity of S-VLBI missions which implement the phase-referencing technique.

THE APPLICATION OF MULTIVIEW METHODS FOR HIGH-PRECISION ASTROMETRIC SPACE VLBI AT LOW FREQUENCIES

International Nuclear Information System (INIS)

Dodson, R.; Rioja, M.; Imai, H.; Asaki, Y.; Hong, X.-Y.; Shen, Z.

2013-01-01

High-precision astrometric space very long baseline interferometry (S-VLBI) at the low end of the conventional frequency range, i.e., 20 cm, is a requirement for a number of high-priority science goals. These are headlined by obtaining trigonometric parallax distances to pulsars in pulsar-black hole pairs and OH masers anywhere in the Milky Way and the Magellanic Clouds. We propose a solution for the most difficult technical problems in S-VLBI by the MultiView approach where multiple sources, separated by several degrees on the sky, are observed simultaneously. We simulated a number of challenging S-VLBI configurations, with orbit errors up to 8 m in size and with ionospheric atmospheres consistent with poor conditions. In these simulations we performed MultiView analysis to achieve the required science goals. This approach removes the need for beam switching requiring a Control Moment Gyro, and the space and ground infrastructure required for high-quality orbit reconstruction of a space-based radio telescope. This will dramatically reduce the complexity of S-VLBI missions which implement the phase-referencing technique.

The Potential for a Ka-band (32 GHz) Worldwide VLBI Network

Science.gov (United States)

Jacobs, C. S.; Bach, U.; Colomer, F.; Garcia-Miro, C.; Gomez-Gonzalez, J.; Gulyaev, S.; Horiuchi, S.; Ichikawa, R.; Kraus, A.; Kronschnabl, G.;

Basic Earth's Parameters as estimated from VLBI observations

Directory of Open Access Journals (Sweden)

Ping Zhu

2017-11-01

Full Text Available The global Very Long Baseline Interferometry observation for measuring the Earth rotation's parameters was launched around 1970s. Since then the precision of the measurements is continuously improving by taking into account various instrumental and environmental effects. The MHB2000 nutation model was introduced in 2002, which is constructed based on a revised nutation series derived from 20 years VLBI observations (1980–1999. In this work, we firstly estimated the amplitudes of all nutation terms from the IERS-EOP-C04 VLBI global solutions w.r.t. IAU1980, then we further inferred the BEPs (Basic Earth's Parameters by fitting the major nutation terms. Meanwhile, the BEPs were obtained from the same nutation time series using a BI (Bayesian Inversion. The corrections to the precession rate and the estimated BEPs are in an agreement, independent of which methods have been applied.

ostglacial rebound from VLBI Geodesy: On Establishing Vertical Reference

Science.gov (United States)

Argus, Donald .

1996-01-01

I propose that a useful reference frame for vertical motions is that found by minimizing differences between vertical motions observed with VLBI [Ma and Ryan, 1995] and predictions from postglacial rebound predictions [Peltier, 1995].

Leveraging geodetic data to reduce losses from earthquakes

Science.gov (United States)

Murray, Jessica R.; Roeloffs, Evelyn A.; Brooks, Benjamin A.; Langbein, John O.; Leith, William S.; Minson, Sarah E.; Svarc, Jerry L.; Thatcher, Wayne R.

2018-04-23

Seismic hazard assessments that are based on a variety of data and the best available science, coupled with rapid synthesis of real-time information from continuous monitoring networks to guide post-earthquake response, form a solid foundation for effective earthquake loss reduction. With this in mind, the Earthquake Hazards Program (EHP) of the U.S. Geological Survey (USGS) Natural Hazards Mission Area (NHMA) engages in a variety of undertakings, both established and emergent, in order to provide high quality products that enable stakeholders to take action in advance of and in response to earthquakes. Examples include the National Seismic Hazard Model (NSHM), development of tools for improved situational awareness such as earthquake early warning (EEW) and operational earthquake forecasting (OEF), research about induced seismicity, and new efforts to advance comprehensive subduction zone science and monitoring. Geodetic observations provide unique and complementary information directly relevant to advancing many aspects of these efforts (fig. 1). EHP scientists have long leveraged geodetic data for a range of influential studies, and they continue to develop innovative observation and analysis methods that push the boundaries of the field of geodesy as applied to natural hazards research. Given the ongoing, rapid improvement in availability, variety, and precision of geodetic measurements, considering ways to fully utilize this observational resource for earthquake loss reduction is timely and essential. This report presents strategies, and the underlying scientific rationale, by which the EHP could achieve the following outcomes: The EHP is an authoritative source for the interpretation of geodetic data and its use for earthquake loss reduction throughout the United States and its territories.The USGS consistently provides timely, high quality geodetic data to stakeholders.Significant earthquakes are better characterized by incorporating geodetic data into USGS

Multi-geodetic characterization of the seasonal signal at the CERGA geodetic reference, France

Science.gov (United States)

Memin, A.; Viswanathan, V.; Fienga, A.; Santamaría-Gómez, A.; Boy, J. P.

2016-12-01

Crustal deformations due to surface-mass loading account for a significant part of the variability in geodetic time series. A perfect understanding of the loading signal observed by geodetic techniques should help in improving terrestrial reference frame (TRF) realizations. Yet, discrepancies between crustal motion estimates from models of surface-mass loading and observations are still too large so that no model is currently recommended by the IERS for reducing the data. We investigate the discrepancy observed in the seasonal variations of the CERGA station, South of France.We characterize the seasonal motions of the reference geodetic station CERGA from GNSS, SLR and LLR. We compare the station motion observed with GNSS and SLR and we estimate changes in the station-to-the-moon distance using an improved processing strategy. We investigate the consistency between these geodetic techniques and compare the observed station motion with that estimated using models of surface-mass change. In that regard, we compute atmospheric loading effects using surface pressure fields from ECMWF, assuming an ocean response according to the classical inverted barometer (IB) assumption, considered to be valid for periods typically exceeding a week. We also used general circulation ocean models (ECCO and GLORYS) forced by wind, heat and fresh water fluxes. The continental water storage is described using GLDAS/Noah and MERRA-land models.Using the surface-mass models, we estimate the amplitude of the seasonal vertical motion of the CERGA station ranging between 5 and 10 mm with a maximum reached in August, mostly due to hydrology. The horizontal seasonal motion of the station may reach up to 3 mm. Such a station motion should induce a change in the distance to the moon reaching up to 10 mm, large enough to be detected in LLR time series and compared to GNSS- and SLR-derived motion.

Fortaleza Station Report for 2012

Science.gov (United States)

Kaufmann, Pierre; Pereira de Lucena, A. Macilio; Sombra da Silva, Adeildo

2013-01-01

This is a brief report about the activities carried out at the Fortaleza geodetic VLBI station (ROEN: R´adio Observat´orio Espacial do Nordeste), located in Eus´ebio, CE, Brazil, during the period from January until December 2012. The observing activities were resumed in May after the major maintenance that comprised the azimuth bearing replacement. The total observational experiments consisted of 103 VLBI sessions and continuous GPS monitoring recordings.

Early science with the Korean VLBI network: evaluation of system performance

Energy Technology Data Exchange (ETDEWEB)

Lee, Sang-Sung; Byun, Do-Young; Kim, Jongsoo; Jung, Taehyun; Song, Min-Gyu; Oh, Chung Sik; Roh, Duk-Gyoo; Je, Do-Heung; Wi, Seog-Oh; Sohn, Bong Won; Oh, Se-Jin; Kim, Kee-Tae; Yeom, Jae-Hwan; Chung, Moon-Hee; Kang, Jiman; Han, Seog-Tae; Lee, Jung-Won; Kim, Bong Gyu; Chung, Hyunsoo [Korea Astronomy and Space Science Institute, Daedeokdae-ro 776, Yuseong-gu, Daejeon 305-348 (Korea, Republic of); Petrov, Leonid, E-mail: sslee@kasi.re.kr [Astrogeo Center, Falls Church, VA 22043 (United States); and others

2014-04-01

We report the very long baseline interferometry (VLBI) observing performance of the Korean VLBI Network (KVN). The KVN is the first millimeter-dedicated VLBI network in East Asia. The KVN consists of three 21 m radio telescopes with baseline lengths in a range of 305-476 km. The quasi-optical system equipped on the antennas allows simultaneous observations at 22, 43, 86, and 129 GHz. The first fringes of the KVN were obtained at 22 GHz on 2010 June 8. Test observations at 22 and 43 GHz on 2010 September 30 and 2011 April 4 confirmed that the full cycle of VLBI observations works according to specification: scheduling, antenna control system, data recording, correlation, post-correlation data processing, astrometry, geodesy, and imaging analysis. We found that decorrelation due to instability in the hardware at times up to 600 s is negligible. The atmosphere fluctuations at KVN baseline are partly coherent, which allows us to extend integration time under good winter weather conditions up to 600 s without significant loss of coherence. The post-fit residuals at KVN baselines do not exhibit systematic patterns, and the weighted rms of the residuals is 14.8 ps. The KVN is ready to image compact radio sources both in snapshot and full-track modes with residual noise in calibrated phases of less than 2 deg at 22 and 43 GHz and with dynamic ranges of ∼300 for snapshot mode and ∼1000 for full-track mode. With simultaneous multi-frequency observations, the KVN can be used to make parsec-scale spectral index maps of compact radio sources.

DETECTING CHANGING POLARIZATION STRUCTURES IN SAGITTARIUS A* WITH HIGH FREQUENCY VLBI

International Nuclear Information System (INIS)

Fish, Vincent L.; Doeleman, Sheperd S.; Rogers, Alan E. E.; Broderick, Avery E.; Loeb, Abraham

2009-01-01

Sagittarius A* is the source of near infrared, X-ray, radio, and (sub)millimeter emission associated with the supermassive black hole at the Galactic Center. In the submillimeter regime, Sgr A* exhibits time-variable linear polarization on timescales corresponding to 6 M sun black hole. In previous work, we demonstrated the potential for total-intensity (sub)millimeter-wavelength very long baseline interferometry (VLBI) to detect time-variable-and periodic-source structure changes in the Sgr A* black hole system using nonimaging analyses. Here, we extend this work to include full polarimetric VLBI observations. We simulate full-polarization (sub)millimeter VLBI data of Sgr A* using a hot spot model that is embedded within an accretion disk, with emphasis on nonimaging polarimetric data products that are robust against calibration errors. Although the source-integrated linear polarization fraction in the models is typically only a few percent, the linear polarization fraction on small angular scales can be much higher, enabling the detection of changes in the polarimetric structure of Sgr A* on a wide variety of baselines. The shortest baselines track the source-integrated linear polarization fraction, while longer baselines are sensitive to polarization substructures that are beam-diluted by connected-element interferometry. The detection of periodic variability in source polarization should not be significantly affected even if instrumental polarization terms cannot be calibrated out. As more antennas are included in the (sub)millimeter-VLBI array, observations with full polarization will provide important new diagnostics to help disentangle intrinsic source polarization from Faraday rotation effects in the accretion and outflow region close to the black hole event horizon.

DETECTING CHANGING POLARIZATION STRUCTURES IN SAGITTARIUS A* WITH HIGH FREQUENCY VLBI

Energy Technology Data Exchange (ETDEWEB)

Fish, Vincent L; Doeleman, Sheperd S; Rogers, Alan E. E. [Massachusetts Institute of Technology, Haystack Observatory, Route 40, Westford, MA 01886 (United States); Broderick, Avery E [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Loeb, Abraham [Institute for Theory and Computation, Harvard University, Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2009-12-01

Sagittarius A* is the source of near infrared, X-ray, radio, and (sub)millimeter emission associated with the supermassive black hole at the Galactic Center. In the submillimeter regime, Sgr A* exhibits time-variable linear polarization on timescales corresponding to <10 Schwarzschild radii of the presumed 4 x 10{sup 6} M {sub sun} black hole. In previous work, we demonstrated the potential for total-intensity (sub)millimeter-wavelength very long baseline interferometry (VLBI) to detect time-variable-and periodic-source structure changes in the Sgr A* black hole system using nonimaging analyses. Here, we extend this work to include full polarimetric VLBI observations. We simulate full-polarization (sub)millimeter VLBI data of Sgr A* using a hot spot model that is embedded within an accretion disk, with emphasis on nonimaging polarimetric data products that are robust against calibration errors. Although the source-integrated linear polarization fraction in the models is typically only a few percent, the linear polarization fraction on small angular scales can be much higher, enabling the detection of changes in the polarimetric structure of Sgr A* on a wide variety of baselines. The shortest baselines track the source-integrated linear polarization fraction, while longer baselines are sensitive to polarization substructures that are beam-diluted by connected-element interferometry. The detection of periodic variability in source polarization should not be significantly affected even if instrumental polarization terms cannot be calibrated out. As more antennas are included in the (sub)millimeter-VLBI array, observations with full polarization will provide important new diagnostics to help disentangle intrinsic source polarization from Faraday rotation effects in the accretion and outflow region close to the black hole event horizon.

Three-dimensional stochastic adjustment of volcano geodetic network in Arenal volcano, Costa Rica

Science.gov (United States)

Muller, C.; van der Laat, R.; Cattin, P.-H.; Del Potro, R.

2009-04-01

before it is built. Moreover, a posterior analysis enables identifying, and hence dismissing, measurement errors (antenna height, atmospheric effects, etc.). Here we present a preliminary effort to apply this technique to volcano deformation. A geodetic network has been developed on the western flank of the Arenal volcano in Costa Rica. It is surveyed with GNSS, angular and EDM (Electronic Distance Measurements) measurements. Three measurement campaigns were carried out between February and June 2008. The results show consistent and accurate output of deformation and uncertainty for each of the 12 benchmarks surveyed. The three campaigns also prove the repeatability and consistency of the statistical indicators and the displacement vectors. Although, this methodology has only recently been applied to volcanoes, we suggest that due to its cost-effective high-quality results it has the potential to be incorporated into the design and analysis of volcano geodetic networks worldwide.

Imaging VLBI polarimetry data from Active Galactic Nuclei using the Maximum Entropy Method

Directory of Open Access Journals (Sweden)

Coughlan Colm P.

2013-12-01

Full Text Available Mapping the relativistic jets emanating from AGN requires the use of a deconvolution algorithm to account for the effects of missing baseline spacings. The CLEAN algorithm is the most commonly used algorithm in VLBI imaging today and is suitable for imaging polarisation data. The Maximum Entropy Method (MEM is presented as an alternative with some advantages over the CLEAN algorithm, including better spatial resolution and a more rigorous and unbiased approach to deconvolution. We have developed a MEM code suitable for deconvolving VLBI polarisation data. Monte Carlo simulations investigating the performance of CLEAN and the MEM code on a variety of source types are being carried out. Real polarisation (VLBA data taken at multiple wavelengths have also been deconvolved using MEM, and several of the resulting polarisation and Faraday rotation maps are presented and discussed.

Earth Rotation Parameters from DSN VLBI: 1996

Science.gov (United States)

Steppe, J. A.; Oliveau, S. H.; Sovers, O. J.

1996-01-01

A despcription of the DSN VLBI data set and of most aspects of the data analysis can be found in the IERS Technical Note 17, pp. R-19 to R-32 (see also IERS Technical Note 19, pp. R-21 to R-27). The main changes in this year's analysis form last year's are simply due to including another year's data.

Proceedings of the Sixth General Meeting of the International VLBI Service for Geodesy and Astrometry

Science.gov (United States)

Behrend, Dirk (Editor); Baver, Karen D. (Editor)

2010-01-01

This volume is the proceedings of the sixth General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS), held in Hobart, Tasmania, Australia, February 7-13, 2010. The contents of this volume also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/gm2010. The keynote of the sixth GM was the new perspectives of the next generation VLBI system under the theme "VLBI2010: From Vision to Reality". The goal of the meeting was to provide an interesting and informative program for a wide cross-section of IVS members, including station operators, program managers, and analysts. This volume contains 88 papers. All papers were edited by the editors for usage of the English language, form, and minor content-related issues.

Methodology for the combination of sub-daily Earth rotation from GPS and VLBI observations

Science.gov (United States)

Artz, T.; Bernhard, L.; Nothnagel, A.; Steigenberger, P.; Tesmer, S.

2012-03-01

A combination procedure of Earth orientation parameters from Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) observations was developed on the basis of homogeneous normal equation systems. The emphasis and purpose of the combination was the determination of sub-daily polar motion (PM) and universal time (UT1) for a long time-span of 13 years. Time series with an hourly resolution and a model for tidal variations of PM and UT1-TAI (dUT1) were estimated. In both cases, 14-day nutation corrections were estimated simultaneously with the ERPs. Due to the combination procedure, it was warranted that the strengths of both techniques were preserved. At the same time, only a minimum of de-correlating or stabilizing constraints were necessary. Hereby, a PM time series was determined, whose precision is mainly dominated by GPS observations. However, this setup benefits from the fact that VLBI delivered nutation and dUT1 estimates at the same time. An even bigger enhancement can be seen for the dUT1 estimation, where the high-frequency variations are provided by GPS, while the long term trend is defined by VLBI. The estimated combined tidal PM and dUT1 model was predominantly determined from the GPS observations. Overall, the combined tidal model for the first time completely comprises the geometrical benefits of VLBI and GPS observations. In terms of root mean squared (RMS) differences, the tidal amplitudes agree with other empirical single-technique tidal models below 4 μ as in PM and 0.25 μ s in dUT1. The noise floor of the tidal ERP model was investigated in three ways resulting in about 1 μ as for diurnal PM and 0.07 μ s for diurnal dUT1 while the semi-diurnal components have a slightly better accuracy.

Research in Application of Geodetic GPS Receivers in Time Synchronization

Science.gov (United States)

Zhang, Q.; Zhang, P.; Sun, Z.; Wang, F.; Wang, X.

2018-04-01

In recent years, with the development of satellite orbit and clock parameters accurately determining technology and the popularity of geodetic GPS receivers, Common-View (CV) which proposed in 1980 by Allan has gained widespread application and achieved higher accuracy time synchronization results. GPS Common View (GPS CV) is the technology that based on multi-channel geodetic GPS receivers located in different place and under the same common-view schedule to receiving same GPS satellite signal at the same time, and then calculating the time difference between respective local receiver time and GPST by weighted theory, we will obtain the difference between above local time of receivers that installed in different station with external atomic clock. Multi-channel geodetic GPS receivers have significant advantages such as higher stability, higher accuracy and more common-view satellites in long baseline time synchronization application over the single-channel geodetic GPS receivers. At present, receiver hardware delay and surrounding environment influence are main error factors that affect the accuracy of GPS common-view result. But most error factors will be suppressed by observation data smoothing and using of observation data from different satellites in multi-channel geodetic GPS receiver. After the SA (Selective Availability) cancellation, using a combination of precise satellite ephemeris, ionospheric-free dual-frequency P-code observations and accurately measuring of receiver hardware delay, we can achieve time synchronization result on the order of nanoseconds (ns). In this paper, 6 days observation data of two IGS core stations with external atomic clock (PTB, USNO distance of two stations about 6000 km) were used to verify the GPS common-view theory. Through GPS observation data analysis, there are at least 2-4 common-view satellites and 5 satellites in a few tracking periods between two stations when the elevation angle is 15°, even there will be at least

RESEARCH IN APPLICATION OF GEODETIC GPS RECEIVERS IN TIME SYNCHRONIZATION

Directory of Open Access Journals (Sweden)

Q. Zhang

2018-04-01

Full Text Available In recent years, with the development of satellite orbit and clock parameters accurately determining technology and the popularity of geodetic GPS receivers, Common-View (CV which proposed in 1980 by Allan has gained widespread application and achieved higher accuracy time synchronization results. GPS Common View (GPS CV is the technology that based on multi-channel geodetic GPS receivers located in different place and under the same common-view schedule to receiving same GPS satellite signal at the same time, and then calculating the time difference between respective local receiver time and GPST by weighted theory, we will obtain the difference between above local time of receivers that installed in different station with external atomic clock. Multi-channel geodetic GPS receivers have significant advantages such as higher stability, higher accuracy and more common-view satellites in long baseline time synchronization application over the single-channel geodetic GPS receivers. At present, receiver hardware delay and surrounding environment influence are main error factors that affect the accuracy of GPS common-view result. But most error factors will be suppressed by observation data smoothing and using of observation data from different satellites in multi-channel geodetic GPS receiver. After the SA (Selective Availability cancellation, using a combination of precise satellite ephemeris, ionospheric-free dual-frequency P-code observations and accurately measuring of receiver hardware delay, we can achieve time synchronization result on the order of nanoseconds (ns. In this paper, 6 days observation data of two IGS core stations with external atomic clock (PTB, USNO distance of two stations about 6000 km were used to verify the GPS common-view theory. Through GPS observation data analysis, there are at least 2–4 common-view satellites and 5 satellites in a few tracking periods between two stations when the elevation angle is 15°, even

VLBI observations of Infrared-Faint Radio Sources

Science.gov (United States)

Middelberg, Enno; Phillips, Chris; Norris, Ray; Tingay, Steven

2006-10-01

We propose to observe a small sample of radio sources from the ATLAS project (ATLAS = Australia Telescope Large Area Survey) with the LBA, to determine their compactness and map their structures. The sample consists of three radio sources with no counterpart in the co-located SWIRE survey (3.6 um to 160 um), carried out with the Spitzer Space Telescope. This rare class of sources, dubbed Infrared-Faint Radio Sources, or IFRS, is inconsistent with current galaxy evolution models. VLBI observations are an essential way to obtain further clues on what these objects are and why they are hidden from infrared observations: we will map their structure to test whether they resemble core-jet or double-lobed morphologies, and we will measure the flux densities on long baselines, to determine their compactness. Previous snapshot-style LBA observations of two other IFRS yielded no detections, hence we propose to use disk-based recording with 512 Mbps where possible, for highest sensitivity. With the observations proposed here, we will increase the number of VLBI-observed IFRS from two to five, soon allowing us to draw general conclusions about this intriguing new class of objects.

Current status of the EPOS WG4 - GNSS and Other Geodetic Data

Science.gov (United States)

Fernandes, Rui; Bastos, Luisa; Bruyninx, Carine; D'Agostino, Nicola; Dousa, Jan; Ganas, Athanassios; Lidberg, Martin; Nocquet, Jean-Mathieu

2014-05-01

WG4 - "EPOS Geodetic Data and Other Geodetic Data" is the Working Group of the EPOS project in charge of defining and preparing the integration of the existing Pan-European Geodetic Infrastructures that will support European Geosciences, which is the ultimate goal of the EPOS project. The WG4 is formed by representatives of the participating EPOS countries (23) but it is also open to the entire geodetic community. In fact, WG4 also already includes members from countries that formally are not integrating EPOS in this first step. The geodetic component of EPOS (WG4) is dealing essentially with Research Infrastructures focused on continuous operating GNSS (cGNSS) in the current phase. The option of concentrating the efforts on the presently most generalized geodetic tool supporting research on Solid Earth was decided in order to optimize the existing resources. Nevertheless, WG4 will continue to pursue the development of tools and methodologies that permit the access of the EPOS community to other geodetic information (e.g., gravimetry). Furthermore, although the focus is on Solid Earth applications, other research and technical applications (e.g., reference frames, meteorology, space weather) can also benefit from the efforts of WG4 EPOS towards the optimization of the geodetic resources in Europe. We will present and discuss the plans for the implementation of the thematic and core services (TCS) for geodetic data within EPOS and the related business plan. We will focus on strategies towards the implementation of the best solutions that will permit to the end-users, and in particular geo-scientists, to access the geodetic data, derived solutions, and associated metadata using transparent and uniform processes. Five pillars have been defined proposed for the TCS: Dissemination, Preservation, Monitoring, and Analysis of geodetic data plus the Support and Governance Infrastructure. Current proposals and remaining open questions will be discussed.

MODEST: A Tool for Geodesy and Astronomy

Science.gov (United States)

Sovers, Ojars J.; Jacobs, Christopher S.; Lanyi, Gabor E.

2004-01-01

Features of the JPL VLBI modeling and estimation software "MODEST" are reviewed. Its main advantages include thoroughly documented model physics, portability, and detailed error modeling. Two unique models are included: modeling of source structure and modeling of both spatial and temporal correlations in tropospheric delay noise. History of the code parallels the development of the astrometric and geodetic VLBI technique and the software retains many of the models implemented during its advancement. The code has been traceably maintained since the early 1980s, and will continue to be updated with recent IERS standards. Scripts are being developed to facilitate user-friendly data processing in the era of e-VLBI.

Geodetic achievement and avoidance games for graphs | Haynes ...

African Journals Online (AJOL)

Let G = (V,E) be a nontrivial connected graph. For a subset S ⊆ V, the geodesic closure (S) of S is the set of all vertices on geodesics (shortest paths) between two vertices of S. We study the geodetic achievement and avoidance games defined by Buckley and Harary (Geodetic games for graphs, Quaestiones Math.

THE IMPACT OF FREQUENCY STANDARDS ON COHERENCE IN VLBI AT THE HIGHEST FREQUENCIES

Energy Technology Data Exchange (ETDEWEB)

Rioja, M.; Dodson, R. [ICRAR, University of Western Australia, Perth (Australia); Asaki, Y. [Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Chuou, Sagamihara, Kanagawa 252-5210 (Japan); Hartnett, J. [School of Physics, University of Western Australia, Perth (Australia); Tingay, S., E-mail: maria.rioja@icrar.org [ICRAR, Curtin University, Perth (Australia)

2012-10-01

We have carried out full imaging simulation studies to explore the impact of frequency standards in millimeter and submillimeter very long baseline interferometry (VLBI), focusing on the coherence time and sensitivity. In particular, we compare the performance of the H-maser, traditionally used in VLBI, to that of ultra-stable cryocooled sapphire oscillators over a range of observing frequencies, weather conditions, and analysis strategies. Our simulations show that at the highest frequencies, the losses induced by H-maser instabilities are comparable to those from high-quality tropospheric conditions. We find significant benefits in replacing H-masers with cryocooled sapphire oscillator based frequency references in VLBI observations at frequencies above 175 GHz in sites which have the best weather conditions; at 350 GHz we estimate a 20%-40% increase in sensitivity over that obtained when the sites have H-masers, for coherence losses of 20%-10%, respectively. Maximum benefits are to be expected by using co-located Water Vapor Radiometers for atmospheric correction. In this case, we estimate a 60%-120% increase in sensitivity over the H-maser at 350 GHz.

International VLBI Service for Geodesy and Astrometry: 2000 General Meeting Proceedings

Science.gov (United States)

Vandenberg, Nancy R. (Editor); Baver, Karen D. (Editor)

2000-01-01

This volume is the proceedings of the first General Meeting of the International Very Long Base Interferometry (VLBI) Service for Geodesy and Astrometry (IVS), held in Koetzting, Germany, February 21-24, 2000. The content of this volume also appears on the IVS web site at: http://ivscc.gsfc.nasa.gov/publications/gm2000. The goal of the program committee for the General Meeting was to provide an interesting and informative program for a wide cross section of IVS members, including station operators, program managers, and analysts. The program included reports, tutorials, invited and contributed papers, and poster presentations. The tutorial papers should be particularly useful references because each one provides an overview and introduction to a topic relevant to VLBI.

The Global Geodetic Observing System: Recent Activities and Accomplishments

Science.gov (United States)

Gross, R. S.

2017-12-01

The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) provides the basis on which future advances in geosciences can be built. By considering the Earth system as a whole (including the geosphere, hydrosphere, cryosphere, atmosphere and biosphere), monitoring Earth system components and their interactions by geodetic techniques and studying them from the geodetic point of view, the geodetic community provides the global geosciences community with a powerful tool consisting mainly of high-quality services, standards and references, and theoretical and observational innovations. The mission of GGOS is: (a) to provide the observations needed to monitor, map and understand changes in the Earth's shape, rotation and mass distribution; (b) to provide the global frame of reference that is the fundamental backbone for measuring and consistently interpreting key global change processes and for many other scientific and societal applications; and (c) to benefit science and society by providing the foundation upon which advances in Earth and planetary system science and applications are built. The goals of GGOS are: (1) to be the primary source for all global geodetic information and expertise serving society and Earth system science; (2) to actively promote, sustain, improve, and evolve the integrated global geodetic infrastructure needed to meet Earth science and societal requirements; (3) to coordinate with the international geodetic services that are the main source of key parameters and products needed to realize a stable global frame of reference and to observe and study changes in the dynamic Earth system; (4) to communicate and advocate the benefits of GGOS to user communities, policy makers, funding organizations, and society. In order to accomplish its mission and goals, GGOS depends on the IAG Services, Commissions, and Inter-Commission Committees. The Services provide the infrastructure and products on which all contributions

Propagation of uncertainty by Monte Carlo simulations in case of basic geodetic computations

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Wyszkowska Patrycja

2017-12-01

Full Text Available The determination of the accuracy of functions of measured or adjusted values may be a problem in geodetic computations. The general law of covariance propagation or in case of the uncorrelated observations the propagation of variance (or the Gaussian formula are commonly used for that purpose. That approach is theoretically justified for the linear functions. In case of the non-linear functions, the first-order Taylor series expansion is usually used but that solution is affected by the expansion error. The aim of the study is to determine the applicability of the general variance propagation law in case of the non-linear functions used in basic geodetic computations. The paper presents errors which are a result of negligence of the higher-order expressions and it determines the range of such simplification. The basis of that analysis is the comparison of the results obtained by the law of propagation of variance and the probabilistic approach, namely Monte Carlo simulations. Both methods are used to determine the accuracy of the following geodetic computations: the Cartesian coordinates of unknown point in the three-point resection problem, azimuths and distances of the Cartesian coordinates, height differences in the trigonometric and the geometric levelling. These simulations and the analysis of the results confirm the possibility of applying the general law of variance propagation in basic geodetic computations even if the functions are non-linear. The only condition is the accuracy of observations, which cannot be too low. Generally, this is not a problem with using present geodetic instruments.

Propagation of uncertainty by Monte Carlo simulations in case of basic geodetic computations

Science.gov (United States)

Wyszkowska, Patrycja

2017-12-01

The determination of the accuracy of functions of measured or adjusted values may be a problem in geodetic computations. The general law of covariance propagation or in case of the uncorrelated observations the propagation of variance (or the Gaussian formula) are commonly used for that purpose. That approach is theoretically justified for the linear functions. In case of the non-linear functions, the first-order Taylor series expansion is usually used but that solution is affected by the expansion error. The aim of the study is to determine the applicability of the general variance propagation law in case of the non-linear functions used in basic geodetic computations. The paper presents errors which are a result of negligence of the higher-order expressions and it determines the range of such simplification. The basis of that analysis is the comparison of the results obtained by the law of propagation of variance and the probabilistic approach, namely Monte Carlo simulations. Both methods are used to determine the accuracy of the following geodetic computations: the Cartesian coordinates of unknown point in the three-point resection problem, azimuths and distances of the Cartesian coordinates, height differences in the trigonometric and the geometric levelling. These simulations and the analysis of the results confirm the possibility of applying the general law of variance propagation in basic geodetic computations even if the functions are non-linear. The only condition is the accuracy of observations, which cannot be too low. Generally, this is not a problem with using present geodetic instruments.

An attempt to evaluate horizontal crustal movement by geodetic and geological approach in the Horonobe area, Northern Hokkaido, Japan

International Nuclear Information System (INIS)

Tokiwa, Tetsuya; Niizato, Tadafumi; Nohara, Tsuyoshi; Asamori, Koichi; Matsuura, Yuki; Kosaka, Hideki

2011-01-01

In this study, we present the preliminary results for the estimation of a horizontal crustal movement by using geodetic and geological approach in the Horonobe area, northern Hokkaido, Japan. The estimations have been carried out by using a GPS data and a geological cross section obtained by applying balanced-section method. As results of this study, both of the shortening rates estimated by GPS data and balanced-section method indicate several millimeters per year. Namely, there is no contradiction between geodetic and geological data, and it is considered that Horonobe area is still situated similar tendency and magnitude of a crustal movement. It is seemingly considered that geodetic data is unhelpful for estimating the long-term crustal movement, because period of geodetic observations is a very short. However, the result of this study indicates that geodetic data provide valuable information for estimating the long-term crustal movement in the area, and it is considered that geodetic approach play an important role in improvement of the credibility of evaluation for prediction of long-term stability. (author)

Earth orientation parameters from VLBI determined with a Kalman filter

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Maria Karbon

2017-11-01

We prove that the Kalman filter is more than on par with the classical least squares method and that it is a valuable alternative, especially on the advent of the VLBI2010 Global Observing System and within the GGOS frame work.

Identifying and Allocating Geodetic Systems to historical oil gas wells by using high-resolution satellite imagery

Science.gov (United States)

Alvarez, Gabriel O.

2018-05-01

Hydrocarbon exploration in Argentina started long before the IGM created a single, high-precision geodetic reference network for the whole country. Several geodetic surveys were conducted in every producing basin, which have ever since then supported well placement. Currently, every basin has a huge amount of information referenced to the so-called "local" geodetic systems, such as Chos Malal - Quiñi Huao in the Neuquén Basin, and Pampa del Castillo in the San Jorge Basin, which differ to a greater or lesser extent from the national Campo Inchauspe datum established by the IGM in 1969 as the official geodetic network. However, technology development over the last few years and the expansion of satellite positioning systems such as GPS resulted in a new world geodetic order. Argentina rapidly joined this new geodetic order through the implementation of a new national geodetic system by the IGM: POSGAR network, which replaced the old national Campo Inchauspe system. However, this only helped to worsen the data georeferencing issue for oil companies, as a third reference system was added to each basin. Now every basin has a local system, the national system until 1997 (Campo Inchauspe), and finally the newly created POSGAR network national satellite system, which is geocentric unlike the former two planimetric datums. The purpose of this paper is to identify and allocate geodetic systems of coordinates to historical wells, whose geodetic system is missing or has been erroneously allocated, by using currently available technological resources such as geographic information systems and high-resolution satellite imagery.

An Overview of Geodetic Volcano Research in the Canary Islands

Science.gov (United States)

Fernández, José; González, Pablo J.; Camacho, Antonio G.; Prieto, Juan F.; Brú, Guadalupe

2015-11-01

The Canary Islands are mostly characterized by diffuse and scattered volcanism affecting a large area, with only one active stratovolcano, the Teide-Pico Viejo complex (Tenerife). More than 2 million people live and work in the 7,447 km2 of the archipelago, resulting in an average population density three times greater than the rest of Spain. This fact, together with the growth of exposure during the past 40 years, increases volcanic risk with respect previous eruptions, as witnessed during the recent 2011-2012 El Hierro submarine eruption. Therefore, in addition to purely scientific reasons there are economic and population-security reasons for developing and maintaining an efficient volcano monitoring system. In this scenario geodetic monitoring represents an important part of the monitoring system. We describe volcano geodetic monitoring research carried out in the Canary Islands and the results obtained. We consider for each epoch the two main existing constraints: the level of volcanic activity in the archipelago, and the limitations of the techniques available at the time. Theoretical and observational aspects are considered, as well as the implications for operational volcano surveillance. Current challenges of and future perspectives in geodetic volcano monitoring in the Canaries are also presented.

Japanese VLBI Network Observations of a Gamma-Ray Narrow ...

Indian Academy of Sciences (India)

J. Astrophys. Astr. (2014) 35, 215–218 c Indian Academy of Sciences. Japanese VLBI Network Observations of a Gamma-Ray. Narrow-Line Seyfert 1 Galaxy 1H 0323+342. Kiyoaki Wajima1,∗. , Kenta Fujisawa2, Masaaki Hayashida3. & Naoki Isobe4. 1Shanghai Astronomical Observatory, Chinese Academy of Sciences,.

Enhanced three-dimensional stochastic adjustment for combined volcano geodetic networks

Science.gov (United States)

Del Potro, R.; Muller, C.

2009-12-01

Volcano geodesy is unquestionably a necessary technique in studies of physical volcanology and for eruption early warning systems. However, as every volcano geodesist knows, obtaining measurements of the required resolution using traditional campaigns and techniques is time consuming and requires a large manpower. Moreover, most volcano geodetic networks worldwide use a combination of data from traditional techniques; levelling, electronic distance measurements (EDM), triangulation and Global Navigation Satellite Systems (GNSS) but, in most cases, these data are surveyed, analysed and adjusted independently. This then leaves it to the authors’ criteria to decide which technique renders the most realistic results in each case. Herein we present a way of solving the problem of inter-methodology data integration in a cost-effective manner following a methodology were all the geodetic data of a redundant, combined network (e.g. surveyed by GNSS, levelling, distance, angular data, INSAR, extensometers, etc.) is adjusted stochastically within a single three-dimensional referential frame. The adjustment methodology is based on the least mean square method and links the data with its geometrical component providing combined, precise, three-dimensional, displacement vectors, relative to external reference points as well as stochastically-quantified, benchmark-specific, uncertainty ellipsoids. Three steps in the adjustment allow identifying, and hence dismissing, flagrant measurement errors (antenna height, atmospheric effects, etc.), checking the consistency of external reference points and a final adjustment of the data. Moreover, since the statistical indicators can be obtained from expected uncertainties in the measurements of the different geodetic techniques used (i.e. independent of the measured data), it is possible to run a priori simulations of a geodetic network in order to constrain its resolution, and reduce logistics, before the network is even built. In this

Comparison of direct and geodetic mass balances on a multi-annual time scale

Directory of Open Access Journals (Sweden)

A. Fischer

2011-02-01

Full Text Available The geodetic mass balances of six Austrian glaciers over 19 periods between 1953 and 2006 are compared to the direct mass balances over the same periods. For two glaciers, Hintereisferner and Kesselwandferner, case studies showing possible reasons for discrepancies between the geodetic and the direct mass balance are presented. The mean annual geodetic mass balance for all periods is −0.5 m w.e. a⁻¹, the mean annual direct mass balance −0.4 m w.e. a⁻¹. The mean cumulative difference is −0.6 m w.e., the minimum −7.3 m w.e., and the maximum 5.6 m w.e. The accuracy of geodetic mass balance may depend on the accuracy of the DEMs, which ranges from 2 m w.e. for photogrammetric data to 0.02 m w.e. for airborne laser scanning (LiDAR data. Basal melt, seasonal snow cover, and density changes of the surface layer also contribute up to 0.7 m w.e. to the difference between the two methods over the investigated period of 10 yr. On Hintereisferner, the fraction of area covered by snow or firn has been changing within 1953–2006. The accumulation area is not identical with the firn area, and both are not coincident with areas of volume gain. Longer periods between the acquisition of the DEMs do not necessarily result in a higher accuracy of the geodetic mass balance. Trends in the difference between the direct and the geodetic data vary from glacier to glacier and can differ systematically for specific glaciers under specific types of climate forcing. Ultimately, geodetic and direct mass balance data are complementary, and great care must be taken when attempting to combine them.

General Relativistic Theory of the VLBI Time Delay in the Gravitational Field of Moving Bodies

Science.gov (United States)

Kopeikin, Sergei

2003-01-01

The general relativistic theory of the gravitational VLBI experiment conducted on September 8, 2002 by Fomalont and Kopeikin is explained. Equations of radio waves (light) propagating from the quasar to the observer are integrated in the time-dependent gravitational field of the solar system by making use of either retarded or advanced solutions of the Einstein field equations. This mathematical technique separates explicitly the effects associated with the propagation of gravity from those associated with light in the integral expression for the relativistic VLBI time delay of light. We prove that the relativistic correction to the Shapiro time delay, discovered by Kopeikin (ApJ, 556, L1, 2001), changes sign if one retains direction of the light propagation but replaces the retarded for the advanced solution of the Einstein equations. Hence, this correction is associated with the propagation of gravity. The VLBI observation measured its speed, and that the retarded solution is the correct one.

ESTIMATING THE PARAMETERS OF SAGITTARIUS A*'s ACCRETION FLOW VIA MILLIMETER VLBI

Energy Technology Data Exchange (ETDEWEB)

Broderick, Avery E [Canadian Institute for Theoretical Astrophysics, 60 St. George St., Toronto, ON M5S 3H8 (Canada); Fish, Vincent L; Doeleman, Sheperd S [Massachusetts Institute of Technology, Haystack Observatory, Route 40, Westford, MA 01886 (United States); Loeb, Abraham [Institute for Theory and Computation, Harvard University, Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)

2009-05-20

Recent millimeter-VLBI observations of Sagittarius A* (Sgr A*) have, for the first time, directly probed distances comparable to the horizon scale of a black hole. This provides unprecedented access to the environment immediately around the horizon of an accreting black hole. We leverage both existing spectral and polarization measurements and our present understanding of accretion theory to produce a suite of generic radiatively inefficient accretion flow (RIAF) models of Sgr A*, which we then fit to these recent millimeter-VLBI observations. We find that if the accretion flow onto Sgr A* is well described by an RIAF model, the orientation and magnitude of the black hole's spin are constrained to a two-dimensional surface in the spin, inclination, position angle parameter space. For each of these, we find the likeliest values and their 1{sigma} and 2{sigma} errors to be a = 0{sup +0.4+0.7}, {theta}=50{sup o+10{sup o}}{sup +30{sup o}}{sub -10{sup o}}{sub -10{sup o}}, and {xi}=-20{sup o+31{sup o}}{sup +107{sup o}}{sub -16{sup o}}{sub -29{sup o}}, when the resulting probability distribution is marginalized over the others. The most probable combination is a = 0{sup +0.2+0.4}, {theta}=90{sup o}{sub -40{sup o}}{sub -50{sup o}}, and {xi}=-14{sup o+7{sup o}}{sup +11{sup o}}{sub -7{sup o}}{sub -11{sup o}}, though the uncertainties on these are very strongly correlated, and high probability configurations exist for a variety of inclination angles above 30 deg. and spins below 0.99. Nevertheless, this demonstrates the ability millimeter-VLBI observations, even with only a few stations, to significantly constrain the properties of Sgr A*.

IVS: Current Status and Future Plans

Science.gov (United States)

Behrend, D.; Nothnagel, A.; Petrachenko, W. T.; Tuccari, G.

2016-12-01

The International VLBI Service for Geodesy and Astrometry (IVS) is a globally operating service that coordinates and performs Very Long Baseline Interferometry (VLBI) activities through its constituent components. The VLBI activities are associated with the creation, provision, dissemination, and archiving of relevant VLBI data and products. The products mostly pertain to the determination of the celestial and terrestrial reference frames, the Earth orientation parameters (EOP), atmospheric parameters as well as other ancillary parameters. The IVS observational network currently consists of about 40 radio telescopes worldwide. Subsets of these telescopes (8-12 stations) participate in 24-hour observing sessions that are run several times per week and in 1-hour intensive sessions for UT1 determination every day. The current VLBI network was developed mainly in the 1970s and 1980s. A number of factors, including aging infrastructure and demanding new scientific requirements, started to challenge its future sustainability and relevance. In response, the IVS and other groups developed and started implementing the next generation VLBI system, called VGOS (VLBI Global Observing System), at existing and new sites. The VGOS network is expected to reach maturity in the early 2020s. We describe the current status, progress, and anticipated prospects of geodetic/astrometric VLBI and the IVS.

VLBI imaging of CTA 102

International Nuclear Information System (INIS)

Wehrle, A.E.; Cohen, M.

1989-01-01

The object CTA 102, a low-frequency variable quasar, was observed with a VLBI Global Array in 1987.5 and 1988.5 at 5.0 GHz. The structure is complex, with three compact components along a line at PA = 157 deg, and several extended, ill-defined components east of the southernmost compact component. The components have no detectable relative motions, with mu less than 0.5 mas/yr along the main axis. This contrasts with the observation reported by Baath (1987), who found mu = 0.65 + or - 0.15 mas/yr at 932 MHz, which is exceptionally high. The new upper limit allows CTA 102 to be in the normal range of superluminal sources. 11 refs

Next Generation NASA Initiative for Space Geodesy

Science.gov (United States)

Merkowitz, S. M.; Desai, S.; Gross, R. S.; Hilliard, L.; Lemoine, F. G.; Long, J. L.; Ma, C.; McGarry J. F.; Murphy, D.; Noll, C. E.;

Detection of Intrinsic Source Structure at ∼3 Schwarzschild Radii with Millimeter-VLBI Observations of SAGITTARIUS A*

Science.gov (United States)

Lu, Ru-Sen; Krichbaum, Thomas P.; Roy, Alan L.; Fish, Vincent L.; Doeleman, Sheperd S.; Johnson, Michael D.; Akiyama, Kazunori; Psaltis, Dimitrios; Alef, Walter; Asada, Keiichi; Beaudoin, Christopher; Bertarini, Alessandra; Blackburn, Lindy; Blundell, Ray; Bower, Geoffrey C.; Brinkerink, Christiaan; Broderick, Avery E.; Cappallo, Roger; Crew, Geoffrey B.; Dexter, Jason; Dexter, Matt; Falcke, Heino; Freund, Robert; Friberg, Per; Greer, Christopher H.; Gurwell, Mark A.; Ho, Paul T. P.; Honma, Mareki; Inoue, Makoto; Kim, Junhan; Lamb, James; Lindqvist, Michael; Macmahon, David; Marrone, Daniel P.; Martí-Vidal, Ivan; Menten, Karl M.; Moran, James M.; Nagar, Neil M.; Plambeck, Richard L.; Primiani, Rurik A.; Rogers, Alan E. E.; Ros, Eduardo; Rottmann, Helge; SooHoo, Jason; Spilker, Justin; Stone, Jordan; Strittmatter, Peter; Tilanus, Remo P. J.; Titus, Michael; Vertatschitsch, Laura; Wagner, Jan; Weintroub, Jonathan; Wright, Melvyn; Young, Ken H.; Zensus, J. Anton; Ziurys, Lucy M.

2018-05-01

We report results from very long baseline interferometric (VLBI) observations of the supermassive black hole in the Galactic center, Sgr A*, at 1.3 mm (230 GHz). The observations were performed in 2013 March using six VLBI stations in Hawaii, California, Arizona, and Chile. Compared to earlier observations, the addition of the APEX telescope in Chile almost doubles the longest baseline length in the array, provides additional uv coverage in the N–S direction, and leads to a spatial resolution of ∼30 μas (∼3 Schwarzschild radii) for Sgr A*. The source is detected even at the longest baselines with visibility amplitudes of ∼4%–13% of the total flux density. We argue that such flux densities cannot result from interstellar refractive scattering alone, but indicate the presence of compact intrinsic source structure on scales of ∼3 Schwarzschild radii. The measured nonzero closure phases rule out point-symmetric emission. We discuss our results in the context of simple geometric models that capture the basic characteristics and brightness distributions of disk- and jet-dominated models and show that both can reproduce the observed data. Common to these models are the brightness asymmetry, the orientation, and characteristic sizes, which are comparable to the expected size of the black hole shadow. Future 1.3 mm VLBI observations with an expanded array and better sensitivity will allow more detailed imaging of the horizon-scale structure and bear the potential for a deep insight into the physical processes at the black hole boundary.

Comparison between geodetic and oceanographic approaches to estimate mean dynamic topography for vertical datum unification: evaluation at Australian tide gauges

Science.gov (United States)

Filmer, M. S.; Hughes, C. W.; Woodworth, P. L.; Featherstone, W. E.; Bingham, R. J.

2018-04-01

The direct method of vertical datum unification requires estimates of the ocean's mean dynamic topography (MDT) at tide gauges, which can be sourced from either geodetic or oceanographic approaches. To assess the suitability of different types of MDT for this purpose, we evaluate 13 physics-based numerical ocean models and six MDTs computed from observed geodetic and/or ocean data at 32 tide gauges around the Australian coast. We focus on the viability of numerical ocean models for vertical datum unification, classifying the 13 ocean models used as either independent (do not contain assimilated geodetic data) or non-independent (do contain assimilated geodetic data). We find that the independent and non-independent ocean models deliver similar results. Maximum differences among ocean models and geodetic MDTs reach >150 mm at several Australian tide gauges and are considered anomalous at the 99% confidence level. These differences appear to be of geodetic origin, but without additional independent information, or formal error estimates for each model, some of these errors remain inseparable. Our results imply that some ocean models have standard deviations of differences with other MDTs (using geodetic and/or ocean observations) at Australian tide gauges, and with levelling between some Australian tide gauges, of ˜ ± 50 mm . This indicates that they should be considered as an alternative to geodetic MDTs for the direct unification of vertical datums. They can also be used as diagnostics for errors in geodetic MDT in coastal zones, but the inseparability problem remains, where the error cannot be discriminated between the geoid model or altimeter-derived mean sea surface.

Explicitly computing geodetic coordinates from Cartesian coordinates

Science.gov (United States)

Zeng, Huaien

2013-04-01

This paper presents a new form of quartic equation based on Lagrange's extremum law and a Groebner basis under the constraint that the geodetic height is the shortest distance between a given point and the reference ellipsoid. A very explicit and concise formulae of the quartic equation by Ferrari's line is found, which avoids the need of a good starting guess for iterative methods. A new explicit algorithm is then proposed to compute geodetic coordinates from Cartesian coordinates. The convergence region of the algorithm is investigated and the corresponding correct solution is given. Lastly, the algorithm is validated with numerical experiments.

Analysis of the performance of hydrogen maser clocks at the ...

African Journals Online (AJOL)

Hydrogen maser frequency standards are commonly utilised in various space geodetic techniques such as Very Long Baseline Interferometry (VLBI) as local reference clocks. The Hartebeesthoek Radio Astronomy Observatory in South Africa is currently operating two maser frequency standards i.e., an EFOS28 and an ...

SN 1986J VLBI. IV. The Nature of the Central Component

Science.gov (United States)

Bietenholz, Michael F.; Bartel, Norbert

2017-12-01

We report on Very Large Array measurements between 1 and 45 GHz of the evolving radio spectral energy distribution (SED) of SN 1986J, made in conjunction with very long baseline interferometry (VLBI) imaging. The SED of SN 1986J is unique among supernovae, and shows an inversion point and a high-frequency turnover. Both are due to the central component seen in the VLBI images, and both are progressing downward in frequency with time. The optically thin spectral index of the central component is almost the same as that of the shell. We fit a simple model to the evolving SED consisting of an optically thin shell and a partly absorbed central component. The evolution of the SED is consistent with that of a homologously expanding system. Both components are fading, but the shell is fading more rapidly. We conclude that the central component is physically inside the expanding shell, and not a surface hotspot central only in projection. Our observations are consistent with the central component being due to interaction of the shock with the dense and highly structured circumstellar medium that resulted from a period of common-envelope evolution of the progenitor. However, a young pulsar-wind nebula or emission from an accreting black hole can also not be ruled out at this point.

NASA's Contribution to Global Space Geodesy Networks

Science.gov (United States)

Bosworth, John M.

1999-01-01

The NASA Space Geodesy program continues to be a major provider of space geodetic data for the international earth science community. NASA operates high performance Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI) and Global Positioning System (GPS) ground receivers at well over 30 locations around the world and works in close cooperation with space geodetic observatories around the world. NASA has also always been at the forefront in the quest for technical improvement and innovation in the space geodesy technologies to make them even more productive, accurate and economical. This presentation will highlight the current status of NASA's networks; the plans for partnerships with international groups in the southern hemisphere to improve the geographic distribution of space geodesy sites and the status of the technological improvements in SLR and VLBI that will support the new scientific thrusts proposed by interdisciplinary earth scientists. In addition, the expanding role of the NASA Space geodesy data archive, the CDDIS will be described.

Automated Simultaneous Local Ties with GNSS and Robot Tacheometer

Science.gov (United States)

Kallio, Ulla; Lösler, Michael; Bergstrand, Sten; Haas, Rüdiger; Eschelbach, Cornelia

2016-12-01

We have used GPS-based local-tie measurements simultaneously with geo-VLBI observations since 2008 during every geodetic VLBI session at Metsähovi. This system uses gimbal-mounted GNSS antennas that are mounted on the reflector of the Metsähovi 14-m radio telescope. A similar system was installed in 2013 at the Onsala 20-m radio telescope and has been used for a large number of VLBI sessions, including, e.g., the 15-day-long CONT14 campaign. In order to verify the results of the two systems, we performed a dedicated measurement campaign in the framework of the SIB60 project, involving both Metsähovi and Onsala. During this campaign the local ties at the two stations were measured simultaneously during two VLBI sessions in August and September 2015 where both stations participated. The robot tacheometer monitoring system HEIMDALL was used for the automated classical monitoring of the telescopes at both stations. Moreover, additional local terrestrial measurements were performed several times to derive the full IVS-IGS local ties at both sites. The kinematic GPS measurements at the two stations were analyzed with two independently developed analysis programs. We present here the preparations of the campaign, the measurement process, and preliminary results.

VLBI-derived troposphere parameters during CONT08

Science.gov (United States)

Heinkelmann, R.; Böhm, J.; Bolotin, S.; Engelhardt, G.; Haas, R.; Lanotte, R.; MacMillan, D. S.; Negusini, M.; Skurikhina, E.; Titov, O.; Schuh, H.

2011-07-01

Time-series of zenith wet and total troposphere delays as well as north and east gradients are compared, and zenith total delays ( ZTD) are combined on the level of parameter estimates. Input data sets are provided by ten Analysis Centers (ACs) of the International VLBI Service for Geodesy and Astrometry (IVS) for the CONT08 campaign (12-26 August 2008). The inconsistent usage of meteorological data and models, such as mapping functions, causes systematics among the ACs, and differing parameterizations and constraints add noise to the troposphere parameter estimates. The empirical standard deviation of ZTD among the ACs with regard to an unweighted mean is 4.6 mm. The ratio of the analysis noise to the observation noise assessed by the operator/software impact (OSI) model is about 2.5. These and other effects have to be accounted for to improve the intra-technique combination of VLBI-derived troposphere parameters. While the largest systematics caused by inconsistent usage of meteorological data can be avoided and the application of different mapping functions can be considered by applying empirical corrections, the noise has to be modeled in the stochastic model of intra-technique combination. The application of different stochastic models shows no significant effects on the combined parameters but results in different mean formal errors: the mean formal errors of the combined ZTD are 2.3 mm (unweighted), 4.4 mm (diagonal), 8.6 mm [variance component (VC) estimation], and 8.6 mm (operator/software impact, OSI). On the one hand, the OSI model, i.e. the inclusion of off-diagonal elements in the cofactor-matrix, considers the reapplication of observations yielding a factor of about two for mean formal errors as compared to the diagonal approach. On the other hand, the combination based on VC estimation shows large differences among the VCs and exhibits a comparable scaling of formal errors. Thus, for the combination of troposphere parameters a combination of the two

EVIDENCE FOR LOW BLACK HOLE SPIN AND PHYSICALLY MOTIVATED ACCRETION MODELS FROM MILLIMETER-VLBI OBSERVATIONS OF SAGITTARIUS A*

Energy Technology Data Exchange (ETDEWEB)

Broderick, Avery E [Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Fish, Vincent L; Doeleman, Sheperd S [Massachusetts Institute of Technology, Haystack Observatory, Route 40, Westford, MA 01886 (United States); Loeb, Abraham [Institute for Theory and Computation, Harvard University, Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2011-07-10

Millimeter very long baseline interferometry (mm-VLBI) provides the novel capacity to probe the emission region of a handful of supermassive black holes on sub-horizon scales. For Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, this provides access to the region in the immediate vicinity of the horizon. Broderick et al. have already shown that by leveraging spectral and polarization information as well as accretion theory, it is possible to extract accretion-model parameters (including black hole spin) from mm-VLBI experiments containing only a handful of telescopes. Here we repeat this analysis with the most recent mm-VLBI data, considering a class of aligned, radiatively inefficient accretion flow (RIAF) models. We find that the combined data set rules out symmetric models for Sgr A*'s flux distribution at the 3.9{sigma} level, strongly favoring length-to-width ratios of roughly 2.4:1. More importantly, we find that physically motivated accretion flow models provide a significantly better fit to the mm-VLBI observations than phenomenological models, at the 2.9{sigma} level. This implies that not only is mm-VLBI presently capable of distinguishing between potential physical models for Sgr A*'s emission, but further that it is sensitive to the strong gravitational lensing associated with the propagation of photons near the black hole. Based upon this analysis we find that the most probable magnitude, viewing angle, and position angle for the black hole spin are a = 0.0{sup +0.64+0.86}, {theta}=68{sup o+5o+9o}{sub -20}{sup o}{sub -28}{sup o}, and {xi}=-52{sup o+17o+33o}{sub -15}{sup o}{sub -24}{sup o} east of north, where the errors quoted are the 1{sigma} and 2{sigma} uncertainties.

EVIDENCE FOR LOW BLACK HOLE SPIN AND PHYSICALLY MOTIVATED ACCRETION MODELS FROM MILLIMETER-VLBI OBSERVATIONS OF SAGITTARIUS A*

International Nuclear Information System (INIS)

Broderick, Avery E.; Fish, Vincent L.; Doeleman, Sheperd S.; Loeb, Abraham

2011-01-01

Millimeter very long baseline interferometry (mm-VLBI) provides the novel capacity to probe the emission region of a handful of supermassive black holes on sub-horizon scales. For Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, this provides access to the region in the immediate vicinity of the horizon. Broderick et al. have already shown that by leveraging spectral and polarization information as well as accretion theory, it is possible to extract accretion-model parameters (including black hole spin) from mm-VLBI experiments containing only a handful of telescopes. Here we repeat this analysis with the most recent mm-VLBI data, considering a class of aligned, radiatively inefficient accretion flow (RIAF) models. We find that the combined data set rules out symmetric models for Sgr A*'s flux distribution at the 3.9σ level, strongly favoring length-to-width ratios of roughly 2.4:1. More importantly, we find that physically motivated accretion flow models provide a significantly better fit to the mm-VLBI observations than phenomenological models, at the 2.9σ level. This implies that not only is mm-VLBI presently capable of distinguishing between potential physical models for Sgr A*'s emission, but further that it is sensitive to the strong gravitational lensing associated with the propagation of photons near the black hole. Based upon this analysis we find that the most probable magnitude, viewing angle, and position angle for the black hole spin are a = 0.0 +0.64+0.86 , θ=68 o+5 o +9 o -20 o -28 o , and ξ=-52 o+17 o +33 o -15 o -24 o east of north, where the errors quoted are the 1σ and 2σ uncertainties.

Digital Base Band Converter As Radar Vlbi Backend / Dbbc Kā Ciparošanas Sistēma Radara Vlbi Novērojumiem

Science.gov (United States)

Tuccari, G.; Bezrukovs, Vl.; Nechaeva, M.

2012-12-01

A digital base band converter (DBBC) system has been developed by the Istituto di Radioastronomia (Noto, Italy) for increasing the sensitivity of European VLBI Network (EVN) by expanding the full observed bandwidth using numerical methods. The output data rate of this VLBI-backend is raised from 1 to 4 Gbps for each radiotelescope. All operations related to the signal processing (frequency translation, amplification, frequency generation with local oscillators, etc.) are transferred to the digital domain, which allows - in addition to well-known advantages coming from digital technologies - achieving better repeatability, precision, simplicity, etc. The maximum input band of DBBC system is 3.5 GHz, and the instantaneous bandwidth is up to 1 GHz for each radio frequency/intermediate frequency (RF/IF) out of the eight possible. This backend is a highly powerful platform for other radioastronomy applications, and a number of additional so-called personalities have been developed and used. This includes PFB (polyphase filter bank) receivers and Spectra for high resolution spectroscopy. An additional new development with the same aim - to use the DBBC system as a multi-purpose backend - is related to the bi-static radar observations including Radar VLBI. In such observations it is possible to study the population of space debris, with detection of even centimetre class fragments. A powerful transmitter is used to illuminate the sky region to be analyzed, and the echoes coming from known or unknown objects are reflected to one or more groundbased telescopes thus producing a single-dish or interferometric detection. The DBBC Radar VLBI personality is able to realize a high-resolution spectrum analysis, maintaining in the central area the echo signal at the expected frequency including the Doppler shift of frequency. For extremely weak signals a very large integration time is needed, so for this personality different input parameters are provided. The realtime information

Sciences of geodesy II innovations and future developments

CERN Document Server

Xu, Guochang

2014-01-01

This series of reference books describes the sciences of different fields in and around geodesy. Each chapter, is written by experts in the respective fields and covers an individual field and describes the history, theory, the objective, the technology, and the development, the highlight of the research, the applications, the problems, as well as future directions. Contents of Volume II include: Geodetic LEO Satellite Missions, Satellite Altimetry, Airborne Lidar, GNSS Software Receiver, Geodetic Boundary Problem, GPS and INS, VLBI, Geodetic Reference Systems, Spectral Analysis, Earth Tide and Ocean Loading Tide, Remote Sensing, Photogrammetry, Occultation, Geopotential Determination, Geoid Determination, Local Gravity Field, Geopotential Determination, Magnet Field, Mobile Mapping, General Relativity, Wide-area Precise Positioning etc.

Establishment of 2000 National Geodetic Control Network of China and It’s Technological Progress

Directory of Open Access Journals (Sweden)

CHEN Junyong

2007-02-01

Full Text Available Objectives: 2000’ National Geodetic Control Network of China is an important fundamental scientific engineering project in China. It consists of three parts which are establishment of 2000 National GPS Geodetic Network, its combination adjustment with national astro-geodetic network and 2000 National Gravity Fundamental network. It provides the high precise coordinate reference and gravity reference for three dimensional geo-center national coordinates system and gravity system, respectively. Additionally, it provides precise unified geometric and physical geodesy information for the economic construction, the national defense and the scientific research. Methods: 1. The larger number of data are processed in triple networks adjustment of 2000 National GPS Geodetic Network, which are chosen from the GPS monitoring stations, such as grade A, B of national GPS network , grade 1st and 2nd of national GPS network, crustal movement observation network of China, and others crustal deformation monitoring stations. Finally, the data of 2666 GPS stations are used in the data processing of 2000 National GPS Geodetic Network, including 124 external stations and 2542 internal stations. In order to the results of triple networks adjustment are corresponding to that of three dimensional geo-center coordinates system, ITRF 97 and epoch 2000.0 are chosen as the coordinate reference frame and epoch reference, respectively. The methods of “strong reference” and “weak reference” are combined used in the control data selection of triple networks adjustment. The scale and rotation scales are adopted for each sub network. The least square adjustment is firstly adopted in each sub network adjustment. The data of obvious abnormal baselines are found and rejected firstly. And the method of double factor robust estimation is adopted in the data processing. 2. The combined adjustment of 2000 National GPS Geodetic Network and national astro-geodetic network is

Long-term millimeter VLBI monitoring of M 87 with KVN at milliarcsecond resolution: nuclear spectrum

Science.gov (United States)

Kim, Jae-Young; Lee, Sang-Sung; Hodgson, Jeffrey A.; Algaba, Juan-Carlos; Zhao, Guang-Yao; Kino, Motoki; Byun, Do-Young; Kang, Sincheol

2018-02-01

We study the centimeter- to millimeter-wavelength synchrotron spectrum of the core of the radio galaxy M 87 at ≲0.8 mas 110Rs spatial scales using four years of fully simultaneous, multi-frequency VLBI data obtained by the Korean VLBI Network (KVN). We find a core spectral index α of ≳‑0.37 (S ∝ ν+α) between 22 and 129 GHz. By combining resolution-matched flux measurements from the Very Long Baseline Array (VLBA) at 15 GHz and taking the Event Horizon Telescope (EHT) 230 GHz core flux measurements in epochs 2009 and 2012 as lower limits, we find evidence of a nearly flat core spectrum across 15 and 129 GHz, which could naturally connect the 230 GHz VLBI core flux. The extremely flat spectrum is a strong indication that the jet base does not consist of a simple homogeneous plasma, but of inhomogeneous multi-energy components, with at least one component with the turn-over frequency ≳ 100 GHz. The spectral shape can be qualitatively explained if both the strongly (compact, optically thick at >100 GHz) and the relatively weakly magnetized (more extended, optically thin at <100 GHz) plasma components are colocated in the footprint of the relativistic jet.

First mm-VLBI Observations between the TRAO 14-m and the NRO 45-m Telescopes: Observations of 86 GHz SiO Masers in VY Canis Majoris

Science.gov (United States)

Shibata, Katsunori M.; Chung, Hyung-Soo; Kameno, Seiji; Roh, Duk-Gyoo; Umemoto, Tomofumi; Kim, Kwang-Dong; Asada, Keiichi; Han, Seog-Tae; Mochizuki, Nanako; Cho, Se-Hyung; Sawada-Satoh, Satoko; Kim, Hyun-Goo; Bushimata, Takeshi; Minh, Young Chol; Miyaji, Takeshi; Kuno, Nario; Mikoshiba, Hiroshi; Sunada, Kazuyoshi; Inoue, Makoto; Kobayashi, Hideyuki

2004-06-01

We have made VLBI observations at 86GHz using a 1000-km baseline between Korea and Japan with successful detections of SiO v = 1, J = 2 - 1 maser emissions from VY CMa and Orion KL in 2001 June. This was the first VLBI result for this baseline and the first astronomical VLBI observation for the Korean telescope. Since then, we observed SiO v = 1, J = 2 - 1 maser emission in VY CMa in 2002 January and 2003 February and derived the distributions of the maser emissions. Our results show that the maser emissions extend over 2-4 stellar radii, and were within the inner radius of the dust shell. We observed other SiO maser sources and continuum sources, and 86-GHz continuum emissions were detected from three continuum sources. It was verified that this baseline has a performance comparable to the most sensitive baseline in the VLBA and the CMVA, and is capable of investigating the proper motions of maser features in circumstellar envelopes using monitoring observations.

Plate motions and deformations from geologic and geodetic data

Science.gov (United States)

Jordan, T. H.

1986-06-01

Research effort on behalf of the Crustal Dynamics Project focused on the development of methodologies suitable for the analysis of space-geodetic data sets for the estimation of crustal motions, in conjunction with results derived from land-based geodetic data, neo-tectonic studies, and other geophysical data. These methodologies were used to provide estimates of both global plate motions and intraplate deformation in the western U.S. Results from the satellite ranging experiment for the rate of change of the baseline length between San Diego and Quincy, California indicated that relative motion between the North American and Pacific plates over the course of the observing period during 1972 to 1982 were consistent with estimates calculated from geologic data averaged over the past few million years. This result, when combined with other kinematic constraints on western U.S. deformation derived from land-based geodesy, neo-tectonic studies, and other geophysical data, places limits on the possible extension of the Basin and Range province, and implies significant deformation is occurring west of the San Andreas fault. A new methodology was developed to analyze vector-position space-geodetic data to provide estimates of relative vector motions of the observing sites. The algorithm is suitable for the reduction of large, inhomogeneous data sets, and takes into account the full position covariances, errors due to poorly resolved Earth orientation parameters and vertical positions, and reduces baises due to inhomogeneous sampling of the data. This methodology was applied to the problem of estimating the rate-scaling parameter of a global plate tectonic model using satellite laser ranging observations over a five-year interval. The results indicate that the mean rate of global plate motions for that interval are consistent with those averaged over several million years, and are not consistent with quiescent or greatly accelerated plate motions. This methodology was also

Seismology and space-based geodesy

Science.gov (United States)

Tralli, David M.; Tajima, Fumiko

1993-01-01

The potential of space-based geodetic measurement of crustal deformation in the context of seismology is explored. The achievements of seismological source theory and data analyses, mechanical modeling of fault zone behavior, and advances in space-based geodesy are reviewed, with emphasis on realizable contributions of space-based geodetic measurements specifically to seismology. The fundamental relationships between crustal deformation associated with an earthquake and the geodetically observable data are summarized. The response and spatial and temporal resolution of the geodetic data necessary to understand deformation at various phases of the earthquake cycle is stressed. The use of VLBI, SLR, and GPS measurements for studying global geodynamics properties that can be investigated to some extent with seismic data is discussed. The potential contributions of continuously operating strain monitoring networks and globally distributed geodetic observatories to existing worldwide modern digital seismographic networks are evaluated in reference to mutually addressable problems in seismology, geophysics, and tectonics.

Geodetic precession or dragging of inertial frames?

International Nuclear Information System (INIS)

Ashby, N.; Shahid-Saless, B.

1990-01-01

In metric theories of gravity the principle of general covariance allows one to describe phenomena by means of any convenient choice of coordinate system. In this paper it is shown that in an appropriately chosen coordinate system, geodetic precession of a gyroscope orbiting a spherically symmetric, spinning mass can be recast as a Lense-Thirring frame-dragging effect without invoking spatial curvature. The origin of this reference frame moves around the source but the frame axes point in fixed directions. The drag can be interpreted to arise from the orbital angular momentum of the source around the origin of the reference frame. In this reference frame the effects of geodetic precession and Lense-Thirring drag due to intrinsic angular momentum of the source have the same origin, namely, gravitomagnetism

A VLBI resolution of the Pleiades distance controversy.

Science.gov (United States)

Melis, Carl; Reid, Mark J; Mioduszewski, Amy J; Stauffer, John R; Bower, Geoffrey C

2014-08-29

Because of its proximity and its youth, the Pleiades open cluster of stars has been extensively studied and serves as a cornerstone for our understanding of the physical properties of young stars. This role is called into question by the "Pleiades distance controversy," wherein the cluster distance of 120.2 ± 1.5 parsecs (pc) as measured by the optical space astrometry mission Hipparcos is significantly different from the distance of 133.5 ± 1.2 pc derived with other techniques. We present an absolute trigonometric parallax distance measurement to the Pleiades cluster that uses very long baseline radio interferometry (VLBI). This distance of 136.2 ± 1.2 pc is the most accurate and precise yet presented for the cluster and is incompatible with the Hipparcos distance determination. Our results cement existing astrophysical models for Pleiades-age stars. Copyright © 2014, American Association for the Advancement of Science.

Very Long Baseline Interferometry: Dependencies on Frequency Stability

Science.gov (United States)

Nothnagel, Axel; Nilsson, Tobias; Schuh, Harald

2018-04-01

Very Long Baseline Interferometry (VLBI) is a differential technique observing radiation of compact extra-galactic radio sources with pairs of radio telescopes. For these observations, the frequency standards at the telescopes need to have very high stability. In this article we discuss why this is, and we investigate exactly how precise the frequency standards need to be. Four areas where good clock performance is needed are considered: coherence, geodetic parameter estimation, correlator synchronization, and UT1 determination. We show that in order to ensure the highest accuracy of VLBI, stability similar to that of a hydrogen maser is needed for time-scales up to a few hours. In the article, we are considering both traditional VLBI where extra-galactic radio sources are observed, as well as observation of man-made artificial radio sources emitted by satellites or spacecrafts.

Seismic and Geodetic Monitoring of the Nicoya, Costa Rica, Seismic Gap

Science.gov (United States)

Protti, M.; Gonzalez, V.; Schwartz, S.; Dixon, T.; Kato, T.; Kaneda, Y.; Simila, G.; Sampson, D.

2007-05-01

The Nicoya segment of the Middle America Trench has been recognized as a mature seismic gap with potential to generate a large earthquake in the near future (it ruptured with large earthquakes in 1853, 1900 and 1950). Low level of background seismicity and fast crustal deformation of the forearc are indicatives of strong coupling along the plate interface. Given its high seismic potential, the available data and especially the fact that the Nicoya peninsula extends over large part of the rupture area, this gap was selected as one of the two sites for a MARGINS-SEIZE experiment. With the goal of documenting the evolution of loading and stress release along this seismic gap, an international effort involving several institutions from Costa Rica, the United States and Japan is being carried out for over a decade in the region. This effort involves the installation of temporary and permanent seismic and geodetic networks. The seismic network includes short period, broad band and strong motion instruments. The seismic monitoring has provided valuable information on the geometry and characteristics of the plate interface. The geodetic network includes temporary and permanent GPS stations as well as surface and borehole tiltmeters. The geodetic networks have helped quantify the extend and degree of coupling. A continuously recording, three- station GPS network on the Nicoya Peninsula, Costa Rica, recorded what we believe is the first slow slip event observed along the plate interface of the Costa Rica subduction zone. We will present results from these monitoring networks. Collaborative international efforts are focused on expanding these seismic and geodetic networks to provide improved resolution of future creep events, to enhanced understanding of the mechanical behavior of the Nicoya subduction segment of the Middle American Trench and possibly capture the next large earthquake and its potential precursor deformation.

Influence of bad measurements in properties of GeodeticNnetwork

Directory of Open Access Journals (Sweden)

Vincent Jakub

2008-12-01

Full Text Available In establishment of LGS (Local geodetic Net some given coordinated points from the relevant area are used, new points areestablished and the required distances and angles among the points are measured. If some measurements are defective, the netadjustment with the obtained values is depreciated, unacceptable. In the paper there is given an identification method of incorrectmeasurement results. The faulty results are eliminated in a new adjustment or the relevant defective measurements are repeated forobtaining correct values.

Volcano-tectonic deformation in the Kivu Region, Central Africa: Results from six years of continuous GNSS observations of the Kivu Geodetic Network (KivuGNet)

Science.gov (United States)

Geirsson, Halldor; d'Oreye, Nicolas; Mashagiro, Niche; Syauswa, Muhindo; Celli, Gilles; Kadufu, Benjamin; Smets, Benoît; Kervyn, François

2017-10-01

We present an overview of the installation, operation, and initial results of the 15-station KivuGNet (Kivu Geodetic Network) in the Kivu Region, Central Africa. The network serves primarily as a research and monitoring tool for active volcanic, earthquake, and plate boundary processes in the region. Continuous operation of in-situ measurement networks in naturally and politically harsh environments is challenging, but has proven fruitful in this case. During the operation of the network since 2009, KivuGNet has captured: co-eruptive deformation from two eruptions of Nyamulagira (in 2010 and 2011-2012); inter-eruptive deformation, which we interpret as a combination of plate motion across the Western - East Africa Rift, and decreasing deep-seated magma accumulation under the Nyiragongo-Nyamulagira region; co-seismic deformation from the Mw5.8 August 7, 2015 Lwiro earthquake at the western border of Lake Kivu. We hope that this study will serve as a motivation for further implementation of in-situ geodetic networks in under-monitored and under-studied sections of the East African Rift.

Ionospheric Response to the Total Solar Eclipse of 22 July 2009 as Deduced from VLBI and GPS Data

Science.gov (United States)

Guo, L.; Shu, F. C.; Zheng, W. M.; Kondo, T.; Ichikawa, R.; Hasegawa, S.; Sekido, M.

2010-01-01

A total solar eclipse occurred over China at latitudes of about 30 N on the morning of 22 July 2009, providing a unique opportunity to investigate the influence of the sun on the earth's upper ionosphere. GPS observations from Shanghai GPS Local Network and VLBI observations from stations Shanghai, Urumqi, and Kashima were used to observe the response of TEC to the total solar eclipse. From the GPS data reduction, the sudden decrease of TEC at the time of the eclipse, amounting to 2.8 TECU, and gradual increase of TEC after the eclipse were found by analyzing the diurnal variations. More distinctly, the variations of TEC were studied along individual satellite passes. The delay in reaching the minimum level of TEC with the maximum phase of eclipse was 5-10 min. Besides, we also compared the ionospheric activity derived from different VLBI stations with the GPS results and found a strong correlation between them.

VLBI observations of the nuclei of a mixed sample of bright galaxies and quasars at 327 MHz

International Nuclear Information System (INIS)

Ananthakrishnan, S.; Kulkarni, V.K.

1989-01-01

The first VLBI observations using the Ooty telescope are presented. An array consisting of telescopes at Ooty (India), Crimea (USSR), Torun (Poland), Westerbork (Netherlands) and Jodrell Bank (United Kingdom) was operated in 1983 December at a frequency of 327 MHz. Nearby galaxies, compact quasars and SS433 were observed in this pilot experiment. Most of the galaxies were found to be well resolved. The structure of SS433 (visible only on the shortest baseline) is consistent with that obtained in previous high-frequency VLBI work. The visibilities of the compact quasars indicate that large-scale scattering may be taking place in the interplanetary medium. (author)

LONG-TERM STABILITY OF THE LOCAL GROUND CONTROL NETWORK AT THE CO-LOCATION SITE OF MEDICINA

Science.gov (United States)

Abbondanza, C.; Sarti, P.; Legrand, J.

2009-12-01

ITRF combinations rely on the availability of accurate tie vectors linking reference points of space geodetic techniques. Co-located instruments are assumed to move consistently and no local relative motion is taken into account. Instabilities may degrade the quality of the co-location itself and perturb the result of ITRF combinations. This work aims to determine the stability of the local ground control network at Medicina (Italy) with independent surveying methods. The observatory hosts a co-location between a VLBI telescope and two GPS antennas, MEDI and MSEL. It is located in the Po Plain where thick layers of clays are the prevalent soil characteristics. Hence, provision of long term stability of geodetic monuments is a challenge and monitoring their stability is an issue. MEDI and the VLBI station regularly contribute to the determination of ITRF, while MSEL is part of the EUREF network. A set of five tie vectors observations linking the VLBI and MEDI reference points was acquired between 2001 and 2007. It is our main tool for performing local deformation analysis. Additionally, the GPS time series of MEDI and MSEL were used to cross check and confirm the local instability detected by terrestrial methods. To achieve a rigorous and reliable investigation of the local stability, multi-epoch terrestrial observations were homogeneously processed according to common parameterizations in a consistent reference frame. Similarly, continuous GPS observations from MEDI and MSEL were analysed according to the new EPN reprocessing strategy in order to monitor the short baseline between MEDI and MSEL; to spotlight any change in its length. Both approaches confirm differential motions at the site which can be related to monument instabilities originated by the particularly unfavourable local geological setting and the inapt design of the monuments foundation. The monuments move non homogeneously at rates reaching up to 1.6 mm/year, this value being comparable to intra

Demonstration of the Cascadia G‐FAST geodetic earthquake early warning system for the Nisqually, Washington, earthquake

Science.gov (United States)

Crowell, Brendan; Schmidt, David; Bodin, Paul; Vidale, John; Gomberg, Joan S.; Hartog, Renate; Kress, Victor; Melbourne, Tim; Santillian, Marcelo; Minson, Sarah E.; Jamison, Dylan

2016-01-01

A prototype earthquake early warning (EEW) system is currently in development in the Pacific Northwest. We have taken a two‐stage approach to EEW: (1) detection and initial characterization using strong‐motion data with the Earthquake Alarm Systems (ElarmS) seismic early warning package and (2) the triggering of geodetic modeling modules using Global Navigation Satellite Systems data that help provide robust estimates of large‐magnitude earthquakes. In this article we demonstrate the performance of the latter, the Geodetic First Approximation of Size and Time (G‐FAST) geodetic early warning system, using simulated displacements for the 2001Mw 6.8 Nisqually earthquake. We test the timing and performance of the two G‐FAST source characterization modules, peak ground displacement scaling, and Centroid Moment Tensor‐driven finite‐fault‐slip modeling under ideal, latent, noisy, and incomplete data conditions. We show good agreement between source parameters computed by G‐FAST with previously published and postprocessed seismic and geodetic results for all test cases and modeling modules, and we discuss the challenges with integration into the U.S. Geological Survey’s ShakeAlert EEW system.

Geodetic alignment of laser power installations

International Nuclear Information System (INIS)

Shtorm, V.V.; Gostev, A.M.; Drobikov, A.V.

1989-01-01

Main problems occuring in applied geodesy under initial alignment of laser power installation optical channel are considered. Attention is paid to alignment of lens beamguide telescopic pairs and alignment quality control. Methods and means of geodetic measurements under alignment are indicated. Conclusions are made about the degree of working through certain aspects of the problem

Geodetic Control Points - Multi-State Control Point Database

Data.gov (United States)

NSGIC State | GIS Inventory — The Multi-State Control Point Database (MCPD) is a database of geodetic and mapping control covering Idaho and Montana. The control were submitted by registered land...

Consistent realization of Celestial and Terrestrial Reference Frames

Science.gov (United States)

Kwak, Younghee; Bloßfeld, Mathis; Schmid, Ralf; Angermann, Detlef; Gerstl, Michael; Seitz, Manuela

2018-03-01

The Celestial Reference System (CRS) is currently realized only by Very Long Baseline Interferometry (VLBI) because it is the space geodetic technique that enables observations in that frame. In contrast, the Terrestrial Reference System (TRS) is realized by means of the combination of four space geodetic techniques: Global Navigation Satellite System (GNSS), VLBI, Satellite Laser Ranging (SLR), and Doppler Orbitography and Radiopositioning Integrated by Satellite. The Earth orientation parameters (EOP) are the link between the two types of systems, CRS and TRS. The EOP series of the International Earth Rotation and Reference Systems Service were combined of specifically selected series from various analysis centers. Other EOP series were generated by a simultaneous estimation together with the TRF while the CRF was fixed. Those computation approaches entail inherent inconsistencies between TRF, EOP, and CRF, also because the input data sets are different. A combined normal equation (NEQ) system, which consists of all the parameters, i.e., TRF, EOP, and CRF, would overcome such an inconsistency. In this paper, we simultaneously estimate TRF, EOP, and CRF from an inter-technique combined NEQ using the latest GNSS, VLBI, and SLR data (2005-2015). The results show that the selection of local ties is most critical to the TRF. The combination of pole coordinates is beneficial for the CRF, whereas the combination of Δ UT1 results in clear rotations of the estimated CRF. However, the standard deviations of the EOP and the CRF improve by the inter-technique combination which indicates the benefits of a common estimation of all parameters. It became evident that the common determination of TRF, EOP, and CRF systematically influences future ICRF computations at the level of several μas. Moreover, the CRF is influenced by up to 50 μas if the station coordinates and EOP are dominated by the satellite techniques.

VizieR Online Data Catalog: VLBI Ecliptic Plane Survey: VEPS-1 (Shu+, 2017)

Science.gov (United States)

Shu, F.; Petrov, L.; Jiang, W.; Xia, B.; Jiang, T.; Cui, Y.; Takefuji, K.; McCallum, J.; Lovell, J.; Yi, S.-O.; Hao, L.; Yang, W.; Zhang, H.; Chen, Z.; Li, J.

2017-08-01

We began observations in the search mode in 2015 February. The participating stations included the three core stations of the Chinese VLBI Network (CVN): seshan25, kunming, and urumqi. Depending on the participating stations, the longest baseline length in each session can be varied from 3200km to 9800km. Our observations were performed at a 2048Mbps data rate, with 16 Intermediate Frequency (IF) channels and 2-bit sampling. The first eight IFs of 32MHz bandwidth were distributed in the range of [8.188, 8.444]GHz, and the remaining eight IFs of 32MHz bandwidth were in the range of [8.700, 8.956]GHz. Table 1: Summary of the VLBI Ecliptic Plane Survey (VEPS) observations in search mode: --------------------------------------------------- Date Dur. Code Stations Number of (Y/M/D) (h) Targets --------------------------------------------------- 2015 Feb 13 24 VEPS01 ShKmUr 293 2015 Feb 14 24 VEPS02 ShKmUr 338 2015 Apr 23 24 VEPS03 UrKv 300 2015 Apr 24 24 VEPS04 ShKmUrKv 400 2015 Aug 10 25 VEPS05 ShKmKvHo 252 2015 Aug 19 25 VEPS06 ShKmKvHo 277 2016 Mar 02 24 VEPS07 ShKmUrKb 333 2016 Mar 11 24 VEPS08 ShKmUrKb 477 2016 May 13 24 VEPS09 ShUrHo 291 2016 May 14 22 VEPS10 ShUrKv 322 2016 Jul 06 24 VEPS11 ShUrKb 307 2016 Sep 02 23 VEPS12 ShUr 424 2016 Sep 03 23 VEPS13 ShKmUr 344 --------------------------------------------------- Sh=Seshan25; Km=Kunming; Ur=Urumqi; Kv=Sejong; Kb=Kashim34; Ho=Hobart26. --------------------------------------------------- We ran two absolute astrometry dual-band VLBA programs that targeted ecliptic plane compact radio sources: the dedicated survey of weak ecliptic plane calibrators with the VLBA BS250 program in 2016 March-May, and the VLBA Calibrator Survey 9 (VCS-9) in 2015 August-2016 September. The International VLBI Service for Geodesy and Astrometry (IVS) runs a number of VLBI observing programs. We made an attempt to improve the coordinates of some VEPS sources detected in the search mode and provide additional measurements of telescope

The effects of mantle and anelasticity on nutations, earth tides, and tidal variations in rotation rate

Science.gov (United States)

Wahr, John; Bergen, Zachary

1986-01-01

The paper models the effects of mantle anelasticity on luni-solar nutations, on tidal deformation, on tidal variations in rotation rate, and on the eigenfrequency of the free core nutation. The results can be used to invert observations to solve for the anelastic contributions to the shear and bulk moduli of the upper and lower mantle. Specific anelastic models are used to numerically estimate the effects of anelasticity on these geodetic observables. The nutation estimates are compared with observational results. Among the conclusions: (1) mantle anelasticity is likely to be the most important source of damping for the free core nutation; (2) present VLBI nutation results are, in principle, accurate enough to usefully bound anelasticity at diurnal periods. But the discrepancy between the VLBI observed nutations and the 1984 IAU nutation model cannot be explained by anelasticity and is not yet well enough understood to allow anelasticity to be determined from the data.

El Nino, La Nina and VLBI Measured LOD

Science.gov (United States)

Clark, Thomas A.; Gipson, J. M.; Ma, C.

1998-01-01

VLBI is one of the most important techniques for measuring Earth orientation parameters (EOP), and is unique in its ability to make high accuracy measurements of UT1, and its time derivative, which is related to changes in the length of day, conventionally called LOD. These measurements of EOP give constraints on geophysical models of the solid-Earth, atmosphere and oceans. Changes in EOP are due either to external torques from gravitational forces, or to the exchange of angular momentum between the Earth, atmosphere and oceans. The effect of the external torques is strictly harmonic and nature, and is therefore easy to remove. We analyze an LOD time series derived from VLBI measurements with the goal of comparing this to predictions from AAM, and various ENSO indices. Previous work by ourselves and other investigators demonstrated a high degree of coherence between atmospheric angular momentum (AAM) and EOP. We continue to see this. As the angular momentum of the atmosphere increases, the rate of rotation of the Earth decreases, and vice versa. The signature of the ENSO is particularly strong. At the peak of the 1982-83 El Nino increased LOD by almost 1 ms. This was subsequently followed by a reduction in LOD of 0.75 ms. At its peak, in February of 1998, the 1997-98 El Nino increased LOD by 0.8 msec. As predicted at the 1998 Spring AGU, this has been followed by an abrupt decrease in LOD which is currently -0.4 ms. At this time (August, 1998) the current ENSO continues to develop in new and unexpected ways. We plan to update our analysis with all data available prior to the Fall AGU.

A Comparison of Geodetic and Geologic Rates Prior to Large Strike-Slip Earthquakes: A Diversity of Earthquake-Cycle Behaviors?

Science.gov (United States)

Dolan, James F.; Meade, Brendan J.

2017-12-01

Comparison of preevent geodetic and geologic rates in three large-magnitude (Mw = 7.6-7.9) strike-slip earthquakes reveals a wide range of behaviors. Specifically, geodetic rates of 26-28 mm/yr for the North Anatolian fault along the 1999 MW = 7.6 Izmit rupture are ˜40% faster than Holocene geologic rates. In contrast, geodetic rates of ˜6-8 mm/yr along the Denali fault prior to the 2002 MW = 7.9 Denali earthquake are only approximately half as fast as the latest Pleistocene-Holocene geologic rate of ˜12 mm/yr. In the third example where a sufficiently long pre-earthquake geodetic time series exists, the geodetic and geologic rates along the 2001 MW = 7.8 Kokoxili rupture on the Kunlun fault are approximately equal at ˜11 mm/yr. These results are not readily explicable with extant earthquake-cycle modeling, suggesting that they may instead be due to some combination of regional kinematic fault interactions, temporal variations in the strength of lithospheric-scale shear zones, and/or variations in local relative plate motion rate. Whatever the exact causes of these variable behaviors, these observations indicate that either the ratio of geodetic to geologic rates before an earthquake may not be diagnostic of the time to the next earthquake, as predicted by many rheologically based geodynamic models of earthquake-cycle behavior, or different behaviors characterize different fault systems in a manner that is not yet understood or predictable.

The current state of the creation and modernization of national geodetic and cartographic resources in Poland

Directory of Open Access Journals (Sweden)

Doskocz Adam

2016-01-01

Full Text Available All official data are currently integrated and harmonized in a spatial reference system. This paper outlines a national geodetic and cartographic resources in Poland. The national geodetic and cartographic resources are an important part of the spatial information infrastructure in the European Community. They also provide reference data for other resources of Spatial Data Infrastructure (SDI, including: main and detailed geodetic control networks, base maps, land and buildings registries, geodetic registries of utilities and topographic maps. This paper presents methods of producing digital map data and technical standards for field surveys, and in addition paper also presents some aspects of building Global and Regional SDI.

International VLBI Service for Geodesy and Astrometry. Delivering high-quality products and embarking on observations of the next generation

Science.gov (United States)

Nothnagel, A.; Artz, T.; Behrend, D.; Malkin, Z.

2017-07-01

The International VLBI Service for Geodesy and Astrometry (IVS) regularly produces high-quality Earth orientation parameters from observing sessions employing extensive networks or individual baselines. The master schedule is designed according to the telescope days committed by the stations and by the need for dense sampling of the Earth orientation parameters (EOP). In the pre-2011 era, the network constellations with their number of telescopes participating were limited by the playback and baseline capabilities of the hardware (Mark4) correlators. This limitation was overcome by the advent of software correlators, which can now accommodate many more playback units in a flexible configuration. In this paper, we describe the current operations of the IVS with special emphasis on the quality of the polar motion results since these are the only EOP components which can be validated against independent benchmarks. The polar motion results provided by the IVS have improved continuously over the years, now providing an agreement with IGS results at the level of 20-25 μas in a WRMS sense. At the end of the paper, an outlook is given for the realization of the VLBI Global Observing System.

A comparative study of amplitude calibrations for the East Asia VLBI Network: A priori and template spectrum methods

Science.gov (United States)

Cho, Ilje; Jung, Taehyun; Zhao, Guang-Yao; Akiyama, Kazunori; Sawada-Satoh, Satoko; Kino, Motoki; Byun, Do-Young; Sohn, Bong Won; Shibata, Katsunori M.; Hirota, Tomoya; Niinuma, Kotaro; Yonekura, Yoshinori; Fujisawa, Kenta; Oyama, Tomoaki

2017-12-01

We present the results of a comparative study of amplitude calibrations for the East Asia VLBI Network (EAVN) at 22 and 43 GHz using two different methods of an "a priori" and a "template spectrum", particularly on lower declination sources. Using observational data sets of early EAVN observations, we investigated the elevation-dependence of the gain values at seven stations of the KaVA (KVN and VERA Array) and three additional telescopes in Japan (Takahagi 32 m, Yamaguchi 32 m, and Nobeyama 45 m). By comparing the independently obtained gain values based on these two methods, we found that the gain values from each method were consistent within 10% at elevations higher than 10°. We also found that the total flux densities of two images produced from the different amplitude calibrations were in agreement within 10% at both 22 and 43 GHz. By using the template spectrum method, furthermore, the additional radio telescopes can participate in KaVA (i.e., EAVN), giving a notable sensitivity increase. Therefore, our results will constrain the detailed conditions in order to measure the VLBI amplitude reliably using EAVN, and discuss the potential of possible expansion to telescopes comprising EAVN.

Precise Orbital and Geodetic Parameter Estimation using SLR Observations for ILRS AAC

Directory of Open Access Journals (Sweden)

Young-Rok Kim

2013-12-01

Full Text Available In this study, we present results of precise orbital geodetic parameter estimation using satellite laser ranging (SLR observations for the International Laser Ranging Service (ILRS associate analysis center (AAC. Using normal point observations of LAGEOS-1, LAGEOS-2, ETALON-1, and ETALON-2 in SLR consolidated laser ranging data format, the NASA/ GSFC GEODYN II and SOLVE software programs were utilized for precise orbit determination (POD and finding solutions of a terrestrial reference frame (TRF and Earth orientation parameters (EOPs. For POD, a weekly-based orbit determination strategy was employed to process SLR observations taken from 20 weeks in 2013. For solutions of TRF and EOPs, loosely constrained scheme was used to integrate POD results of four geodetic SLR satellites. The coordinates of 11 ILRS core sites were determined and daily polar motion and polar motion rates were estimated. The root mean square (RMS value of post-fit residuals was used for orbit quality assessment, and both the stability of TRF and the precision of EOPs by external comparison were analyzed for verification of our solutions. Results of post-fit residuals show that the RMS of the orbits of LAGEOS-1 and LAGEOS-2 are 1.20 and 1.12 cm, and those of ETALON-1 and ETALON-2 are 1.02 and 1.11 cm, respectively. The stability analysis of TRF shows that the mean value of 3D stability of the coordinates of 11 ILRS core sites is 7.0 mm. An external comparison, with respect to International Earth rotation and Reference systems Service (IERS 08 C04 results, shows that standard deviations of polar motion Xp and Yp are 0.754 milliarcseconds (mas and 0.576 mas, respectively. Our results of precise orbital and geodetic parameter estimation are reasonable and help advance research at ILRS AAC.

THE BENEFITS OF VLBI ASTROMETRY TO PULSAR TIMING ARRAY SEARCHES FOR GRAVITATIONAL RADIATION

Energy Technology Data Exchange (ETDEWEB)

Madison, D. R.; Chatterjee, S.; Cordes, J. M. [Department of Astronomy and Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14850 (United States)

2013-11-10

Precision astrometry is an integral component of successful pulsar timing campaigns. Astrometric parameters are commonly derived by fitting them as parameters of a timing model to a series of pulse times of arrival (TOAs). TOAs measured to microsecond precision over spans of several years can yield position measurements with sub-milliarcsecond precision. However, timing-based astrometry can become biased if a pulsar displays any red spin noise or a red signal produced by the stochastic gravitational wave background. We investigate how noise of different spectral types is absorbed by timing models, leading to significant estimation biases in the astrometric parameters. We find that commonly used techniques for fitting timing models in the presence of red noise (Cholesky whitening) prevent the absorption of noise into the timing model remarkably well if the time baseline of observations exceeds several years, but are inadequate for dealing with shorter pulsar data sets. Independent of timing, pulsar-optimized very long baseline interferometry (VLBI) is capable of providing position estimates precise to the sub-milliarcsecond levels needed for high-precision timing. In order to make VLBI astrometric parameters useful in pulsar timing models, the transformation between the International Celestial Reference Frame (ICRF) and the dynamical solar system ephemeris used for pulsar timing must be constrained to within a few microarcseconds. We compute a transformation between the ICRF and pulsar timing frames and quantitatively discuss how the transformation will improve in coming years. We find that incorporating VLBI astrometry into the timing models of pulsars for which only a couple of years of timing data exist will lead to more realistic assessments of red spin noise and could enhance the amplitude of gravitational wave signatures in post-fit timing residuals by factors of 20 or more.

Added-value joint source modelling of seismic and geodetic data

Science.gov (United States)

Sudhaus, Henriette; Heimann, Sebastian; Walter, Thomas R.; Krueger, Frank

2013-04-01

In tectonically active regions earthquake source studies strongly support the analysis of the current faulting processes as they reveal the location and geometry of active faults, the average slip released or more. For source modelling of shallow, moderate to large earthquakes often a combination of geodetic (GPS, InSAR) and seismic data is used. A truly joint use of these data, however, usually takes place only on a higher modelling level, where some of the first-order characteristics (time, centroid location, fault orientation, moment) have been fixed already. These required basis model parameters have to be given, assumed or inferred in a previous, separate and highly non-linear modelling step using one of the these data sets alone. We present a new earthquake rupture model implementation that realizes a fully combined data integration of surface displacement measurements and seismic data in a non-linear optimization of simple but extended planar ruptures. The model implementation allows for fast forward calculations of full seismograms and surface deformation and therefore enables us to use Monte Carlo global search algorithms. Furthermore, we benefit from the complementary character of seismic and geodetic data, e. g. the high definition of the source location from geodetic data and the sensitivity of the resolution of the seismic data on moment releases at larger depth. These increased constraints from the combined dataset make optimizations efficient, even for larger model parameter spaces and with a very limited amount of a priori assumption on the source. A vital part of our approach is rigorous data weighting based on the empirically estimated data errors. We construct full data error variance-covariance matrices for geodetic data to account for correlated data noise and also weight the seismic data based on their signal-to-noise ratio. The estimation of the data errors and the fast forward modelling opens the door for Bayesian inferences of the source

An Autonomous, Low Cost Platform for Seafloor Geodetic Observations

Science.gov (United States)

Ericksen, T.; Foster, J. H.; Bingham, B. S.

2013-12-01

The high cost of acquiring geodetic data from the sea floor has limited the observations available to help us understand and model the behavior of seafloor geodetic processes. To address this problem, the Pacific GPS Facility at the University of Hawaii is developing a cost effective approach for accurately measuring short-term vertical motions of the seafloor and maintaining a continuous long-term record of seafloor pressure without the requirement for costly ship time. There is a recognized need to vastly increase our underwater geodetic observing capacity. Most of the largest recorded earthquakes and most devastating tsunamis are generated at subduction zones underwater. Similarly, many volcanoes are partly (e.g. Santorini) or completely (e.g. Loihi) submerged, and are not well observed and understood. Furthermore, landslide features ring many ocean basins, and huge debris deposits surround many volcanic oceanic islands. Our approach will lower the cost of collecting sea-floor geodetic data, reducing the barriers preventing us from acquiring the information we need to observe and understand these types of structures and provide a direct societal benefit in improving hazard assessment. The capability is being developed by equipping one of the University of Hawaii Wave Gliders with an integrated acoustic telemetry package, a dual frequency geodetic-grade Global Positioning System (GPS) receiver, processing unit, and cellular communications. The Wave Glider will interrogate high accuracy pressure sensors on the sea floor to maintain a near-continuous stream of pressure and temperature data, but seafloor pressure data includes contribution from a variety of sources and on its own may not provide the accuracy required for geodetic investigations. Independent measurements of sea surface pressure and sea surface height can be used to remove these contributions from the observed sea floor pressure timeseries. We will integrate our seafloor pressure measurements with air

Error Propagation in Geodetic Networks Studied by FEMLAB

DEFF Research Database (Denmark)

Borre, Kai

2009-01-01

Geodetic networks can be described by discrete models. The observations may be height differences, distances, and directions. Geodesists always make more observations than necessary and estimate the solution by using the principle of least squares. Contemporary networks often contain several thou...

Prospects for UT1 Measurements from VLBI Intensive Sessions

Science.gov (United States)

Boehm, Johannes; Nilsson, Tobias; Schuh, Harald

2010-01-01

Very Long Baseline Interferometry (VLBI) Intensives are one-hour single baseline sessions to provide Universal Time (UT1) in near real-time up to a delay of three days if a site is not e-transferring the observational data. Due to the importance of UT1 estimates for the prediction of Earth orientation parameters, as well as any kind of navigation on Earth or in space, there is not only the need to improve the timeliness of the results but also their accuracy. We identify the asymmetry of the tropospheric delays as the major error source, and we provide two strategies to improve the results, in particular of those Intensives which include the station Tsukuba in Japan with its large tropospheric variation. We find an improvement when (1) using ray-traced delays from a numerical weather model, and (2) when estimating tropospheric gradients within the analysis of Intensive sessions. The improvement is shown in terms of reduction of rms of length-of-day estimates w.r.t. those derived from Global Positioning System observations

Geodynamical behavior of some active area in Egypt, as deduced from geodetic and gravity data

Science.gov (United States)

Issawy, E.; Mrlina, J.; Radwan, A.; Mahmoud, S.; Rayan, A.

2009-04-01

Temporal gravity variation in parallel with the space geodetic technique (GPS) had been started in Egypt for real campaigns in 1997. The geodetic networks around the High Dam, Aswan area was the first net to be measured. More than five measurement epochs were performed. The results had a considerable limit of coincidence between gravity and GPS observations. The trend of gravity changes indicated a positive stress and had the vertical displacement observed for leveling points. The lowest gravity changes along Kalabsha fault reflect extensional and/or strike component of the stress field. Also, the areas around Cairo (Greater Cairo) and due to the occurrence of an earthquake of 1992, such type of measurements were useful for monitoring the recent activity. The data of the geodetic network around Cairo after 5 campaigns showed that, the estimated horizontal velocities for almost all points are 5.5± mm/year in approximately NW-SE direction. The non-tidal changes can explain the dynamic process within the upper crust related to the development of local stress conditions. The trends of gravity changes are more or less coincident with that deduced from GPS deformation analysis and the occurrence of the main shocks in the area. In additions, in 2005 the geodetic network around the southern part of Sinai and the Gulf of Suez were established. One campaign of measurements had been performed and the gravity values were obtained.

Geodetic Control Points, Benchmarks; Vertical elevation bench marks for monumented geodetic survey control points for which mean sea level elevations have been determined., Published in 1995, 1:24000 (1in=2000ft) scale, Rhode Island and Providence Plantations.

Data.gov (United States)

NSGIC State | GIS Inventory — Geodetic Control Points dataset current as of 1995. Benchmarks; Vertical elevation bench marks for monumented geodetic survey control points for which mean sea level...

Long-Term Evaluation of Ocean Tidal Variation Models of Polar Motion and UT1

Science.gov (United States)

Karbon, Maria; Balidakis, Kyriakos; Belda, Santiago; Nilsson, Tobias; Hagedoorn, Jan; Schuh, Harald

2018-04-01

Recent improvements in the development of VLBI (very long baseline interferometry) and other space geodetic techniques such as the global navigation satellite systems (GNSS) require very precise a-priori information of short-period (daily and sub-daily) Earth rotation variations. One significant contribution to Earth rotation is caused by the diurnal and semi-diurnal ocean tides. Within this work, we developed a new model for the short-period ocean tidal variations in Earth rotation, where the ocean tidal angular momentum model and the Earth rotation variation have been setup jointly. Besides the model of the short-period variation of the Earth's rotation parameters (ERP), based on the empirical ocean tide model EOT11a, we developed also ERP models, that are based on the hydrodynamic ocean tide models FES2012 and HAMTIDE. Furthermore, we have assessed the effect of uncertainties in the elastic Earth model on the resulting ERP models. Our proposed alternative ERP model to the IERS 2010 conventional model considers the elastic model PREM and 260 partial tides. The choice of the ocean tide model and the determination of the tidal velocities have been identified as the main uncertainties. However, in the VLBI analysis all models perform on the same level of accuracy. From these findings, we conclude that the models presented here, which are based on a re-examined theoretical description and long-term satellite altimetry observation only, are an alternative for the IERS conventional model but do not improve the geodetic results.

Integration of space geodesy: a US National Geodetic Observatory

Science.gov (United States)

Yunck, Thomas P.; Neilan, Ruth

2003-01-01

In the interest of improving the performance and efficiency of space geodesy a diverse group in the U.S., in collaboration with IGGOS, has begun to establish a unified National Geodetic Observatory (NGO).

First-order design of geodetic networks using the simulated annealing method

Science.gov (United States)

Berné, J. L.; Baselga, S.

2004-09-01

The general problem of the optimal design for a geodetic network subject to any extrinsic factors, namely the first-order design problem, can be dealt with as a numeric optimization problem. The classic theory of this problem and the optimization methods are revised. Then the innovative use of the simulated annealing method, which has been successfully applied in other fields, is presented for this classical geodetic problem. This method, belonging to iterative heuristic techniques in operational research, uses a thermodynamical analogy to crystalline networks to offer a solution that converges probabilistically to the global optimum. Basic formulation and some examples are studied.

Aftershock distribution as a constraint on the geodetic model of coseismic slip for the 2004 Parkfield earthquake

Science.gov (United States)

Bennington, Ninfa; Thurber, Clifford; Feigl, Kurt; ,

2011-01-01

Several studies of the 2004 Parkfield earthquake have linked the spatial distribution of the event’s aftershocks to the mainshock slip distribution on the fault. Using geodetic data, we find a model of coseismic slip for the 2004 Parkfield earthquake with the constraint that the edges of coseismic slip patches align with aftershocks. The constraint is applied by encouraging the curvature of coseismic slip in each model cell to be equal to the negative of the curvature of seismicity density. The large patch of peak slip about 15 km northwest of the 2004 hypocenter found in the curvature-constrained model is in good agreement in location and amplitude with previous geodetic studies and the majority of strong motion studies. The curvature-constrained solution shows slip primarily between aftershock “streaks” with the continuation of moderate levels of slip to the southeast. These observations are in good agreement with strong motion studies, but inconsistent with the majority of published geodetic slip models. Southeast of the 2004 hypocenter, a patch of peak slip observed in strong motion studies is absent from our curvature-constrained model, but the available GPS data do not resolve slip in this region. We conclude that the geodetic slip model constrained by the aftershock distribution fits the geodetic data quite well and that inconsistencies between models derived from seismic and geodetic data can be attributed largely to resolution issues.

Time Biases in laser ranging measurements; impacts on geodetic products (Reference Frame and Orbitography)

Science.gov (United States)

Belli, A.; Exertier, P.; Lemoine, F. G.; Chinn, D. S.; Zelensky, N. P.

2017-12-01

The GGOS objectives are to maintain a geodetic network with an accuracy of 1 mm and a stability of 0.1 mm per year. For years, the laser ranging technique, which provide very accurate absolute distances to geodetic targets enable to determine the scale factor as well as coordinates of the geocenter. In order to achieve this goal, systematic errors appearing in the laser ranging measurements must be considered and solved. In addition to Range Bias (RB), which is the primary source of uncertainty of the technique, Time Bias (TB) has been recently detected by using the Time Transfer by Laser Link (T2L2) space instrument capability on-board the satellite Jason-2. Instead of determining TB through the precise orbit determination that is applied to commonly used geodetic targets like LAGEOS to estimate global geodetic products, we have developed, independently, a dedicated method to transfer time between remote satellite laser ranging stations. As a result, the evolving clock phase shift to UTC of around 30 stations has been determined under the form of time series of time bias per station from 2008 to 2016 with an accuracy of 3-4 ns. It demonstrated the difficulty, in terms of Time & Frequency used technologies, to locally maintain accuracy and long term stability at least in the range of 100 ns that is the current requirement for time measurements (UTC) for the laser ranging technique. Because some laser ranging stations oftently exceed this limit (from 100 ns to a few μs) we have been studying these effects first on the precision orbit determination itself, second on the station positioning. We discuss the impact of TB on LAGEOS and Jason-2 orbits, which appears to affect the along-track component essentially. We also investigate the role of TB in global geodetic parameters as the station coordinates. Finally, we propose to provide the community with time series of time bias of laser ranging stations, under the form of a data- handling-file in order to be included in

The Space Geodesy Project and Radio Frequency Interference Characterization and Mitigation

Science.gov (United States)

Lawrence, Hilliard M.; Beaudoin, C.; Corey, B. E.; Tourain, C. L.; Petrachenko, B.; Dickey, John

2013-01-01

The Space Geodesy Project (SGP) development by NASA is an effort to co-locate the four international geodetic techniques Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR), Very Long Baseline Interferometry (VLBI), Global Navigation Satellite System (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) into one tightly referenced campus and coordinated reference frame analysis. The SGP requirement locates these stations within a small area to maintain line-of-sight and frequent automated survey known as the vector tie system. This causes a direct conflict with the new broadband VLBI technique. Broadband means 2-14 GHz, and RFI susceptibility at -80 dBW or higher due to sensitive RF components in the front end of the radio receiver.

3D geodetic monitoring slope deformations

Directory of Open Access Journals (Sweden)

Weiss Gabriel

1996-06-01

Full Text Available For plenty of slope failures that can be found in Slovakia is necessary and very important their geodetic monitoring (because of their activity, reactivisations, checks. The paper gives new methodologies for these works, using 3D terrestrial survey technologies for measurements in convenient deformation networks. The design of an optimal type of deformation model for various kinds of landslides and their exact processing with an efficient testing procedure to determine the kinematics of the slope deformations are presented too.

Motion and properties of nuclear radio components in Seyfert galaxies seen with VLBI

Science.gov (United States)

Middelberg, E.; Roy, A. L.; Nagar, N. M.; Krichbaum, T. P.; Norris, R. P.; Wilson, A. S.; Falcke, H.; Colbert, E. J. M.; Witzel, A.; Fricke, K. J.

2004-04-01

We report EVN, MERLIN and VLBA observations at 18 cm, 6 cm and 3.6 cm of the Seyfert galaxies NGC 7674, NGC 5506, NGC 2110 and Mrk 1210 to study their structure and proper motions on pc scales and to add some constraints on the many possible causes of the radio-quietness of Seyferts. The component configurations in NGC 7674 and NGC 2110 are simple, linear structures, whereas the configurations in NGC 5506 and Mrk 1210 have multiple components with no clear axis of symmetry. We suggest that NGC 7674 is a low-luminosity compact symmetric object. Comparing the images at different epochs, we find a proper motion in NGC 7674 of (0.92±0.07) c between the two central components separated by 282 pc and, in NGC 5506, we find a 3 σ upper limit of 0.50 c for the components separated by 3.8 pc. Our results confirm and extend earlier work showing that the outward motion of radio components in Seyfert galaxies is non-relativistic on pc scales. We briefly discuss whether this non-relativistic motion is intrinsic to the jet-formation process or results from deceleration of an initially relativistic jet by interaction with the pc or sub-pc scale interstellar medium. We combined our sample with a list compiled from the literature of VLBI observations made of Seyfert galaxies, and found that most Seyfert nuclei have at least one flat-spectrum component on the VLBI scale, which was not seen in the spectral indices measured at arcsec resolution. We found also that the bimodal alignment of pc and kpc radio structures displayed by radio galaxies and quasars is not displayed by this sample of Seyferts, which shows a uniform distribution of misalignment between 0° and 90°. The frequent misalignment could result from jet precession or from deflection of the jet by interaction with gas in the interstellar medium.

Adjustment of positional geodetic networks by unconventional estimations

Directory of Open Access Journals (Sweden)

Silvia Gašincová

2010-06-01

Full Text Available The content of this paper is the adjustment of positional geodetic networks by robust estimations. The techniques (basedon the unconventional estimations of repeated least-square method which have turned out to be suitable and applicable in the practisehave been demonstrated on the example of the local geodetic network, which was founded to compose this thesis. In the thesisthe following techniques have been chosen to compare the Method of least-squares with those many published in foreign literature:M-estimation of Biweight,M-estimation of Welsch and Danish method. All presented methods are based on the repeated least-squaremethod principle with gradual changing of weight of individual measurements. In the first stage a standard least-square method wascarried out in the following steps – iterations we gradually change individual weights according to the relevant instructions/ regulation(so-called weight function. Iteration process will be stopped when no deviated measurements are found in the file of measured data.MatLab programme version 5.2 T was used to implement mathematical adjustment.

Establishing a Modern Ground Network for Space Geodesy Applications

Science.gov (United States)

Pearlman, M.; Pavlis, E.; Altamimi, Z.; Noll, C.

2010-01-01

Ground-based networks of co-located space-geodesy techniques (VLBI, SLR, GLASS, DORIS) are the basis for the development and maintenance of the :International Terrestrial deference Frame (ITRE), which is the basis for our metric measurements of global change. The Global Geodetic Observing System (GGOS) within the International Association of Geodesy has established a task to develop a strategy to design, integrate and maintain the fundamental geodetic network and supporting infrastructure in a sustainable way to satisfy the long-term requirements for the reference frame. The GGOS goal is an origin definition at I mm or better and a temporal stability on the order of 0.1 mm/y, with similar numbers for the scale and orientation components. These goals are based on scientific requirements to address sea level rise with confidence. As a first step, simulations focused on establishing the optimal global SLR and VLBI network, since these two techniques alone are sufficient to define the reference frame. The GLASS constellations will then distribute the reference frame to users anywhere on the Earth. Using simulated data to be collected by the future networks, we investigated various designs and the resulting accuracy in the origin, scale and orientation of the resulting ITRF. We present here the results of extensive simulation studies aimed at designing optimal global geodetic networks to support GGOS science products. Current estimates are the network will require 24 - 32 globally distributed co-location sites. Stations in the near global network will require geologically stable sites witla good weather, established infrastructure, and local support and personnel. EGOS will seek groups that are interested in participation. GGOS intends to issues a Call for Participation of groups that would like to take part in the network implementation and operation_ Some examples of integrated stations currently in operation or under development will be presented. We will examine

Instituto Geografico Nacional of Spain

Science.gov (United States)

Colomer, Francisco; Garcia-Espada, Susana; Gomez-Gonzalez, Jesus; Lopez-Fernandez, Jose Antonio; Santamaria-Gomez, Alvaro; De Vicente, Pablo

2013-01-01

This report updates the description of the space geodesy facilities of the Spanish National Geographic Institute (IGN). The current 40-meter radio telescope at Yebes, a network station for IVS, has performed geodetic VLBI observations regularly since September 2008. In addition to this, the project to establish an Atlantic Network of Geodynamical and Space Stations (RAEGE) is progressing with the construction of the first antenna, which is being erected at Yebes.

Recent surface displacements in the Upper Rhine Graben — Preliminary results from geodetic networks

Science.gov (United States)

Fuhrmann, Thomas; Heck, Bernhard; Knöpfler, Andreas; Masson, Frédéric; Mayer, Michael; Ulrich, Patrice; Westerhaus, Malte; Zippelt, Karl

2013-08-01

Datasets of the GNSS Upper Rhine Graben Network (GURN) and the national levelling networks in Germany, France and Switzerland are investigated with respect to current surface displacements in the Upper Rhine Graben (URG) area. GURN consists of about 80 permanent GNSS (Global Navigation Satellite Systems) stations. The terrestrial levelling network comprises 1st and 2nd order levelling lines that have been remeasured at intervals of roughly 25 years, starting in 1922. Compared to earlier studies national institutions and private companies made available raw data, allowing for consistent solutions for the URG region. We focussed on the southern and eastern parts of the investigation area. Our preliminary results show that the levelling and GNSS datasets are sensitive to resolve small surface displacement rates down to an order of magnitude of 0.2 mm/a and 0.4 mm/a, respectively. The observed horizontal velocity components for a test region south of Strasbourg, obtained from GNSS coordinate time series, vary around 0.5 mm/a. The results are in general agreement with interseismic strain built-up in a sinistral strike-slip regime. Since the accuracy of the GNSS derived vertical component is insufficient, data of precise levelling networks is used to determine vertical displacement rates. More than 75% of the vertical rates obtained from a kinematic adjustment of 1st order levelling lines in the eastern part of URG vary between - 0.2 mm/a and + 0.2 mm/a, indicating that this region behaves stable. Higher rates up to 0.5 mm/a in a limited region south of Freiburg are in general agreement with active faulting. We conclude that both networks deliver stable results that reflect real surface movements in the URG area. We note, however, that geodetically observed surface displacements generally result from a superposition of different effects, and that a separation in tectonic and non-tectonic processes needs additional information and expertise.

New Antarctic Gravity Anomaly Grid for Enhanced Geodetic and Geophysical Studies in Antarctica.

Science.gov (United States)

Scheinert, M; Ferraccioli, F; Schwabe, J; Bell, R; Studinger, M; Damaske, D; Jokat, W; Aleshkova, N; Jordan, T; Leitchenkov, G; Blankenship, D D; Damiani, T M; Young, D; Cochran, J R; Richter, T D

2016-01-28

Gravity surveying is challenging in Antarctica because of its hostile environment and inaccessibility. Nevertheless, many ground-based, airborne and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s. We present the first modern Antarctic-wide gravity data compilation derived from 13 million data points covering an area of 10 million km 2 , which corresponds to 73% coverage of the continent. The remove-compute-restore technique was applied for gridding, which facilitated levelling of the different gravity datasets with respect to an Earth Gravity Model derived from satellite data alone. The resulting free-air and Bouguer gravity anomaly grids of 10 km resolution are publicly available. These grids will enable new high-resolution combined Earth Gravity Models to be derived and represent a major step forward towards solving the geodetic polar data gap problem. They provide a new tool to investigate continental-scale lithospheric structure and geological evolution of Antarctica.

New Antarctic Gravity Anomaly Grid for Enhanced Geodetic and Geophysical Studies in Antarctica

Science.gov (United States)

Scheinert, M.; Ferraccioli, F.; Schwabe, J.; Bell, R.; Studinger, M.; Damaske, D.; Jokat, W.; Aleshkova, N.; Jordan, T.; Leitchenkov, G.; Blankenship, D. D.; Damiani, T. M.; Young, D.; Cochran, J. R.; Richter, T. D.

2018-01-01

Gravity surveying is challenging in Antarctica because of its hostile environment and inaccessibility. Nevertheless, many ground-based, airborne and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s. We present the first modern Antarctic-wide gravity data compilation derived from 13 million data points covering an area of 10 million km2, which corresponds to 73% coverage of the continent. The remove-compute-restore technique was applied for gridding, which facilitated levelling of the different gravity datasets with respect to an Earth Gravity Model derived from satellite data alone. The resulting free-air and Bouguer gravity anomaly grids of 10 km resolution are publicly available. These grids will enable new high-resolution combined Earth Gravity Models to be derived and represent a major step forward towards solving the geodetic polar data gap problem. They provide a new tool to investigate continental-scale lithospheric structure and geological evolution of Antarctica. PMID:29326484

Verification of Positional Accuracy of ZVS3003 Geodetic Control ...

African Journals Online (AJOL)

The International GPS Service (IGS) has provided GPS orbit products to the scientific community with increased precision and timeliness. Many users interested in geodetic positioning have adopted the IGS precise orbits to achieve centimeter level accuracy and ensure long-term reference frame stability. Positioning with ...

A two-level approach to VLBI terrestrial and celestial reference frames using both least-squares adjustment and Kalman filter algorithms

Science.gov (United States)

Soja, B.; Krasna, H.; Boehm, J.; Gross, R. S.; Abbondanza, C.; Chin, T. M.; Heflin, M. B.; Parker, J. W.; Wu, X.

2017-12-01

The most recent realizations of the ITRS include several innovations, two of which are especially relevant to this study. On the one hand, the IERS ITRS combination center at DGFI-TUM introduced a two-level approach with DTRF2014, consisting of a classical deterministic frame based on normal equations and an optional coordinate time series of non-tidal displacements calculated from geophysical loading models. On the other hand, the JTRF2014 by the combination center at JPL is a time series representation of the ITRF determined by Kalman filtering. Both the JTRF2014 and the second level of the DTRF2014 are thus able to take into account short-term variations in the station coordinates. In this study, based on VLBI data, we combine these two approaches, applying them to the determination of both terrestrial and celestial reference frames. Our product has two levels like DTRF2014, with the second level being a Kalman filter solution like JTRF2014. First, we compute a classical TRF and CRF in a global least-squares adjustment by stacking normal equations from 5446 VLBI sessions between 1979 and 2016 using the Vienna VLBI and Satellite Software VieVS (solution level 1). Next, we obtain coordinate residuals from the global adjustment by applying the level-1 TRF and CRF in the single-session analysis and estimating coordinate offsets. These residuals are fed into a Kalman filter and smoother, taking into account the stochastic properties of the individual stations and radio sources. The resulting coordinate time series (solution level 2) serve as an additional layer representing irregular variations not considered in the first level of our approach. Both levels of our solution are implemented in VieVS in order to test their individual and combined performance regarding the repeatabilities of estimated baseline lengths, EOP, and radio source coordinates.

Slip deficit on the san andreas fault at parkfield, california, as revealed by inversion of geodetic data.

Science.gov (United States)

Segall, P; Harris, R

1986-09-26

A network of geodetic lines spanning the San Andreas fault near the rupture zone of the 1966 Parkfield, California, earthquake (magnitude M = 6) has been repeatedly surveyed since 1959. In the study reported here the average rates of line-length change since 1966 were inverted to determine the distribution of interseismic slip rate on the fault. These results indicate that the Parkfield rupture surface has not slipped significantly since 1966. Comparison of the geodetically determined seismic moment of the 1966 earthquake with the interseismic slip-deficit rate suggests that the strain released by the latest shock will most likely be restored between 1984 and 1989, although this may not occur until 1995. These results lend independent support to the earlier forecast of an M = 6 earthquake near Parkfield within 5 years of 1988.

Remote Control and Monitoring of VLBI Experiments by Smartphones

Science.gov (United States)

Ruztort, C. H.; Hase, H.; Zapata, O.; Pedreros, F.

2012-12-01

For the remote control and monitoring of VLBI operations, we developed a software optimized for smartphones. This is a new tool based on a client-server architecture with a Web interface optimized for smartphone screens and cellphone networks. The server uses variables of the Field System and its station specific parameters stored in the shared memory. The client running on the smartphone by a Web interface analyzes and visualizes the current status of the radio telescope, receiver, schedule, and recorder. In addition, it allows commands to be sent remotely to the Field System computer and displays the log entries. The user has full access to the entire operation process, which is important in emergency cases. The software also integrates a webcam interface.

Misbheaving Faults: The Expanding Role of Geodetic Imaging in Unraveling Unexpected Fault Slip Behavior

Science.gov (United States)

Barnhart, W. D.; Briggs, R.

2015-12-01

Geodetic imaging techniques enable researchers to "see" details of fault rupture that cannot be captured by complementary tools such as seismology and field studies, thus providing increasingly detailed information about surface strain, slip kinematics, and how an earthquake may be transcribed into the geological record. For example, the recent Haiti, Sierra El Mayor, and Nepal earthquakes illustrate the fundamental role of geodetic observations in recording blind ruptures where purely geological and seismological studies provided incomplete views of rupture kinematics. Traditional earthquake hazard analyses typically rely on sparse paleoseismic observations and incomplete mapping, simple assumptions of slip kinematics from Andersonian faulting, and earthquake analogs to characterize the probabilities of forthcoming ruptures and the severity of ground accelerations. Spatially dense geodetic observations in turn help to identify where these prevailing assumptions regarding fault behavior break down and highlight new and unexpected kinematic slip behavior. Here, we focus on three key contributions of space geodetic observations to the analysis of co-seismic deformation: identifying near-surface co-seismic slip where no easily recognized fault rupture exists; discerning non-Andersonian faulting styles; and quantifying distributed, off-fault deformation. The 2013 Balochistan strike slip earthquake in Pakistan illuminates how space geodesy precisely images non-Andersonian behavior and off-fault deformation. Through analysis of high-resolution optical imagery and DEMs, evidence emerges that a single fault map slip as both a strike slip and dip slip fault across multiple seismic cycles. These observations likewise enable us to quantify on-fault deformation, which account for ~72% of the displacements in this earthquake. Nonetheless, the spatial distribution of on- and off-fault deformation in this event is highly spatially variable- a complicating factor for comparisons

Towards Cloud Processing of GGOS Big Data

Science.gov (United States)

Weston, Stuart; Kim, Bumjun; Litchfield, Alan; Gulyaev, Sergei; Hall, Dylan; Chorao, Carlos; Ruthven, Andrew; Davies, Glyn; Lagos, Bruno; Christie, Don

2017-04-01

We report on our initial steps towards development of a cloud-like correlation infrastructure for geodetic Very Long Baseline Interferometry (VLBI), which in its raw format is of the order of 10-100 TB (big data). Data is generated by multiple VLBI radio telescopes, and is then used by for geodetic, geophysical, and astrometric research and operational activities through the International VLBI Service (IVS), as well as for corrections of GPS satellite orbits. Currently IVS data is correlated in several international Correlators (Correlation Centres), which receive data from individual radio telescope stations either in hard drives via regular mail service or via fibre using e-transfer mode. The latter is strongly limited by connectivity of existing correlation centres, which creates bottle necks and slows down the turnover of the data. This becomes critical in many applications - for example, it currently takes 1-2 weeks to generate the dUT1 parameter for corrections of GNSS orbits while less than 1-2 days delay is desirable. We started with a blade server at the AUT campus to emulate a cloud server using Virtual Machines (VMWare). The New Zealand Data Head node is connected to the high speed (100 Gbps) network ring circuit courtesy of the Research and Education Advanced Network New Zealand (REANNZ), with the additional nodes at remote physical sites connected via 10 Gbps fibre. We use real Australian Long Baseline Array (LBA) observational data from 6 radio telescopes in Australia, South Africa and New Zealand (15 baselines) of 1.5 hours in duration making 8 TB to emulate data transfer from remote locations and to provide a meaningful benchmark dataset for correlation. Data was successfully transferred using bespoke UDT network transfer tools and correlated with the speed-up factor of 0.8 using DiFX software correlator. In partnership with the New Zealand office of Catalyst IT Ltd we have moved this environment into Catalyst Cloud and report on the first

18 centimeter VLBI observations of the quasar NRAO 140 during and after a low-frequency outburst

International Nuclear Information System (INIS)

Marscher, A.P.; Broderick, J.J.; Padrielli, L.; Bartel, N.; Romney, J.D.; Virginia Polytechnic Institute and State Univ., Blacksburg; CNR, Istituto di Radioastronomia, Bologna, Italy; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA; Natitonal Radio Astronomy Observatory, Charlottesville, VA)

1987-01-01

VLBI and spectra observations have been used to identify the specific site of a low-frequency outburst in the quasar NRAO 140. The properties of the low-frequency variability in the quasar are compared with the predictions of several models. The refractive scintillation model alone does not account for the source's properties. 32 references

ALGORITHMS VARIANTS OF ELABORATION OF THE PRECISE GNSS NETWORK ESTABLISHED FOR GEODETIC SERVICE OF BUILDING OF THE MINING FACILITY

Directory of Open Access Journals (Sweden)

Ryszard MIELIMĄKA

2014-10-01

Full Text Available The article presents the problem of the usage of post‐processing services of the ASG‐EUPOS system on the example of GNSS network established for geodetic service of building of the inclined drift, to make coal deposit accessible, and also building associated objects. For the purpose of geodetic service of construction realization network was established outside the planned objects. The network consists of six new ground points and four control points belonging to ASG‐EUPOS network. Simultaneous, static measurements of the network were performed in three‐hour observation session, using multi‐frequency and multi‐system satellite receivers – Trimble R8. The paper presents three variants of post‐processing of the observation results. Calculations were performed using POZGEO‐D service and geodetic software package GEONET. The results of the calculation process revealed, that homogeneous vector networks should be adjusted on the ellipsoid or in the geocentric system. Model of adjustment of the vector network on the plane adopted in the GEONET software package should not be applied for elaboration of this type of network (long reference vectors more than 50km.

A comparative study for the estimation of geodetic point velocity by ...

Indian Academy of Sciences (India)

Geodetic point velocity; artificial neural networks; back propagation; radial basis function; Kriging. J. Earth Syst. Sci. ...... The employment of BPANN is an alternative tool to KRIG for .... Computational Intelligence and Multimedia Applications.

Geodetic and seismological investigation in the Ionian area

Directory of Open Access Journals (Sweden)

F. Riguzzi

1997-06-01

Full Text Available Geodetic and seismic evidence of crustal deformations in the Ionian area are shown in this paper. The Ionian GPS network, composed of nine sites crossing the Ionian Sea from Calabria, Southern Italy, to Northwestern Greece, was established and surveyed in 1991, 1994, 1995 within the framework of the TYRGEONET project (Anzidei et al., 1996. In 1996 a return campaign was carried out after the occurrence of seismic activity in 1995. The displacement pattern obtained for the Greek side of the network agrees well with those previously displayed, both in magnitude and direction, confirming a mean displacement rate of about 1-2 cm1/yr. The same agreement is not found for the Italian side of the network, where no significant deformations were detected between 1994 and 1996. Seismic deformation was also studied for the same area, starting from the moment tensors of events which occurred in the last 20 years with magnitude greater than 5.0; evident similarity with the displacement field exhibited by the Greek side of the Ionian Sea by geodetic surveys was inferred. On the contrary, the motion detected for the Italian area cannot be simply related to seismic activity.

The Impact of Sea Level Rise on Geodetic Vertical Datum of Peninsular Malaysia

Science.gov (United States)

Din, A. H. M.; Abazu, I. C.; Pa'suya, M. F.; Omar, K. M.; Hamid, A. I. A.

2016-09-01

Sea level rise is rapidly turning into major issues among our community and all levels of the government are working to develop responses to ensure these matters are given the uttermost attention in all facets of planning. It is more interesting to understand and investigate the present day sea level variation due its potential impact, particularly on our national geodetic vertical datum. To determine present day sea level variation, it is vital to consider both in-situ tide gauge and remote sensing measurements. This study presents an effort to quantify the sea level rise rate and magnitude over Peninsular Malaysia using tide gauge and multi-mission satellite altimeter. The time periods taken for both techniques are 32 years (from 1984 to 2015) for tidal data and 23 years (from 1993 to 2015) for altimetry data. Subsequently, the impact of sea level rise on Peninsular Malaysia Geodetic Vertical Datum (PMGVD) is evaluated in this study. the difference between MSL computed from 10 years (1984 - 1993) and 32 years (1984 - 2015) tidal data at Port Kelang showed that the increment of sea level is about 27mm. The computed magnitude showed an estimate of the long-term effect a change in MSL has on the geodetic vertical datum of Port Kelang tide gauge station. This will help give a new insight on the establishment of national geodetic vertical datum based on mean sea level data. Besides, this information can be used for a wide variety of climatic applications to study environmental issues related to flood and global warming in Malaysia.

THE IMPACT OF SEA LEVEL RISE ON GEODETIC VERTICAL DATUM OF PENINSULAR MALAYSIA

Directory of Open Access Journals (Sweden)

A. H. M. Din

2016-09-01

Full Text Available Sea level rise is rapidly turning into major issues among our community and all levels of the government are working to develop responses to ensure these matters are given the uttermost attention in all facets of planning. It is more interesting to understand and investigate the present day sea level variation due its potential impact, particularly on our national geodetic vertical datum. To determine present day sea level variation, it is vital to consider both in-situ tide gauge and remote sensing measurements. This study presents an effort to quantify the sea level rise rate and magnitude over Peninsular Malaysia using tide gauge and multi-mission satellite altimeter. The time periods taken for both techniques are 32 years (from 1984 to 2015 for tidal data and 23 years (from 1993 to 2015 for altimetry data. Subsequently, the impact of sea level rise on Peninsular Malaysia Geodetic Vertical Datum (PMGVD is evaluated in this study. the difference between MSL computed from 10 years (1984 – 1993 and 32 years (1984 – 2015 tidal data at Port Kelang showed that the increment of sea level is about 27mm. The computed magnitude showed an estimate of the long-term effect a change in MSL has on the geodetic vertical datum of Port Kelang tide gauge station. This will help give a new insight on the establishment of national geodetic vertical datum based on mean sea level data. Besides, this information can be used for a wide variety of climatic applications to study environmental issues related to flood and global warming in Malaysia.

Cooperative research in space geodesy and crustal dynamics

Science.gov (United States)

1994-01-01

This research grant, which covered the period of July 1991 to August 1994, was concerned with a variety of topics within the geodesy and crustal dynamics fields. The specific topics of this grant included satellite tracking and gravity field determinations and crustal dynamics (this concentrated of space geodetic site stability for VLBI sites). Summaries of the specific research projects are included along with a list of publications and presentations supported by this research grant.

GPU Based Software Correlators - Perspectives for VLBI2010

Science.gov (United States)

Hobiger, Thomas; Kimura, Moritaka; Takefuji, Kazuhiro; Oyama, Tomoaki; Koyama, Yasuhiro; Kondo, Tetsuro; Gotoh, Tadahiro; Amagai, Jun

2010-01-01

Caused by historical separation and driven by the requirements of the PC gaming industry, Graphics Processing Units (GPUs) have evolved to massive parallel processing systems which entered the area of non-graphic related applications. Although a single processing core on the GPU is much slower and provides less functionality than its counterpart on the CPU, the huge number of these small processing entities outperforms the classical processors when the application can be parallelized. Thus, in recent years various radio astronomical projects have started to make use of this technology either to realize the correlator on this platform or to establish the post-processing pipeline with GPUs. Therefore, the feasibility of GPUs as a choice for a VLBI correlator is being investigated, including pros and cons of this technology. Additionally, a GPU based software correlator will be reviewed with respect to energy consumption/GFlop/sec and cost/GFlop/sec.

Extending Resolution of Fault Slip With Geodetic Networks Through Optimal Network Design

Science.gov (United States)

Sathiakumar, Sharadha; Barbot, Sylvain Denis; Agram, Piyush

2017-12-01

Geodetic networks consisting of high precision and high rate Global Navigation Satellite Systems (GNSS) stations continuously monitor seismically active regions of the world. These networks measure surface displacements and the amount of geodetic strain accumulated in the region and give insight into the seismic potential. SuGar (Sumatra GPS Array) in Sumatra, GEONET (GNSS Earth Observation Network System) in Japan, and PBO (Plate Boundary Observatory) in California are some examples of established networks around the world that are constantly expanding with the addition of new stations to improve the quality of measurements. However, installing new stations to existing networks is tedious and expensive. Therefore, it is important to choose suitable locations for new stations to increase the precision obtained in measuring the geophysical parameters of interest. Here we describe a methodology to design optimal geodetic networks that augment the existing system and use it to investigate seismo-tectonics at convergent and transform boundaries considering land-based and seafloor geodesy. The proposed network design optimization would be pivotal to better understand seismic and tsunami hazards around the world. Land-based and seafloor networks can monitor fault slip around subduction zones with significant resolution, but transform faults are more challenging to monitor due to their near-vertical geometry.

Ostrogradski Hamiltonian approach for geodetic brane gravity

International Nuclear Information System (INIS)

Cordero, Ruben; Molgado, Alberto; Rojas, Efrain

2010-01-01

We present an alternative Hamiltonian description of a branelike universe immersed in a flat background spacetime. This model is named geodetic brane gravity. We set up the Regge-Teitelboim model to describe our Universe where such field theory is originally thought as a second order derivative theory. We refer to an Ostrogradski Hamiltonian formalism to prepare the system to its quantization. This approach comprize the manage of both first- and second-class constraints and the counting of degrees of freedom follows accordingly.

VLBI-simulations for the estimation of degree-three Love and Shida numbers h3 and l3

Science.gov (United States)

Mendes Cerveira, P. J.; Boehm, J.; Wresnik, J.; Spicakova, H.; Schuh, H.

2007-12-01

For the displacement due to solid Earth tides, the IERS Conventions 2003 recommend several corrections to nominal values. One of these corrections is the in-phase contribution by using the real Love and Shida numbers h3 and l3 at all degree-3 tides, where only the contribution of the moon is relevant. The maximum predicted radial displacement is in the order of 1.7 mm. The nominal values are 0.292 for h3, and 0.015 for l3, respectively. Using realistic station and source catalogues, we simulated VLBI (Very Long Baseline Interferometry) group time delays, with a white noise going up to 2 cm, and taking into account the solid Earth tides displacement. Goal of this study was to investigate whether degree-3 Love and Shida numbers can be unambiguously determined from VLBI observations. Therefore, several setups w.r.t., e.g., station constellation, cutoff angle, time span, sampling interval, and different levels of white noise were tested. Attention was put into the separability and correlation between the degree-2 and degree-3 Love and Shida numbers.

Geodetic refraction effects of electromagnetic wave propagation through the atmosphere

CERN Document Server

1984-01-01

With very few exceptions, geodetic measurements use electro­ magnetic radiation in order to measure directions, distances, time delays, and Doppler frequency shifts, to name the main ter­ restrial and space observables. Depending on the wavelength of the radiation and the purpose of the measurements, the follow­ ing parameters of the electromagnetic wave are measured: ampli­ tude, phase, angle-of-arrival, polarisation and frequency. Ac­ curate corrections have to be applied to the measurements in order to take into account the effects of the intervening medium between transmitter and receiver. The known solutions use at­ mospheric models, special observation programs, remote sensing techniques and instrumental methods. It has been shown that the effects of the earth's atmospheric envelope present a fundamental limitation to the accuracy and precision of geodetic measurements. This applies equally to ter­ restrial and space applications. Instrumental accuracies are al­ ready below the atmospherically i...

Mark III VLBI observations of the nucleus of M81 at 2.3 and 8.3 GHz

International Nuclear Information System (INIS)

Bartel, N.; Corey, B.E.; Shapiro, I.I.; Rogers, A.E.E.; Whitney, A.R.; Preston, R.A.

1982-01-01

The authors report here on simultaneous VLBI observations made with the Mark III system at 2.3 and 8.3 GHz. Observations on 14 and 16 March 1981 utilized the 100 m diameter telescope in Effelsberg, W. Germany (MPIR); the 43 m telescope at Green Bank, WV (NRAO); and the 40 m telescope near Big Pine, CA (OVRO). (Auth.)

Dynamic rupture modeling of the M7.2 2010 El Mayor-Cucapah earthquake: Comparison with a geodetic model

Science.gov (United States)

Kyriakopoulos, Christos; Oglesby, David D.; Funning, Gareth J.; Ryan, Kenneth

2017-01-01

The 2010 Mw 7.2 El Mayor-Cucapah earthquake is the largest event recorded in the broader Southern California-Baja California region in the last 18 years. Here we try to analyze primary features of this type of event by using dynamic rupture simulations based on a multifault interface and later compare our results with space geodetic models. Our results show that starting from homogeneous prestress conditions, slip heterogeneity can be achieved as a result of variable dip angle along strike and the modulation imposed by step over segments. We also considered effects from a topographic free surface and find that although this does not produce significant first-order effects for this earthquake, even a low topographic dome such as the Cucapah range can affect the rupture front pattern and fault slip rate. Finally, we inverted available interferometric synthetic aperture radar data, using the same geometry as the dynamic rupture model, and retrieved the space geodetic slip distribution that serves to constrain the dynamic rupture models. The one to one comparison of the final fault slip pattern generated with dynamic rupture models and the space geodetic inversion show good agreement. Our results lead us to the following conclusion: in a possible multifault rupture scenario, and if we have first-order geometry constraints, dynamic rupture models can be very efficient in predicting large-scale slip heterogeneities that are important for the correct assessment of seismic hazard and the magnitude of future events. Our work contributes to understanding the complex nature of multifault systems.

On the effect of ionospheric delay on geodetic relative GPS positioning

NARCIS (Netherlands)

Georgiadou, P.Y.; Kleusberg, A.

1988-01-01

Uncorrected ionospheric delay is one of the factors limiting the accuracy in geodetic relative positioning with single frequency Global Positioning System (GPS) carrier phase observations. Dual frequency measurements can be combined to eliminate the ionospheric delay in the observations. A

Frequent VLBI Monitoring on Parsec-Scales of 450+ Extragalactic FERMI Sources at 8 and 32 GHz

Science.gov (United States)

Jacobs, Christopher S.; Majid, W. A.; Romero-Wolf, A.; García-Mirí, C.; Horiuchi, S.; Snedeker, L. G.; Sotuela, I.

2012-10-01

Executive Summary: An existing Ka-band (32 GHz, 9mm) catalog of 450+ sources is being monitored every 6-10 weeks on Giga-lambda baselines. These observations are sensitive to parsec scale activity in the AGN cores providing unique tests of gamma ray emission models. Abstract: The Fermi Large Area Telescope (LAT) has now released the 2nd catalog of high-energy gamma-ray sources (2FGL) derived from the first 24 months of mission science data with 1873 sources detected and characterized in the 100 MeV to 100 GeV range. 1017 of 1873 sources at high Galactic latitude (abs(b) > 10 degrees) are associated statistically with active galactic nuclei (AGNs). Parsec-scale VLBI measurements play an important role in characterizing the nature of the candidate AGNs by providing crucial extra information to improve the probability of correct identification - VLBI filters out objects which do not host strong compact jets at parsec scale. We are carrying out regular VLBI monitoring of 450+ compact extragalactic sources using Deep Space Network (DSN) 34-meter antennas over intercontinental baselines simultaneously at 8 and 32 GHz. In addition to precision astrometric measurements of AGN compact cores used to maintain the JPL extragalactic reference frame, this program has the potential to provide regular simultaneous flux density measurements at 8 and 32 GHz with precision level of ~20%. By providing measurements on both East-West and North-South baselines with large antennas and Gbit/s recording capability, our program can probe sources down to a flux limit of 30 mJy (10-sigma), potentially increasing the sample to a fainter population of sources. In these regards, our program complements well existing northern and southern hemisphere VLBI monitoring programs, by providing flux measurements at 32 GHz, covering a fainter population sample, and by filling the gap for sources in the -20 to -45 degree declination range. Further, our program also provides additional flexibility for

Wavelet based comparison of high frequency oscillations in the geodetic and fluid excitation functions of polar motion

Science.gov (United States)

Kosek, W.; Popinski, W.; Niedzielski, T.

2011-10-01

It has been already shown that short period oscillations in polar motion, with periods less than 100 days, are very chaotic and are responsible for increase in short-term prediction errors of pole coordinates data. The wavelet technique enables to compare the geodetic and fluid excitation functions in the high frequency band in many different ways, e.g. by looking at the semblance function. The waveletbased semblance filtering enables determination the common signal in both geodetic and fluid excitation time series. In this paper the considered fluid excitation functions consist of the atmospheric, oceanic and land hydrology excitation functions from ECMWF atmospheric data produced by IERS Associated Product Centre Deutsches GeoForschungsZentrum, Potsdam. The geodetic excitation functions have been computed from the combined IERS pole coordinates data.

High-Precision Global Geodetic Systems: Revolution And Revelation In Fluid And 'Solid' Earth Tracking (Invited)

Science.gov (United States)

Minster, J. H.; Altamimi, Z.; Blewitt, G.; Carter, W. E.; Cazenave, A. A.; Davis, J. L.; Dragert, H.; Feary, D. A.; Herring, T.; Larson, K. M.; Ries, J. C.; Sandwell, D. T.; Wahr, J. M.

2009-12-01

Over the past half-century, space geodetic technologies have changed profoundly the way we look at the planet, not only in the matter of details and accuracy, but also in the matter of how the entire planet changes with time, even on “human” time scales. The advent of space geodesy has provided exquisite images of the ever-changing land and ocean topography and global gravity field of the planet. We now enjoy an International Terrestrial Reference System with a time-dependent geocenter position accurate to a few millimeters. We can image small and large tectonic deformations of the surface before, during, and after earthquakes and volcanic eruptions. We measure both the past subtle changes as well as the recent dramatic changes in the ice sheets, and track global and regional sea-level change to a precision of a millimeter per year or better. The remarkable achievements of Earth observing missions over the past two decades, and the success of future international missions described in the Decadal Survey depend both implicitly and explicitly on the continued availability and enhancement of a reliable and resilient global infrastructure for precise geodesy, and on ongoing advances in geodetic science that are linked to it. This allows us to deal with global scientific, technological and social issues such as climate change and natural hazards, but the impact of the global precise geodetic infrastructure also permeates our everyday lives. Nowadays drivers, aviators, and sailors can determine their positions inexpensively to meter precision in real time, anywhere on the planet. In the foreseeable future, not only will we be able to know a vehicle’s position to centimeter accuracy in real time, but also to control that position, and thus introduce autonomous navigation systems for many tasks which are beyond the reach of “manual” navigation capabilities. This vision will only be realized with sustained international support of the precise global geodetic

Development of Very Long Baseline Interferometry (VLBI) techniques in New Zealand: Array simulation, image synthesis and analysis

Science.gov (United States)

Weston, S. D.

2008-04-01

This thesis presents the design and development of a process to model Very Long Base Line Interferometry (VLBI) aperture synthesis antenna arrays. In line with the Auckland University of Technology (AUT) Institute for Radiophysics and Space Research (IRSR) aims to develop the knowledge, skills and experience within New Zealand, extensive use of existing radio astronomical software has been incorporated into the process namely AIPS (Astronomical Imaging Processing System), MIRIAD (a radio interferometry data reduction package) and DIFMAP (a program for synthesis imaging of visibility data from interferometer arrays of radio telescopes). This process has been used to model various antenna array configurations for two proposed New Zealand sites for antenna in a VLBI array configuration with existing Australian facilities and a passable antenna at Scott Base in Antarctica; and the results are presented in an attempt to demonstrate the improvement to be gained by joint trans-Tasman VLBI observation. It is hoped these results and process will assist the planning and placement of proposed New Zealand radio telescopes for cooperation with groups such as the Australian Long Baseline Array (LBA), others in the Pacific Rim and possibly globally; also potential future involvement of New Zealand with the SKA. The developed process has also been used to model a phased building schedule for the SKA in Australia and the addition of two antennas in New Zealand. This has been presented to the wider astronomical community via the Royal Astronomical Society of New Zealand Journal, and is summarized in this thesis with some additional material. A new measure of quality ("figure of merit") for comparing the original model image and final CLEAN images by utilizing normalized 2-D cross correlation is evaluated as an alternative to the existing subjective visual operator image comparison undertaken to date by other groups. This new unit of measure is then used ! in the presentation of the

Robust adjustment of a geodetic network measured by satellite technology in the Dargovských Hrdinov suburb

Directory of Open Access Journals (Sweden)

Slavomír Labant

2011-12-01

Full Text Available This article addresses the adjustment of a 3D geodetic network in the Dargovských Hrdinov suburbs using Global Navigation SatelliteSystems (GNSS for the purposes of deformation analysis. The advantage of using the GNSS compared to other terrestrial technology is thatit is not influenced by unpredictability in the ground level atmosphere and individual visibilities between points in the observed network arenot necessary. This article also includes the planning of GNSS observations using Planning Open Source software from Trimble as well assubsequent observations at individual network points. The geodetic network is processing on the basis of the Gauss-Markov model usingthe least square method and robust adjustment. From robust methods, Huber’s Robust M-estimation and Hampel’s Robust M-estimationwere used. Individual adjustments were tested and subsequently the results of analysis were graphically visualised using absolute confidenceellipsoids.

Geodetic and geophysical observations in Antarctica an overview in the IPY perspective

CERN Document Server

Capra, Alessandro

2008-01-01

This book is a collection of papers on various aspects of the geodetic and geophysical investigation and observation techniques. It includes material from the Arctic and Antarctica, as well as covering work from both temporary and permanent observatories.

COORDINATE TRANSFORMATION USING FEATHERSTONE AND VANÍČEK PROPOSED APPROACH - A CASE STUDY OF GHANA GEODETIC REFERENCE NETWORK

Directory of Open Access Journals (Sweden)

Yao Yevenyo Ziggah

2017-03-01

Full Text Available Most developing countries like Ghana are yet to adopt the geocentric datum for its surveying and mapping purposes. It is well known and documented that non-geocentric datums based on its establishment have more distortions in height compared with satellite datums. Most authors have argued that combining such height with horizontal positions (latitude and longitude in the transformation process could introduce unwanted distortions to the network. This is because the local geodetic height in most cases is assumed to be determined to a lower accuracy compared with the horizontal positions. In the light of this, a transformation model was proposed by Featherstone and Vaníček (1999 which avoids the use of height in both global and local datums in coordinate transformation. It was confirmed that adopting such a method reduces the effect of distortions caused by geodetic height on the transformation parameters estimated. Therefore, this paper applied Featherstone and Vaníček (FV model for the first time to a set of common points coordinates in Ghana geodetic reference network. The FV model was used to transform coordinates from global datum (WGS84 to local datum (Accra datum. The results obtained based on the Root Mean Square Error (RMSE and Mean Absolute Error (MAE in both Eastings and Northings were satisfactory. Thus, a RMSE value of 0.66 m and 0.96 m were obtained for the Eastings and Northings while 0.76 m and 0.73 m were the MAE values achieved. Also, the FV model attained a transformation accuracy of 0.49 m. Hence, this study will serve as a preliminary investigation in avoiding the use of height in coordinate transformation within Ghana’s geodetic reference network.

Use of GPS TEC Maps for Calibrating Single Band VLBI Sessions

Science.gov (United States)

Gordon, David

2010-01-01

GPS TEC ionosphere maps were first applied to a series of K and Q band VLBA astrometry sessions to try to eliminate a declination bias in estimated source positions. Their usage has been expanded to calibrate X-band only VLBI observations as well. At K-band, approx.60% of the declination bias appears to be removed with the application of GPS ionosphere calibrations. At X-band however, it appears that up to 90% or more of the declination bias is removed, with a corresponding increase in RA and declination uncertainties of approx.0.5 mas. GPS ionosphere calibrations may be very useful for improving the estimated positions of the X-only and S-only sources in the VCS and RDV sessions.

Operational radio interferometry observation network (ORION) mobile VLBI station. [for NASA Crustal Dynamics Project

Science.gov (United States)

Renzetti, N. A.; Vegos, C. J.; Parks, G. S.; Sniffin, R. W.; Gannon, D. L.; Nishimura, H. G.; Clements, P. A.; Mckinney, R. P.; Menninger, F. J.; Vandenberg, N. R.

1983-01-01

The design and current status of the ORION mobile VLBI station is described. The station consists of a five-meter antenna, a receiving and recording system installed in a mobile antenna transporter, and an electronics transporter. The station is designed for field operation by a two-person crew at the rate of two sites per week. The various subsystems are described in detail, including the antenna, housing facilities for electronics and crew, microwave equipment, receiver, data acquisition subsystem, frequency and timing subsystem, phase calibration, monitoring and control, water vapor radiometer, and communications.

Encouraging Deep Approach to Learning in Civil and Geodetic Engineering

Directory of Open Access Journals (Sweden)

Gašper Mrak

2016-10-01

Full Text Available This paper presents activities and changes applied to the teaching process within selected courses offered by Faculty of civil and geodetic engineering, University of Ljubljana, Slovenia. Theoretical background, evaluated from the point of the technical education needs, is presented. It can be seen that special focus has to be made to the students' motivation for deep learning which guarantees optimal balance between acquisition of concepts and skills, information processing and integration of fragmented pieces of knowledge into complex structures. Three case studies used to test theoretical points of departure are presented. Results of the introduced novelties and changes have been evaluated through the assessment of knowledge, students' satisfaction and teaching staff evaluations. For conclusive results, monitoring over a longer period of time should be conducted.

How well can online GPS PPP post-processing services be used to establish geodetic survey control networks?

Science.gov (United States)

Ebner, R.; Featherstone, W. E.

2008-09-01

Establishing geodetic control networks for subsequent surveys can be a costly business, even when using GPS. Multiple stations should be occupied simultaneously and post-processed with scientific software. However, the free availability of online GPS precise point positioning (PPP) post-processing services offer the opportunity to establish a whole geodetic control network with just one dual-frequency receiver and one field crew. To test this idea, we compared coordinates from a moderate-sized (~550 km by ~440 km) geodetic network of 46 points over part of south-western Western Australia, which were processed both with the Bernese v5 scientific software and with the CSRS (Canadian Spatial Reference System) PPP free online service. After rejection of five stations where the antenna type was not recognised by CSRS, the PPP solutions agreed on average with the Bernese solutions to 3.3 mm in east, 4.8 mm in north and 11.8 mm in height. The average standard deviations of the Bernese solutions were 1.0 mm in east, 1.2 mm in north and 6.2 mm in height, whereas for CSRS they were 3.9 mm in east, 1.9 mm in north and 7.8 mm in height, reflecting the inherently lower precision of PPP. However, at the 99% confidence level, only one CSRS solution was statistically different to the Bernese solution in the north component, due to a data interruption at that site. Nevertheless, PPP can still be used to establish geodetic survey control, albeit with a slightly lower quality because of the larger standard deviations. This approach may be of particular benefit in developing countries or remote regions, where geodetic infrastructure is sparse and would not normally be established without this approach.

Geodetic contributions to IWRM-projects in middle Java, Indonesia

Science.gov (United States)

Schmitt, Günter

2010-12-01

The district of Gunung Kidul in middle Java is one of the poorest regions in Indonesia. The essential reason is the acute water scarcity in this karst region during the months of the dry season. As a consequence of the poor living conditions many people have migrated away and therefore the development of the region is stagnating. During the last few years two projects have been initiated under the theme “Integrated Water Resources Management” in order to improve the water supply situation, both funded by the German Federal Ministry of Education and Research, and realized essentially by institutes of the University of Karlsruhe. Geodetic sub-projects are integrated into both projects. Special surveying activities had been, and have still to be, carried out to realise the geometrical basis for several other sub-projects. The particular contributions are 3D cave measurements for visualisation and planning, staking out of drilling points and construction axes, the definition of a common reference system, the surveying of the water distribution network and its technical facilities, the setting up and the management of a geographical information system (GIS), as well as special measurements such as dam monitoring or controlling of a vertical drilling machine. The paper reviews these projects and describes the geodetic activities.

ESPACE - a geodetic Master's program for the education of Satellite Application Engineers

Science.gov (United States)

Hedman, K.; Kirschner, S.; Seitz, F.

2012-04-01

In the last decades there has been a rapid development of new geodetic and other Earth observation satellites. Applications of these satellites such as car navigation systems, weather predictions, and, digital maps (such as Google Earth or Google Maps) play a more and more important role in our daily life. For geosciences, satellite applications such as remote sensing and precise positioning/navigation have turned out to be extremely useful and are meanwhile indispensable. Today, researchers within geodesy, climatology, oceanography, meteorology as well as within Earth system science are all dependent on up-to-date satellite data. Design, development and handling of these missions require experts with knowledge not only in space engineering, but also in the specific applications. That gives rise to a new kind of engineers - satellite application engineers. The study program for these engineers combines parts of different classical disciplines such as geodesy, aerospace engineering or electronic engineering. The satellite application engineering program Earth Oriented Space Science and Technology (ESPACE) was founded in 2005 at the Technische Universität München, mainly from institutions involved in geodesy and aerospace engineering. It is an international, interdisciplinary Master's program, and is open to students with a BSc in both Science (e.g. Geodesy, Mathematics, Informatics, Geophysics) and Engineering (e.g. Aerospace, Electronical and Mechanical Engineering). The program is completely conducted in English. ESPACE benefits from and utilizes its location in Munich with its unique concentration of expertise related to space science and technology. Teaching staff from 3 universities (Technische Universität München, Ludwig-Maximilian University, University of the Federal Armed Forces), research institutions (such as the German Aerospace Center, DLR and the German Geodetic Research Institute, DGFI) and space industry (such as EADS or Kayser-Threde) are

Deformation offshore Northern Chile monitored by a seafloor geodetic network (GeoSEA)

Science.gov (United States)

Hannemann, Katrin; Lange, Dietrich; Kopp, Heidrun; Petersen, Florian; Contreras-Reyes, Eduardo

2017-04-01

The Nazca-South American plate boundary around 21°S has last ruptured in an earthquake in 1877 and was identified as a seismic gap prior to the 2014 Iquique earthquake (Mw=8.1). The southern portion of this segment is still unbroken. The geodetic monitoring of the Chilean subduction zone is crucial to understand the deformation processes in this area. Most geodetic measurements rely on GPS and are therefore limited to onshore campaigns. In December 2015, we installed the GeoSEA (Geodetic Earthquake Observatory on the SEAfloor) array around 21°S of the Nazca-South American plate boundary with RV SONNE to extend the geodetic observations to the offshore areas. The GeoSEA array consists of autonomous acoustic seafloor transponders mounted on 4 m high tripods. These transponders are able to continuously measure the two-way travel time of acoustic signals between station pairs (baselines) and the properties of the sea water (sound speed, temperature and pressure) at each transponder. These measurements are used to retrieve the distances between the transponders and give insights into the deformation of the seafloor. At the Chilean subduction zone, we installed in total 23 transponders in 3 subarrays with interstation distances of up to 2500 m. On the middle continental slope in 2300 m water depth, an array consisting of 8 transponders measures across crustal faults seen in AUV mapping. A second array of 5 stations located on the outer rise monitors extension across normal plate-bending faults. The deepest deployment in 5000 m water depth located on the lower continental slope with 10 stations is designed to measure diffuse strain build-up. The transponders are intended to monitor the seafloor deformation for 3.5 years. In November 2016 during a cruise of RV Langseth, the first 11 months of data were successfully uploaded via an acoustic modem. Furthermore, an additional component of the network, GeoSURF, a self-steering autonomous vehicle (wave glider), was

Monitoring Coral Growth - the Dichotomy Between Underwater Photogrammetry and Geodetic Control Network

Science.gov (United States)

Neyer, F.; Nocerino, E.; Gruen, A.

2018-05-01

Creating 3-dimensional (3D) models of underwater scenes has become a common approach for monitoring coral reef changes and its structural complexity. Also in underwater archeology, 3D models are often created using underwater optical imagery. In this paper, we focus on the aspect of detecting small changes in the coral reef using a multi-temporal photogrammetric modelling approach, which requires a high quality control network. We show that the quality of a good geodetic network limits the direct change detection, i.e., without any further registration process. As the photogrammetric accuracy is expected to exceed the geodetic network accuracy by at least one order of magnitude, we suggest to do a fine registration based on a number of signalized points. This work is part of the Moorea Island Digital Ecosystem Avatar (IDEA) project that has been initiated in 2013 by a group of international researchers (https://mooreaidea.ethz.ch/).

Beyond the usual mapping functions in GPS, VLBI and Deep Space tracking.

Science.gov (United States)

Barriot, Jean-Pierre; Serafini, Jonathan; Sichoix, Lydie

2014-05-01

We describe here a new algorithm to model the water contents of the atmosphere (including ZWD) from GPS slant wet delays relative to a single receiver. We first make the assumption that the water vapor contents are mainly governed by a scale height (exponential law), and secondly that the departures from this decaying exponential can be mapped as a set of low degree 3D Zernike functions (w.r.t. space) and Tchebyshev polynomials (w.r.t. time.) We compare this new algorithm with previous algorithms known as mapping functions in GPS, VLBI and Deep Space tracking and give an example with data acquired over a one day time span at the Geodesy Observatory of Tahiti.

A Static Displacement Monitoring System for VLBI Antenna Using Close-Range Photogrammetry

Directory of Open Access Journals (Sweden)

Hyukgil Kim

2017-11-01

Full Text Available In this study, a static displacement monitoring program was developed to maintain the accurate performance of a Very Long Baseline Interferometry (VLBI antenna by monitoring its structural stability. The monitoring program was designed to measure static displacement, among the many displacements of the antenna’s main reflector, which can directly affect its performance. The program measures the position of a monitored object with mm-level accuracy through close-range photogrammetry that uses high-resolution Charge Coupled Device (CCD cameras. The developed program will be used to evaluate the structural soundness of an antenna based on continuous displacement measurements, which can also be used as basic data for repair and reinforcement work in the future.

Atmospheric pressure loading parameters from very long baseline interferometry observations

Science.gov (United States)

Macmillan, D. S.; Gipson, John M.

1994-01-01

Atmospheric mass loading produces a primarily vertical displacement of the Earth's crust. This displacement is correlated with surface pressure and is large enough to be detected by very long baseline interferometry (VLBI) measurements. Using the measured surface pressure at VLBI stations, we have estimated the atmospheric loading term for each station location directly from VLBI data acquired from 1979 to 1992. Our estimates of the vertical sensitivity to change in pressure range from 0 to -0.6 mm/mbar depending on the station. These estimates agree with inverted barometer model calculations (Manabe et al., 1991; vanDam and Herring, 1994) of the vertical displacement sensitivity computed by convolving actual pressure distributions with loading Green's functions. The pressure sensitivity tends to be smaller for stations near the coast, which is consistent with the inverted barometer hypothesis. Applying this estimated pressure loading correction in standard VLBI geodetic analysis improves the repeatability of estimated lengths of 25 out of 37 baselines that were measured at least 50 times. In a root-sum-square (rss) sense, the improvement generally increases with baseline length at a rate of about 0.3 to 0.6 ppb depending on whether the baseline stations are close to the coast. For the 5998-km baseline from Westford, Massachusetts, to Wettzell, Germany, the rss improvement is about 3.6 mm out of 11.0 mm. The average rss reduction of the vertical scatter for inland stations ranges from 2.7 to 5.4 mm.

Connecting VLBI and Gaia celestial reference frames

Directory of Open Access Journals (Sweden)

Zinovy Malkin

2016-09-01

Full Text Available The current state of the link problem between radio and optical celestial reference frames is considered.The main objectives of the investigations in this direction during the next few years are the preparation of a comparisonand the mutual orientation and rotation between the optical it Gaia Celestial Reference Frame (GCRFand the 3rd generation radio International Celestial Reference Frame (ICRF3, obtained from VLBI observations.Both systems, ideally, should be a realization of the ICRS (International Celestial Reference System at micro-arcsecond level accuracy.Therefore, the link accuracy between the ICRF and GCRF should be obtained with similar error level, which is not a trivial taskdue to relatively large systematic and random errors in source positions at different frequency bands.In this paper, a brief overview of recent work on the GCRF--ICRF link is presented.Additional possibilities to improve the GCRF--ICRF link accuracy are discussed.The suggestion is made to use astrometric radio sources with optical magnitude to 20$^m$ rather than to 18$^m$ as currently plannedfor the GCRF--ICRF link.In addition, the use of radio stars is also a prospective method to obtain independent and accurate orientation between the Gaia frame and the ICRF.

Connecting VLBI and Gaia Celestial Reference Frames

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Malkin, Zinovy, E-mail: malkin@gao.spb.ru [Department of Radio Astronomy Research, The Pulkovo Astronomical Observatory, St. Petersburg (Russian Federation); Institute of Earth Sciences, St. Petersburg State University, St. Petersburg (Russian Federation); Astronomy and Cosmic Geodesy Department, Kazan Federal University, Kazan (Russian Federation)

2016-09-12

The current state of the link problem between radio and optical celestial reference frames is considered. The main objectives of the investigations in this direction during the next few years are the preparation of a comparison and the mutual orientation and rotation between the optical Gaia Celestial Reference Frame (GCRF) and the 3rd generation radio International Celestial Reference Frame (ICRF3), obtained from VLBI observations. Both systems, ideally, should be a realization of the ICRS (International Celestial Reference System) at micro-arcsecond level accuracy. Therefore, the link accuracy between the ICRF and GCRF should be obtained with similar error level, which is not a trivial task due to relatively large systematic and random errors in source positions at different frequency bands. In this paper, a brief overview of recent work on the GCRF–ICRF link is presented. Additional possibilities to improve the GCRF–ICRF link accuracy are discussed. The suggestion is made to use astrometric radio sources with optical magnitude to 20{sup m} rather than to 18{sup m} as currently planned for the GCRF–ICRF link. In addition, the use of radio stars is also a prospective method to obtain independent and accurate orientation between the Gaia frame and the ICRF.

The combined geodetic network adjusted on the reference ellipsoid – a comparison of three functional models for GNSS observations

Directory of Open Access Journals (Sweden)

Kadaj Roman

2016-12-01

Full Text Available The adjustment problem of the so-called combined (hybrid, integrated network created with GNSS vectors and terrestrial observations has been the subject of many theoretical and applied works. The network adjustment in various mathematical spaces was considered: in the Cartesian geocentric system on a reference ellipsoid and on a mapping plane. For practical reasons, it often takes a geodetic coordinate system associated with the reference ellipsoid. In this case, the Cartesian GNSS vectors are converted, for example, into geodesic parameters (azimuth and length on the ellipsoid, but the simple form of converted pseudo-observations are the direct differences of the geodetic coordinates. Unfortunately, such an approach may be essentially distorted by a systematic error resulting from the position error of the GNSS vector, before its projection on the ellipsoid surface. In this paper, an analysis of the impact of this error on the determined measures of geometric ellipsoid elements, including the differences of geodetic coordinates or geodesic parameters is presented. Assuming that the adjustment of a combined network on the ellipsoid shows that the optimal functional approach in relation to the satellite observation, is to create the observational equations directly for the original GNSS Cartesian vector components, writing them directly as a function of the geodetic coordinates (in numerical applications, we use the linearized forms of observational equations with explicitly specified coefficients. While retaining the original character of the Cartesian vector, one avoids any systematic errors that may occur in the conversion of the original GNSS vectors to ellipsoid elements, for example the vector of the geodesic parameters. The problem is theoretically developed and numerically tested. An example of the adjustment of a subnet loaded from the database of reference stations of the ASG-EUPOS system was considered for the preferred functional

Resolution testing and limitations of geodetic and tsunami datasets for finite fault inversions along subduction zones

Science.gov (United States)

Williamson, A.; Newman, A. V.

2017-12-01

Finite fault inversions utilizing multiple datasets have become commonplace for large earthquakes pending data availability. The mixture of geodetic datasets such as Global Navigational Satellite Systems (GNSS) and InSAR, seismic waveforms, and when applicable, tsunami waveforms from Deep-Ocean Assessment and Reporting of Tsunami (DART) gauges, provide slightly different observations that when incorporated together lead to a more robust model of fault slip distribution. The merging of different datasets is of particular importance along subduction zones where direct observations of seafloor deformation over the rupture area are extremely limited. Instead, instrumentation measures related ground motion from tens to hundreds of kilometers away. The distance from the event and dataset type can lead to a variable degree of resolution, affecting the ability to accurately model the spatial distribution of slip. This study analyzes the spatial resolution attained individually from geodetic and tsunami datasets as well as in a combined dataset. We constrain the importance of distance between estimated parameters and observed data and how that varies between land-based and open ocean datasets. Analysis focuses on accurately scaled subduction zone synthetic models as well as analysis of the relationship between slip and data in recent large subduction zone earthquakes. This study shows that seafloor deformation sensitive datasets, like open-ocean tsunami waveforms or seafloor geodetic instrumentation, can provide unique offshore resolution for understanding most large and particularly tsunamigenic megathrust earthquake activity. In most environments, we simply lack the capability to resolve static displacements using land-based geodetic observations.

Geodetic, Geologic and Seismic Interdisciplinary Research of Tectonically Caused Movements in the Wider Area of the City of Zagreb

Science.gov (United States)

Dapo, A.; Pribicevic, B.; Herak, M.; Prelogovic, E.

2012-04-01

Since the last great earthquake in 1880 which shook the Zagreb area with IX° MCS, tectonic movements and models of numerous Zagreb faults have been the focal point of Croatian geologists, seismologists and in the last 15 years also geodetic scientists, who all have been working in the scope of their scientific branches on bringing the light to the tectonic mechanisms in the wider Zagreb area. Since it is tectonically very active area and being the Capitol city of the Croatia with very high population density it is of utmost importance to understand those mechanisms and to according to them find the best possible measures for protecting people and valuables. Best results are certainly going to be achieved through the interdisciplinary approach. That is why this paper presents first interdisciplinary results from geodetic, geologic and seismic researches and their contribution to the collective knowledge about tectonic movements in the wider area of the City of Zagreb.

Astrometria diferencial de precision con VLBI el triangulo de Draco (y estudios de SN1993J)

Science.gov (United States)

Ros, E.

1997-11-01

The Very Long Baseline Interferometry (VLBI) technique provides unprecedented resolutions in astronomy. In this PhD we show progress in the study of high precision phase-delay differential astrometry through observations of the radio source triangle formed by the BL-Lac objects 1803+784 and 2007+777, and the QSO 1928+738, in the Northern constellation of Draco (the Dragon), from observations carried out on 20/21 November 1991 with an intercontinental interferometric array simultaneously at the frequencies of 2.3 and 8.4 GHz. We have determined the angular separations among the three radio sources with submilliarcsecond accuracy from a weighted least squares analysis of the differential phase delay from the three celestial bodies. Our present work introduces important advances with respect to previous astrometric studies, carried out over radio source pairs separated by smaller angular distances. We have consistently modeled the parameters involved in an astrometric VLBI observation, in order to reproduce the differential phase observed for radio sources separated by almost 7o on the sky. We have demonstrated the possibility of phase-connection over these angular distances at 8.4 GHz, even at an epoch of a maximum in the solar activity. After the phase-connection we have corrected the effects of the extended structure of the radio source and of the ionosphere. This last correction is one of the main technical achievements of this thesis: it is possible to remove the ionospheric contribution with independent measurements of the ionosphere total electron content obtained at Global Positioning Systems (GPS) sites the VLBI observing stations. The triangular geometry introduces constraints in parameter space that allow a better estimation of the angular separations among the radio sources. It is possible to test the consistency of the astrometric results through the Sky-Closure, defined as the circular sum of the angular separations of the three radio sources, determined

An improved evaluation of the seismic/geodetic deformation-rate ratio for the Zagros Fold-and-Thrust collisional belt

Science.gov (United States)

Palano, Mimmo; Imprescia, Paola; Agnon, Amotz; Gresta, Stefano

2018-04-01

We present an improved picture of the ongoing crustal deformation field for the Zagros Fold-and-Thrust Belt continental collision zone by using an extensive combination of both novel and published GPS observations. The main results define the significant amount of oblique Arabia-Eurasia convergence currently being absorbed within the Zagros: right-lateral shear along the NW trending Main Recent fault in NW Zagros and accommodated between fold-and-thrust structures and NS right-lateral strike-slip faults on Southern Zagros. In addition, taking into account the 1909-2016 instrumental seismic catalogue, we provide a statistical evaluation of the seismic/geodetic deformation-rate ratio for the area. On Northern Zagros and on the Turkish-Iranian Plateau, a moderate to large fraction (˜49 and >60 per cent, respectively) of the crustal deformation occurs seismically. On the Sanandaj-Sirjan zone, the seismic/geodetic deformation-rate ratio suggests that a small to moderate fraction (<40 per cent) of crustal deformation occurs seismically; locally, the occurrence of large historic earthquakes (M ≥ 6) coupled with the high geodetic deformation, could indicate overdue M ≥ 6 earthquakes. On Southern Zagros, aseismic strain dominates crustal deformation (the ratio ranges in the 15-33 per cent interval). Such aseismic deformation is probably related to the presence of the weak evaporitic Hormuz Formation which allows the occurrence of large aseismic motion on both subhorizontal faults and surfaces of décollement. These results, framed into the seismotectonic framework of the investigated region, confirm that the fold-and-thrust-dominated deformation is driven by buoyancy forces; by contrast, the shear-dominated deformation is primary driven by plate stresses.

About the Modeling of Radio Source Time Series as Linear Splines

Science.gov (United States)

Karbon, Maria; Heinkelmann, Robert; Mora-Diaz, Julian; Xu, Minghui; Nilsson, Tobias; Schuh, Harald

2016-12-01

Many of the time series of radio sources observed in geodetic VLBI show variations, caused mainly by changes in source structure. However, until now it has been common practice to consider source positions as invariant, or to exclude known misbehaving sources from the datum conditions. This may lead to a degradation of the estimated parameters, as unmodeled apparent source position variations can propagate to the other parameters through the least squares adjustment. In this paper we will introduce an automated algorithm capable of parameterizing the radio source coordinates as linear splines.

Uncertainty assessment in geodetic network adjustment by combining GUM and Monte-Carlo-simulations

Science.gov (United States)

Niemeier, Wolfgang; Tengen, Dieter

2017-06-01

In this article first ideas are presented to extend the classical concept of geodetic network adjustment by introducing a new method for uncertainty assessment as two-step analysis. In the first step the raw data and possible influencing factors are analyzed using uncertainty modeling according to GUM (Guidelines to the Expression of Uncertainty in Measurements). This approach is well established in metrology, but rarely adapted within Geodesy. The second step consists of Monte-Carlo-Simulations (MC-simulations) for the complete processing chain from raw input data and pre-processing to adjustment computations and quality assessment. To perform these simulations, possible realizations of raw data and the influencing factors are generated, using probability distributions for all variables and the established concept of pseudo-random number generators. Final result is a point cloud which represents the uncertainty of the estimated coordinates; a confidence region can be assigned to these point clouds, as well. This concept may replace the common concept of variance propagation and the quality assessment of adjustment parameters by using their covariance matrix. It allows a new way for uncertainty assessment in accordance with the GUM concept for uncertainty modelling and propagation. As practical example the local tie network in "Metsähovi Fundamental Station", Finland is used, where classical geodetic observations are combined with GNSS data.

The University, the Market, and the Geodetic Engineer or

DEFF Research Database (Denmark)

Stubkjær, Erik

2002-01-01

In Europe, universities have existed for more than 800 years. The university is the place in society for higher learning and related research. Through the ages, the universities have enjoyed a remarkably freedom relative to religious and secular powers. In recent years, the objectives and practises...... project, which concerned the education of geodetic engineers in Slovenia. The body of the paper presents a selection of ideas that shaped the university through the centuries, with a view to balance the present interest in advancing market-directed behaviour....

DETECTION OF COASTLINE DEFORMATION USING REMOTE SENSING AND GEODETIC SURVEYS

Directory of Open Access Journals (Sweden)

A. Sabuncu

2016-06-01

Full Text Available The coastal areas are being destroyed due to the usage that effect the natural balance. Unconsciously sand mining from the sea for nearshore nourishment and construction uses are the main ones. Physical interferences for mining of sand cause an ecologic threat to the coastal environment. However, use of marine sand is inevitable because of economic reasons or unobtainable land-based sand resources. The most convenient solution in such a protection–usage dilemma is to reduce negative impacts of sand production from marine. This depends on the accurate determination of criteriaon production place, style, and amount of sand. With this motivation, nearshore geodedic surveying studies performed on Kilyos Campus of Bogazici University located on the Black Sea coast, north of Istanbul, Turkey between 2001-2002. The study area extends 1 km in the longshore. Geodetic survey was carried out in the summer of 2001 to detect the initial condition for the shoreline. Long-term seasonal changes in shoreline positions were determined biannually. The coast was measured with post-processed kinematic GPS. Besides, shoreline change has studied using Landsat imagery between the years 1986-2015. The data set of Landsat 5 imageries were dated 05.08.1986 and 31.08.2007 and Landsat 7 imageries were dated 21.07.2001 and 28.07.2015. Landcover types in the study area were analyzed on the basis of pixel based classification method. Firstly, unsupervised classification based on ISODATA (Iterative Self Organizing Data Analysis Technique has been applied and spectral clusters have been determined that gives prior knowledge about the study area. In the second step, supervised classification was carried out by using the three different approaches which are minimum-distance, parallelepiped and maximum-likelihood. All pixel based classification processes were performed with ENVI 4.8 image processing software. Results of geodetic studies and classification outputs will be

Single-dish and VLBI observations of Cygnus X-3 during the 2016 giant flare episode

Science.gov (United States)

Egron, E.; Pellizzoni, A.; Giroletti, M.; Righini, S.; Stagni, M.; Orlati, A.; Migoni, C.; Melis, A.; Concu, R.; Barbas, L.; Buttaccio, S.; Cassaro, P.; De Vicente, P.; Gawroński, M. P.; Lindqvist, M.; Maccaferri, G.; Stanghellini, C.; Wolak, P.; Yang, J.; Navarrini, A.; Loru, S.; Pilia, M.; Bachetti, M.; Iacolina, M. N.; Buttu, M.; Corbel, S.; Rodriguez, J.; Markoff, S.; Wilms, J.; Pottschmidt, K.; Cadolle Bel, M.; Kalemci, E.; Belloni, T.; Grinberg, V.; Marongiu, M.; Vargiu, G. P.; Trois, A.

2017-11-01

In 2016 September, the microquasar Cygnus X-3 underwent a giant radio flare, which was monitored for 6 d with the Medicina Radio Astronomical Station and the Sardinia Radio Telescope. Long observations were performed in order to follow the evolution of the flare on an hourly scale, covering six frequency ranges from 1.5 to 25.6 GHz. The radio emission reached a maximum of 13.2 ± 0.7 Jy at 7.2 GHz and 10 ± 1 Jy at 18.6 GHz. Rapid flux variations were observed at high radio frequencies at the peak of the flare, together with rapid evolution of the spectral index: α steepened from 0.3 to 0.6 (with Sν ∝ ν-α) within 5 h. This is the first time that such fast variations are observed, giving support to the evolution from optically thick to optically thin plasmons in expansion moving outward from the core. Based on the Italian network (Noto, Medicina and SRT) and extended to the European antennas (Torun, Yebes, Onsala), very long baseline interferometry (VLBI) observations were triggered at 22 GHz on five different occasions, four times prior to the giant flare, and once during its decay phase. Flux variations of 2 h duration were recorded during the first session. They correspond to a mini-flare that occurred close to the core 10 d before the onset of the giant flare. From the latest VLBI observation we infer that 4 d after the flare peak the jet emission was extended over 30 mas.

Using geodetic data to infer the kinematic and mechanical properties of deformation sources on Kilauea Volcano, Hawaii

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Cervelli, Peter Francis

2002-09-01

Paradoxically, one of the greatest hazards associated with oceanic volcanoes is not volcanic. Rather, it is the potential for catastrophic flank failure resulting in devastating tsunamis, which threaten not just the immediate vicinity, but coastal cities along the entire rim of an ocean basin. Kilauea volcano on the Island of Hawaii, USA, a potential source of such flank failures, is monitored by a network of continuously recording geodetic instruments, including Global Positioning System (GPS) receivers, tiltmeters, and strainmeters. In this thesis, methodology is developed for using these geodetic data to estimate the geometry and type of active deformation sources, such as dikes, magma chambers, and faults. The methodology is then applied to two episodes of deformation that occurred at Kilauea Volcano in 1999 and 2000. First, the deformation associated with an earthquake swarm on September 12, 1999 in the Upper East Rift Zone of Kilauea Volcano, which was recorded by continuous GPS receivers, tiltmeters, campaign GPS, leveling, and InSAR, is analyzed and interpreted as a west to east propagating dike intrusion. Lack of premonitory inflation of Kilauea's summit suggests that the immediate cause of the intrusion was probably tensile failure in the shallow crust of the Upper East Rift, rather than forceful magma injection. Second, in early November 2000, the geodetic network recorded transient southeastward displacements, which we interpret as an episode of aseismic fault slip. The duration of the event was about 36 hours; it had an equivalent moment magnitude of M5.7, and a maximum slip velocity of about 6 cm/day. Inversion of the GPS data images a shallowly dipping thrust at a depth of 4.5 km that we interpret as the down dip extension of the Hilina Pali fault system. Thus it is demonstrated that continuous geodetic networks can detect accelerating slip, potentially leading to warnings of imminent volcanic flank collapse. Finally, in the last chapter of the

Earth Rotation Dynamics: Review and Prospects

Science.gov (United States)

Chao, Benjamin F.

2004-01-01

Modem space geodetic measurement of Earth rotation variations, particularly by means of the VLBI technique, has over the years allowed studies of Earth rotation dynamics to advance in ever-increasing precision, accuracy, and temporal resolution. A review will be presented on our understanding of the geophysical and climatic causes, or "excitations", for length-of-day change, polar motion, and nutations. These excitations sources come from mass transports that constantly take place in the Earth system comprised of the atmosphere, hydrosphere, cryosphere, lithosphere, mantle, and the cores. In this sense, together with other space geodetic measurements of time-variable gravity and geocenter motion, Earth rotation variations become a remote-sensing tool for the integral of all mass transports, providing valuable information about the latter on a wide range of spatial and temporal scales. Future prospects with respect to geophysical studies with even higher accuracy and resolution will be discussed.

Geodetic reanalysis of annual glaciological mass balances (2001-2011) of Hintereisferner, Austria

Science.gov (United States)

Klug, Christoph; Bollmann, Erik; Galos, Stephan Peter; Nicholson, Lindsey; Prinz, Rainer; Rieg, Lorenzo; Sailer, Rudolf; Stötter, Johann; Kaser, Georg

2018-03-01

This study presents a reanalysis of the glaciologically obtained annual glacier mass balances at Hintereisferner, Ötztal Alps, Austria, for the period 2001-2011. The reanalysis is accomplished through a comparison with geodetically derived mass changes, using annual high-resolution airborne laser scanning (ALS). The grid-based adjustments for the method-inherent differences are discussed along with associated uncertainties and discrepancies of the two methods of mass balance measurements. A statistical comparison of the two datasets shows no significant difference for seven annual, as well as the cumulative, mass changes over the 10-year record. Yet, the statistical view hides significant differences in the mass balance years 2002/03 (glaciological minus geodetic records = +0.92 m w.e.), 2005/06 (+0.60 m w.e.), and 2006/07 (-0.45 m w.e.). We conclude that exceptional meteorological conditions can render the usual glaciological observational network inadequate. Furthermore, we consider that ALS data reliably reproduce the annual mass balance and can be seen as validation or calibration tools for the glaciological method.

A Community-based Partnership for a Sustainable GNSS Geodetic Network

Science.gov (United States)

Dokka, R. K.

2009-12-01

Geodetic networks offer unparalleled opportunities to monitor and understand many of the rhythms of the Earth most vital to the sustainability of modern and future societies, i.e., crustal motions, sea-level, and the weather. For crustal deformation studies, the advantage is clear. Modern measurements allow us to document not only the permanent strains incurred over a seismic cycle, for example, but also the ephemeral strains that are critical for understanding the underlying physical mechanism. To be effective for science, however, geodetic networks must be properly designed, capitalized, and maintained over sufficient time intervals to fully capture the processes in action. Unfortunately, most networks lack interoperability and lack a business plan to ensure long term sustainability. The USA, for example, lacks a unified nation-wide GNSS network that can sustain its self over the coming years, decades, and century. Current federal priorities do not yet envision such a singular network. Publicly and privately funded regional networks exist, but tend to be parochial in scope, and optimized for a special user community, e.g., surveying, crustal motions, etc. Data sharing is common, but the lack of input at the beginning limits the functionality of the system for non-primary users. Funding for private networks depend heavily on the user demand, business cycle, and regulatory requirements. Agencies funding science networks offer no guarantee of sustained support. An alternative model (GULFNet) developed in Louisiana is meeting user needs, is sustainable, and is helping engineers, surveyors, and geologists become more spatially enabled. The common denominator among all participants is the view that accurate, precise, and timely geodetic data have tangible value for all segments of society. Although operated by a university (LSU), GULFNet is a community-based partnership between public and private sectors. GULFNet simultaneously achieves scientific goals by providing

Determining Coastal Mean Dynamic Topography by Geodetic Methods

Science.gov (United States)

Huang, Jianliang

2017-11-01

In geodesy, coastal mean dynamic topography (MDT) was traditionally determined by spirit leveling technique. Advances in navigation satellite positioning (e.g., GPS) and geoid determination enable space-based leveling with an accuracy of about 3 cm at tide gauges. Recent CryoSat-2, a satellite altimetry mission with synthetic aperture radar (SAR) and SAR interferometric measurements, extends the space-based leveling to the coastal ocean with the same accuracy. However, barriers remain in applying the two space-based geodetic methods for MDT determination over the coastal ocean because current geoid modeling focuses primarily on land as a substitute to spirit leveling to realize the vertical datum.

Global Positioning System (GPS) survey of Augustine Volcano, Alaska, August 3-8, 2000: data processing, geodetic coordinates and comparison with prior geodetic surveys

Science.gov (United States)

Pauk, Benjamin A.; Power, John A.; Lisowski, Mike; Dzurisin, Daniel; Iwatsubo, Eugene Y.; Melbourne, Tim

2001-01-01

Between August 3 and 8,2000,the Alaska Volcano Observatory completed a Global Positioning System (GPS) survey at Augustine Volcano, Alaska. Augustine is a frequently active calcalkaline volcano located in the lower portion of Cook Inlet (fig. 1), with reported eruptions in 1812, 1882, 1909?, 1935, 1964, 1976, and 1986 (Miller et al., 1998). Geodetic measurements using electronic and optical surveying techniques (EDM and theodolite) were begun at Augustine Volcano in 1986. In 1988 and 1989, an island-wide trilateration network comprising 19 benchmarks was completed and measured in its entirety (Power and Iwatsubo, 1998). Partial GPS surveys of the Augustine Island geodetic network were completed in 1992 and 1995; however, neither of these surveys included all marks on the island.Additional GPS measurements of benchmarks A5 and A15 (fig. 2) were made during the summers of 1992, 1993, 1994, and 1996. The goals of the 2000 GPS survey were to:1) re-measure all existing benchmarks on Augustine Island using a homogeneous set of GPS equipment operated in a consistent manner, 2) add measurements at benchmarks on the western shore of Cook Inlet at distances of 15 to 25 km, 3) add measurements at an existing benchmark (BURR) on Augustine Island that was not previously surveyed, and 4) add additional marks in areas of the island thought to be actively deforming. The entire survey resulted in collection of GPS data at a total of 24 sites (fig. 1 and 2). In this report we describe the methods of GPS data collection and processing used at Augustine during the 2000 survey. We use this data to calculate coordinates and elevations for all 24 sites surveyed. Data from the 2000 survey is then compared toelectronic and optical measurements made in 1988 and 1989. This report also contains a general description of all marks surveyed in 2000 and photographs of all new marks established during the 2000 survey (Appendix A).

Verification of the astrometric performance of the Korean VLBI network, using comparative SFPR studies with the VLBA AT 14/7 mm

Energy Technology Data Exchange (ETDEWEB)

Rioja, María J.; Dodson, Richard; Jung, TaeHyun; Sohn, Bong Won; Byun, Do-Young; Cho, Se-Hyung; Lee, Sang-Sung; Kim, Jongsoo; Kim, Kee-Tae; Oh, Chung Sik; Han, Seog-Tae; Je, Do-Heung; Chung, Moon-Hee; Wi, Seog-Oh; Kang, Jiman; Lee, Jung-Won; Chung, Hyunsoo; Kim, Hyo Ryoung; Kim, Hyun-Goo [Korea Astronomy and Space Science Institute, Daedeokdae-ro 776, Yuseong-gu, Daejeon 305-348 (Korea, Republic of); Agudo, Iván, E-mail: maria.rioja@icrar.org [Joint Institute for VLBI in Europe, Postbus 2, NL-7990 AA Dwingeloo (Netherlands); and others

2014-11-01

The Korean VLBI Network (KVN) is a new millimeter VLBI dedicated array with the capability to simultaneously observe at multiple frequencies, up to 129 GHz. The innovative multi-channel receivers present significant benefits for astrometric measurements in the frequency domain. The aim of this work is to verify the astrometric performance of the KVN using a comparative study with the VLBA, a well-established instrument. For that purpose, we carried out nearly contemporaneous observations with the KVN and the VLBA, at 14/7 mm, in 2013 April. The KVN observations consisted of simultaneous dual frequency observations, while the VLBA used fast frequency switching observations. We used the Source Frequency Phase Referencing technique for the observational and analysis strategy. We find that having simultaneous observations results in superior compensation for all atmospheric terms in the observables, in addition to offering other significant benefits for astrometric analysis. We have compared the KVN astrometry measurements to those from the VLBA. We find that the structure blending effects introduce dominant systematic astrometric shifts, and these need to be taken into account. We have tested multiple analytical routes to characterize the impact of the low-resolution effects for extended sources in the astrometric measurements. The results from the analysis of the KVN and full VLBA data sets agree within 2σ of the thermal error estimate. We interpret the discrepancy as arising from the different resolutions. We find that the KVN provides astrometric results with excellent agreement, within 1σ, when compared to a VLBA configuration that has a similar resolution. Therefore, this comparative study verifies the astrometric performance of the KVN using SFPR at 14/7 mm, and validates the KVN as an astrometric instrument.

Geodetic Slip Solution for the Mw=7.4 Champerico (Guatemala) Earthquake of 07 November 2012

Science.gov (United States)

Ellis, A. P.; DeMets, C.; Briole, P.; Molina, E.; Flores, O.; Rivera, J.; Lasserre, C.; Lyon-Caen, H.; Lord, N. E.

2014-12-01

As the first large subduction thrust earthquake off the coast of western Guatemala in the past several decades, the 07 November 2012 Mw=7.4 earthquake offers the first opportunity for a geodetic study of coseismic and postseismic behavior for a segment of the Middle America trench where frictional coupling makes a transition from weak coupling off the coast of El Salvador to strong coupling in southern Mexico. We use measurements at 19 continuous GPS sites in Guatemala, El Salvador, and Mexico to estimate the coseismic slip and post-seismic deformation of the November 2012 Champerico (Guatemala) earthquake. Coseismic offsets range from ~47 mm near the epicenter to El Salvador. An inversion of the geodetic data indicate that that up to ~2 m of coseismic slip occurred on a ~30 km by 30 km rupture area between ~10 and 30 km depth, encouragingly close to the global CMT epicenter. The geodetic moment of 13 x 1019 N·m and corresponding magnitude of 7.4 both agree well with independent seismological estimates. An inversion for the postseismic fault afterslip shows that the transient postseismic motions recorded at 11 GPS sites are well fit with a logarithmically decaying function. More than 70 per cent of the postseismic slip occurred at the same depth or directly downdip from the main shock epicenter. At the upper limit, afterslip that occurred within 6 months of the earthquake released energy equivalent to only ~20 per cent of the coseismic moment. The seismologically derived slip solution from Ye et al. (2012), which features more highly concentrated slip than our own, fits our GPS offsets reasonably well provided that we translate their slip centroid ~51 km to the west to a position close to our own slip centroid. The geodetic and seismologic slip solutions thus suggest bounds of 2-5 m for the peak slip along a region of the interface no larger than 30 x 30 km and possibly much smaller.

Agile Big Data Analytics of High-Volume Geodetic Data Products for Improving Science and Hazard Response

Data.gov (United States)

National Aeronautics and Space Administration — Geodetic imaging is revolutionizing geophysics, but the scope of discovery has been limited by labor-intensive technological implementation of the analyses. The...

The Crustal Dynamics Data Information System: A Resource to Support Scientific Analysis Using Space Geodesy

Science.gov (United States)

Noll. Carey E.

2010-01-01

Since 1982. the Crustal Dynamics Data Information System (CDDIS) has supported the archive and distribution of geodetic data products acquired by the National Aeronautics and Space Administration (NASA) as well as national and international programs. The CDDIS provides easy, timely, and reliable access to a variety of data sets, products, and information about these data. These measurements. obtained from a global network of nearly 650 instruments at more than 400 distinct sites, include DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite), GNSS (Global Navigation Satellite System), SLR and LLR (Satellite and Lunar Laser Ranging), and VLBI (Very Long Baseline Interferometry). The CDDIS data system and its archive have become increasingly important to many national and international science communities, particularly several of the operational services within the International Association of Geodesy (IAG) and its observing system the Global Geodetic Observing System (GGOS), including the International DORIS Service (IDS), the International GNSS Service (IGS). the International Laser Ranging Service (ILRS), the International VLBI Service for Geodesy and Astrometry (IVS). and the International Earth rotation and Reference frame Service (IERS), Investigations resulting from the data and products available through the CDDIS support research in many aspects of Earth system science and global change. Each month, the CDDIS archives more than one million data and derived product files totaling over 90 Gbytes in volume. In turn. the global user community downloads nearly 1.2 TBytes (over 10.5 million files) of data and products from the CDDIS each month. The requirements of analysts have evolved since the start of the CDDIS; the specialized nature of the system accommodates the enhancements required to support diverse data sets and user needs. This paper discusses the CDDIS. including background information about the system and its. user communities

The Importance of Geodetically Controlled Data Sets: THEMIS Controlled Mosaics of Mars, a Case Study

Science.gov (United States)

Fergason, R. L.; Weller, L.

2018-04-01

Accurate image registration is necessary to answer questions that are key to addressing fundamental questions about our universe. To provide such a foundational product for Mars, we have geodetically controlled and mosaicked THEMIS IR images.

Exploring deformation scenarios in Timanfaya volcanic area (Lanzarote, Canary Islands) from GNSS and ground based geodetic observations

Science.gov (United States)

Riccardi, U.; Arnoso, J.; Benavent, M.; Vélez, E.; Tammaro, U.; Montesinos, F. G.

2018-05-01

We report on a detailed geodetic continuous monitoring in Timanfaya volcanic area (TVA), where the most intense geothermal anomalies of Lanzarote Island are located. We analyze about three years of GNSS data collected on a small network of five permanent stations, one of which at TVA, deployed on the island, and nearly 20 years of tiltmeter and strainmeter records acquired at Los Camelleros site settled in the facilities of the Geodynamics Laboratory of Lanzarote within TVA. This study is intended to contribute to understanding the active tectonics on Lanzarote Island and its origin, mainly in TVA. After characterizing and filtering out the seasonal periodicities related to "non-tectonic" sources from the geodetic records, a tentative ground deformation field is reconstructed through the analysis of both tilt, strain records and the time evolution of the baselines ranging the GNSS stations. The joint interpretation of the collected geodetic data show that the area of the strongest geothermal anomaly in TVA is currently undergoing a SE trending relative displacement at a rate of about 3 mm/year. This area even experiences a significant subsidence with a maximum rate of about 6 mm/year. Moreover, we examine the possible relation between the observed deformations and atmospheric effects by modelling the response functions of temperature and rain recorded in the laboratory. Finally, from the retrieval of the deformation patterns and the joint analysis of geodetic and environmental observations, we propose a qualitative model of the interplaying role between the hydrological systems and the geothermal anomalies. Namely, we explain the detected time correlation between rainfall and ground deformation because of the enhancement of the thermal transfer from the underground heat source driven by the infiltration of meteoric water.

Development of web tools to disseminate space geodesy data-related products

Science.gov (United States)

Soudarin, Laurent; Ferrage, Pascale; Mezerette, Adrien

2015-04-01

In order to promote the products of the DORIS system, the French Space Agency CNES has developed and implemented on the web site of the International DORIS Service (IDS) a set of plot tools to interactively build and display time series of site positions, orbit residuals and terrestrial parameters (scale, geocenter). An interactive global map is also available to select sites, and to get access to their information. Besides the products provided by the CNES Orbitography Team and the IDS components, these tools allow comparing time evolutions of coordinates for collocated DORIS and GNSS stations, thanks to the collaboration with the Terrestrial Frame Combination Center of the International GNSS Service (IGS). A database was created to improve robustness and efficiency of the tools, with the objective to propose a complete web service to foster data exchange with the other geodetic services of the International Association of Geodesy (IAG). The possibility to visualize and compare position time series of the four main space geodetic techniques DORIS, GNSS, SLR and VLBI is already under way at the French level. A dedicated version of these web tools has been developed for the French Space Geodesy Research Group (GRGS). It will give access to position time series provided by the GRGS Analysis Centers involved in DORIS, GNSS, SLR and VLBI data processing for the realization of the International Terrestrial Reference Frame. In this presentation, we will describe the functionalities of these tools, and we will address some aspects of the time series (content, format).

Recent results from the VLNDEF network

Science.gov (United States)

Capra, Alessandro; Zanutta, Antonio; Negusini, Monia; Gandolfi, Stefano; Sarti, Pierguido; Vittuari, Luca; Salvini, Francesco; Cianfarra, Paola; Sterzai, Paolo

2013-04-01

measurements, geomagnetic field measurements and other geophysical observations. The deformation patterns obtained with GPS observations over the VLNDEF network are coupled with the data acquired during the geological and geomorphological surveys; the set of observations is used to study the neo-tectonics of NVL. We present the most recent geodetic results derived from the VLNDEF GPS data set and a recent cinematic model of the whole area. We present the preliminary geoid model in the northern part of the network.

A Comparative Study of the Applied Methods for Estimating Deflection of the Vertical in Terrestrial Geodetic Measurements

Directory of Open Access Journals (Sweden)

Luca Vittuari

2016-04-01

Full Text Available This paper compares three different methods capable of estimating the deflection of the vertical (DoV: one is based on the joint use of high precision spirit leveling and Global Navigation Satellite Systems (GNSS, a second uses astro-geodetic measurements and the third gravimetric geoid models. The working data sets refer to the geodetic International Terrestrial Reference Frame (ITRF co-location sites of Medicina (Northern, Italy and Noto (Sicily, these latter being excellent test beds for our investigations. The measurements were planned and realized to estimate the DoV with a level of precision comparable to the angular accuracy achievable in high precision network measured by modern high-end total stations. The three methods are in excellent agreement, with an operational supremacy of the astro-geodetic method, being faster and more precise than the others. The method that combines leveling and GNSS has slightly larger standard deviations; although well within the 1 arcsec level, which was assumed as threshold. Finally, the geoid model based method, whose 2.5 arcsec standard deviations exceed this threshold, is also statistically consistent with the others and should be used to determine the DoV components where local ad hoc measurements are lacking.

Imaging Simulations for the Korean VLBI Network (KVN

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Tae-Hyun Jung

2005-03-01

Full Text Available The Korean VLBI Network (KVN will open a new field of research in astronomy, geodesy and earth science using the newest three 21m radio telescopes. This will expand our ability to look at the Universe in the millimeter regime. Imaging capability of radio interferometry is highly dependent upon the antenna configuration, source size, declination and the shape of target. In this paper, imaging simulations are carried out with the KVN system configuration. Five test images were used which were a point source, multi-point sources, a uniform sphere with two different sizes compared to the synthesis beam of the KVN and a Very Large Array (VLA image of Cygnus A. The declination for the full time simulation was set as +60 degrees and the observation time range was --6 to +6 hours around transit. Simulations have been done at 22GHz, one of the KVN observation frequency. All these simulations and data reductions have been run with the Astronomical Image Processing System (AIPS software package. As the KVN array has a resolution of about 6 mas (milli arcsecond at 22GHz, in case of model source being approximately the beam size or smaller, the ratio of peak intensity over RMS shows about 10000:1 and 5000:1. The other case in which model source is larger than the beam size, this ratio shows very low range of about 115:1 and 34:1. This is due to the lack of short baselines and the small number of antenna. We compare the coordinates of the model images with those of the cleaned images. The result shows mostly perfect correspondence except in the case of the 12mas uniform sphere. Therefore, the main astronomical targets for the KVN will be the compact sources and the KVN will have an excellent performance in the astrometry for these sources.

Stress coupling in the seismic cycle indicated from geodetic measurements

Science.gov (United States)

Wang, L.; Hainzl, S.; Zoeller, G.; Holschneider, M.

2012-12-01

The seismic cycle includes several phases, the interseismic, coseismic and postseismic phase. In the interseismic phase, strain gradually builds up around the overall locked fault in tens to thousands of years, while it is coseismically released in seconds. In the postseismic interval, stress relaxation lasts months to years, indicated by evident aseismic deformations which have been indicated to release comparable or even higher strain energy than the main shocks themselves. Benefiting from the development of geodetic observatory, e.g., Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) in the last two decades, the measurements of surface deformation have been significantly improved and become valuable information for understanding the stress evolution on the large fault plane. In this study, we utilize the GPS/InSAR data to investigate the slip deficit during the interseismic phase, the coseismic slip and the early postseismic creep on the fault plane. However, it is already well-known that slip inversions based only on the surface measurements are typically non-unique and subject to large uncertainties. To reduce the ambiguity, we utilize the assumption of stress coupling between interseismic and coseismic phases, and between coseismic and postseismic phases. We use a stress constrained joint inversion in Bayesian approach (Wang et al., 2012) to invert simultaneously for (1) interseismic slip deficit and coseismic slip, and (2) coseismic slip and postseismic creep. As case studies, we analyze earthquakes occurred in well-instrumented regions such as the 2004 M6.0 Parkfield earthquake, the 2010 M8.7 earthquake and the 2011 M9.1 Tohoku-Oki earthquake. We show that the inversion with the stress-coupling constraint leads to better constrained slip distributions. Meanwhile, the results also indicate that the assumed stress coupling is reasonable and can be well reflected from the available geodetic measurements. Reference: Lifeng

Land water storage from space and the geodetic infrastructure

Science.gov (United States)

Cazenave, A.; Larson, K.; Wahr, J.

2009-04-01

In recent years, remote sensing techniques have been increasingly used to monitor components of the water balance of large river basins. By complementing scarce in situ observations and hydrological modelling, space observations have the potential to significantly improve our understanding of hydrological processes at work in river basins and their relationship with climate variability and socio-economic life. Among the remote sensing tools used in land hydrology, several originate from space geodesy and are integral parts of the Global Geodetic Observing System. For example, satellite altimetry is used for systematic monitoring of water levels of large rivers, lakes and floodplains. InSAR allows the detection of surface water change. GRACE-based space gravity offers for the first time the possibility of directly measuring the spatio-temporal variations of the vertically integrated water storage in large river basins. GRACE is also extremely useful for measuring changes in mass of the snow pack in boreal regions. Vertical motions of the ground induced by changes in water storage in aquifers can be measured by both GPS and InSAR. These techniques can also be used to investigate water loading effects. Recently GPS has been used to measure changes in surface soil moisture, which would be important for agriculture, weather prediction, and for calibrationg satellite missions such as SMOS and SMAP. These few examples show that space and ground geodetic infrastructures are increasingly important for hydrological sciences and applications. Future missions like SWOT (Surface Waters Ocean Topography; a wide swath interferometric altimetry mission) and GRACE 2 (space gravimetry mission based on new technology) will provide a new generation of hydrological products with improved precision and resolution.

The Parallax of the Red Hypergiant VX Sgr with Accurate Tropospheric Delay Calibration

Science.gov (United States)

Xu, Shuangjing; Zhang, Bo; Reid, Mark J.; Menten, Karl M.; Zheng, Xingwu; Wang, Guangli

2018-05-01

We report astrometric results of VLBI phase-referencing observations of 22 GHz H2O masers emission toward the red hypergiant VX Sgr, one of most massive and luminous red hypergiant stars in our Galaxy, using the Very Long Baseline Array. A background source, J1820‑2528, projected 4.°4 from the target VX Sgr, was used as the phase reference. For the low decl. of these sources, such a large separation normally would seriously degrade the relative astrometry. We use a two-step method of tropospheric delay calibration, which combines the VLBI geodetic-block (or Global Positioning System) calibration with an image-optimization calibration, to obtain a trigonometric parallax of 0.64 ± 0.04 mas, corresponding to a distance of {1.56}-0.10+0.11 kpc. The measured proper motion of VX Sgr is 0.36 ± 0.76 and ‑2.92 ± 0.78 mas yr‑1 in the eastward and northward directions. The parallax and proper motion confirms that VX Sgr belong to the Sgr OB1 association. Rescaling bolometric luminosities in the literature to our parallax distance, we find that the luminosity of VX Sgr is (1.95 ± 0.62) × 105 L ⊙, where the uncertainty is dominated by differing photometry measurements.

Evaluation on the performance of single and dual frequency low cost GPS module observation using geodetic antenna

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Dedi Atunggal

2018-06-01

Full Text Available GPS modules have been used for various applications in recent years. Its early development came in parallel with the advancement of Unmanned Aerial Vehicle (UAV technology. Nowadays, it is also used in in geographic information system (GIS data acquisition/census, mapping surveys, structure stability monitoring systems and many other applications. GPS modules generally have several positioning features, including standard positioning service (SPS, static positioning, precise point positioning (PPP, post processing kinematic (PPK and real time kinematic (RTK GPS. GPS modules in general are only equipped with a microstrip-type antenna or better known as patch antenna. Results from related research show that GPS module with this type of antenna has sub meter accuracy when used for PPK or RTK GPS method. The use of geodetic antennas is very potential to increase GPS position accuracy by up to centimeter level. This paper discusses the evaluation of GPS module measurements with geodetic type antennas for precise positioning using RTK GPS. This paper is focused on the resolution of GPS cycle ambiguity that is often expressed by the term fixing ratio and the accuracy of measurement results obtained. To provide a comprehensive description of the performance of GPS module, in this research two types of GPS module were used; single and dual frequency. Both types of GPS modules were used to conduct simultaneous observation on an open and obstructed observation location.

Application of median-equation approach for outlier detection in geodetic networks

Directory of Open Access Journals (Sweden)

Serif Hekimoglu

Full Text Available In geodetic measurements some outliers may occur sometimes in data sets, depending on different reasons. There are two main approaches to detect outliers as Tests for outliers (Baarda's and Pope's Tests and robust methods (Danish method, Huber method etc.. These methods use the Least Squares Estimation (LSE. The outliers affect the LSE results, especially it smears the effects of the outliers on the good observations and sometimes wrong results may be obtained. To avoid these effects, a method that does not use LSE should be preferred. The median is a high breakdown point estimator and if it is applied for the outlier detection, reliable results can be obtained. In this study, a robust method which uses median with or as a treshould value on median residuals that are obtained from median equations is proposed. If the a priori variance of the observations is known, the reliability of the new approch is greater than the one in the case where the a priori variance is unknown.

Slow Earthquake Hunters: A New Citizen Science Project to Identify and Catalog Slow Slip Events in Geodetic Data

Science.gov (United States)

Bartlow, N. M.

2017-12-01

Slow Earthquake Hunters is a new citizen science project to detect, catalog, and monitor slow slip events. Slow slip events, also called "slow earthquakes", occur when faults slip too slowly to generate significant seismic radiation. They typically take between a few days and over a year to occur, and are most often found on subduction zone plate interfaces. While not dangerous in and of themselves, recent evidence suggests that monitoring slow slip events is important for earthquake hazards, as slow slip events have been known to trigger damaging "regular" earthquakes. Slow slip events, because they do not radiate seismically, are detected with a variety of methods, most commonly continuous geodetic Global Positioning System (GPS) stations. There is now a wealth of GPS data in some regions that experience slow slip events, but a reliable automated method to detect them in GPS data remains elusive. This project aims to recruit human users to view GPS time series data, with some post-processing to highlight slow slip signals, and flag slow slip events for further analysis by the scientific team. Slow Earthquake Hunters will begin with data from the Cascadia subduction zone, where geodetically detectable slow slip events with a duration of at least a few days recur at regular intervals. The project will then expand to other areas with slow slip events or other transient geodetic signals, including other subduction zones, and areas with strike-slip faults. This project has not yet rolled out to the public, and is in a beta testing phase. This presentation will show results from an initial pilot group of student participants at the University of Missouri, and solicit feedback for the future of Slow Earthquake Hunters.

Cansiglio Karst Plateau: 10 Years of Geodetic-Hydrological Observations in Seismically Active Northeast Italy

Science.gov (United States)

Grillo, Barbara; Braitenberg, Carla; Nagy, Ildikó; Devoti, Roberto; Zuliani, David; Fabris, Paolo

2018-04-01

Ten years' geodetic observations (2006-2016) in a natural cave of the Cansiglio Plateau (Bus de la Genziana), a limestone karstic area in northeastern Italy, are discussed. The area is of medium-high seismic risk: a strong earthquake in 1936 below the plateau (M m = 6.2) and the 1976 disastrous Friuli earthquake (M m = 6.5) are recent events. At the foothills of the karstic massif, three springs emerge, with average flow from 5 to 10 m3/s, and which are the sources of a river. The tiltmeter station is set in a natural cavity that is part of a karstic system. From March 2013, a multiparametric logger (temperature, stage, electrical conductivity) was installed in the siphon at the bottom of the cave to discover the underground hydrodynamics. The tilt records include signals induced by hydrologic and tectonic effects. The tiltmeter signals have a clear correlation to the rainfall, the discharge series of the river and the data recorded by multiparametric loggers. Additionally, the data of a permanent GPS station located on the southern slopes of the Cansiglio Massif (CANV) show also a clear correspondence with the river level. The fast water infiltration into the epikarst, closely related to daily rainfall, is distinguished in the tilt records from the characteristic time evolution of the karstic springs, which have an impulsive level increase with successive exponential decay. It demonstrates the usefulness of geodetic measurements to reveal the hydrological response of the karst. One outcome of the work is that the tiltmeters can be used as proxies for the presence of flow channels and the pressure that builds up due to the water flow. With 10 years of data, a new multidisciplinary frontier was opened between the geodetic studies and the karstic hydrogeology to obtain a more complete geologic description of the karst plateau.

International VLBI Service for Geodesy and Astrometry: General Meeting Proceedings

Science.gov (United States)

Vandenberg, Nancy R. (Editor); Baver, Karen D. (Editor)

2002-01-01

This volume contains the proceedings of the second General Meeting of the International VLBI Service for Geodesy and Astrometry (IVS), held in Tsukuba, Japan, February 4-7, 2002. The contents of this volume also appear on the IVS Web site at http://ivscc.gsfc.nasa.gov/publications/gm2002. The key-note of the second GM was prospectives for the future, in keeping with the re-organization of the IAG around the motivation of geodesy as 'an old science with a dynamic future' and noting that providing reference frames for Earth system science that are consistent over decades on the highest accuracy level will provide a challenging role for IVS. The goal of the meeting was to provide an interesting and informative program for a wide cross section of IVS members, including station operators, program managers, and analysts. This volume contains 72 papers and five abstracts of papers presented at the GM. The volume also includes reports about three splinter meetings held in conjunction with the GM: a mini-TOW (Technical Operations Workshop), the third IVS Analysis Workshop and a meeting of the analysis working group on geophysical modeling.

GeoSEA: Geodetic Earthquake Observatory on the Seafloor

Science.gov (United States)

Kopp, Heidrun; Lange, Dietrich; Flueh, Ernst R.; Petersen, Florian; Behrmann, Jan-Hinrich; Devey, Colin

2014-05-01

Space geodetic observations of crustal deformation have contributed greatly to our understanding of plate tectonic processes in general, and plate subduction in particular. Measurements of interseismic strain have documented the active accumulation of strain, and subsequent strain release during earthquakes. However, techniques such as GPS cannot be applied below the water surface because the electromagnetic energy is strongly attenuated in the water column. Evidence suggests that much of the elastic strain build up and release (and particularly that responsible for both tsunami generation and giant earthquakes) occurs offshore. To quantify strain accumulation and assess the resultant hazard potential we urgently need systems to resolve seafloor crustal deformation. Here we report on first results of sea trials of a newly implemented seafloor geodesy array. The GeoSEA (Geodetic Earthquake Observatory on the Seafloor) array consists of a seafloor transponder network comprising 35 units and a wave glider acting as a surface unit (GeoSURF) to ensure satellite correspondence, data transfer and monitor system health. Seafloor displacement occurs in the horizontal (x,y) and vertical direction (z). The vertical displacement is measured by monitoring pressure variations at the seafloor. Horizontal seafloor displacement can be measured either using an acoustic/GPS combination to provide absolute positioning (requiring a suitably equipped vessel to perform repeated cruises to provide the GPS fixes) or by long-term acoustic telemetry between different beacons fixed on the seafloor to determine relative distances by using the travel time observations to each other, which is the technique tested during our short sea trials. For horizontal direct path measurements, the system utilizes acoustic ranging techniques with a ranging precision better than 15 mm and long term stability over 2 km distances. Vertical motion is obtained from pressure gauges. Integrated inclinometers

Detecting Changing Polarization Structures in Sagittarius A* with High Frequency VLBI

Science.gov (United States)

Fish, Vincent L.; Doeleman, Sheperd S.; Broderick, Avery E.; Loeb, Abraham; Rogers, Alan E. E.

2009-12-01

Sagittarius A* is the source of near infrared, X-ray, radio, and (sub)millimeter emission associated with the supermassive black hole at the Galactic Center. In the submillimeter regime, Sgr A* exhibits time-variable linear polarization on timescales corresponding to errors. Although the source-integrated linear polarization fraction in the models is typically only a few percent, the linear polarization fraction on small angular scales can be much higher, enabling the detection of changes in the polarimetric structure of Sgr A* on a wide variety of baselines. The shortest baselines track the source-integrated linear polarization fraction, while longer baselines are sensitive to polarization substructures that are beam-diluted by connected-element interferometry. The detection of periodic variability in source polarization should not be significantly affected even if instrumental polarization terms cannot be calibrated out. As more antennas are included in the (sub)millimeter-VLBI array, observations with full polarization will provide important new diagnostics to help disentangle intrinsic source polarization from Faraday rotation effects in the accretion and outflow region close to the black hole event horizon.

Global geodetic observing system meeting the requirements of a global society on a changing planet in 2020

CERN Document Server

Plag, Hans-Peter

2009-01-01

Geodesy plays a key role in geodynamics, geohazards, the global water cycle, global change, atmosphere and ocean dynamics. This book covers geodesy's contribution to science and society and identifies user needs regarding geodetic observations and products.

GOZCARDS Source Data for Temperature Monthly Zonal Averages on a Geodetic Latitude and Pressure Grid V1.00

Data.gov (United States)

National Aeronautics and Space Administration — The GOZCARDS Source Data for Temperature Monthly Zonal Averages on a Geodetic Latitude and Pressure Grid product (GozSmlpT) contains zonal means and related...

Geodetic analysis of disputed accurate qibla direction

Science.gov (United States)

Saksono, Tono; Fulazzaky, Mohamad Ali; Sari, Zamah

2018-04-01

Muslims perform the prayers facing towards the correct qibla direction would be the only one of the practical issues in linking theoretical studies with practice. The concept of facing towards the Kaaba in Mecca during the prayers has long been the source of controversy among the muslim communities to not only in poor and developing countries but also in developed countries. The aims of this study were to analyse the geodetic azimuths of qibla calculated using three different models of the Earth. The use of ellipsoidal model of the Earth could be the best method for determining the accurate direction of Kaaba from anywhere on the Earth's surface. A muslim cannot direct himself towards the qibla correctly if he cannot see the Kaaba due to setting out process and certain motions during the prayer this can significantly shift the qibla direction from the actual position of the Kaaba. The requirement of muslim prayed facing towards the Kaaba is more as spiritual prerequisite rather than physical evidence.

GOZCARDS Source Data for Ozone Monthly Zonal Means on a Geodetic Latitude and Pressure Grid V1.01

Data.gov (United States)

National Aeronautics and Space Administration — The GOZCARDS Source Data for Ozone Monthly Zonal Averages on a Geodetic Latitude and Pressure Grid product (GozSmlpO3) contains zonal means and related information...

GOZCARDS Merged Data for Ozone Monthly Zonal Means on a Geodetic Latitude and Pressure Grid V1.01

Data.gov (United States)

National Aeronautics and Space Administration — The GOZCARDS Merged Data for Ozone Monthly Zonal Averages on a Geodetic Latitude and Pressure Grid product (GozMmlpO3) contains zonal means and related information...

RDBE Development and Progress

Science.gov (United States)

Neill, A.; Bark, M.; Beaudoin, C.; Brisken, W.; Ben Frej, H.; Doeleman, S.; Durand, S.; Guerra, Ml; Hinton, A.; Luce, M.; McWhirter, R.; Morris, K.; Peck, G.; Revnell, M.; Rogers, A.; Romney, J.; Ruszczyk, C; Taveniku, M.; Walker, R.; Whitney, A.

2010-12-01

A digital backend based on the ROACH board has been developed jointly by the National Radio Astronomy Observatory and MIT Haystack Observatory. The RDBE will have both Polyphase Filterbank and Digital Downconverter personalities. The initial configuration outputs sixteen 32-MHz channels, comprised of half the channels from the PFB processing of the two IF inputs, for use in the VLBI2010 geodetic system and in the VLBA sensitivity upgrade project. The output rate is 2x10^9 bits/second (1x10^9 bits/sec = 1 Gbps) over a 10 GigE connection to the Mark 5C with the data written in Mark 5B format on disk.

RDBE Development and Progress

Science.gov (United States)

Niell, A.; Bark, M.; Beaudoin, C.; Brisken, W.; Frej, H. Ben; Doeleman, S.; Durand, S.; Guerra, M.; Hinton, A.; Luce, M.;

Earth rotation excitation mechanisms derived from geodetic space observations

Science.gov (United States)

Göttl, F.; Schmidt, M.

2009-04-01

Earth rotation variations are caused by mass displacements and motions in the subsystems of the Earth. Via the satellite Gravity and Climate Experiment (GRACE) gravity field variations can be identified which are caused by mass redistribution in the Earth system. Therefore time variable gravity field models (GFZ RL04, CSR RL04, JPL RL04, ITG-Grace03, GRGS, ...) can be used to derive different impacts on Earth rotation. Furthermore satellite altimetry provides accurate information on sea level anomalies (AVISO, DGFI) which are caused by mass and volume changes of seawater. Since Earth rotation is solely affected by mass variations and motions the volume (steric) effect has to be reduced from the altimetric observations in order to infer oceanic contributions to Earth rotation variations. Therefore the steric effect is estimated from physical ocean parameters such as temperature and salinity changes in the oceans (WOA05, Ishii). In this study specific individual geophysical contributions to Earth rotation variations are identified by means of a multitude of accurate geodetic space observations in combination with a realistic error propagation. It will be shown that due to adjustment of altimetric and/or gravimetric solutions the results for polar motion excitations can be improved.

The potential role of real-time geodetic observations in tsunami early warning

Science.gov (United States)

Tinti, Stefano; Armigliato, Alberto

2016-04-01

Tsunami warning systems (TWS) have the final goal to launch a reliable alert of an incoming dangerous tsunami to coastal population early enough to allow people to flee from the shore and coastal areas according to some evacuation plans. In the last decade, especially after the catastrophic 2004 Boxing Day tsunami in the Indian Ocean, much attention has been given to filling gaps in the existing TWSs (only covering the Pacific Ocean at that time) and to establishing new TWSs in ocean regions that were uncovered. Typically, TWSs operating today work only on earthquake-induced tsunamis. TWSs estimate quickly earthquake location and size by real-time processing seismic signals; on the basis of some pre-defined "static" procedures (either based on decision matrices or on pre-archived tsunami simulations), assess the tsunami alert level on a large regional scale and issue specific bulletins to a pre-selected recipients audience. Not unfrequently these procedures result in generic alert messages with little value. What usually operative TWSs do not do, is to compute earthquake focal mechanism, to calculate the co-seismic sea-floor displacement, to assess the initial tsunami conditions, to input these data into tsunami simulation models and to compute tsunami propagation up to the threatened coastal districts. This series of steps is considered nowadays too time consuming to provide the required timely alert. An equivalent series of steps could start from the same premises (earthquake focal parameters) and reach the same result (tsunami height at target coastal areas) by replacing the intermediate steps of real-time tsunami simulations with proper selection from a large archive of pre-computed tsunami scenarios. The advantage of real-time simulations and of archived scenarios selection is that estimates are tailored to the specific occurring tsunami and alert can be more detailed (less generic) and appropriate for local needs. Both these procedures are still at an

Geodetic measurement of deformation east of the San Andreas Fault in Central California

Science.gov (United States)

Sauber, Jeanne; Solomon, Sean C.; Lisowski, Michael

1988-01-01

The shear strain rates in the Diablo Range of California have been calculated, and the slip rate along the Calaveras and Paicines faults in Central California have been estimated, on the basis of triangulation and trilateration data from two geodetic networks located between the western edge of the Great Valley and the San Andreas Fault. The orientation of the principal compressive strain predicted from the azimuth of the major structures in the region is N 25 deg E, leading to an average shear strain value that corresponds to a relative shortening rate of 4.5 + or - 2.4 mm/yr. It is inferred that the measured strain is due to compression across the fold of this area. The hypothesized uniform, fault-normal compression within the Coast Ranges is not supported by these results.

LOD estimation from DORIS observations

Science.gov (United States)

Stepanek, Petr; Filler, Vratislav; Buday, Michal; Hugentobler, Urs

2016-04-01

The difference between astronomically determined duration of the day and 86400 seconds is called length of day (LOD). The LOD could be also understood as the daily rate of the difference between the Universal Time UT1, based on the Earth rotation, and the International Atomic Time TAI. The LOD is estimated using various Satellite Geodesy techniques as GNSS and SLR, while absolute UT1-TAI difference is precisely determined by VLBI. Contrary to other IERS techniques, the LOD estimation using DORIS (Doppler Orbitography and Radiopositioning Integrated by satellite) measurement did not achieve a geodetic accuracy in the past, reaching the precision at the level of several ms per day. However, recent experiments performed by IDS (International DORIS Service) analysis centre at Geodetic Observatory Pecny show a possibility to reach accuracy around 0.1 ms per day, when not adjusting the cross-track harmonics in the Satellite orbit model. The paper presents the long term LOD series determined from the DORIS solutions. The series are compared with C04 as the reference. Results are discussed in the context of accuracy achieved with GNSS and SLR. Besides the multi-satellite DORIS solutions, also the LOD series from the individual DORIS satellite solutions are analysed.

Multifrequency radio VLBI observations of the superluminal low-frequency variable quasar NRAO 140

International Nuclear Information System (INIS)

Marscher, A.P.; Broderick, J.J.

1985-01-01

VLBI maps of the quasar NRAO 140 at three wavelengths: 18, 6, and 2.8 cm are presented. The source consists of a jetlike structure delineated by a nearly colinear series of components which are progressively more compact toward the northwestern end of the source. The multifrequency observations make it possible to dissect accurately the spectrum of the source, which leads to an affirmation of the previously reported Compton problem and superluminal motion. The Compton problem requires relativistic motion with Doppler factor delta greater than 3.7. One of the components is separating from the core at a rate of 0.15 milliarcsec/yr, which translates to an apparent velocity between 4c and 13c, depending on the values of H(0) and q(0). The energy in relativistic electrons in one of the components far exceeds the energy in magnetic field, but the total energy requirement need not exceed approximately 10 to the 54th ergs. 27 references

Use of Geodetic Surveys of Leveling Lines and Dry Tilt Arrays to Study Faults and Volcanoes in Undergraduate Field Geophysics Classes

Science.gov (United States)

Polet, J.; Alvarez, K.; Elizondo, K.

2017-12-01

In the early 1980's and 1990's numerous leveling lines and dry tilt arrays were installed throughout Central and Southern California by United States Geological Survey scientists and other researchers (e.g. Sylvester, 1985). These lines or triangular arrays of geodetic monuments commonly straddle faults or have been installed close to volcanic areas, where significant motion is expected over relatively short time periods. Over the past year, we have incorporated geodetic surveys of these arrays as part of our field exercises in undergraduate and graduate level classes on topics such as shallow subsurface geophysics and field geophysics. In some cases, the monuments themselves first had to be located based on only limited information, testing students' Brunton use and map reading skills. Monuments were then surveyed using total stations and global navigation satellite system (GNSS) receivers, using a variety of experimental procedures. The surveys were documented with tables, photos, maps and graphs in field reports, as well as in wiki pages created by student groups for a geophysics field class this June. The measurements were processed by the students and compared with similar data from surveys conducted soon after installation of the arrays, to analyze the deformation that occurred over the last few decades. The different geodetic techniques were also compared and an error analysis was conducted. The analysis and processing of these data challenged and enhanced students' quantitative literacy and technology skills. The final geodetic measurements are being incorporated into several senior and MSc thesis projects. Further surveys are planned for additional classes, in topics that could include seismology, geodesy, volcanology and global geophysics. We are also considering additional technologies, such as structure from motion (SfM) photogrammetry.

GEOdetic Data assimilation and EStimation of references for climate change InvEstigation. An overall presentation of the French GEODESIE project

Science.gov (United States)

Nahmani, S.; Coulot, D.; Biancale, R.; Bizouard, C.; Bonnefond, P.; Bouquillon, S.; Collilieux, X.; Deleflie, F.; Garayt, B.; Lambert, S. B.; Laurent-Varin, S.; Marty, J. C.; Mercier, F.; Metivier, L.; Meyssignac, B.; Pollet, A.; Rebischung, P.; Reinquin, F.; Richard, J. Y.; Tertre, F.; Woppelmann, G.

2017-12-01

Many major indicators of climate change are monitored with space observations. This monitoring is highly dependent on references that only geodesy can provide. The current accuracy of these references does not permit to fully support the challenges that the constantly evolving Earth system gives rise to, and can consequently limit the accuracy of these indicators. Thus, in the framework of the GGOS, stringent requirements are fixed to the International Terrestrial Reference Frame (ITRF) for the next decade: an accuracy at the level of 1 mm and a stability at the level of 0.1 mm/yr. This means an improvement of the current quality of ITRF by a factor of 5-10. Improving the quality of the geodetic references is an issue which requires a thorough reassessment of the methodologies involved. The most relevant and promising method to improve this quality is the direct combination of the space-geodetic measurements used to compute the official references of the IERS. The GEODESIE project aims at (i) determining highly-accurate global and consistent references and (ii) providing the geophysical and climate research communities with these references, for a better estimation of geocentric sea level rise, ice mass balance and on-going climate changes. Time series of sea levels computed from altimetric data and tide gauge records with these references will also be provided. The geodetic references will be essential bases for Earth's observation and monitoring to support the challenges of the century. The geocentric time series of sea levels will permit to better apprehend (i) the drivers of the global mean sea level rise and of regional variations of sea level and (ii) the contribution of the global climate change induced by anthropogenic greenhouse gases emissions to these drivers. All the results and computation and quality assessment reports will be available at geodesie_anr.ign.fr.This project, supported by the French Agence Nationale de la Recherche (ANR) for the period

GOZCARDS Merged Data for Hydrogen Chloride Monthly Zonal Means on a Geodetic Latitude and Pressure Grid V1.01

Data.gov (United States)

National Aeronautics and Space Administration — The GOZCARDS Merged Data for Hydrogen Chloride Monthly Zonal Averages on a Geodetic Latitude and Pressure Grid product (GozMmlpHCl) contains zonal means and related...

The Wettzell System Monitoring Concept and First Realizations

Science.gov (United States)

Ettl, Martin; Neidhardt, Alexander; Muehlbauer, Matthias; Ploetz, Christian; Beaudoin, Christopher

2010-01-01

Automated monitoring of operational system parameters for the geodetic space techniques is becoming more important in order to improve the geodetic data and to ensure the safety and stability of automatic and remote-controlled observations. Therefore, the Wettzell group has developed the system monitoring software, SysMon, which is based on a reliable, remotely-controllable hardware/software realization. A multi-layered data logging system based on a fanless, robust industrial PC with an internal database system is used to collect data from several external, serial, bus, or PCI-based sensors. The internal communication is realized with Remote Procedure Calls (RPC) and uses generative programming with the interface software generator idl2rpc.pl developed at Wettzell. Each data monitoring stream can be configured individually via configuration files to define the logging rates or analog-digital-conversion parameters. First realizations are currently installed at the new laser ranging system at Wettzell to address safety issues and at the VLBI station O Higgins as a meteorological data logger. The system monitoring concept should be realized for the Wettzell radio telescope in the near future.

An Investigation on the Use of Different Centroiding Algorithms and Star Catalogs in Astro-Geodetic Observations

Science.gov (United States)

Basoglu, Burak; Halicioglu, Kerem; Albayrak, Muge; Ulug, Rasit; Tevfik Ozludemir, M.; Deniz, Rasim

2017-04-01

In the last decade, the importance of high-precise geoid determination at local or national level has been pointed out by Turkish National Geodesy Commission. The Commission has also put objective of modernization of national height system of Turkey to the agenda. Meanwhile several projects have been realized in recent years. In Istanbul city, a GNSS/Levelling geoid was defined in 2005 for the metropolitan area of the city with an accuracy of ±3.5cm. In order to achieve a better accuracy in this area, "Local Geoid Determination with Integration of GNSS/Levelling and Astro-Geodetic Data" project has been conducted in Istanbul Technical University and Bogazici University KOERI since January 2016. The project is funded by The Scientific and Technological Research Council of Turkey. With the scope of the project, modernization studies of Digital Zenith Camera System are being carried on in terms of hardware components and software development. Accentuated subjects are the star catalogues, and centroiding algorithm used to identify the stars on the zenithal star field. During the test observations of Digital Zenith Camera System performed between 2013-2016, final results were calculated using the PSF method for star centroiding, and the second USNO CCD Astrograph Catalogue (UCAC2) for the reference star positions. This study aims to investigate the position accuracy of the star images by comparing different centroiding algorithms and available star catalogs used in astro-geodetic observations conducted with the digital zenith camera system.

GOZCARDS Source Data for Nitric Acid Monthly Zonal Means on a Geodetic Latitude and Pressure Grid V1.01

Data.gov (United States)

National Aeronautics and Space Administration — The GOZCARDS Source Data for Nitric Acid Monthly Zonal Averages on a Geodetic Latitude and Pressure Grid product (GozSmlpHNO3) contains zonal means and related...

GOZCARDS Merged Data for Nitric Acid Monthly Zonal Means on a Geodetic Latitude and Pressure Grid V1.01

Data.gov (United States)

National Aeronautics and Space Administration — The GOZCARDS Merged Data for Nitric Acid Monthly Zonal Averages on a Geodetic Latitude and Pressure Grid product (GozMmlpHNO3) contains zonal means and related...

INTERFEROMETRIC MONITORING OF GAMMA-RAY BRIGHT AGNs. I. THE RESULTS OF SINGLE-EPOCH MULTIFREQUENCY OBSERVATIONS

Energy Technology Data Exchange (ETDEWEB)

Lee, Sang-Sung; Wajima, Kiyoaki; Algaba, Juan-Carlos; Zhao, Guang-Yao; Hodgson, Jeffrey A.; Byun, Do-Young; Kang, Sincheol; Kim, Soon-Wook; Kino, Motoki [Korea Astronomy and Space Science Institute, 776 Daedeok-daero, Yuseong-gu, Daejeon 34055 (Korea, Republic of); Kim, Dae-Won; Park, Jongho; Kim, Jae-Young; Trippe, Sascha [Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826 (Korea, Republic of); Miyazaki, Atsushi [Japan Space Forum, 3-2-1, Kandasurugadai, Chiyoda-ku, Tokyo 101-0062 Japan (Japan); Kim, Jeong-Sook, E-mail: sslee@kasi.re.kr [National Astronomical Observatory of Japan, 2211 Osawa, Mitaka, Tokyo 1818588 (Japan)

2016-11-01

We present results of single-epoch very long baseline interferometry (VLBI) observations of gamma-ray bright active galactic nuclei (AGNs) using the Korean VLBI Network (KVN) at the 22, 43, 86, and 129 GHz bands, which are part of a KVN key science program, Interferometric Monitoring of Gamma-Ray Bright AGNs. We selected a total of 34 radio-loud AGNs of which 30 sources are gamma-ray bright AGNs with flux densities of >6 × 10{sup −10} ph cm{sup −2} s{sup −1}. Single-epoch multifrequency VLBI observations of the target sources were conducted during a 24 hr session on 2013 November 19 and 20. All observed sources were detected and imaged at all frequency bands, with or without a frequency phase transfer technique, which enabled the imaging of 12 faint sources at 129 GHz, except for one source. Many of the target sources are resolved on milliarcsecond scales, yielding a core-jet structure, with the VLBI core dominating the synchrotron emission on a milliarcsecond scale. CLEAN flux densities of the target sources are 0.43–28 Jy, 0.32–21 Jy, 0.18–11 Jy, and 0.35–8.0 Jy in the 22, 43, 86, and 129 GHz bands, respectively. Spectra of the target sources become steeper at higher frequency, with spectral index means of −0.40, −0.62, and −1.00 in the 22–43 GHz, 43–86 GHz and 86–129 GHz bands, respectively, implying that the target sources become optically thin at higher frequencies (e.g., 86–129 GHz).

The impact of using jason-1 and cryosat-2 geodetic mission altimetry for gravity field modeling

DEFF Research Database (Denmark)

Andersen, Ole Baltazar; Jain, Maulik; Knudsen, Per

2016-01-01

Since the release of the Danish Technical University DTU10 global marine gravity field in 2010, the amount of geodetic mission altimetry data has nearly tripled. The Cryosat-2 satellite have provided data along its 369 day near repeat since 2010 and as of May 2012 the Jason-1 satellite has been o...

GOZCARDS Source Data for Nitrous Oxide Monthly Zonal Means on a Geodetic Latitude and Pressure Grid V1.01

Data.gov (United States)

National Aeronautics and Space Administration — The GOZCARDS Source Data for Nitrous Oxide Monthly Zonal Averages on a Geodetic Latitude and Pressure Grid product (GozSmlpN2O) contains zonal means and related...

GOZCARDS Merged Data for Nitrous Oxide Monthly Zonal Means on a Geodetic Latitude and Pressure Grid V1.01

Data.gov (United States)

National Aeronautics and Space Administration — The GOZCARDS Merged Data for Nitrous Oxide Monthly Zonal Averages on a Geodetic Latitude and Pressure Grid product (GozMmlpN2O) contains zonal means and related...

GOZCARDS Merged Data for Water Vapor Monthly Zonal Means on a Geodetic Latitude and Pressure Grid V1.01

Data.gov (United States)

National Aeronautics and Space Administration — The GOZCARDS Merged Data for Water Vapor Monthly Zonal Averages on a Geodetic Latitude and Pressure Grid product (GozMmlpH2O) contains zonal means and related...

MOONLIGHT: A NEW LUNAR LASER RANGING RETROREFLECTOR AND THE LUNAR GEODETIC PRECESSION

Directory of Open Access Journals (Sweden)

M. Martini

2013-12-01

Full Text Available Since the 1970s Lunar Laser Ranging (LLR to the Apollo Cube Corner Retroreflector (CCR arrays (developed by the University of Maryland, UMD supplied almost all significant tests of General Relativity (Alley et al., 1970; Chang et al., 1971; Bender et al.,1973: possible changes in the gravitational constant, gravitational self-energy, weak equivalence principle, geodetic precession, inverse-square force-law. The LNF group, in fact, has just completed a new measurement of the lunar geodetic precession with Apollo array, with accuracy of 9 × 10−3, comparable to the best measurement to date. LLR has also provided significant information on the composition and origin of the moon. This is the only Apollo experiment still in operation. In the 1970s Apollo LLR arrays contributed a negligible fraction of the ranging error budget. Since the ranging capabilities of ground stations improved by more than two orders of magnitude, now, because of the lunar librations, Apollo CCR arrays dominate the error budget. With the project MoonLIGHT (Moon Laser Instrumentation for General relativity High-accuracy Tests, in 2006 INFN-LNF joined UMD in the development and test of a new-generation LLR payload made by a single, large CCR (100mm diameter unaffected by the effect of librations. With MoonLIGHT CCRs the accuracy of the measurement of the lunar geodetic precession can be improved up to a factor 100 compared to Apollo arrays. From a technological point of view, INFN-LNF built and is operating a new experimental apparatus (Satellite/lunar laser ranging Characterization Facility, SCF and created a new industry-standard test procedure (SCF-Test to characterize and model the detailed thermal behavior and the optical performance of CCRs in accurately laboratory-simulated space conditions, for industrial and scientific applications. Our key experimental innovation is the concurrent measurement and modeling of the optical Far Field Diffraction Pattern (FFDP and the

Geodetic Imaging: Expanding the Boundaries of Geodesy in the 21st Century

Science.gov (United States)

Fernandez Diaz, J. C.; Carter, W. E.; Shrestha, R. L.; Glennie, C. L.

2013-12-01

High resolution (sub-meter) geodetic images covering tens to thousands of square kilometers have extended the boundaries of geodesy into related areas of the earth sciences, such as geomorphology and geodynamics, during the past decade, to archaeological exploration and site mapping during the past few years, and are now poised to transform studies of flora and fauna in the more remote regions of the world. Geodetic images produced from airborne laser scanning (ALS), a.k.a. airborne light detection and ranging (LiDAR) have proven transformative to the modern practice of geomorphology where researchers have used decimeter resolution digital elevation models (DEMs) to determine the spatial frequencies of evenly spaced features in terrain, and developed models and mathematical equations to explain how the terrain evolved to its present state and how it is expected to change in the future (Perron et al., 2009). In geodynamics researchers have used ';before' and ';after' geodetic images of the terrain near earthquakes, such as the 2010 El Mayor-Cucapah Earthquake, to quantify surface displacements and suggest models to explain the observed deformations (Oskin et. al., 2012). In archaeology, the ability of ALS to produce ';bare earth' DEMs of terrain covered with dense vegetation, including even tropical rain forests, has revolutionized the study of archaeology in highly forested areas, finding ancient structures and human modifications of landscapes not discovered by archaeologists working at sites for decades (Chase et al., 2011 & Evans et al., 2013), and finding previously unknown ruins in areas that ground exploration has not been able to penetrate since the arrival of the conquistadors in the new world in the 17th century (Carter et al., 2012). The improved spatial resolution and ability of the third generation ALS units to obtain high resolution bare earth DEMs and canopy models in areas covered in dense forests, brush, and even shallow water (steams, lakes, and

Discoveries and Controversies in Geodetic Imaging of Deformation Before and After the M=9 Tohoku-oki Earthquake

Science.gov (United States)

Wang, K.; Sun, T.; Hino, R.; Iinuma, T.; Tomita, F.; Kido, M.

2017-12-01

Numerous observations pertaining to the M=9.0 2011 Tohoku-oki earthquake have led to new understanding of subduction zone earthquakes. By synthesizing published research results and our own findings, we explore what has been learned about fault behavior and Earth rheology from geodetic imaging of crustal deformation before and after the earthquake. Before the earthquake, megathrust locking models based on land-based geodetic observations correctly outlined the along-strike location of the future rupture zone, showing that land-based observations are capable of resolving along-strike variations in locking and creep at wavelengths comparable to distances from the network. But they predicted a locked zone that was much deeper than the actual rupture in 2011. The incorrect definition of the locking pattern in the dip direction demonstrates not only the need for seafloor geodesy but also the importance of modeling interseismic viscoelastic stress relaxation and stress shadowing. The discovery of decade-long accelerated slip downdip of the future rupture zone raises new questions on fault mechanics. After the earthquake, seafloor geodetic discovery of opposing motion offshore provided unambiguous evidence for the dominance of viscoelastic relaxation in short-term postseismic deformation. There is little deep afterslip in the fault area where the decade-long pre-earthquake slip acceleration is observed. The complementary spatial distribution of pre-slip and afterslip calls for new scientific research. However, the near absence of deep afterslip directly downdip of the main rupture is perceived to be controversial because some viscoelastic models do predict large afterslip here, although less than predicted by purely elastic models. We show that the large afterslip in these models is largely an artefact due to the use of a layered Earth model without a subducting slab. The slab acts as an "anchor" in the mantle and retards landward motion following a subduction earthquake

GeoNetGIS: a Geodetic Network Geographical Information System to manage GPS networks in seismic and volcanic areas

Science.gov (United States)

Cristofoletti, P.; Esposito, A.; Anzidei, M.

2003-04-01

This paper presents the methodologies and issues involved in the use of GIS techniques to manage geodetic information derived from networks in seismic and volcanic areas. Organization and manipulation of different geodetical, geological and seismic database, give us a new challenge in interpretation of information that has several dimensions, including spatial and temporal variations, also the flexibility and brand range of tools available in GeoNetGIS, make it an attractive platform for earthquake risk assessment. During the last decade the use of geodetic networks based on the Global Positioning System, devoted to geophysical applications, especially for crustal deformation monitoring in seismic and volcanic areas, increased dramatically. The large amount of data provided by these networks, combined with different and independent observations, such as epicentre distribution of recent and historical earthquakes, geological and structural data, photo interpretation of aerial and satellite images, can aid for the detection and parameterization of seismogenic sources. In particular we applied our geodetic oriented GIS to a new GPS network recently set up and surveyed in the Central Apennine region: the CA-GeoNet. GeoNetGIS is designed to analyze in three and four dimensions GPS sources and to improve crustal deformation analysis and interpretation related with tectonic structures and seismicity. It manages many database (DBMS) consisting of different classes, such as Geodesy, Topography, Seismicity, Geology, Geography and Raster Images, administrated according to Thematic Layers. GeoNetGIS represents a powerful research tool allowing to join the analysis of all data layers to integrate the different data base which aid for the identification of the activity of known faults or structures and suggesting the new evidences of active tectonics. A new approach to data integration given by GeoNetGIS capabilities, allow us to create and deliver a wide range of maps, digital

NEAR REAL-TIME DETERMINATION OF EARTHQUAKE SOURCE PARAMETERS FOR TSUNAMI EARLY WARNING FROM GEODETIC OBSERVATIONS

Directory of Open Access Journals (Sweden)

S. Manneela

2016-06-01

Full Text Available Exemplifying the tsunami source immediately after an earthquake is the most critical component of tsunami early warning, as not every earthquake generates a tsunami. After a major under sea earthquake, it is very important to determine whether or not it has actually triggered the deadly wave. The near real-time observations from near field networks such as strong motion and Global Positioning System (GPS allows rapid determination of fault geometry. Here we present a complete processing chain of Indian Tsunami Early Warning System (ITEWS, starting from acquisition of geodetic raw data, processing, inversion and simulating the situation as it would be at warning center during any major earthquake. We determine the earthquake moment magnitude and generate the centroid moment tensor solution using a novel approach which are the key elements for tsunami early warning. Though the well established seismic monitoring network, numerical modeling and dissemination system are currently capable to provide tsunami warnings to most of the countries in and around the Indian Ocean, the study highlights the critical role of geodetic observations in determination of tsunami source for high-quality forecasting.

Uvođenje novih geodetskih referentnih sistema u Bosni i Hercegovini : Introduction of a new geodetic reference systems in Bosnia and Herzegovina

Directory of Open Access Journals (Sweden)

Šeho Zimić

2017-12-01

Full Text Available The introduction of a new reference system in Bosnia and Herzegovina is not only a necessity, but an obligation imposed by the United Nations (UN and the European Union (EU. At the General Assembly on February 26, 2015, the UN has adopted a resolution titled "Global Geodetic Reference Frame for Sustainable Development - GGRF", which for the first time raise the geodetic issue as a political issue at such a high level. The resolution highlights the strong need for more precise positioning and navigation from the use of smartphones to the study of climate changes, population migrations and other scientific researches of relevance to the whole world (http://www.unggrf.org/. All this is not possible without a global exchange of geodata and a common global geodetic reference system. Through the Inspire Directive, the EU has clearly specified which coordinate and heights systems are being applied in Europe. The countries in the region have adopted the European terrestrial reference system ETRS89 as a new reference system in their legislation. Through the EUREF campaign BALKAN98 and the introduction of the Network of permanent GNSS stations Bosnia and Herzegovina has joined the famil

Geodetic determinations for the NuMI project at Fermilab

International Nuclear Information System (INIS)

Bocean, V.

1999-01-01

As a part of the Neutrinos at the Main Injector (NuMI) project, the MINOS (Main Injector Neutrino Oscillation Search) experiment will search for neutrino mass by looking for neutrino oscillations. The project plans to direct a beam of muon neutrinos from the Main Injector towards both nearby and far-off detectors capable of counting all three types of neutrinos. The beam will travel 735 km through the Earth towards a remote iron mine in northern Minnesota where, 710 m below surface, a massive 5400 metric tons detector will be built. For the neutrino energy spectrum physics test to work properly, the primary proton beam must be within ± 12 m from its ideal position at Soudan, MN, corresponding to ± 1.63 x 10-5 radians, i.e. 3.4 arc-seconds. Achieving this tolerance requires a rather exact knowledge of the geometry of the beam, expressed in terms of the azimuth and the slope of the vector joining the two sites. This paper summarizes the concepts, the methodology, the implementation, and the results of the geodetic surveying efforts made up to date for determining the absolute positions of the Fermilab and the Soudan underground mine sites, from which the beam orientation parameters are computed. (author)

Multi-scale model of the ionosphere from the combination of modern space-geodetic satellite techniques - project status and first results

Science.gov (United States)

Schmidt, M.; Hugentobler, U.; Jakowski, N.; Dettmering, D.; Liang, W.; Limberger, M.; Wilken, V.; Gerzen, T.; Hoque, M.; Berdermann, J.

2012-04-01

Near real-time high resolution and high precision ionosphere models are needed for a large number of applications, e.g. in navigation, positioning, telecommunications or astronautics. Today these ionosphere models are mostly empirical, i.e., based purely on mathematical approaches. In the DFG project 'Multi-scale model of the ionosphere from the combination of modern space-geodetic satellite techniques (MuSIK)' the complex phenomena within the ionosphere are described vertically by combining the Chapman electron density profile with a plasmasphere layer. In order to consider the horizontal and temporal behaviour the fundamental target parameters of this physics-motivated approach are modelled by series expansions in terms of tensor products of localizing B-spline functions depending on longitude, latitude and time. For testing the procedure the model will be applied to an appropriate region in South America, which covers relevant ionospheric processes and phenomena such as the Equatorial Anomaly. The project connects the expertise of the three project partners, namely Deutsches Geodätisches Forschungsinstitut (DGFI) Munich, the Institute of Astronomical and Physical Geodesy (IAPG) of the Technical University Munich (TUM) and the German Aerospace Center (DLR), Neustrelitz. In this presentation we focus on the current status of the project. In the first year of the project we studied the behaviour of the ionosphere in the test region, we setup appropriate test periods covering high and low solar activity as well as winter and summer and started the data collection, analysis, pre-processing and archiving. We developed partly the mathematical-physical modelling approach and performed first computations based on simulated input data. Here we present information on the data coverage for the area and the time periods of our investigations and we outline challenges of the multi-dimensional mathematical-physical modelling approach. We show first results, discuss problems

A case for inherent geometric and geodetic accuracy in remotely sensed VNIR and SWIR imaging products

Science.gov (United States)

Driver, J. M.

1982-01-01

Significant aberrations can occur in acquired images which, unless compensated on board the spacecraft, can seriously impair throughput and timeliness for typical Earth observation missions. Conceptual compensations options are advanced to enable acquisition of images with inherent geometric and geodetic accuracy. Research needs are identified which, when implemented, can provide inherently accurate images. Agressive pursuit of these research needs is recommended.

Thin-plate spline quadrature of geodetic integrals

Science.gov (United States)

Vangysen, Herman

1989-01-01

Thin-plate spline functions (known for their flexibility and fidelity in representing experimental data) are especially well-suited for the numerical integration of geodetic integrals in the area where the integration is most sensitive to the data, i.e., in the immediate vicinity of the evaluation point. Spline quadrature rules are derived for the contribution of a circular innermost zone to Stoke's formula, to the formulae of Vening Meinesz, and to the recursively evaluated operator L(n) in the analytical continuation solution of Molodensky's problem. These rules are exact for interpolating thin-plate splines. In cases where the integration data are distributed irregularly, a system of linear equations needs to be solved for the quadrature coefficients. Formulae are given for the terms appearing in these equations. In case the data are regularly distributed, the coefficients may be determined once-and-for-all. Examples are given of some fixed-point rules. With such rules successive evaluation, within a circular disk, of the terms in Molodensky's series becomes relatively easy. The spline quadrature technique presented complements other techniques such as ring integration for intermediate integration zones.

Improving deformation models by discounting transient signals in geodetic data: 2. Geodetic data, stress directions, and long-term strain rates in Italy

Science.gov (United States)

Carafa, Michele M. C.; Bird, Peter

2016-07-01

The lithosphere of Italy is exposed to a number of different short-term strain transients, including but not limited to landslides, postseismic relaxation, and volcanic inflation/deflation. These transients affect GPS velocities and complicate the assessment of the long-term tectonic component of the surface deformation. In a companion paper we present a method for anticipating the principal patterns of nontectonic, short-term strains and building this information into the covariance matrix of the geodetic velocities. In this work we apply this method to Italian GPS velocities to build an augmented covariance matrix that characterizes all expected discrepancies between short- and long-term velocities. We find that formal uncertainties usually reported for GPS measurements are smaller than the variability of the same benchmarks across a geologic time span. Furthermore, we include in our modeling the azimuths of most compressive horizontal principal stresses (SHmax) because GPS data cannot resolve the active kinematics of coastal and offshore areas. We find that the final tectonic model can be made relatively insensitive to short-term interfering processes if the augmented covariance matrix and SHmax data records are used in the objective function. This results in a preferred neotectonic model that is also in closer agreement with independent geologic and seismological constraints and has the advantage of reducing short-term biases in forecasts of long-term seismicity.

Field Installation and Real-Time Data Processing of the New Integrated SeismoGeodetic System with Real-Time Acceleration and Displacement Measurements for Earthquake Characterization Based on High-Rate Seismic and GPS Data

Science.gov (United States)

Zimakov, Leonid; Jackson, Michael; Passmore, Paul; Raczka, Jared; Alvarez, Marcos; Barrientos, Sergio

2015-04-01

We will discuss and show the results obtained from an integrated SeismoGeodetic System, model SG160-09, installed in the Chilean National Network. The SG160-09 provides the user high rate GNSS and accelerometer data, full epoch-by-epoch measurement integrity and, using the Trimble Pivot™ SeismoGeodetic App, the ability to create combined GNSS and accelerometer high-rate (200Hz) displacement time series in real-time. The SG160-09 combines seismic recording with GNSS geodetic measurement in a single compact, ruggedized package. The system includes a low-power, 220-channel GNSS receiver powered by the latest Trimble-precise Maxwell™6 technology and supports tracking GPS, GLONASS and Galileo signals. The receiver incorporates on-board GNSS point positioning using Real-Time Precise Point Positioning (PPP) technology with satellite clock and orbit corrections delivered over IP networks. The seismic recording element includes an ANSS Class A, force balance triaxial accelerometer with the latest, low power, 24-bit A/D converter, which produces high-resolution seismic data. The SG160-09 processor acquires and packetizes both seismic and geodetic data and transmits it to the central station using an advanced, error-correction protocol with back fill capability providing data integrity between the field and the processing center. The SG160-09 has been installed in the seismic station close to the area of the Iquique earthquake of April 1, 2014, in northern Chile, a seismically prone area at the current time. The hardware includes the SG160-09 system, external Zephyr Geodetic-2 GNSS antenna, and high-speed Internet communication media. Both acceleration and displacement data was transmitted in real-time to the National Seismological Center in Santiago for real-time data processing using Earthworm / Early Bird software. Command/Control of the field station and real-time GNSS position correction are provided via the Pivot software suite. Data from the SG160-09 system was

Seismicity and seismic hazard in Sabah, East Malaysia from earthquake and geodetic data

Science.gov (United States)

Gilligan, A.; Rawlinson, N.; Tongkul, F.; Stephenson, R.

2017-12-01

While the levels of seismicity are low in most of Malaysia, the state of Sabah in northern Borneo has moderate levels of seismicity. Notable earthquakes in the region include the 1976 M6.2 Lahad Datu earthquake and the 2015 M6 Ranau earthquake. The recent Ranau earthquake resulted in the deaths of 18 people on Mt Kinabalu, an estimated 100 million RM ( US$23 million) damage to buildings, roads, and infrastructure from shaking, and flooding, reduced water quality, and damage to farms from landslides. Over the last 40 years the population of Sabah has increased to over four times what it was in 1976, yet seismic hazard in Sabah remains poorly understood. Using seismic and geodetic data we hope to better quantify the hazards posed by earthquakes in Sabah, and thus help to minimize risk. In order to do this we need to know about the locations of earthquakes, types of earthquakes that occur, and faults that are generating them. We use data from 15 MetMalaysia seismic stations currently operating in Sabah to develop a region-specific velocity model from receiver functions and a pre-existing surface wave model. We use this new velocity model to (re)locate earthquakes that occurred in Sabah from 2005-2016, including a large number of aftershocks from the 2015 Ranau earthquake. We use a probabilistic nonlinear earthquake location program to locate the earthquakes and then refine their relative locations using a double difference method. The recorded waveforms are further used to obtain moment tensor solutions for these earthquakes. Earthquake locations and moment tensor solutions are then compared with the locations of faults throughout Sabah. Faults are identified from high-resolution IFSAR images and subsequent fieldwork, with a particular focus on the Lahad Datau and Ranau areas. Used together, these seismic and geodetic data can help us to develop a new seismic hazard model for Sabah, as well as aiding in the delivery of outreach activities regarding seismic hazard

GBIS (Geodetic Bayesian Inversion Software): Rapid Inversion of InSAR and GNSS Data to Estimate Surface Deformation Source Parameters and Uncertainties

Science.gov (United States)

Bagnardi, M.; Hooper, A. J.

2017-12-01

Inversions of geodetic observational data, such as Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) measurements, are often performed to obtain information about the source of surface displacements. Inverse problem theory has been applied to study magmatic processes, the earthquake cycle, and other phenomena that cause deformation of the Earth's interior and of its surface. Together with increasing improvements in data resolution, both spatial and temporal, new satellite missions (e.g., European Commission's Sentinel-1 satellites) are providing the unprecedented opportunity to access space-geodetic data within hours from their acquisition. To truly take advantage of these opportunities we must become able to interpret geodetic data in a rapid and robust manner. Here we present the open-source Geodetic Bayesian Inversion Software (GBIS; available for download at http://comet.nerc.ac.uk/gbis). GBIS is written in Matlab and offers a series of user-friendly and interactive pre- and post-processing tools. For example, an interactive function has been developed to estimate the characteristics of noise in InSAR data by calculating the experimental semi-variogram. The inversion software uses a Markov-chain Monte Carlo algorithm, incorporating the Metropolis-Hastings algorithm with adaptive step size, to efficiently sample the posterior probability distribution of the different source parameters. The probabilistic Bayesian approach allows the user to retrieve estimates of the optimal (best-fitting) deformation source parameters together with the associated uncertainties produced by errors in the data (and by scaling, errors in the model). The current version of GBIS (V1.0) includes fast analytical forward models for magmatic sources of different geometry (e.g., point source, finite spherical source, prolate spheroid source, penny-shaped sill-like source, and dipping-dike with uniform opening) and for dipping faults with uniform

CASA Uno GPS orbit and baseline experiments

Science.gov (United States)

Schutz, B. E.; Ho, C. S.; Abusali, P. A. M.; Tapley, B. D.

1990-01-01

CASA Uno data from sites distributed in longitude from Australia to Europe have been used to determine orbits of the GPS satellites. The characteristics of the orbits determined from double difference phase have been evaluated through comparisons of two-week solutions with one-week solutions and by comparisons of predicted and estimated orbits. Evidence of unmodeled effects is demonstrated, particularly associated with the orbit planes that experience solar eclipse. The orbit accuracy has been assessed through the repeatability of unconstrained estimated baseline vectors ranging from 245 km to 5400 km. Both the baseline repeatability and the comparison with independent space geodetic methods give results at the level of 1-2 parts in 100,000,000. In addition, the Mojave/Owens Valley (245 km) and Kokee Park/Ft. Davis (5409 km) estimates agree with VLBI and SLR to better than 1 part in 100,000,000.

Geodetic Measurements and Mechanical Models of Cyclic Deformation at Okmok Volcano, Alaska

Science.gov (United States)

Feigl, K.; Masterlark, T.; Lu, Z.; Ohlendorf, S. J.; Thurber, C. H.; Sigmundsson, F.

2009-12-01

The 1997 and 2008 eruptions of Okmok volcano, Alaska, provide a rare opportunity for conducting a rheological experiment to unravel the complex processes associated with magma migration, storage, and eruption in an active volcano. In this experiment, the magma flux during the eruption provides the “impulse” and the subsequent, transient deformation, the “response”. By simulating the impulse, measuring the response, and interpreting the constitutive relations between the two, one can infer the rheology. Okmok is an excellent natural laboratory for such an experiment because a complete cycle of deformation has been monitored using geodetic and seismic means, including: (a) geodetic time series from Interferometric Synthetic Aperture Radar (InSAR) and the Global Positioning System (GPS), (b) earthquake locations; and (c) seismic tomography. We are developing quantitative models using the Finite Element Method (FEM) to simulate the timing and location of the observed seismicity and deformation by accounting for: (a) the geometry and loading of the magma chamber and lava flow, (b) the spatial distribution of material properties; and (c) the constitutive (rheological) relations between stress and strain. Here, we test the hypothesis that the deformation following the 1997 eruption did not reach a steady state before the eruption in 2008. To do so, we iteratively confront the FEM models with the InSAR measurements using the General Inversion of Phase Technique (GIPhT). This approach models the InSAR phase data directly, without unwrapping, as developed, validated, and applied by Feigl and Thurber [Geophys. J. Int., 2009]. By minimizing a cost function that quantifies the misfit between observed and modeled values in terms of “wrapped” phase (with values ranging from -1/2 to +1/2 cycles), GIPhT can estimate parameters in a geophysical model. By avoiding the pitfalls of phase-unwrapping approaches, GIPhT allows the analysis, interpretation and modeling of more

How Well do we Know Near-Surface Density When Determining Mass Balance by the Geodetic Method?

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Kuhn, M. H.; Matzi, E.

2005-12-01

From a data set of firn pits in the accumulation area of Hintereisferner in the years 1964 - 2002 the behavior of density and water equivalent was analyzed with a view to estimating the potential errors in the application of the geodetic method. Since annual specific balance ranged from 100 to 3300 mm w.e. the profiles were scaled to total depth. For the uppermost 10% of the annual deposit at a typical location the 1964-2002 mean density would be 350 kg/m-3 with a standard deviation of 110 kg/m-3; for the 10% layer at the base of the annual snowpack the respective figures are 510 +- 30 kg/m-3. The normalized long term means of an ensemble of 9 pits ranged from 310 to 380 kg/m-3 in the top layer and from 510 to 540 kg/m-3 in the bottom layer. When one outlier is removed the the range in the bottom layer reduces to 525 to 540 kg/m-3. This small local variance encourages the use of the geodetic method. The comparison of elevation models of 1969 and 1997 yields a mass change that agrees very well with the results of the glaciological method provided the volume change is converted to mass with a density of 900 kg/m-3. While this may be true for the entire glacier on long terms, it will fail for individual years in the accumulation area. Possible errors are calculated from the data set emphasizing the role of year to year changes of specific balance and accumulation area ratio.

Data Records derived from GEOSAT Geodetic Mission (GM) and Exact Repeat Mission (ERM) data from 30 March 1985 to 31 December 1989

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This collection contains Sensor Data Records (SDRs), Geodetic Data Records (GDRs), Waveform Data Records (WDRs), and Crossover Difference data Records (XDRs) from...

Evaluating Commercial and Private Cloud Services for Facility-Scale Geodetic Data Access, Analysis, and Services

Science.gov (United States)

Meertens, C. M.; Boler, F. M.; Ertz, D. J.; Mencin, D.; Phillips, D.; Baker, S.

2017-12-01

UNAVCO, in its role as a NSF facility for geodetic infrastructure and data, has succeeded for over two decades using on-premises infrastructure, and while the promise of cloud-based infrastructure is well-established, significant questions about suitability of such infrastructure for facility-scale services remain. Primarily through the GeoSciCloud award from NSF EarthCube, UNAVCO is investigating the costs, advantages, and disadvantages of providing its geodetic data and services in the cloud versus using UNAVCO's on-premises infrastructure. (IRIS is a collaborator on the project and is performing its own suite of investigations). In contrast to the 2-3 year time scale for the research cycle, the time scale of operation and planning for NSF facilities is for a minimum of five years and for some services extends to a decade or more. Planning for on-premises infrastructure is deliberate, and migrations typically take months to years to fully implement. Migrations to a cloud environment can only go forward with similar deliberate planning and understanding of all costs and benefits. The EarthCube GeoSciCloud project is intended to address the uncertainties of facility-level operations in the cloud. Investigations are being performed in a commercial cloud environment (Amazon AWS) during the first year of the project and in a private cloud environment (NSF XSEDE resource at the Texas Advanced Computing Center) during the second year. These investigations are expected to illuminate the potential as well as the limitations of running facility scale production services in the cloud. The work includes running parallel equivalent cloud-based services to on premises services and includes: data serving via ftp from a large data store, operation of a metadata database, production scale processing of multiple months of geodetic data, web services delivery of quality checked data and products, large-scale compute services for event post-processing, and serving real time data

An Inequality Constrained Least-Squares Approach as an Alternative Estimation Procedure for Atmospheric Parameters from VLBI Observations

Science.gov (United States)

Halsig, Sebastian; Artz, Thomas; Iddink, Andreas; Nothnagel, Axel

2016-12-01

On its way through the atmosphere, radio signals are delayed and affected by bending and attenuation effects relative to a theoretical path in vacuum. In particular, the neutral part of the atmosphere contributes considerably to the error budget of space-geodetic observations. At the same time, space-geodetic techniques become more and more important in the understanding of the Earth's atmosphere, because atmospheric parameters can be linked to the water vapor content in the atmosphere. The tropospheric delay is usually taken into account by applying an adequate model for the hydrostatic component and by additionally estimating zenith wet delays for the highly variable wet component. Sometimes, the Ordinary Least Squares (OLS) approach leads to negative estimates, which would be equivalent to negative water vapor in the atmosphere and does, of course, not reflect meteorological and physical conditions in a plausible way. To cope with this phenomenon, we introduce an Inequality Constrained Least Squares (ICLS) method from the field of convex optimization and use inequality constraints to force the tropospheric parameters to be non-negative allowing for a more realistic tropospheric parameter estimation in a meteorological sense. Because deficiencies in the a priori hydrostatic modeling are almost fully compensated by the tropospheric estimates, the ICLS approach urgently requires suitable a priori hydrostatic delays. In this paper, we briefly describe the ICLS method and validate its impact with regard to station positions.

Incorporating Geodetic Technologies in to Field and Campus Courses at the University of Michigan: Best Practices and Lessons Learned

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Niemi, N. A.; Clark, M. K.

2017-12-01

For the past 6 years, the University of Michigan has implemented geodetic techniques into both summer field courses and on-campus courses. The primary means for incorporating these technologies has been a partnership with UNAVCO to introduce terrestrial laser scanning (TLS) at summer field courses, although employing Structure from Motion(SfM), ArcCollector for iPads and RTK GPS surveying have also been explored. The nature of these types of data lend themselves readily to geomorphology, environmental, and natural hazards-based projects, and we have developed field projects or labs around neotectonics (fault-scarp scanning and diffusion analysis), change detection (braided stream evolution, landslide and rock glacier motion, coastal change) and mass wasting processes (rock avalanche scanning and analysis). While we have primarily developed multi-day projects that use these tools in a field camp setting, we have also developed weekend field trip projects and traditional afternoon lab exercises associated with on-campus courses. The use of geodetic technology is generally well received by students. Reasons for this are the use of somewhat different skill sets from traditional geologic mapping problems, including research survey design, real-time data acquisition, and quantitative data analysis. Students also perceive that they are engaged in learning technology which they may use in their future employment. Challenges encountered, particularly in the field, include managing large student groups with a finite pool of equipment, rapid data processing pressures, variable student experience with analysis software and limited technical support for field-based computational resources. We will describe the positive attributes of incorporating geodetic technologies into undergraduate courses and elaborate on some best practices learned from our experiences.

Effect of lunar gravity models on Chang'E-2 orbit determination using VLBI tracking data

Directory of Open Access Journals (Sweden)

Erhu Wei

2016-11-01

Full Text Available The precise orbit determination of Chang'E-2 is the most important issue for successful mission and scientific applications, while the lunar gravity field model with big uncertainties has large effect on Chang'E-2 orbit determination. Recently, several new gravity models have been produced using the latest lunar satellites tracking data, such as LP165P, SGM150J, GL0900D and GRGM900C. In this paper, the four gravity models mentioned above were evaluated through the power spectra analysis, admittance and coherence analysis. Effect of four lunar gravity models on Chang'E-2 orbit determination performance is investigated and assessed using Very Long Baseline Interferometry (VLBI tracking data. The overlap orbit analysis, the posteriori data residual, and the orbit prediction are used to evaluate the orbit precision between successive arcs. The LP165P model has better orbit overlap performance than the SGM150J model for Chang'E-2100 km × 100 km orbit and the SGM150J model performs better for Chang'E-2100 km × 15 km orbit, while GL0900D and GRGM900C have the best orbit overlap results for the two types of Chang'E-2 orbit. For the orbit prediction, GRGM900C has the best orbit prediction performance in the four models.

Feasibility of Construction of the Continuously Operating Geodetic GPS Network of Sinaloa, Mexico

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Vazquez, G. E.; Jacobo, C.

2011-12-01

This research is based on the study and analysis of feasibility for the construction of the geodetic network for GPS continuous operation for Sinaloa, hereafter called (RGOCSIN). A GPS network of continuous operation is defined as that materialized structure physically through permanent monuments where measurements to the systems of Global Positioning (GPS) is performed continuously throughout a region. The GPS measurements in this network are measurements of accuracy according to international standards to define its coordinates, thus constituting the basic structure of geodetic referencing for a country. In this context is that in the near future the RGOCSIN constitutes a system state only accurate and reliable georeferencing in real-time (continuous and permanent operation) and will be used for different purposes; i.e., in addition to being fundamental basis for any lifting topographic or geodetic survey, and other areas such as: (1) Different construction processes (control and monitoring of engineering works); (2) Studies of deformation of the Earth's crust (before and after a seismic event); (3) GPS meteorology (weather forecasting); (4) Demarcation projects (natural and political); (5) Establishment of bases to generate mapping (necessary for the economic and social development of the state); (6) Precision agriculture (optimization of economic resources to the various crops); (7) Geographic information systems (Organization and planning activities associated with the design and construction of public services); (8) Urban growth (possible settlements in the appropriate form and taking care of the environmental aspect), among others. However there are criteria and regulations according to the INEGI (Instituto Nacional de Estadística y Geografía, http://www.inegi.org.mx/) that must be met; even for this stage of feasibility of construction that sees this project as a first phase. The fundamental criterion to be taken into account according to INEGI is a

Need for denser geodetic network to get real constrain on the fault behavior along the Main Marmara Sea segments of the NAF, toward an optimized GPS network.

Science.gov (United States)

Klein, E.; Masson, F.; Duputel, Z.; Yavasoglu, H.; Agram, P. S.

2016-12-01

Over the last two decades, the densification of GPS networks and the development of new radar satellites offered an unprecedented opportunity to study crustal deformation due to faulting. Yet, submarine strike slip fault segments remain a major issue, especially when the landscape appears unfavorable to the use of SAR measurements. It is the case of the North Anatolian fault segments located in the Main Marmara Sea, that remain unbroken ever since the Mw7.4 earthquake of Izmit in 1999, which ended a eastward migrating seismic sequence of Mw > 7 earthquakes. Located directly offshore Istanbul, evaluation of seismic hazard appears capital. But a strong controversy remains over whether these segments are accumulating strain and are likely to experience a major earthquake, or are creeping, resulting both from the simplicity of current geodetic models and the scarcity of geodetic data. We indeed show that 2D infinite fault models cannot account for the complexity of the Marmara fault segments. But current geodetic data in the western region of Istanbul are also insufficient to invert for the coupling using a 3D geometry of the fault. Therefore, we implement a global optimization procedure aiming at identifying the most favorable distribution of GPS stations to explore the strain accumulation. We present here the results of this procedure that allows to determine both the optimal number and location of the new stations. We show that a denser terrestrial survey network can indeed locally improve the resolution on the shallower part of the fault, even more efficiently with permanent stations. But data closer from the fault, only possible by submarine measurements, remain necessary to properly constrain the fault behavior and its potential along strike coupling variations.

A new velocity field for Africa from combined GPS and DORIS space geodetic Solutions: Contribution to the definition of the African reference frame (AFREF)

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Saria, E.; Calais, E.; Altamimi, Z.; Willis, P.; Farah, H.

2013-04-01

We analyzed 16 years of GPS and 17 years of Doppler orbitography and radiopositioning integrated by satellite (DORIS) data at continuously operating geodetic sites in Africa and surroundings to describe the present-day kinematics of the Nubian and Somalian plates and constrain relative motions across the East African Rift. The resulting velocity field describes horizontal and vertical motion at 133 GPS sites and 9 DORIS sites. Horizontal velocities at sites located on stable Nubia fit a single plate model with a weighted root mean square residual of 0.6 mm/yr (maximum residual 1 mm/yr), an upper bound for plate-wide motions and for regional-scale deformation in the seismically active southern Africa and Cameroon volcanic line. We confirm significant southward motion ( ˜ 1.5 mm/yr) in Morocco with respect to Nubia, consistent with earlier findings. We propose an updated angular velocity for the divergence between Nubia and Somalia, which provides the kinematic boundary conditions to rifting in East Africa. We update a plate motion model for the East African Rift and revise the counterclockwise rotation of the Victoria plate and clockwise rotation of the Rovuma plate with respect to Nubia. Vertical velocities range from - 2 to +2 mm/yr, close to their uncertainties, with no clear geographic pattern. This study provides the first continent-wide position/velocity solution for Africa, expressed in International Terrestrial Reference Frame (ITRF2008), a contribution to the upcoming African Reference Frame (AFREF). Except for a few regions, the African continent remains largely under-sampled by continuous space geodetic data. Efforts are needed to augment the geodetic infrastructure and openly share existing data sets so that the objectives of AFREF can be fully reached.

Constraining proposed combinations of ice history and Earth rheology using VLBI determined baseline length rates in North America

Science.gov (United States)

Mitrovica, J. X.; Davis, J. L.; Shapiro, I. I.

1993-01-01

We predict the present-day rates of change of the lengths of 19 North American baselines due to the glacial isostatic adjustment process. Contrary to previously published research, we find that the three dimensional motion of each of the sites defining a baseline, rather than only the radial motions of these sites, needs to be considered to obtain an accurate estimate of the rate of change of the baseline length. Predictions are generated using a suite of Earth models and late Pleistocene ice histories, these include specific combinations of the two which have been proposed in the literature as satisfying a variety of rebound related geophysical observations from the North American region. A number of these published models are shown to predict rates which differ significantly from the VLBI observations.

RTX Correction Accuracy and Real-Time Data Processing of the New Integrated SeismoGeodetic System with Real-Time Acceleration and Displacement Measurements for Earthquake Characterization Based on High-Rate Seismic and GPS Data

Science.gov (United States)

Zimakov, L. G.; Raczka, J.; Barrientos, S. E.

2016-12-01

We will discuss and show the results obtained from an integrated SeismoGeodetic System, model SG160-09, installed in the Chile (Chilean National Network), Italy (University of Naples Network), and California. The SG160-09 provides the user high rate GNSS and accelerometer data, full epoch-by-epoch measurement integrity and the ability to create combined GNSS and accelerometer high-rate (200Hz) displacement time series in real-time. The SG160-09 combines seismic recording with GNSS geodetic measurement in a single compact, ruggedized case. The system includes a low-power, 220-channel GNSS receiver powered by the latest Trimble-precise Maxwell™6 technology and supports tracking GPS, GLONASS and Galileo signals. The receiver incorporates on-board GNSS point positioning using Real-Time Precise Point Positioning (PPP) technology with satellite clock and orbit corrections delivered over IP networks. The seismic recording includes an ANSS Class A, force balance accelerometer with the latest, low power, 24-bit A/D converter, producing high-resolution seismic data. The SG160-09 processor acquires and packetizes both seismic and geodetic data and transmits it to the central station using an advanced, error-correction protocol providing data integrity between the field and the processing center. The SG160-09 has been installed in three seismic stations in different geographic locations with different Trimble global reference stations coverage The hardware includes the SG160-09 system, external Zephyr Geodetic-2 GNSS antenna, both radio and high-speed Internet communication media. Both acceleration and displacement data was transmitted in real-time to the centralized Data Acquisition Centers for real-time data processing. Command/Control of the field station and real-time GNSS position correction are provided via the Pivot platform. Data from the SG160-09 system was used for seismic event characterization along with data from traditional seismic and geodetic stations

Implementing a C++ Version of the Joint Seismic-Geodetic Algorithm for Finite-Fault Detection and Slip Inversion for Earthquake Early Warning

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Smith, D. E.; Felizardo, C.; Minson, S. E.; Boese, M.; Langbein, J. O.; Guillemot, C.; Murray, J. R.

2015-12-01

The earthquake early warning (EEW) systems in California and elsewhere can greatly benefit from algorithms that generate estimates of finite-fault parameters. These estimates could significantly improve real-time shaking calculations and yield important information for immediate disaster response. Minson et al. (2015) determined that combining FinDer's seismic-based algorithm (Böse et al., 2012) with BEFORES' geodetic-based algorithm (Minson et al., 2014) yields a more robust and informative joint solution than using either algorithm alone. FinDer examines the distribution of peak ground accelerations from seismic stations and determines the best finite-fault extent and strike from template matching. BEFORES employs a Bayesian framework to search for the best slip inversion over all possible fault geometries in terms of strike and dip. Using FinDer and BEFORES together generates estimates of finite-fault extent, strike, dip, preferred slip, and magnitude. To yield the quickest, most flexible, and open-source version of the joint algorithm, we translated BEFORES and FinDer from Matlab into C++. We are now developing a C++ Application Protocol Interface for these two algorithms to be connected to the seismic and geodetic data flowing from the EEW system. The interface that is being developed will also enable communication between the two algorithms to generate the joint solution of finite-fault parameters. Once this interface is developed and implemented, the next step will be to run test seismic and geodetic data through the system via the Earthworm module, Tank Player. This will allow us to examine algorithm performance on simulated data and past real events.

Self-force correction to geodetic spin precession in Kerr spacetime

Science.gov (United States)

Akcay, Sarp

2017-08-01

We present an expression for the gravitational self-force correction to the geodetic spin precession of a spinning compact object with small, but non-negligible mass in a bound, equatorial orbit around a Kerr black hole. We consider only conservative backreaction effects due to the mass of the compact object (m1), thus neglecting the effects of its spin s1 on its motion; i.e., we impose s1≪G m12/c and m1≪m2, where m2 is the mass parameter of the background Kerr spacetime. We encapsulate the correction to the spin precession in ψ , the ratio of the accumulated spin-precession angle to the total azimuthal angle over one radial orbit in the equatorial plane. Our formulation considers the gauge-invariant O (m1) part of the correction to ψ , denoted by Δ ψ , and is a generalization of the results of Akcay et al. [Classical Quantum Gravity 34, 084001 (2017), 10.1088/1361-6382/aa61d6] to Kerr spacetime. Additionally, we compute the zero-eccentricity limit of Δ ψ and show that this quantity differs from the circular orbit Δ ψcirc by a gauge-invariant quantity containing the gravitational self-force correction to general relativistic periapsis advance in Kerr spacetime. Our result for Δ ψ is expressed in a manner that readily accommodates numerical/analytical self-force computations, e.g., in the radiation gauge, and paves the way for the computation of a new eccentric-orbit Kerr gauge invariant beyond the generalized redshift.

Polarised Multiangular Reflectance Measurements Using the Finnish Geodetic Institute Field Goniospectrometer

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Jouni Peltoniemi

2009-05-01

Full Text Available The design, operation, and properties of the Finnish Geodetic Institute Field Goniospectrometer (FIGIFIGO are presented. FIGIFIGO is a portable instrument for the measurement of surface Bidirectional Reflectance Factor (BRF for samples with diameters of 10 – 50 cm. A set of polarising optics enable the measurement of linearly polarised BRF over the full solar spectrum (350 – 2,500 nm. FIGIFIGO is designed mainly for field operation using sunlight, but operation in a laboratory environment is also possible. The acquired BRF have an accuracy of 1 – 5% depending on wavelength, sample properties, and measurement conditions. The angles are registered at accuracies better than 2°. During 2004 – 2008, FIGIFIGO has been used in the measurement of over 150 samples, all around northern Europe. The samples concentrate mostly on boreal forest understorey, snow, urban surfaces, and reflectance calibration surfaces.

Geodetic methods to determine the relativistic redshift at the level of 10^{-18} in the context of international timescales: a review and practical results

Science.gov (United States)

Denker, Heiner; Timmen, Ludger; Voigt, Christian; Weyers, Stefan; Peik, Ekkehard; Margolis, Helen S.; Delva, Pacôme; Wolf, Peter; Petit, Gérard

2017-12-01

The frequency stability and uncertainty of the latest generation of optical atomic clocks is now approaching the one part in 10^{18} level. Comparisons between earthbound clocks at rest must account for the relativistic redshift of the clock frequencies, which is proportional to the corresponding gravity (gravitational plus centrifugal) potential difference. For contributions to international timescales, the relativistic redshift correction must be computed with respect to a conventional zero potential value in order to be consistent with the definition of Terrestrial Time. To benefit fully from the uncertainty of the optical clocks, the gravity potential must be determined with an accuracy of about 0.1 m2 s^{-2} , equivalent to about 0.01 m in height. This contribution focuses on the static part of the gravity field, assuming that temporal variations are accounted for separately by appropriate reductions. Two geodetic approaches are investigated for the derivation of gravity potential values: geometric levelling and the Global Navigation Satellite Systems (GNSS)/geoid approach. Geometric levelling gives potential differences with millimetre uncertainty over shorter distances (several kilometres), but is susceptible to systematic errors at the decimetre level over large distances. The GNSS/geoid approach gives absolute gravity potential values, but with an uncertainty corresponding to about 2 cm in height. For large distances, the GNSS/geoid approach should therefore be better than geometric levelling. This is demonstrated by the results from practical investigations related to three clock sites in Germany and one in France. The estimated uncertainty for the relativistic redshift correction at each site is about 2 × 10^{-18}.

STRUCTURAL MONITORING WITH GEODETIC SURVEY OF QUADRIFOGLIO CONDOMINIUM (LECCE

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D. Costantino

2014-01-01

Full Text Available Monitoring buildings for moving elements has been always a problem of great importance for their conservation and preservation, as well as for risk mitigation. In particular, topographic surveying allows, through the use of the principles and instruments of the geodetic survey, to control moving points which have been identified and measured. In this study case, twelve survey campaigns were done for monitoring a building located in the city of Lecce. The condominium was built five years ago on an old quarry filled with debris to allow construction. Later in time, obviously, cracks started to appear on walls within the property, and for this legal actions were taken. The survey schema adopted has been that of triangulation/trilateration, from two vertices with known coordinates. With this methodologies four cornerstones have been identified, established with forced centering on pillars with anchor plates, connected to same number of framework points, considered stable. From these, 23 control points located on the structure with rotating prisms anchored at the same manner have been surveyed. The elaboration has been carried out by generating redundancy of the measures and compensating the values with least mean squares. The results obtained by the activity of survey and elaboration have confirmed the existence of ongoing phenomena. The causes that have generated the phenomenon have been, subsequently, investigated and have been considered attributable to the existence of a sewer pipeline and a water pipeline not properly put in place and consequently broke down due to the geological characteristics of the site.

Undergraduate teaching modules featuring geodesy data applied to critical social topics (GETSI: GEodetic Tools for Societal Issues)

Science.gov (United States)

Pratt-Sitaula, B. A.; Walker, B.; Douglas, B. J.; Charlevoix, D. J.; Miller, M. M.

2015-12-01

The GETSI project, funded by NSF TUES, is developing and disseminating teaching and learning materials that feature geodesy data applied to critical societal issues such as climate change, water resource management, and natural hazards (serc.carleton.edu/getsi). It is collaborative between UNAVCO (NSF's geodetic facility), Mt San Antonio College, and Indiana University. GETSI was initiated after requests by geoscience faculty for geodetic teaching resources for introductory and majors-level students. Full modules take two weeks but module subsets can also be used. Modules are developed and tested by two co-authors and also tested in a third classroom. GETSI is working in partnership with the Science Education Resource Center's (SERC) InTeGrate project on the development, assessment, and dissemination to ensure compatibility with the growing number of resources for geoscience education. Two GETSI modules are being published in October 2015. "Ice mass and sea level changes" includes geodetic data from GRACE, satellite altimetry, and GPS time series. "Imaging Active Tectonics" has students analyzing InSAR and LiDAR data to assess infrastructure earthquake vulnerability. Another three modules are in testing during fall 2015 and will be published in 2016. "Surface process hazards" investigates mass wasting hazard and risk using LiDAR data. "Water resources and geodesy" uses GRACE, vertical GPS, and reflection GPS data to have students investigating droughts in California and the High Great Plains. "GPS, strain, and earthquakes" helps students learn about infinitesimal and coseismic strain through analysis of horizontal GPS data and includes an extension module on the Napa 2014 earthquake. In addition to teaching resources, the GETSI project is compiling recommendations on successful development of geodesy curricula. The chief recommendations so far are the critical importance of including scientific experts in the authorship team and investing significant resources in

THE ROLE OF ASTRO-GEODETIC IN PRECISE GUIDANCE OF LONG TUNNELS

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M. Mirghasempour

2015-12-01

Full Text Available One of prime aspects of surveying projects is guidance of paths of a long tunnel from different directions and finally ending all paths in a specific place. This kind of underground surveying, because of particular condition, has some different points in relation to the ground surveying, including Improper geometry in underground transverse, low precise measurement in direction and length due to condition such as refraction, distinct gravity between underground point and corresponding point on the ground (both value and direction of gravity and etc. To solve this problems, astro-geodetic that is part of geodesy science, can help surveying engineers. In this article, the role of astronomy is defined in two subjects: 1- Azimuth determination of directions from entrance and exit nets of tunnel and also calibration of gyro-theodolite to use them in Underground transvers: By astronomical methods, azimuth of directions can be determine with an accuracy of 0.5 arcsecond, whereas, nowadays, no gyroscope can measure the azimuth in this accuracy; For instance, accuracy of the most precise gyroscope (Gyromat 5000 is 1.2 cm over a distance of one kilometre (2.4 arcsecond. Furthermore, the calibration methods that will be mention in this article, have significance effects on underground transverse. 2- Height relation between entrance point and exit point is problematic and time consuming; For example, in a 3 km long tunnel ( in Arak- Khoram Abad freeway, to relate entrance point to exit point, it is necessary to perform levelling about 90 km. Other example of this boring and time consuming levelling is in Kerman tunnel. This tunnel is 36 km length, but to transfer the entrance point height to exit point, 150 km levelling is needed. According to this paper, The solution for this difficulty is application of astro-geodetic and determination of vertical deflection by digital zenith camera system TZK2-D. These two elements make possible to define geoid profile

The Extragalactic Lens VLBI Imaging Survey (ELVIS): Investigating galaxy cores and black holes with gravitational lens central images

Science.gov (United States)

Boyce, Edward R.

This thesis describes the Extragalactic Lens VLBI Imaging Survey (ELVIS), a search for central images in gravitational lenses. We present the first four ELVIS targets, for which we have radio VLBI observations with resolutions of a few milli-arcseconds and sensitivities of 15 - 38mJy. For PMN J1838-3427, CLASS B0739+366 and CLASS B0445+123 we have not detected any central images, but have set stringent upper limits on their flux densities. For CLASS B2319+051 we have made a tentative detection of a third radio source, which may be either a central image or radio emission from the lens galaxy. Using the upper limits on the central image flux densities, we gain new information about the matter distributions in the lens galaxies of these systems. We fit a broken power law model for the matter profile, and constrain the allowed break radii and inner index of this model. To demagnify the central images to the observed level the matter profiles must be slightly shallower than or steeper than isothermal, which is consistent with previous studies of early type galaxy profiles. The presence of a super-massive black hole weakens the constraints somewhat, but the profiles are still close to isothermal. Relative to previous work, we reduce the maximum sizes of shallow cores by factors of 2 to 3, and raise the indices of r 0( r -g central cusps by g = 0.05 - 0.35. If we take the source in B2319+051 to be a central image, then we select a narrow band of allowed break radii and inner indices, finding that a constant density core has size 150--380 pc, and a pure power law has index g = 1.5 - 1.67. Our constraints still allow sufficiently shallow profiles that some super-massive black holes may form central image pairs rather than eliminating the central image, and these image pairs may be detected with future instruments. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

A geodetic matched-filter search for slow slip with application to the Mexico subduction zone

Science.gov (United States)

Rousset, B.; Campillo, M.; Lasserre, C.; Frank, W.; Cotte, N.; Walpersdorf, A.; Socquet, A.; Kostoglodov, V.

2017-12-01

Since the discovery of slow slip events, many methods have been successfully applied to model obvious transient events in geodetic time series, such as the widely used network strain filter. Independent seismological observations of tremors or low frequency earthquakes and repeating earthquakes provide evidence of low amplitude slow deformation but do not always coincide with clear occurrences of transient signals in geodetic time series. Here, we aim to extract the signal corresponding to slow slips hidden in the noise of GPS time series, without using information from independent datasets. We first build a library of synthetic slow slip event templates by assembling a source function with Green's functions for a discretized fault. We then correlate the templates with post-processed GPS time series. Once the events have been detected in time, we estimate their duration T and magnitude Mw by modelling a weighted stack of GPS time series. An analysis of synthetic time series shows that this method is able to resolve the correct timing, location, T and Mw of events larger than Mw 6.0 in the context of the Mexico subduction zone. Applied on a real data set of 29 GPS time series in the Guerrero area from 2005 to 2014, this technique allows us to detect 28 transient events from Mw 6.3 to 7.2 with durations that range from 3 to 39 days. These events have a dominant recurrence time of 40 days and are mainly located at the down dip edges of the Mw > 7.5 SSEs.

A geodetic matched filter search for slow slip with application to the Mexico subduction zone

Science.gov (United States)

Rousset, B.; Campillo, M.; Lasserre, C.; Frank, W. B.; Cotte, N.; Walpersdorf, A.; Socquet, A.; Kostoglodov, V.

2017-12-01

Since the discovery of slow slip events, many methods have been successfully applied to model obvious transient events in geodetic time series, such as the widely used network strain filter. Independent seismological observations of tremors or low-frequency earthquakes and repeating earthquakes provide evidence of low-amplitude slow deformation but do not always coincide with clear occurrences of transient signals in geodetic time series. Here we aim to extract the signal corresponding to slow slips hidden in the noise of GPS time series, without using information from independent data sets. We first build a library of synthetic slow slip event templates by assembling a source function with Green's functions for a discretized fault. We then correlate the templates with postprocessed GPS time series. Once the events have been detected in time, we estimate their duration T and magnitude Mw by modeling a weighted stack of GPS time series. An analysis of synthetic time series shows that this method is able to resolve the correct timing, location, T, and Mw of events larger than Mw 6 in the context of the Mexico subduction zone. Applied on a real data set of 29 GPS time series in the Guerrero area from 2005 to 2014, this technique allows us to detect 28 transient events from Mw 6.3 to 7.2 with durations that range from 3 to 39 days. These events have a dominant recurrence time of 40 days and are mainly located at the downdip edges of the Mw>7.5 slow slip events.

Interseismic and coseismic surface deformation deduced from space geodetic observations : with inferences on seismic hazard, tectonic processes, earthquake complexity, and slip distribution

NARCIS (Netherlands)

Bos, A.G. (Annemarie Gerredina)

2003-01-01

In this thesis I am concerned with modeling the kinematics of surface deformation using space geodetic observations in order to advance insight in both interseismic and coseismic surface response. To model the surface deformation field I adopt the method of Spakman and Nyst (2002) which resolves the

Aspects Regarding the Establishment of the Scale Coefficient in the Case of Distances Measurements in an Geodetic Network

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Mircea Ortelecan

2016-11-01

Full Text Available The paper analyzes the possibility to establish the coefficient of scale towards the total station scale triangulation network in the conduct of geodetic and topographic observations in the points with known coordinates (old points or points whose coordinates we want to determine (new points. The purpose of the study is undertaken to simplify computing operations to reduce distances measured from the topographic surface to the Stereo 70 projection plan.

Optimization of observation plan based on the stochastic characteristics of the geodetic network

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Pachelski Wojciech

2016-06-01

Full Text Available Optimal design of geodetic network is a basic subject of many engineering projects. An observation plan is a concluding part of the process. Any particular observation within the network has through adjustment a different contribution and impact on values and accuracy characteristics of unknowns. The problem of optimal design can be solved by means of computer simulation. This paper presents a new method of simulation based on sequential estimation of individual observations in a step-by-step manner, by means of the so-called filtering equations. The algorithm aims at satisfying different criteria of accuracy according to various interpretations of the covariance matrix. Apart of them, the optimization criterion is also amount of effort, defined as the minimum number of observations required.

Archiving Space Geodesy Data for 20+ Years at the CDDIS

Science.gov (United States)

Noll, Carey E.; Dube, M. P.

2004-01-01

Since 1982, the Crustal Dynamics Data Information System (CDDIS) has supported the archive and distribution of geodetic data products acquired by NASA programs. These data include GPS (Global Positioning System), GLONASS (GLObal NAvigation Satellite System), SLR (Satellite Laser Ranging), VLBI (Very Long Baseline Interferometry), and DORIS (Doppler Orbitography and Radiolocation Integrated by Satellite). The data archive supports NASA's space geodesy activities through the Solid Earth and Natural Hazards (SENH) program. The CDDIS data system and its archive have become increasingly important to many national and international programs, particularly several of the operational services within the International Association of Geodesy (IAG), including the International GPS Service (IGS), the International Laser Ranging Service (ILRS), the International VLBI Service for Geodesy and Astrometry (IVS), the International DORIS Service (IDS), and the International Earth Rotation Service (IERS). The CDDIS provides easy and ready access to a variety of data sets, products, and information about these data. The specialized nature of the CDDIS lends itself well to enhancement and thus can accommodate diverse data sets and user requirements. All data sets and metadata extracted from these data sets are accessible to scientists through ftp and the web; general information about each data set is accessible via the web. The CDDIS, including background information about the system and its user communities, the computer architecture, archive contents, available metadata, and future plans will be discussed.

NASA space geodesy program: Catalogue of site information

Science.gov (United States)

Bryant, M. A.; Noll, C. E.

1993-01-01

This is the first edition of the NASA Space Geodesy Program: Catalogue of Site Information. This catalogue supersedes all previous versions of the Crustal Dynamics Project: Catalogue of Site Information, last published in May 1989. This document is prepared under the direction of the Space Geodesy and Altimetry Projects Office (SGAPO), Code 920.1, Goddard Space Flight Center. SGAPO has assumed the responsibilities of the Crustal Dynamics Project, which officially ended December 31, 1991. The catalog contains information on all NASA supported sites as well as sites from cooperating international partners. This catalog is designed to provde descriptions and occupation histories of high-accuracy geodetic measuring sites employing space-related techniques. The emphasis of the catalog has been in the past, and continues to be with this edition, station information for facilities and remote locations utilizing the Satellite Laser Ranging (SLR), Lunar Laser Ranging (LLR), and Very Long Baseline Interferometry (VLBI) techniques. With the proliferation of high-quality Global Positioning System (GPS) receivers and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) transponders, many co-located at established SLR and VLBI observatories, the requirement for accurate station and localized survey information for an ever broadening base of scientists and engineers has been recognized. It is our objective to provide accurate station information to scientific groups interested in these facilities.

Congruence analysis of geodetic networks - hypothesis tests versus model selection by information criteria

Science.gov (United States)

Lehmann, Rüdiger; Lösler, Michael

2017-12-01

Geodetic deformation analysis can be interpreted as a model selection problem. The null model indicates that no deformation has occurred. It is opposed to a number of alternative models, which stipulate different deformation patterns. A common way to select the right model is the usage of a statistical hypothesis test. However, since we have to test a series of deformation patterns, this must be a multiple test. As an alternative solution for the test problem, we propose the p-value approach. Another approach arises from information theory. Here, the Akaike information criterion (AIC) or some alternative is used to select an appropriate model for a given set of observations. Both approaches are discussed and applied to two test scenarios: A synthetic levelling network and the Delft test data set. It is demonstrated that they work but behave differently, sometimes even producing different results. Hypothesis tests are well-established in geodesy, but may suffer from an unfavourable choice of the decision error rates. The multiple test also suffers from statistical dependencies between the test statistics, which are neglected. Both problems are overcome by applying information criterions like AIC.

A Three-decade X-band VLBI Study of 3CR Lobe-dominated Quasar Nuclei

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Hough David H.

2013-12-01

Full Text Available We report X-band VLBI observations of several 3CR lobe-dominated quasar nuclei from 1981 to 2010, mostly obtained with the NRAO VLBA. The goal is to follow flux density outbursts and to fully determine the jet morphology and kinematics on 1-100 pc scales. In 3C207, the core region has flux outbursts at mean intervals of ~7 yr; one of these is actually a double outburst from a stationary true core and a swinging component ~0.5 mas apart. The position angle (PA of the swinging component varies by ~40°, while the PA values of the jet components span ~25°. The jet extends to ~25 mas. Average superluminal speeds are ~10c. One component shows apparent acceleration from 7c to 14c at 2-3 mas from the true core, in a jet recollimation zone that redirects the flow toward PA ~90°. Individual jet components expand until reaching the recollimation zone. In 3C263 and other objects, some of the same phenomena are seen, including ejection of jet components over a range in PA, superluminal motion, and apparent acceleration, but to a lesser degree. Possible physical interpretations involving beaming, orientation, projection, precession, and magnetic effects are discussed.

Geostatistical Investigations of Displacements on the Basis of Data from the Geodetic Monitoring of a Hydrotechnical Object

Science.gov (United States)

Namysłowska-Wilczyńska, Barbara; Wynalek, Janusz

2017-12-01

Geostatistical methods make the analysis of measurement data possible. This article presents the problems directed towards the use of geostatistics in spatial analysis of displacements based on geodetic monitoring. Using methods of applied (spatial) statistics, the research deals with interesting and current issues connected to space-time analysis, modeling displacements and deformations, as applied to any large-area objects on which geodetic monitoring is conducted (e.g., water dams, urban areas in the vicinity of deep excavations, areas at a macro-regional scale subject to anthropogenic influences caused by mining, etc.). These problems are very crucial, especially for safety assessment of important hydrotechnical constructions, as well as for modeling and estimating mining damage. Based on the geodetic monitoring data, a substantial basic empirical material was created, comprising many years of research results concerning displacements of controlled points situated on the crown and foreland of an exemplary earth dam, and used to assess the behaviour and safety of the object during its whole operating period. A research method at a macro-regional scale was applied to investigate some phenomena connected with the operation of the analysed big hydrotechnical construction. Applying a semivariogram function enabled the spatial variability analysis of displacements. Isotropic empirical semivariograms were calculated and then, theoretical parameters of analytical functions were determined, which approximated the courses of the mentioned empirical variability measure. Using ordinary (block) kriging at the grid nodes of an elementary spatial grid covering the analysed object, the values of the Z* estimated means of displacements were calculated together with the accompanying assessment of uncertainty estimation - a standard deviation of estimation σk. Raster maps of the distribution of estimated averages Z* and raster maps of deviations of estimation σk (in perspective

Processing of a geodetic network determined in ETRS-89 with application of different cofactors

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Slavomír Labant

2012-12-01

Full Text Available At present, manufacturers characterize the accuracy of vectors measured by the static method of GNSS technology usingrelationship 5 mm + 1⋅ D ppm . The advantage of the GNSS system over other terrestrial technologies is that it is not affectedby uncertainties in the ground layers of the atmosphere. The paper presents experimental measurement of the 3D geodetic network usingthe technology of global navigation satellite systems, processing and analysis of measurements taken at the Čierny Váh pumping hydropowerstation. Observations were carried out in July 2008. The aim of the paper is to assess parameters used in the model to estimateparameters of the first and second order of the network structures.

Installation of a seafloor geodetic network offshore northern Chile (GeoSEA)

Science.gov (United States)

Kopp, Heidrun; Lange, Dietrich; Hannemann, Katrin; Petersen, Florian; Contreras-Reyes, Eduardo

2016-04-01

The seafloor stores crucial information on sub-seafloor processes, including stress, elastic strain, and earthquake and tsunami generation. This information may be extracted through the nascent scientific field of seafloor geodesy. The target of the recently installed GeoSEA array (Geodetic Earthquake Observatory on the SEAfloor) is to measure crustal deformation in mm-scale on the marine forearc and outer rise of the South American subduction system around 21°S. This segment of the Nazca-South American plate boundary has last ruptured in an earthquake in 1877 and was identified as a seismic gap prior to the 2014 Iquique/Pisagua earthquake (Mw=8.1). The southern portion of the segment remains unbroken by a recent earthquake. Seafloor geodetic measurements provide a way to monitor crustal deformation at high resolution comparable to the satellite-based GPS technique upon which terrestrial geodesy is largely based. The GeoSEA Network consists of autonomous seafloor transponders installed on 4 m high tripods, which were lowered to the seabed on the deep-sea cable of RV SONNE in December 2015. The transponders within an array intercommunicate via acoustic signals for a period of up to 3.5 years and measure acoustic distance, tilt and pressure. An additional component of the network is GeoSURF, a self-steering autonomous surface vehicle (Wave Glider), which monitors system health and is capable to upload the seafloor data to the sea surface and to transfer it via satellite. We have chosen three areas on the middle and lower slope and the outer rise for the set-up of three sub-arrays. The array in Area 1 on the middle continental slope consists of 8 transponders located in pairs on four topographic ridges, which are surface expressions of faults at depth. Area 2 is located on the outer rise seaward of the trench where 5 stations monitor extension across plate-bending related normal faults. The third area is located at water depth >5000 m on the lower continental slope

Contribution of GNSS CORS Infrastructure to the Mission of Modern Geodesy and Status of GNSS CORS in Thailand

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Chalermchon Satirapod

2011-01-01

Full Text Available Geodesy is the science of measuring and mapping the geometry, orientation and gravity field of the Earth including the associated variations with time. Geodesy has also provided the foundation for high accuracy surveying and mapping. Modern Geodesy involves a range of space and terrestrial technologies that contribute to our knowledge of the solid earth, atmosphere and oceans. These technologies include: Global Positioning System/Global Navigation Satellite Systems (GPS/GNSS, Satellite Laser Ranging (SLR, Very Long Baseline Interferometry (VLBI, Satellite Altimetry, Gravity Mapping Missions such as GRACE, CHAMP and GOCE, satelliteborne Differential Interferometric Synthetic Aperture Radar (DInSAR, Absolute and Relative Gravimetry, and Precise Terrestrial Surveying (Levelling and Traversing. A variety of services have been established in recent years to ensure high accuracy and reliable geodetic products to support geoscientific research. The reference frame defined by Modern Geodesy is now the basis for most national and regional datums. Furthermore, the GPS/GNSS technology is a crucial geopositioning tool for both Geodesy and Surveying. There is therefore a blurring of the distinction between geodetic and surveying GPS/GNSS techniques, and increasingly the ground infrastructure of continuously operating reference stations (CORS receivers attempts to address the needs of both geodesists and other positioning professionals. Yet Geodesy is also striving to increase the level of accuracy by a factor of ten over the next decade in order to address the demands of “global change” studies. The Global Geodetic Observing System (GGOS is an important component of the International Association of Geodesy. GGOS aims to integrate all geodetic observations in order to generate a consistent high quality set of geodetic parameters for monitoring the phenomena and processes within the “System Earth”. Integration implies the inclusion of all relevant

The Earth isn't flat: The (large) influence of topography on geodetic fault slip imaging.

Science.gov (United States)

Thompson, T. B.; Meade, B. J.

2017-12-01

While earthquakes both occur near and generate steep topography, most geodetic slip inversions assume that the Earth's surface is flat. We have developed a new boundary element tool, Tectosaur, with the capability to study fault and earthquake problems including complex fault system geometries, topography, material property contrasts, and millions of elements. Using Tectosaur, we study the model error induced by neglecting topography in both idealized synthetic fault models and for the cases of the MW=7.3 Landers and MW=8.0 Wenchuan earthquakes. Near the steepest topography, we find the use of flat Earth dislocation models may induce errors of more than 100% in the inferred slip magnitude and rake. In particular, neglecting topographic effects leads to an inferred shallow slip deficit. Thus, we propose that the shallow slip deficit observed in several earthquakes may be an artefact resulting from the systematic use of elastic dislocation models assuming a flat Earth. Finally, using this study as an example, we emphasize the dangerous potential for forward model errors to be amplified by an order of magnitude in inverse problems.

Displacement response of a concrete arch dam to seasonal temperature fluctuations and reservoir level rise during the first filling period: evidence from geodetic data

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Cemal Ozer Yigit

2016-07-01

Full Text Available The present study evaluates the dynamic behaviour of the Ermenek Dam, the second highest dam in Turkey, based on conventional geodetic measurements and Finite Element Model (FEM analyses during its first filling period. In total, eight periods of measured deformation are considered from the end of construction until the reservoir reached its full capacity. The displacement response of the dam to the reservoir level and to seasonal temperature variations is examined in detail. Time series of apparent total displacements at the middle of the crest of the dam exhibits periodicity and linear trends. Correlation analysis revealed that periodic and linear displacement responses of the dam are related to variations of seasonal temperature and linearly increased reservoir level, respectively, indicating a relation between temperature, water load and dam deformation. It is also concluded that measured deformations based on geodetic data show good agreement with the predicted deformation obtained by the FEM analysis.

The astro-geodetic use of CCD for gravity field refinement

Science.gov (United States)

Gerstbach, G.

1996-07-01

The paper starts with a review of geoid projects, where vertical deflections are more effective than gravimetry. In alpine regions the economy of astrogeoids is at least 10 times higher, but many countries do not make use of this fact - presumably because the measurements are not fully automated up to now. Based upon the experiences of astrometry of high satellites and own tests the author analyses the use of CCD for astro-geodetic measurements. Automation and speeding up will be possible in a few years, the latter depending on the observation scheme. Sensor characteristics, cooling and reading out of the devices should be harmonized. Using line sensors in small prism astrolabes, the CCD accuracy will reach the visual one (±0.2″) within 5-10 years. Astrogeoids can be combined ideally with geological data, because vertical variation of rock densities does not cause systematic effects (contrary to gravimetry). So a geoid of ±5 cm accuracy (achieved in Austria and other alpine countries by 5-10 points per 1000 km 2) can be improved to ±2 cm without additional observations and border effects.

Azimuth selection for sea level measurements using geodetic GPS receivers

Science.gov (United States)

Wang, Xiaolei; Zhang, Qin; Zhang, Shuangcheng

2018-03-01

Based on analysis of Global Positioning System (GPS) multipath signals recorded by a geodetic GPS receiver, GPS Reflectometry (GPS-R) has demonstrated unique advantages in relation to sea level monitoring. Founded on multipath reflectometry theory, sea level changes can be measured by GPS-R through spectral analysis of recorded signal-to-noise ratio data. However, prior to estimating multipath parameters, it is necessary to define azimuth and elevation angle mask to ensure the reflecting zones are on water. Here, a method is presented to address azimuth selection, a topic currently under active development in the field of GPS-R. Data from three test sites: the Kachemak Bay GPS site PBAY in Alaska (USA), Friday Harbor GPS site SC02 in the San Juan Islands (USA), and Brest Harbor GPS site BRST in Brest (France) are analyzed. These sites are located in different multipath environments, from a rural coastal area to a busy harbor, and they experience different tidal ranges. Estimates by the GPS tide gauges at azimuths selected by the presented method are compared with measurements from physical tide gauges and acceptable correspondence found for all three sites.

VLA and low-frequency VLBI observations of the radio source 0503 + 467 - Austere constraints on interstellar scattering in two media

International Nuclear Information System (INIS)

Spangler, S.R.; Fey, A.L.; Cordes, J.M.; Cornell Univ., Ithaca, NY)

1987-01-01

The radio source 0503 + 467 lies near the Galactic plane (l = 161.0 deg, b = 3.7 deg) and at the edge of the supernova remnant (SNR) HB 9. The VLA observations show that it has a spectrum typical of a compact extragalactic radio source. The resultant small angular size of the source makes it an excellent probe of turbulence in two media: the diffuse, or type A, component of interstellar turbulence and a hypothesized region of hydromagnetic turbulence upstream of the supernova remnant. An eight-station VLBI experiment at 326 MHz indicates that the source is less than about 20 milliarcseconds (mas) in angular diameter. A value of 16 mas is most appropriate as an upper limit to the interstellar scattering contribution to the measured angular size. The implications of this upper limit are twofold. First, the galactocentric radial scale to the type-A turbulence is probably less than or equal to about 6 kpc. Second, no evidence is seen for shock-associated turbulence upstream of HB 9. The measurements make it possible to constrain a parameter which is a function of the rms density fluctuation in the upstream region, the outer scale to the density turbulence, and the thickness of SNR foreshock region. 14 references

Rupture history of the 2008 Mw 7.9 Wenchuan, China, earthquake: Evaluation of separate and joint inversions of geodetic, teleseismic, and strong-motion data

Science.gov (United States)

Hartzell, Stephen; Mendoza, Carlos; Ramírez-Guzmán, Leonardo; Zeng, Yuesha; Mooney, Walter

2013-01-01

An extensive data set of teleseismic and strong-motion waveforms and geodetic offsets is used to study the rupture history of the 2008 Wenchuan, China, earthquake. A linear multiple-time-window approach is used to parameterize the rupture. Because of the complexity of the Wenchuan faulting, three separate planes are used to represent the rupturing surfaces. This earthquake clearly demonstrates the strengths and limitations of geodetic, teleseismic, and strong-motion data sets. Geodetic data (static offsets) are valuable for determining the distribution of shallower slip but are insensitive to deeper faulting and reveal nothing about the timing of slip. Teleseismic data in the distance range 30°–90° generally involve no modeling difficulties because of simple ray paths and can distinguish shallow from deep slip. Teleseismic data, however, cannot distinguish between different slip scenarios when multiple fault planes are involved because steep takeoff angles lead to ambiguity in timing. Local strong-motion data, on the other hand, are ideal for determining the direction of rupture from directivity but can easily be over modeled with inaccurate Green’s functions, leading to misinterpretation of the slip distribution. We show that all three data sets are required to give an accurate description of the Wenchuan rupture. The moment is estimated to be approximately 1.0 × 1021 N · m with the slip characterized by multiple large patches with slips up to 10 m. Rupture initiates on the southern end of the Pengguan fault and proceeds unilaterally to the northeast. Upon reaching the cross-cutting Xiaoyudong fault, rupture of the adjacent Beichuan fault starts at this juncture and proceeds bilaterally to the northeast and southwest.

The crustal velocity field mosaic of the Alpine Mediterranean area (Italy): Insights from new geodetic data

Science.gov (United States)

Farolfi, Gregorio; Del Ventisette, Chiara

2016-04-01

A new horizontal crustal velocity field of Alpine Mediterranean area was determined by continuous long time series (6.5 years) of 113 Global Navigation Satellite System (GNSS) permanent stations. The processing was performed using state-of-the-art absolute antenna phase center correction model and recomputed precise IGS orbits available since April 2014. Moreover, a new more accurate tropospheric mapping function for geodetic applications was adopted. Results provide a new detailed map of the kinematics throughout the entire study area. This area is characterized by a complex tectonic setting driven by the interaction of Eurasian and African plates. The eastern Alps, Corsica, Sardinia and the Tyrrhenian Sea (which is covered only by interpolation data) show small velocity residuals with respect to the Eurasian plate. The whole Apennines axis discriminates two different velocity patterns, the Adriatic and the Tyrrhenian area. The area around Messina Strait, which separates peninsular Italy and Sicily, represents a poorly understood region. Results identify an important boundary zone between two different domains, Calabria and Sicily, which are characterized by different crustal motions. The northeastern part of Sicily and Calabria move like Adriatic area, whilst the rest of Sicily, Malta and Lampedusa are dominated by African motion.

On the Assessment of Global Terrestrial Reference Frame Temporal Variations

Science.gov (United States)

Ampatzidis, Dimitrios; Koenig, Rolf; Zhu, Shengyuan

2015-04-01

Global Terrestrial Reference Frames (GTRFs) as the International Terrestrial Reference Frame (ITRF) provide reliable 4-D position information (3-D coordinates and their evolution through time). The given 3-D velocities play a significant role in precise position acquisition and are estimated from long term coordinate time series from the space-geodetic techniques DORIS, GNSS, SLR, and VLBI. GTRFs temporal evolution is directly connected with their internal stability: The more intense and inhomogeneous velocity field, the less stable TRF is derived. The assessment of the quality of the GTRF is mainly realized by comparing it to each individual technique's reference frame. E.g the comparison of GTRFs to SLR-only based TRF gives the sense of the ITRF stability with respect to the Geocenter and scale and their associated rates respectively. In addition, the comparison of ITRF to the VLBI-only based TRF can be used for the scale validation. However, till now there is not any specified methodology for the total assessment (in terms of origin, orientation and scale respectively) of the temporal evolution and GTRFs associated accuracy. We present a new alternative diagnostic tool for the assessment of GTRFs temporal evolution based on the well-known time-dependent Helmert type transformation formula (three shifts, three rotations and scale rates respectively). The advantage of the new methodology relies on the fact that it uses the full velocity field of the TRF and therefore all points not just the ones common to different techniques. It also examines simultaneously rates of origin, orientation and scale. The methodology is presented and implemented to the two existing GTRFs on the market (ITRF and DTRF which is computed from DGFI) , the results are discussed. The results also allow to compare directly each GTRF dynamic behavior. Furthermore, the correlations of the estimated parameters can also provide useful information to the proposed GTRFs assessment scheme.

The NASA Goddard Group's Source Monitoring Database and Program

Science.gov (United States)

Gipson, John; Le Bail, Karine; Ma, Chopo

2014-12-01

Beginning in 2003, the Goddard VLBI group developed a program to purposefully monitor when sources were observed and to increase the observations of ``under-observed'' sources. The heart of the program consists of a MySQL database that keeps track of, on a session-by-session basis: the number of observations that are scheduled for a source, the number of observations that are successfully correlated, and the number of observations that are used in a session. In addition, there is a table that contains the target number of successful sessions over the last twelve months. Initially this table just contained two categories. Sources in the geodetic catalog had a target of 12 sessions/year; the remaining ICRF-1 defining sources had a target of two sessions/year. All other sources did not have a specific target. As the program evolved, different kinds of sources with different observing targets were added. During the scheduling process, the scheduler has the option of automatically selecting N sources which have not met their target. We discuss the history and present some results of this successful program.

Geodetic slip solutions for the Mw=7.4 Champerico (Guatemala) subduction earthquake of November 7 2012

Science.gov (United States)

Ellis, Andria; DeMets, Charles; Briole, Pierre; Molina, Enrique; Flores, Omar; Rivera, Jeffrey; Lasserre, Cécile; Lyon-Caen, Hélène; Lord, Neal

2014-05-01

As the first large subduction thrust earthquake off the coast of western Guatemala in the past 50 years, the 7 November 2012 Mw=7.4 earthquake offers the first opportunity for a geodetic study of coseismic and postseismic behavior for a segment of the Middle America trench where frictional coupling makes a transition from weak coupling off the coast of El Salvador to strong coupling in southern Mexico. Processing of continuous GPS measurements at 19 stations in Guatemala, El Salvador, and southern Mexico, and at 7 campaign points in Guatemala defines a highly consistent pattern of coseismic offsets during the earthquake, ranging from 47±5 mm of SW movement just inland from the earthquake epicenter to a few mm at sites located in northern Guatemala. Inversions of these offsets to find their best-fitting fault-slip solution in an elastic half space give a geodetic earthquake moment ranging between 0.75 and 1.1 x 1020 Nm, slightly smaller than the seismic estimates that range between 1.2 and 1.45 x 1020 Nm. Slip inversion using a constant slip model, assuming 293° and 29° for the fault azimuth and dip angle, indicates a nearly reverse slip of 2.8 m (rake 78°) on a fault plane 42 km-long and 20 km-wide, centered at 26 km depth. A variable slip inversion indicates that slip concentrated above depths of 40 km may have extended updip to the trench and reached a maximum of only 0.8 m, less than one-sixth the maximum slip indicated by a recent slip solution (5.3 m) obtained from waveform inversion of seismological data. Detailed model comparisons will be discussed. Transient postseismic displacements have been recorded at the nearby continuous GPS sites with amplitudes reaching 20-25 mm at some stations. The duration of the phenomenon is short: using an exponential-decay model, the estimated decay time is 90 ± 10 days. This postseismic signal is consistent with afterslip along a significantly broader area (+50%) of the subduction interface than ruptured coseismically

Research Article. Geodesic equations and their numerical solutions in geodetic and Cartesian coordinates on an oblate spheroid

Directory of Open Access Journals (Sweden)

Panou G.

2017-02-01

Full Text Available The direct geodesic problem on an oblate spheroid is described as an initial value problem and is solved numerically using both geodetic and Cartesian coordinates. The geodesic equations are formulated by means of the theory of differential geometry. The initial value problem under consideration is reduced to a system of first-order ordinary differential equations, which is solved using a numerical method. The solution provides the coordinates and the azimuths at any point along the geodesic. The Clairaut constant is not used for the solution but it is computed, allowing to check the precision of the method. An extensive data set of geodesics is used, in order to evaluate the performance of the method in each coordinate system. The results for the direct geodesic problem are validated by comparison to Karney’s method. We conclude that a complete, stable, precise, accurate and fast solution of the problem in Cartesian coordinates is accomplished.

Lunar Topography: Results from the Lunar Orbiter Laser Altimeter

Science.gov (United States)

Neumann, Gregory; Smith, David E.; Zuber, Maria T.; Mazarico, Erwan

2012-01-01

The Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter (LRO) has been operating nearly continuously since July 2009, accumulating over 6 billion measurements from more than 2 billion in-orbit laser shots. LRO's near-polar orbit results in very high data density in the immediate vicinity of the lunar poles, with full coverage at the equator from more than 12000 orbital tracks averaging less than 1 km in spacing at the equator. LRO has obtained a global geodetic model of the lunar topography with 50-meter horizontal and 1-m radial accuracy in a lunar center-of-mass coordinate system, with profiles of topography at 20-m horizontal resolution, and 0.1-m vertical precision. LOLA also provides measurements of reflectivity and surface roughness down to its 5-m laser spot size. With these data LOLA has measured the shape of all lunar craters 20 km and larger. In the proposed extended mission commencing late in 2012, LOLA will concentrate observations in the Southern Hemisphere, improving the density of the polar coverage to nearly 10-m pixel resolution and accuracy to better than 20 m total position error. Uses for these data include mission planning and targeting, illumination studies, geodetic control of images, as well as lunar geology and geophysics. Further improvements in geodetic accuracy are anticipated from the use of re ned gravity fields after the successful completion of the Gravity Recovery and Interior Laboratory (GRAIL) mission in 2012.

SHARP - V. Modelling gravitationally-lensed radio arcs imaged with global VLBI observations

Science.gov (United States)

Spingola, C.; McKean, J. P.; Auger, M. W.; Fassnacht, C. D.; Koopmans, L. V. E.; Lagattuta, D. J.; Vegetti, S.

2018-05-01

We present milliarcsecond (mas) angular resolution observations of the gravitationally lensed radio source MG J0751+2716 (at z = 3.2) obtained with global Very Long Baseline Interferometry (VLBI) at 1.65 GHz. The background object is highly resolved in the tangential and radial directions, showing evidence of both compact and extended structure across several gravitational arcs that are 200 to 600 mas in size. By identifying compact sub-components in the multiple images, we constrain the mass distribution of the foreground z = 0.35 gravitational lens using analytic models for the main deflector [power-law elliptical mass model; ρ(r)∝r-γ, where γ = 2 corresponds to isothermal] and for the members of the galaxy group. Moreover, our mass models with and without the group find an inner mass-density slope steeper than isothermal for the main lensing galaxy, with γ1 = 2.08 ± 0.02 and γ2 = 2.16 ± 0.02 at the 4.2σ level and 6.8σ level, respectively, at the Einstein radius (b1 = 0.4025 ± 0.0008 and b2 = 0.307 ± 0.002 arcsec, respectively). We find randomly distributed image position residuals of about 3 mas, which are much larger that the measurement errors (40 μas on average). This suggests that at the mas level, the assumption of a smooth mass distribution fails, requiring additional structure in the model. However, given the environment of the lensing galaxy, it is not clear whether this extra mass is in the form of sub-haloes within the lens or along the line of sight, or from a more complex halo for the galaxy group.

Gravity Probe B: final results of a space experiment to test general relativity.

Science.gov (United States)

Everitt, C W F; DeBra, D B; Parkinson, B W; Turneaure, J P; Conklin, J W; Heifetz, M I; Keiser, G M; Silbergleit, A S; Holmes, T; Kolodziejczak, J; Al-Meshari, M; Mester, J C; Muhlfelder, B; Solomonik, V G; Stahl, K; Worden, P W; Bencze, W; Buchman, S; Clarke, B; Al-Jadaan, A; Al-Jibreen, H; Li, J; Lipa, J A; Lockhart, J M; Al-Suwaidan, B; Taber, M; Wang, S

2011-06-03

Gravity Probe B, launched 20 April 2004, is a space experiment testing two fundamental predictions of Einstein's theory of general relativity (GR), the geodetic and frame-dragging effects, by means of cryogenic gyroscopes in Earth orbit. Data collection started 28 August 2004 and ended 14 August 2005. Analysis of the data from all four gyroscopes results in a geodetic drift rate of -6601.8±18.3  mas/yr and a frame-dragging drift rate of -37.2±7.2  mas/yr, to be compared with the GR predictions of -6606.1  mas/yr and -39.2  mas/yr, respectively ("mas" is milliarcsecond; 1  mas=4.848×10(-9)  rad).

Geodezija od Mesopotamije do Globalnog geodetskog opažačkog sistema : Geodesy from Mesopotamie to Global Geodetic Observing System

Directory of Open Access Journals (Sweden)

Medžida Mulić

2015-12-01

Full Text Available Tokom šest milenijuma postojanja civilizacije na Zemlji, geodetske tehnike su doživjele teško sagledive promjene. Definicija i uloga geodezije su se mijenjale u skladu s tim promijenila. Geodezija (viša je evoluirala od svoje originalne klasične definicije da „proučava kretanja nebeskih tijela, oblik i dimenzije Zemlje“ u „znanost koja osim naprijed rečenog, proučava njene promjene i kompleksne dinamičke procese, koji djeluju unutar Zemlje, na njenoj površini i iznad njene površine, kao i u svemiru koji je okružuje. Rad predstavlja detaljan pregled geodetskih tehnika, instrumenata, katastra i kartografije kod starih civilizacija: Mesopotamije, starog Egipta, antičke Grčke, starog Rima, pa sve do Evropljana, između 17. stoljeća do modernog doba. Posebno su opisani geodetski radovi u Bosni i Hercegovini, od doba osmanlija, austro-ugarskog premjera, do savremenih dostignuća u polju premjera i primjene satelitskih modernih tehnika. Globalni geodetski opažački sistem-GGOS, glavna komponenta Internacionalne asocijacije za geodeziju, kao projekat za buduće generacije geodeta, opisan je na kraju. : During the six millennia of the existence of the civilization on the Earth, surveying techniques have been experienced difficult foreseeable changes. The definition and role of geodesy have been changing accordingly. Geodesy has evolved from its original classic definition that "studying the movements of celestial bodies, the shape and dimensions of the Earth" in the "science which, beside it noted above, studies its changes and complex dynamic processes that ongoing inside the Earth, on the surface, above its surfaces, and evironment. The paper is overview of the geodetic techniques and the surveying instruments, cadastre and cartography in the ancien civilizations: Mesopotamia, ancient Egypt, antic Greece, ancient Rome, to the Europeans, from the 17th century to modern times. A detailed description devoted to surveying and geodetic

Space-geodetic Constraints on GIA Models with 3D Viscosity

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Van Der Wal, W.; Xu, Z.

2012-12-01

Models for Glacial Isostatic Adjustment (GIA) are an important correction to observations of mass change in the polar regions. Inputs for GIA models include past ice thickness and deformation parameters of the Earth's mantle, both of which are imperfectly known. Here we focus on the latter by investigating GIA models with 3D viscosity and composite (linear and non-linear) flow laws. It was found recently that GIA models with a composite flow law result in a better fit to historic sea level data, but they predict too low present-day uplift rates and gravity rates. Here GIA models are fit to space-geodetic constraints in Fennoscandia and North America. The preferred models are used to calculate the magnitude of the GIA correction on mass change estimates in Greenland and Antarctica. The observations used are GRACE Release 4 solutions from CSR and GFZ and published GPS solutions for North America and Fennoscandia, as well as historic sea level data. The GIA simulations are performed with a finite element model of a spherical, self-gravitating, incompressible Earth with 2x2 degree elements. Parameters in the flow laws are taken from seismology, heatflow measurements and experimental constraints and the ice loading history is prescribed by ICE-5G. It was found that GRACE and GPS derived uplift rates agree at the level of 1 mm/year in North America and at a level of 0.5 mm/year in Fennoscandia, the difference between the two regions being due to larger GPS errors and under sampling in North America. It can be concluded that both GPS and GRACE see the same process and the effects of filtering, noise and non-GIA processes such as land hydrology are likely to be small. Two GIA models are found that bring present-day uplift rate close to observed values in North America and Fennoscandia. These models result in a GIA correction of -17 Gt/year and -26 Gt/year on Greenland mass balance estimates from GRACE.

Learned Compact Local Feature Descriptor for Tls-Based Geodetic Monitoring of Natural Outdoor Scenes

Science.gov (United States)

Gojcic, Z.; Zhou, C.; Wieser, A.

2018-05-01

The advantages of terrestrial laser scanning (TLS) for geodetic monitoring of man-made and natural objects are not yet fully exploited. Herein we address one of the open challenges by proposing feature-based methods for identification of corresponding points in point clouds of two or more epochs. We propose a learned compact feature descriptor tailored for point clouds of natural outdoor scenes obtained using TLS. We evaluate our method both on a benchmark data set and on a specially acquired outdoor dataset resembling a simplified monitoring scenario where we successfully estimate 3D displacement vectors of a rock that has been displaced between the scans. We show that the proposed descriptor has the capacity to generalize to unseen data and achieves state-of-the-art performance while being time efficient at the matching step due the low dimension.

Geodetic constraints on continental rifting along the Red Sea

Science.gov (United States)

Reilinger, R.; McClusky, S.; Arrajehi, A.; Mahmoud, S.; Rayan, A.; Ghebreab, W.; Ogubazghi, G.; Al-Aydrus, A.

2006-12-01

We are using the Global Positioning System (GPS) to monitor and quantify patterns and rates of tectonic and magmatic deformation associated with active rifting of the continental lithosphere and the transition to sea floor spreading in the Red Sea. Broad-scale motions of the Nubian and Arabian plates indicate coherent plate motion with internal deformation below the current resolution of our measurements (~ 1-2 mm/yr). The GPS-determined Euler vector for Arabia-Nubia is indistinguishable from the geologic Euler vector determined from marine magnetic anomalies, and Arabia-Eurasia relative motion from GPS is equal within uncertainties to relative motion determined from plate reconstructions, suggesting that Arabia plate motion has remained constant (±10%) during at least the past ~10 Ma. The approximate agreement between broad-scale GPS rates of extension (i.e., determined from relative plate motions) and those determined from magnetic anomalies along the Red Sea rift implies that spreading in the central Red Sea is primarily confined to the central rift (±10-20%). Extension appears to be more broadly distributed in the N Red Sea and Gulf of Suez where comparisons with geologic data also indicate a relatively recent (between 500 and 125 kyr BP) change in the motion of the Sinai block that is distinct from both Nubia and Arabia. In the southern Red Sea, GPS results are beginning to define the motion of the "Danakil micro-plate". We investigate and report on a model involving CCW rotation of the Danakil micro-plate relative to Nubia and magmatic inflation below the Afar Triple Junction that is consistent with available geodetic constraints. Running the model back in time suggests that the Danakil micro-plate has been an integral part of rifting/triple junction processes throughout the history of separation of the Arabian and Nubian plates. On the scale of Nubia-Arabia-Eurasia plate interactions, we show that new area formed at spreading centers roughly equals that

Analysis of ILRS Site Ties

Science.gov (United States)

Husson, V. S.; Long, J. L.; Pearlman, M.

2001-12-01

By the end of 2000, 94% of ILRS stations had completed station and site information forms (i.e. site logs). These forms contain six types of information. These six categories include site identifiers, contact information, approximate coordinates, system configuration history, system ranging capabilities, and local survey ties. The ILRS Central Bureau, in conjunction with the ILRS Networks and Engineering Working Group, has developed procedures to quality control site log contents. Part of this verification entails data integrity checks of local site ties and is the primary focus of this paper. Local survey ties are critical to the combination of space geodetic network coordinate solutions (i.e. GPS, SLR, VLBI, DORIS) of the International Terrestrial Reference Frame (ITRF). Approximately 90% of active SLR sites are collocated with at least one other space geodetic technique. The process used to verify these SLR ties, at collocated sites, is identical to the approach used in ITRF2000. Local vectors (X, Y, Z) from each ILRS site log are differenced from its corresponding ITRF2000 position vectors (i.e. no transformations). These X, Y, and Z deltas are converted into North, East, and Up. Any deltas, in any component, larger than 5 millimeter is flagged for investigation. In the absence of ITRF2000 SLR positions, CSR positions were used. To further enhance this comparison and to fill gaps in information, local ties contained in site logs from the other space geodetic services (i.e. IGS, IVS, IDS) were used in addition to ITRF2000 ties. Case studies of two collocated sites (McDonald/Ft. Davis and Hartebeeshtoek) will be explored in-depth. Recommendations on how local site surveys should be conducted and how this information should be managed will also be presented.

NASA's Next Generation Space Geodesy Program

Science.gov (United States)

Merkowitz, S. M.; Desai, S. D.; Gross, R. S.; Hillard, L. M.; Lemoine, F. G.; Long, J. L.; Ma, C.; McGarry, J. F.; Murphy, D.; Noll, C. E.;

Crustal Deformation across the Jericho Valley Section of the Dead Sea Fault as Resolved by Detailed Field and Geodetic Observations

Science.gov (United States)

Hamiel, Yariv; Piatibratova, Oksana; Mizrahi, Yaakov; Nahmias, Yoav; Sagy, Amir

2018-04-01

Detailed field and geodetic observations of crustal deformation across the Jericho Fault section of the Dead Sea Fault are presented. New field observations reveal several slip episodes that rupture the surface, consist with strike slip and extensional deformation along a fault zone width of about 200 m. Using dense Global Positioning System measurements, we obtain the velocities of new stations across the fault. We find that this section is locked for strike-slip motion with a locking depth of 16.6 ± 7.8 km and a slip rate of 4.8 ± 0.7 mm/year. The Global Positioning System measurements also indicate asymmetrical extension at shallow depths of the Jericho Fault section, between 0.3 and 3 km. Finally, our results suggest the vast majority of the sinistral slip along the Dead Sea Fault in southern Jorden Valley is accommodated by the Jericho Fault section.

The local ionospheric modeling by integration ground GPS observations and satellite altimetry data

Directory of Open Access Journals (Sweden)

Mohammad Ali Sharifi

2017-01-01

Full Text Available The free electrons in the ionosphere have a strong impact on the propagation of radio waves. When the signals pass through the ionosphere, both their group and phase velocity are disturbed. Several space geodetic techniques such as satellite altimetry, low Earth orbit (LEO satellite and very long baseline interferometry (VLBI can be used to model the total electron content. At present, the classical input data for development of ionospheric models are based on dual-frequency GPS observations, However, a major problem with this observation type is the nonuniform distribution of the terrestrial GPS reference stations with large gaps notably over the sea surface and ocean where only some single stations are located on islands, leading to lower the precision of the model over these areas. In these regions the dual-frequency satellite altimeters provide precise information about the parameters of the ionosphere. Combination of GPS and satellite altimetry observations allows making best use of the advantages of their different spatial and temporal distributions. In this study, the local ionosphere modeling was done by the combination of space geodetic observations using spherical Slepian function. The combination of the data from ground GPS observations over the western part of the USA and the altimetry mission Jason-2 was performed on the normal equation level in the least-square procedure and a least-square variance component estimation (LS-VCE was applied to take into account the different accuracy levels of the observations. The integrated ionosphere model is more accurate and more reliable than the results derived from the ground GPS observations over the oceans.

Improvements in Space Geodesy Data Discovery at the CDDIS

Science.gov (United States)

Noll, C.; Pollack, N.; Michael, P.

2011-01-01

The Crustal Dynamics Data Information System (CDDIS) supports data archiving and distribution activities for the space geodesy and geodynamics community. The main objectives of the system are to store space geodesy and geodynamics related data products in a central data bank. to maintain information about the archival of these data, and to disseminate these data and information in a timely manner to a global scientific research community. The archive consists of GNSS, laser ranging, VLBI, and DORIS data sets and products derived from these data. The CDDIS is one of NASA's Earth Observing System Data and Information System (EOSDIS) distributed data centers; EOSDIS data centers serve a diverse user community and arc tasked to provide facilities to search and access science data and products. Several activities are currently under development at the CDDIS to aid users in data discovery, both within the current community and beyond. The CDDIS is cooperating in the development of Geodetic Seamless Archive Centers (GSAC) with colleagues at UNAVCO and SIO. TIle activity will provide web services to facilitate data discovery within and across participating archives. In addition, the CDDIS is currently implementing modifications to the metadata extracted from incoming data and product files pushed to its archive. These enhancements will permit information about COOlS archive holdings to be made available through other data portals such as Earth Observing System (EOS) Clearinghouse (ECHO) and integration into the Global Geodetic Observing System (GGOS) portal.

CDDIS: NASA's Archive of Space Geodesy Data and Products Supporting GGOS

Science.gov (United States)

Noll, Carey; Michael, Patrick

2016-01-01

The Crustal Dynamics Data Information System (CDDIS) supports data archiving and distribution activities for the space geodesy and geodynamics community. The main objectives of the system are to store space geodesy and geodynamics related data and products in a central archive, to maintain information about the archival of these data,to disseminate these data and information in a timely manner to a global scientific research community, and provide user based tools for the exploration and use of the archive. The CDDIS data system and its archive is a key component in several of the geometric services within the International Association of Geodesy (IAG) and its observing systemthe Global Geodetic Observing System (GGOS), including the IGS, the International DORIS Service (IDS), the International Laser Ranging Service (ILRS), the International VLBI Service for Geodesy and Astrometry (IVS), and the International Earth Rotation and Reference Systems Service (IERS). The CDDIS provides on-line access to over 17 Tbytes of dataand derived products in support of the IAG services and GGOS. The systems archive continues to grow and improve as new activities are supported and enhancements are implemented. Recently, the CDDIS has established a real-time streaming capability for GNSS data and products. Furthermore, enhancements to metadata describing the contents ofthe archive have been developed to facilitate data discovery. This poster will provide a review of the improvements in the system infrastructure that CDDIS has made over the past year for the geodetic community and describe future plans for the system.

Research Article. A new gravity laboratory in Ny-Ålesund, Svalbard

Directory of Open Access Journals (Sweden)

Breili K.

2017-02-01

Full Text Available The Norwegian Mapping Authority (NMA has recently established a new gravity laboratory in Ny-Ålesund at Svalbard, Norway. The laboratory consists of three independent pillars and is part of the geodetic core station that is presently under construction at Brandal, approximately 1.5 km north of NMA’s old station. In anticipation of future use of the new gravity laboratory, we present benchmark gravity values, gravity gradients, and final coordinates of all new pillars. Test measurements indicate a higher noise level at Brandal compared to the old station. The increased noise level is attributed to higher sensitivity to wind.We have also investigated possible consequences of moving to Brandal when it comes to the gravitational signal of present-day ice mass changes and ocean tide loading. Plausible models representing ice mass changes at the Svalbard archipelago indicate that the gravitational signal at Brandal may differ from that at the old site with a size detectable with modern gravimeters. Users of gravity data from Ny-Ålesund should, therefore, be cautious if future observations from the new observatory are used to extend the existing gravity record. Due to its lower elevation, Brandal is significantly less sensitive to gravitational ocean tide loading. In the future, Brandal will be the prime site for gravimetry in Ny-Ålesund. This ensures gravity measurements collocated with space geodetic techniques like VLBI, SLR, and GNSS.

156th Symposium of the International Astronomical Union

CERN Document Server

Kołaczek, Barbara

1993-01-01

In this review talk, I would like to report on the proper motion analysis, which has been recently carried out together with M. Soma and M. Yoshizawa: There has been a persistent demand in astronomy for accurate stellar positions and proper motions, which are represented by an inertial reference system constructed on the basis of a set of consistent astronomical constants. In the reference system the precessional constant plays a primary role. In a series of papers Fricke (1967a,b, 1977a,b) has deter­ mined the luni-solar precessional correction to Newcomb's value and the fictitious motion of the equinox, which have been adopted in the "IAU (1976) System of Astronomical Con­ stants". Based on the precessional correction and the equinoctial motion thus established, the fundamental reference system, the FK5 system (Fricke et al. 1988) for positions and proper motions, has been constructed. However, for several years geodetic VLBI (McCarthy & Luzum 1991) and LLR (Williams et at. 1991) observations have bee...

Analysis of the GPS Observations of the Site Survey at Sheshan 25-m Radio Telescope in August 2008

Science.gov (United States)

Liu, L.; Cheng, Z. Y.; Li, J. L.

2010-01-01

The processing of the GPS observations of the site survey at Sheshan 25-m radio telescope in August 2008 is reported. Because each session in this survey is only about six hours, not allowing the subdaily high frequency variations in the station coordinates to be reasonably smoothed, and because there are serious cycle slips in the observations and a large volume of data would be rejected during the software automatic adjustment of slips, the ordinary solution settings of GAMIT needed to be adjusted by loosening the constraints in the a priori coordinates to 10 m, adopting the "quick" mode in the solution iteration, and combining Cview manual operation with GAMIT automatic fixing of cycle slips. The resulting coordinates of the local control polygon in ITRF2005 are then compared with conventional geodetic results. Due to large rotations and translations in the two sets of coordinates (geocentric versus quasi-topocentric), the seven transformation parameters cannot be solved for directly. With various trial solutions it is shown that with a partial pre-removal of the large parameters, high precision transformation parameters can be obtained with post-fit residuals at the millimeter level. This analysis is necessary to prepare the follow-on site and transformation survey of the VLBI and SLR telescopes at Sheshan

Space geodetic observations of repeating slow slip events beneath the Bonin Islands

Science.gov (United States)

Arisa, Deasy; Heki, Kosuke

2017-09-01

The Pacific Plate subducts beneath the Philippine Sea Plate along the Izu-Bonin Trench. We investigated crustal movements at the Bonin Islands, using Global Navigation Satellite System and geodetic Very Long Baseline Interferometry data to reveal how the two plates converge in this subduction zone. These islands are located ∼100 km from the trench, just at the middle between the volcanic arc and the trench, making these islands suitable for detecting signatures of episodic deformation such as slow slip events (SSEs). During 2007-2016, we found five SSEs repeating quasi-periodically with similar displacement patterns. In estimating their fault parameters, we assumed that the fault lies on the prescribed plate boundary, and optimized the size, shape and position of the fault and dislocation vectors. Average fault slip was ∼5 cm, and the average moment magnitude was ∼6.9. We also found one SSE occurred in 2008 updip of the repeating SSE in response to an M6 class interplate earthquake. In spite of the frequent occurrence of SSEs, there is no evidence for long-term strain accumulation in the Bonin Islands that may lead to future megathrust earthquakes. Plate convergence in Mariana-type subduction zones may occur, to a large extent, episodically as repeating SSEs.

Geodetic Finite-Fault-based Earthquake Early Warning Performance for Great Earthquakes Worldwide

Science.gov (United States)

Ruhl, C. J.; Melgar, D.; Grapenthin, R.; Allen, R. M.

2017-12-01

GNSS-based earthquake early warning (EEW) algorithms estimate fault-finiteness and unsaturated moment magnitude for the largest, most damaging earthquakes. Because large events are infrequent, algorithms are not regularly exercised and insufficiently tested on few available datasets. The Geodetic Alarm System (G-larmS) is a GNSS-based finite-fault algorithm developed as part of the ShakeAlert EEW system in the western US. Performance evaluations using synthetic earthquakes offshore Cascadia showed that G-larmS satisfactorily recovers magnitude and fault length, providing useful alerts 30-40 s after origin time and timely warnings of ground motion for onshore urban areas. An end-to-end test of the ShakeAlert system demonstrated the need for GNSS data to accurately estimate ground motions in real-time. We replay real data from several subduction-zone earthquakes worldwide to demonstrate the value of GNSS-based EEW for the largest, most damaging events. We compare predicted ground acceleration (PGA) from first-alert-solutions with those recorded in major urban areas. In addition, where applicable, we compare observed tsunami heights to those predicted from the G-larmS solutions. We show that finite-fault inversion based on GNSS-data is essential to achieving the goals of EEW.

New insights into the magma chamber activity under Mauna Loa inferred from SBAS-InSAR and geodetic inversion modelling

Science.gov (United States)

Varugu, B. K.; Amelung, F.

2017-12-01

Mauna Loa volcano, located on the Big Island, Hawaii, is the largest volcano on the earth and historically been one of the most active volcanoes on the earth. Since its last eruption in 1984, there was a decrease in the magmatic activity, yet episodic inflations with increased seismicity sparks interests in the scientific community and there is strong need to monitor the volcano with growing infrastructure close to the flanks of the volcano. Geodetic modelling of the previous inflations illustrate that the magma activity is due to inflation of hydraulically connected dike and magma chamber located from 4-8km beneath the summit (Amelung et al. 2007). Most of the seismicity observed on Mauna Loa is due to the movement along a decollement fault situated at the base of the volcano. Magma inflation under Mauna Loa has started again during the last quarter of 2013 and is continuing still with an increased seismicity. In this study, we used 140 images form COSMO SkyMED between 2013-2017 to derive and model the ground deformation. We carried out time series InSAR analysis using Small Baseline (SB) approach. While the deformation pattern seems similar in many ways to the previous inflation periods, geodetic modelling for inversion of source parameters indicate a significant propagation of the dike ( 1 km) into the South West Rift Zone(SWRZ) and a decreased depth of the dike top from summit, compared to the previous inflations. Such propagation needs to be studied further in view of the steep slope of SWRZ. In understanding the dynamics of this propagating dike, we also observed an increased seismic activity since 2014 in the vicinity of the modelled dike. Here in this study we attempt to characterize the stresses induced by the propagating dike and seaward slipping movement along the basal decollement, to explain the increased seismicity using a finite element model.

Global change and the measurement of absolute sea-level

Science.gov (United States)

Diamante, John M.; Pyle, Thomas E.; Carter, William E.; Scherer, Wolfgang

To quantify properly the long-term response of sea-level to climate change, land motions must be separated from the apparent or relative sea-level change recorded by conventional tide/sea-level gauges. Here we present a concept for global measurement of the true or “absolute” sea-level change, which combines recent advances in space-based geodetic techniques with plans for a global sea-level network under the World Climate Research Programme (WCRP). Data from initial feasibility tests show that land motion, due to global (plate tectonic), regional (glacial rebound), or local (fluid withdrawal) effects, can probably be measured to ±1cm (on a single measurement basis) by an innovative combination of Very Long Baseline Interferometry (VLBI) and Global Positioning System (GPS) tevhniques. By making repeated observations of position at a number of tide gauges using portable, economical GPS receivers in a differential mode relative to the fewer, more stable, but more expensive VLBI observatories, it will be possible to subtract land motion from the relative sea-level signal. Decadal to century scale trends at the 1-2mm y -1 level will be resolvable in the sea-level and vertical land motion time series within about a decade. Detection of subsidence or uplift at specific gauges will allow correction for land motion or deletion of bad data when computing regional or global, i.e. eustatic, sea-level changes. In addition to their applications in oceanography and climate studies, such data will test models by Peltier and other that relate mantle viscosity and deglaciation history to present rates of crustal subsidence or uplift. If the predicted crustal motions are confirmed, we can also have more confidence in the use of historical tide/sea-level gauge records in retrospective studies of sea-level change related to climate variability on decadal or longer time scales. It is concluded that as few as one-third (about 100) of the total number of tide/sea-level gauges (250

Development of AN Open-Source Automatic Deformation Monitoring System for Geodetical and Geotechnical Measurements

Science.gov (United States)

Engel, P.; Schweimler, B.

2016-04-01

The deformation monitoring of structures and buildings is an important task field of modern engineering surveying, ensuring the standing and reliability of supervised objects over a long period. Several commercial hardware and software solutions for the realization of such monitoring measurements are available on the market. In addition to them, a research team at the Neubrandenburg University of Applied Sciences (NUAS) is actively developing a software package for monitoring purposes in geodesy and geotechnics, which is distributed under an open source licence and free of charge. The task of managing an open source project is well-known in computer science, but it is fairly new in a geodetic context. This paper contributes to that issue by detailing applications, frameworks, and interfaces for the design and implementation of open hardware and software solutions for sensor control, sensor networks, and data management in automatic deformation monitoring. It will be discussed how the development effort of networked applications can be reduced by using free programming tools, cloud computing technologies, and rapid prototyping methods.

Twin-Telescope Wettzell (TTW)

Science.gov (United States)

Hase, H.; Dassing, R.; Kronschnabl, G.; Schlüter, W.; Schwarz, W.; Lauber, P.; Kilger, R.

2007-07-01

delay measurements, Mark 5 Memo #043, MIT Haystack Observatory. Rogers, A.E.E. (2006). Some thoughts on the calibration of broadband geodetic VLBI, Mark 5 Memo #044, MIT Haystack Observatory. Rothacher M. (2006). GGOS: the IAG contribution to Earth observation, IGS Workshop 2006 "Perspectives and Visions for 2010 and beyond", May 8-12, Darmstadt, Germany Weinreb, S., Mandi, H. (2006). Pattern and Noise Tests of ETS-Lindgren 3164-05 Quadridge/Vivaldi Antenna, California Institute of Technology. Weinreb, S. (2007). Broadband feeds, E-mail, January. Welch, Wm. J. (2005). The Allen Telescope Array, URSI, UC Berkeley, January.

Integrating Geological and Geodetic Surveying Techniques for Landslide Deformation Monitoring: Istanbul Case

Science.gov (United States)

Menteşe, E. Y.; Kilic, O.; BAS, M.; Tarih, A.; Duran, K.; Gumus, S.; Yapar, E. R.; Karasu, M. E.; Mehmetoğlu, H.; Karaman, A.; Edi˙ger, V.; Kosma, R. C.; Ozalaybey, S.; Zor, E.; Arpat, E.; Polat, F.; Dogan, U.; Cakir, Z.; Erkan, B.

2017-12-01

There are several methods that can be utilized for describing the landslide mechanisms. While some of them are commonly used, there are relatively new methods that have been proven to be useful. Obviously, each method has its own limitations and thus integrated use of these methods contributes to obtaining a realistic landslide model. The slopes of Küçükçekmece and Büyükçekmece Lagoons located at the Marmara Sea coast of İstanbul, Turkey, are among most specific examples of complex type landslides. The landslides in the area started developing at low sea level, and appears to ceased or at least slowed down to be at minimum after the sea level rise, as oppose to the still-active landslides that continue to cause damage especially in the valley slopes above the recent sea level between the two lagoons. To clarify the characteristics of these slope movements and classify them in most accurate way, Directorate of Earthquake and Ground Research of Istanbul Metropolitan Municipality launched a project in cooperation with Marmara Research Center of The Scientific and Technological Research Council of Turkey (TÜBİTAK). The project benefits the utility of the techniques of different disciplines such as geology, geophysics, geomorphology, hydrogeology, geotechnics, geodesy, remote sensing and meteorology. Specifically, this study focuses on two main axes of these techniques, namely: geological and geodetic. The reason for selecting these disciplines is because of their efficiency and power to understand the landslide mechanism in the area. Main approaches used in these studies are comprised of geological drills, inclinometer measurements, GPS surveys and SAR (both satellite and ground based) techniques. Integration of the results gathered from these techniques led the project team to comprehend critical aspects of landslide phenomenon in the area and produce precise landslide hazard maps that are basic instruments for a resilient urban development.

Geodetic antenna calibration test in the Antarctic environment

Science.gov (United States)

Grejner-Brzezinska, A.; Vazquez, E.; Hothem, L.

2006-01-01

TransAntarctic Mountain DEFormation (TAMDEF) Monitoring Network is the NSF-sponsored OSU and USGS project, aimed at measuring crustal motion in the Transantarctic Mountains of Victoria Land using GPS carrier phase measurements. Station monumentation, antenna mounts, antenna types, and data processing strategies were optimized to achieve mm-level estimates for the rates of motion. These data contributes also to regional Antarctic frame definition. Significant amount of data collected over several years allow the investigation of unique aspects of GPS geodesy in Antarctica, to determine how the error spectrum compares to the mid-latitude regions, and to identify the optimum measurement and data processing schemes for Antarctic conditions, in order to test the predicted rates of motion (mm-level w.r.t. time). The data collection for the TAMDEF project was initiated in 1996. The primary antenna used has been the Ashtech L1/L2 Dorne Margolin (D/M) choke ring. A few occupations involved the use of a Trimble D/M choke ring. The data were processed using the antenna calibration data available from the National Geodetic Survey (NGS). The recent developments in new antenna designs that are lighter in weight and lower in cost are being considered as a possible alternative to the bulkier and more expensive D/M choke ring design. In November 2003, in situ testing of three alternative models of L1/L2 antennas was conducted at a site located in the vicinity of McMurdo Station, Antarctica (S77.87, E166.56). The antenna models used in this test were: Ashtech D/M choke ring, Trimble D/M choke ring, Trimble Zephyr, and the NovAtel GPS-702. Two stations, spaced within 30 meters, were used in the test. Both had the characteristics similar to the stations of the TAMDEF network, i.e., the UNAVCO fixed-height, force-centered level mounts with a constant antenna offset were used, ensuring extreme stability of the antenna/ mount/pin set up. During each of the four 3-day test data collection

Modeling and Analysis of Integrated Bathymetric and Geodetic Data for Inventory Surveys of Mining Water Reservoirs

Science.gov (United States)

Ochałek, Agnieszka; Lipecki, Tomasz; Jaśkowski, Wojciech; Jabłoński, Mateusz

2018-03-01

The significant part of the hydrography is bathymetry, which is the empirical part of it. Bathymetry is the study of underwater depth of waterways and reservoirs, and graphic presentation of measured data in form of bathymetric maps, cross-sections and three-dimensional bottom models. The bathymetric measurements are based on using Global Positioning System and devices for hydrographic measurements - an echo sounder and a side sonar scanner. In this research authors focused on introducing the case of obtaining and processing the bathymetrical data, building numerical bottom models of two post-mining reclaimed water reservoirs: Dwudniaki Lake in Wierzchosławice and flooded quarry in Zabierzów. The report includes also analysing data from still operating mining water reservoirs located in Poland to depict how bathymetry can be used in mining industry. The significant issue is an integration of bathymetrical data and geodetic data from tachymetry, terrestrial laser scanning measurements.

Monitoring of Volcanic Activity by Sub-mm Geodetic Analyses

Science.gov (United States)

Miura, S.; Mare, Y.; Ichiki, M.; Demachi, T.; Tachibana, K.; Nishimura, T.

2017-12-01

Volcanic earthquakes have been occurring beneath Zao volcano in northern Honshu, Japan since 2013, following the increase of deep low frequency earthquakes from 2012. On account of a burst of seismicity initiated in April 2015, the JMA announced a warning of eruption, however, the seismicity gradually decreased for the next two months and the warning was canceled in June. In the same time period, minor expansive deformation was observed by GNSS. Small earthquakes are still occurring, and low-freq. earthquakes (LPE) occur sometimes accompanied by static tilt changes. In this study, we try to extract the sub-mm displacements from the LPE waveforms observed by broadband seismometers (BBS) and utilize them for geodetic inversion to monitor volcanic activities. Thun et al. (2015, 2016) devised an efficient method using a running median filter (RMF) to remove LP noises, which contaminate displacement waveforms. They demonstrated the reproducibility of the waveforms corresponding to the experimentally given sub-mm displacements in the laboratory. They also apply the method to the field LPE data obtained from several volcanoes to show static displacements. The procedure is outlined as follows: (1) Unfiltered removal of the instrument response, (2) LP noise estimate by LPF with a corner frequency of 5/M, where M (seconds) is the time window of the RMF and should be at least three times the length of the rise time. (3) Subtract the noise estimated from step (2). (4) Integrate to obtain displacement waveforms. We apply the method to the BBS waveform at a distance of about 1.5 km ESE from the summit crater of Zao Volcano associated with a LPE on April 1, 2017. Assuming the time window M as 300 seconds, we successfully obtained the displacement history: taking the rise time of about 2 minutes, the site was gradually uplifted with the amount of about 50-60 µm and then subsided with HF displacements in the next 2 minutes resulting about 20-30 µm static upheaval. Comparing the

Constraints on the Mass and Location of Planet 9 set by Range and VLBI Observations of Cassini

Science.gov (United States)

Jacobson, Robert Arthur; Folkner, William; Park, Ryan; Williams, James

2018-04-01

Batygin and Brown, 2016 AJ, found that Kuiper belt objects (KBOs) with well determined orbits having periods greater than 4000 years are apsidally aligned. They attribute this orbital clustering to the existence of a distant planet, Planet 9, well beyond Neptune, with a mass roughly ten times that of Earth. If such a planet exists, it would affect the motion of the known solar system planets, in particular Saturn, which is well observed with radiometric ranging from the Cassini spacecraft and VLBI observations of Cassini. The current planetary ephemerides do not account for the postulated Planet 9, yet their fit to the observational data shows no obvious effect that could be attributed to neglecting that planet. However, it is possible that the effect could be absorbed by the estimated parameters used to determine the ephemerides. Those parameters include the planetary orbital elements, mass of the Sun, and the masses of the asteroids that perturb the Martian orbit. We recently updated the Cassini data set and extended it through the end of the mssion in 2017 September. We analyze the sensitivity of these data to the tidal perturbations caused by the postulated Planet 9 for a range of positions on the sky and tidal parameters (the ratio of the mass of Planet 9 to the cube of its distance from Saturn). We determine an upper bound on the tidal parameter and the most probable directions consistent with the observational data.

JTRF2014, the JPL Kalman filter and smoother realization of the International Terrestrial Reference System

Science.gov (United States)

Abbondanza, Claudio; Chin, Toshio M.; Gross, Richard S.; Heflin, Michael B.; Parker, Jay W.; Soja, Benedikt S.; van Dam, Tonie; Wu, Xiaoping

2017-10-01

We present and discuss JTRF2014, the Terrestrial Reference Frame (TRF) the Jet Propulsion Laboratory constructed by combining space-geodetic inputs from very long baseline interferometry (VLBI), satellite laser ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler orbitography and radiopositioning integrated by satellite submitted for the realization of ITRF2014. Determined through a Kalman filter and Rauch-Tung-Striebel smoother assimilating position observations, Earth orientation parameters, and local ties, JTRF2014 is a subsecular, time series-based TRF whose origin is at the quasi-instantaneous center of mass (CM) as sensed by SLR and whose scale is determined by the quasi-instantaneous VLBI and SLR scales. The dynamical evolution of the positions accounts for a secular motion term, annual, and semiannual periodic modes. Site-dependent variances based on the analysis of loading displacements induced by mass redistributions of terrestrial fluids have been used to control the extent of random walk adopted in the combination. With differences in the amplitude of the annual signal within the range 0.5-0.8 mm, JTRF2014-derived center of network-to-center of mass (CM-CN) is in remarkable agreement with the geocenter motion obtained via spectral inversion of GNSS, Gravity Recovery and Climate Experiment (GRACE) observations and modeled ocean bottom pressure from Estimating the Circulation and Climate of the Ocean (ECCO). Comparisons of JTRF2014 to ITRF2014 suggest high-level consistency with time derivatives of the Helmert transformation parameters connecting the two frames below 0.18 mm/yr and weighted root-mean-square differences of the polar motion (polar motion rate) in the order of 30 μas (17 μas/d).

Geodetically resolved slip distribution of the 27 August 2012 Mw=7.3 El Salvador earthquake

Science.gov (United States)

Geirsson, H.; La Femina, P. C.; DeMets, C.; Hernandez, D. A.; Mattioli, G. S.; Rogers, R.; Rodriguez, M.

2013-12-01

On 27 August 2012 a Mw=7.3 earthquake occurred offshore of Central America causing a small tsunami in El Salvador and Nicaragua but little damage otherwise. This is the largest magnitude earthquake in this area since 2001. We use co-seismic displacements estimated from episodic and continuous GPS station time series to model the magnitude and spatial variability of slip for this event. The estimated surface displacements are small (earthquake. We use TDEFNODE to model the displacements using two different modeling approaches. In the first model, we solve for homogeneous slip on free rectangular fault(s), and in the second model we solve for distributed slip on the main thrust, realized using different slab models. The results indicate that we can match the seismic moment release, with models indicating rupture of a large area, with a low magnitude of slip. The slip is at shallow-to-intermediate depths on the main thrust off the coast of El Salvador. Additionally, we observe a deeper region of slip to the east, that reaches towards the Gulf of Fonseca between El Salvador and Nicaragua. The observed tsunami additionally indicates near-trench rupture off the coast of El Salvador. The duration of the rupturing is estimated from seismic data to be 70 s, which indicates a slow rupture process. Since the geodetic moment we obtain agrees with the seismic moment, this indicates that the earthquake was not associated with aseismic slip.

Modeling and Analysis of Integrated Bathymetric and Geodetic Data for Inventory Surveys of Mining Water Reservoirs

Directory of Open Access Journals (Sweden)

Ochałek Agnieszka

2018-01-01

Full Text Available The significant part of the hydrography is bathymetry, which is the empirical part of it. Bathymetry is the study of underwater depth of waterways and reservoirs, and graphic presentation of measured data in form of bathymetric maps, cross-sections and three-dimensional bottom models. The bathymetric measurements are based on using Global Positioning System and devices for hydrographic measurements – an echo sounder and a side sonar scanner. In this research authors focused on introducing the case of obtaining and processing the bathymetrical data, building numerical bottom models of two post-mining reclaimed water reservoirs: Dwudniaki Lake in Wierzchosławice and flooded quarry in Zabierzów. The report includes also analysing data from still operating mining water reservoirs located in Poland to depict how bathymetry can be used in mining industry. The significant issue is an integration of bathymetrical data and geodetic data from tachymetry, terrestrial laser scanning measurements.

VLBI OBSERVATION OF MICROQUASAR CYG X-3 DURING AN X-RAY STATE TRANSITION FROM SOFT TO HARD IN THE 2007 MAY-JUNE FLARE

Energy Technology Data Exchange (ETDEWEB)

Kim, Jeong-Sook; Kim, Sang Joon [School of Space Science, Kyunghee University, Seocheon-dong, Giheung-si, Gyeonggi-do 446-701 (Korea, Republic of); Kim, Soon-Wook [Korea Astronomy and Space Science Institute, 776 Daedeokdaero, Yuseong, Daejeon 305-348 (Korea, Republic of); Kurayama, Tomoharu [Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065 (Japan); Honma, Mareki [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Sasao, Tetsuo, E-mail: evony@kasi.re.kr, E-mail: skim@kasi.re.kr [Yaeyama Star Club, Ookawa, Ishigaki, Okinawa 904-0022 (Japan)

2013-07-20

We present a radio observation of microquasar Cyg X-3 during an X-ray state transition from ultrasoft to hard state in the 2007 May-June flare using the VLBI Exploration of Radio Astrometry at 22 GHz. During the transition, a short-lived mini-flare of {approx}< 3 hr was detected prior to the major flare. In such a transition, a jet ejection is believed to occur, but there have been no direct observations to support it. An analysis of Gaussian fits to the observed visibility amplitudes shows a time variation of the source axis, or a structural change, during the mini-flare. Our model fits, together with other multiwavelength observations in the radio, soft, and hard X-rays, and the shock-in-jet models for other flaring activities at GHz wavebands, suggest a high possibility of synchrotron flares during the mini-flare, indicative of a predominant contribution from jet activity. Therefore, the mini-flare with an associated structural change is indicative of a jet ejection event in the state transition from ultrasoft to hard state.

Geodetic proof of vertical recent movements at the seism generating zone of Acambay, Mexico

Directory of Open Access Journals (Sweden)

Luis Miguel Espinosa-Rodríguez

2016-12-01

Full Text Available The central territorial belt oriented west-east and located along the parallel 19 in the Mexican Republic, is composed of a complex system of faults, that respond to the consequent morphology of a tension arched system, which has been erected to the Volcanic Transmexican or Transversal Belt. This region evidences the dynamics and evolution of a graben and horst tectonic system, as well as volcanic manifestations characterized by stratovolcanoes, monogenetic fields and fisural flows, among others. In particular, in the center of the Mexican regional complex, the fault system which delimits the region of Acambay in the state of Mexico, had showed evidences of seismogenerating activity during a century until the present time. According to the above and based on the geomorphological analysis and the geodetic measurements, the dynamic presented by these morphostructures in a multitemporal comparative study (1998/2003 o 2011 is showed. The rates of vertical tectonic movements reflect recent rise values ranging from + 7,3 to 12,8 mm/year in the northern horst of Santa María Tixmadejé, while in the central graben of Acambay are very weak, of the order of + 0,4 to + 0,5 mm/year.

Geodetic Control Points, Chippewa County has been working on tightening up their control network over the years. The first network was constructed in 1993, with densification done from 2008-2011., Published in 2011, Not Applicable scale, Chippewa County Government.

Data.gov (United States)

NSGIC Local Govt | GIS Inventory — Geodetic Control Points dataset current as of 2011. Chippewa County has been working on tightening up their control network over the years. The first network was...

Geodetic mass balance measurements on debris and clean-ice tropical glaciers in Ecuador

Science.gov (United States)

La Frenierre, J.; Decker, C. R.; Jordan, E.; Wigmore, O.; Hodge, B. E.; Niederriter, C.; Michels, A.

2017-12-01

Glaciers are recognized as highly sensitive indicators of climate change in high altitude, low latitude environments. In the tropical Andes, various analyses of glacier surface area change have helped illuminate the manifestation of climate change in this region, however, information about actual glacier mass balance behavior is much more limited given the relatively small glaciers, difficult access, poor weather, and/or limited local resources common here. Several new technologies, including aerial and terrestrial LIDAR and structure-from-motion photogrammetry using small unmanned aerial vehicles (UAVs), make mass balance measurements using geodetic approaches increasingly feasible in remote mountain locations, which can both further our understanding of changing climatic conditions, and improve our ability to evaluate the downstream hydrologic impacts of ice loss. At Volcán Chimborazo, Ecuador, these new technologies, combined with a unique, 5-meter resolution digital elevation model derived from 1997 aerial imagery, make possible an analysis of the magnitude and spatial patterns of mass balance behavior over the past two decades. Here, we evaluate ice loss between 1997 and 2017 at the tongues of two adjacent glaciers, one debris-covered and detached from its accumulation area (Reschreiter Glacier), and one debris-free and intact (Hans Meyer Glacier). Additionally, we incorporate data from 2012 and 2013 terrestrial LIDAR surveys to evaluate the behavior of the Reschreiter at a finer temporal resolution. We find that on the Hans Meyer, the mean surface deflation rate since 1997 at the present-day tongue has been nearly 3 m yr-1, while on the lower-elevation Reschreiter, the mean deflation rate has been approximately 1 m yr-1. However, the processes by which debris-covered ice becomes exposed results in highly heterogeneous patterns of ice loss, with some areas experiencing surface deflation rates approaching 15 m yr-1 when energy absorption is unimpeded.

Analysis quality of content digital plan of cadastre lines (underground installation

Directory of Open Access Journals (Sweden)

Marinković Goran

2016-01-01

Full Text Available This work presents the results of research quality digital geodetic plans lines and underground installations. The study included the creation of a digital geodetic plan sewerage network vectorization of analogue geodetic plans and creation of digital geodetic plan of the same details from the original data survey and maintenance survey. Based on research results the analysis of the accuracy and reliability digital geodetic plan created vectoring analogue plan or 'digitizing from the screen'. The results obtained in this work, the can be use not only in the Republic of Serbia, but also in other countries where digitalization of geodetic plans are increasingly gaining in importance.

From Wagons to Race Cars, At Least Now We Have A Chassis

Science.gov (United States)

Morrow, A. L.

2003-12-01

For the past 30 years Very-Long-Baseline Interferometry (VLBI) has provided astronomers with the most accurate measurements to date of both distant radio sources as well as the tectonic plates. The resolutions attainable through VLBI are orders of magnitude better than other instruments. In order to transmit radio signals collected at different sites to a correlator for processing the VLBI data was stored on magnetic tapes, and then the magnetic tapes were shipped through the mail to the central processing site. This was not only arduous and inefficient, it was also costly. Now this means of shipment can be replaced by global high speed networks. This means of transmission is called e-VLBI. New protocols must be developed so e-VLBI can become a proficient high bandwidth background user. The protocol agreed upon uses a Real-time Transport Protocol (RTP) framework to preserve timing information and synchronization. The RTP is then transported using the Internet User Datagram Protocol (UDP) with RTP Control Protocol (RTCP) monitoring the networks performance. When this protocol is fully functional astronomers will be able to observe all over the world and receive results in real time.

SIRGAS: the core geodetic infrastructure in Latin America and the Caribbean

Science.gov (United States)

Sanchez, L.; Brunini, C.; Drewes, H.; Mackern, V.; da Silva, A.

2013-05-01

Studying, understanding, and modelling geophysical phenomena, such as global change and geodynamics, require geodetic reference frames with (1) an order of accuracy higher than the magnitude of the effects we want to study, (2) consistency and reliability worldwide (the same accuracy everywhere), and (3) a long-term stability (the same order of accuracy at any time). The definition, realisation, maintenance, and wide-utilisation of the International Terrestrial Reference System (ITRS) are oriented to guarantee a globally unified geometric reference frame with reliability at the mm-level, i.e. the International Terrestrial Reference Frame (ITRF). The densification of the global ITRF in Latin America and The Caribbean is given by SIRGAS (Sistema de Referencia Geocéntrico para Las Américas), primary objective of which is to provide the most precise coordinates in the region. Therefore, SIRGAS is the backbone for all regional projects based on the generation, use, and analysis of geo-referenced data at national as well as at international level. Besides providing the reference for a wide range of scientific applications such as the monitoring of Earth's crust deformations, vertical movements, sea level variations, atmospheric studies, etc., SIRGAS is also the platform for practical applications such as engineering projects, digital administration of geographical data, geospatial data infrastructures, etc. According to this, the present contribution describes the main features of SIRGAS, giving special care to those challenges faced to continue providing the best possible, long-term stable and high-precise reference frame for Latin America and the Caribbean.

Geodetic slip solutions for the Mw = 7.4 Champerico (Guatemala) earthquake of 2012 November 7 and its postseismic deformation

Science.gov (United States)

Ellis, Andria P.; DeMets, Charles; Briole, Pierre; Molina, Enrique; Flores, Omar; Rivera, Jeffrey; Lasserre, Cécile; Lyon-Caen, Hélène; Lord, Neal

2015-05-01

As the first large subduction thrust earthquake off the coast of western Guatemala in the past several decades, the 2012 November 7 Mw = 7.4 earthquake offers the first opportunity to study coseismic and postseismic behaviour along a segment of the Middle America trench where frictional coupling makes a transition from weak coupling off the coast of El Salvador to strong coupling in southern Mexico. We use measurements at 19 continuous GPS sites in Guatemala, El Salvador and Mexico to estimate the coseismic slip and postseismic deformation of the November 2012 Champerico (Guatemala) earthquake. An inversion of the coseismic offsets, which range up to ˜47 mm at the surface near the epicentre, indicates that up to ˜2 m of coseismic slip occurred on a ˜30 × 30 km rupture area between ˜10 and 30 km depth, which is near the global CMT centroid. The geodetic moment of 13 × 1019 N m and corresponding magnitude of 7.4 both agree well with independent seismological estimates. Transient postseismic deformation that was recorded at 11 GPS sites is attributable to a combination of fault afterslip and viscoelastic flow in the lower crust and/or mantle. Modelling of the viscoelastic deformation suggests that it constituted no more than ˜30 per cent of the short-term postseismic deformation. GPS observations that extend six months after the earthquake are well fit by a model in which most afterslip occurred at the same depth or directly downdip from the rupture zone and released energy equivalent to no more than ˜20 per cent of the coseismic moment. An independent seismological slip solution that features more highly concentrated coseismic slip than our own fits the GPS offsets well if its slip centroid is translated ˜50 km to the west to a position close to our slip centroid. The geodetic and seismologic slip solutions thus suggest bounds of 2-7 m for the peak slip along a region of the interface no larger than 30 × 30 km.

Solar-System Tests of Gravitational Theories

Science.gov (United States)

Shapiro, Irwin

1997-01-01

We are engaged in testing gravitational theory by means of observations of objects in the solar system. These tests include an examination of the Principle Of Equivalence (POE), the Shapiro delay, the advances of planetary perihelia, the possibility of a secular variation G in the "gravitational constant" G, and the rate of the de Sitter (geodetic) precession of the Earth-Moon system. These results are consistent with our preliminary results focusing on the contribution of Lunar Laser Ranging (LLR), which were presented at the seventh Marcel Grossmann meeting on general relativity. The largest improvement over previous results comes in the uncertainty for (eta): a factor of five better than our previous value. This improvement reflects the increasing strength of the LLR data. A similar analysis presented at the same meeting by a group at the Jet Propulsion Laboratory gave a similar result for (eta). Our value for (beta) represents our first such result determined simultaneously with the solar quadrupole moment from the dynamical data set. These results are being prepared for publication. We have shown how positions determined from different planetary ephemerides can be compared and how the combination of VLBI and pulse timing information can yield a direct tie between planetary and radio frames. We have continued to include new data in our analysis as they became available. Finally, we have made improvement in our analysis software (PEP) and ported it to a network of modern workstations from its former home on a "mainframe" computer.

Impact of quasar proper motions on the alignment between the International Celestial Reference Frame and the Gaia reference frame

Science.gov (United States)

Liu, J.-C.; Malkin, Z.; Zhu, Z.

2018-03-01

The International Celestial Reference Frame (ICRF) is currently realized by the very long baseline interferometry (VLBI) observations of extragalactic sources with the zero proper motion assumption, while Gaia will observe proper motions of these distant and faint objects to an accuracy of tens of microarcseconds per year. This paper investigates the difference between VLBI and Gaia quasar proper motions and it aims to understand the impact of quasar proper motions on the alignment of the ICRF and Gaia reference frame. We use the latest time series data of source coordinates from the International VLBI Service analysis centres operated at Goddard Space Flight Center (GSF2017) and Paris observatory (OPA2017), as well as the Gaia auxiliary quasar solution containing 2191 high-probability optical counterparts of the ICRF2 sources. The linear proper motions in right ascension and declination of VLBI sources are derived by least-squares fits while the proper motions for Gaia sources are simulated taking into account the acceleration of the Solar system barycentre and realistic uncertainties depending on the source brightness. The individual and global features of source proper motions in GSF2017 and OPA2017 VLBI data are found to be inconsistent, which may result from differences in VLBI observations, data reduction and analysis. A comparison of the VLBI and Gaia proper motions shows that the accuracies of the components of rotation and glide between the two systems are 2-4 μas yr- 1 based on about 600 common sources. For the future alignment of the ICRF and Gaia reference frames at different wavelengths, the proper motions of quasars must necessarily be considered.

Large earthquake rates from geologic, geodetic, and seismological perspectives

Science.gov (United States)

Jackson, D. D.

2017-12-01

Earthquake rate and recurrence information comes primarily from geology, geodesy, and seismology. Geology gives the longest temporal perspective, but it reveals only surface deformation, relatable to earthquakes only with many assumptions. Geodesy is also limited to surface observations, but it detects evidence of the processes leading to earthquakes, again subject to important assumptions. Seismology reveals actual earthquakes, but its history is too short to capture important properties of very large ones. Unfortunately, the ranges of these observation types barely overlap, so that integrating them into a consistent picture adequate to infer future prospects requires a great deal of trust. Perhaps the most important boundary is the temporal one at the beginning of the instrumental seismic era, about a century ago. We have virtually no seismological or geodetic information on large earthquakes before then, and little geological information after. Virtually all-modern forecasts of large earthquakes assume some form of equivalence between tectonic- and seismic moment rates as functions of location, time, and magnitude threshold. That assumption links geology, geodesy, and seismology, but it invokes a host of other assumptions and incurs very significant uncertainties. Questions include temporal behavior of seismic and tectonic moment rates; shape of the earthquake magnitude distribution; upper magnitude limit; scaling between rupture length, width, and displacement; depth dependence of stress coupling; value of crustal rigidity; and relation between faults at depth and their surface fault traces, to name just a few. In this report I'll estimate the quantitative implications for estimating large earthquake rate. Global studies like the GEAR1 project suggest that surface deformation from geology and geodesy best show the geography of very large, rare earthquakes in the long term, while seismological observations of small earthquakes best forecasts moderate earthquakes

Applications of Voronoi and Delaunay Diagrams in the solution of the geodetic boundary value problem

Directory of Open Access Journals (Sweden)

C. A. B. Quintero

Full Text Available Voronoi and Delaunay structures are presented as discretization tools to be used in numerical surface integration aiming the computation of geodetic problems solutions, when under the integral there is a non-analytical function (e. g., gravity anomaly and height. In the Voronoi approach, the target area is partitioned into polygons which contain the observed point and no interpolation is necessary, only the original data is used. In the Delaunay approach, the observed points are vertices of triangular cells and the value for a cell is interpolated for its barycenter. If the amount and distribution of the observed points are adequate, gridding operation is not required and the numerical surface integration is carried out by point-wise. Even when the amount and distribution of the observed points are not enough, the structures of Voronoi and Delaunay can combine grid with observed points in order to preserve the integrity of the original information. Both schemes are applied to the computation of the Stokes' integral, the terrain correction, the indirect effect and the gradient of the gravity anomaly, in the State of Rio de Janeiro, Brazil area.

Constraints on the Mass and Location of Planet 9 set by Range and VLBI Observations of Spacecraft at Saturn

Science.gov (United States)

Jacobson, Robert A.; Folkner, William M.; Park, Ryan S.; Williams, James G.

2017-06-01

Batygin and Brown, 2016 AJ, found that all Kuiper belt objects (KBOs) with well determined orbits having periods greater than 4000 years share nearly the same orbital plane and are apsidally aligned. They attribute this orbital clustering to the existence of a distant planet, Planet 9, well beyond Neptune, with a mass roughly ten times that of Earth. If such a planet exists, it would affect the motion of the known solar system planets, in particular Saturn, which is well observed with radiometric ranging from the Voyager and Cassini spacecraft and VLBI observations of Cassini. The current planetary ephemerides do not account for the postulated Planet 9, yet their fit to the observational data shows no obvious effect that could be attributed to neglecting that planet. However, it is possible that the effect could be absorbed by the estimated parameters used to determine the ephemerides. Those parameters include the planetary orbital elements, mass of the Sun, and the masses of the asteroids that perturb the Martian orbit. We recently updated the Voyager and Cassini data sets and extended the latter through 2017 March. We analyze the sensitivity of these data to the tidal perturbations caused by Planet 9 for a range of positions on the sky and tidal parameters (the ratio of the mass of Planet 9 to the cube of its distance from Saturn). We determine an upper bound on the tidal parameter and the most probable directions consistent with the observational data.

NChina16: A stable geodetic reference frame for geological hazard studies in North China

Science.gov (United States)

Wang, Guoquan; Bao, Yan; Gan, Weijun; Geng, Jianghui; Xiao, Gengru; Shen, Jack S.

2018-04-01

We have developed a stable North China Reference Frame 2016 (NChina16) using five years of continuous GPS observations (2011.8-2016.8) from 12 continuously operating reference stations (CORS) fixed to the North China Craton. Applications of NChina16 in landslide and subsidence studies are illustrated in this article. A method for realizing a regional geodetic reference frame is introduced. The primary result of this study is the seven parameters for transforming Cartesian ECEF (Earth-Centered, Earth-Fixed) coordinates X, Y, and Z from the International GNSS Service Reference Frame 2008 (IGS08) to NChina16. The seven parameters include the epoch that is used to align the regional reference frame to IGS08 and the time derivatives of three translations and three rotations. The GIPSY-OASIS (V6.4) software package was used to obtain the precise point positioning (PPP) daily solutions with respect to IGS08. The frame stability of NChina16 is approximately 0.5 mm/year in both horizontal and vertical directions. This study also developed a regional model for correcting seasonal motions superimposed into the vertical component of the GPS-derived displacement time series. Long-term GPS observations (1999-2016) from five CORS in North China were used to develop the seasonal model. According to this study, the PPP daily solutions with respect to NChina16 could achieve 2-3 mm horizontal accuracy and 4-5 mm vertical accuracy after being modified by the regional model. NChina16 will be critical to study geodynamic problems in North China, such as earthquakes, faulting, subsidence, and landslides. The regional reference frame will be periodically updated every few years to mitigate degradation of the frame with time and be synchronized with the update of IGS reference frame.

Evaluation of a New Prototype Geodetic Astrolabe for Measuring Deflections of the Vertical

Science.gov (United States)

Slater, J. A.; Thompson, N.; Angell, L. E.; Belenkii, M. S.; Bruns, D. G.; Johnson, D. O.

2009-12-01

During the last three years, the National Geospatial-Intelligence Agency (NGA), with assistance from the U.S. Naval Observatory (USNO), sponsored the development of a new electronic geodetic astrolabe for measuring deflections of the vertical (DoV). NGA’s current operational astrolabes, built in 1995, have a number of undesirable features including the need for a pool of liquid mercury as a reflecting surface. The new state-of-the-art prototype instrument, completed by Trex Enterprises in early 2009, was designed to meet a 0.2 arcsec accuracy requirement. It reduces the weight, eliminates the mercury, and dramatically reduces observation times. The new astrolabe consists of a 101 mm aperture telescope with a 1.5° field of view and an inclinometer mounted inside a 92-cm high, 30-cm diameter tube, an external GPS receiver for timing, and a laptop computer that controls and monitors the instrument and performs the computations. Star images are recorded by an astronomical-grade camera with a 2,048 x 2,048 pixel CCD sensor that is externally triggered by time pulses from the GPS receiver. The prototype was designed for nighttime observation of visible stars equal to or brighter than magnitude 10.0. The inclinometer is a system of two orthogonal pendula that define the local gravitational vertical, each consisting of a brass plumb bob suspended from an aluminized polymer ribbon set between two electrodes. An internal reference collimator is rigidly tied to the inclinometer and projects an array of reference points of light onto the CCD sensor. After the astrolabe is coarsely leveled to within 20 arcsec, voice coil actuators automatically adjust and maintain the inclinometer vertical to within 0.02 arcsec. Independent images are collected at 6 second intervals using a 200 msec exposure time. The CCD coordinates are determined for each star and a collimator reference point on each image. Stars are identified by referencing a customized star catalog produced by USNO. A

Multi-source self-calibration: Unveiling the microJy population of compact radio sources

NARCIS (Netherlands)

Radcliffe, J. F.; Garrett, M. A.; Beswick, R. J.; Muxlow, T. W. B.; Barthel, P. D.; Deller, A. T.; Middelberg, E.

2016-01-01

Context. Very long baseline interferometry (VLBI) data are extremely sensitive to the phase stability of the VLBI array. This is especially important when we reach μJy rms sensitivities. Calibration using standard phase-referencing techniques is often used to improve the phase stability of VLBI

Space Geodesy: The Cross-Disciplinary Earth science (Vening Meinesz Medal Lecture)

Science.gov (United States)

Shum, C. K.

2012-04-01

Geodesy during the onset of the 21st Century is evolving into a transformative cross-disciplinary Earth science field. The pioneers before or after the discipline Geodesy was defined include Galileo, Descartes, Kepler, Newton, Euler, Bernoulli, Kant, Laplace, Airy, Kelvin, Jeffreys, Chandler, Meinesz, Kaula, and others. The complicated dynamic processes of the Earth system manifested by interactions between the solid Earth and its fluid layers, including ocean, atmosphere, cryosphere and hydrosphere, and their feedbacks are linked with scientific problems such as global sea-level rise resulting from natural and anthropogenic climate change. Advances in the precision and stability of geodetic and fundamental instrumentations, including clocks, satellite or quasar tracking sensors, altimetry and lidars, synthetic aperture radar interferometry (InSAR), InSAR altimetry, gravimetry and gradiometry, have enabled accentuate and transformative progress in cross-disciplinary Earth sciences. In particular, advances in the measurement of the gravity with modern free-fall methods have reached accuracies of 10-9 g (~1 μGal or 10 nm/s2) or better, allowing accurate measurements of height changes at ~3 mm relative to the Earth's center of mass, and mass transports within the Earth interior or its geophysical fluids, enabling global quantifications of climate-change signals. These contemporary space geodetic and in situ sensors include, but not limited to, satellite radar and laser altimetry/lidars, GNSS/SLR/VLBI/DORIS, InSAR, spaceborne gravimetry from GRACE (Gravity Recovery And Climate Experiment twin-satellite mission) and gradiometry from GOCE (Global Ocean Circulation Experiment), tide gauges, and hydrographic data (XBT/MBT/Argo). The 2007 Intergovernmental Panel for Climate Change (IPCC) study, the Fourth Assessment Report (AR4), substantially narrowed the discrepancy between observation and the known geophysical causes of sea-level rise, but significant uncertainties

A Unified Geodetic Vertical Velocity Field (UGVVF), Version 1.0

Science.gov (United States)

Schmalzle, G.; Wdowinski, S.

2014-12-01

Tectonic motion, volcanic inflation or deflation, as well as oil, gas and water pumping can induce vertical motion. In southern California these signals are inter-mingled. In tectonics, properly identifying regions that are contaminated by other signals can be important when estimating fault slip rates. Until recently vertical deformation rates determined by high precision Global Positioning Systems (GPS) had large uncertainties compared to horizontal components and were rarely used to constrain tectonic models of fault motion. However, many continuously occupied GPS stations have been operating for ten or more years, often delivering uncertainties of ~1 mm/yr or less, providing better constraints for tectonic modeling. Various processing centers produced GPS time series and estimated vertical velocity fields, each with their own set of processing techniques and assumptions. We compare vertical velocity solutions estimated by seven data processing groups as well as two combined solutions (Figure 1). These groups include: Central Washington University (CWU) and New Mexico Institute of Technology (NMT), and their combined solution provided by the Plate Boundary Observatory (PBO) through the UNAVCO website. Also compared are the Jet Propulsion Laboratory (JPL) and Scripps Orbit and Permanent Array Center (SOPAC) and their combined solution provided as part of the NASA MEaSUREs project. Smaller velocity fields included are from Amos et al., 2014, processed at the Nevada Geodetic Laboratory, Shen et al., 2011, processed by UCLA and called the Crustal Motion Map 4.0 (CMM4) dataset, and a new velocity field provided by the University of Miami (UM). Our analysis includes estimating and correcting for systematic vertical velocity and uncertainty differences between groups. Our final product is a unified velocity field that contains the median values of the adjusted velocity fields and their uncertainties. This product will be periodically updated when new velocity fields

Geodetic infrastructure at the Barcelona harbour for sea level monitoring

Science.gov (United States)

Martinez-Benjamin, Juan Jose; Gili, Josep; Lopez, Rogelio; Tapia, Ana; Pros, Francesc; Palau, Vicenc; Perez, Begona

2015-04-01

The presentation is directed to the description of the actual geodetic infrastructure of Barcelona harbour with three tide gauges of different technologies for sea level determination and contribution to regional sea level rise and understanding past and present sea level rise in the Barcelona harbour. It is intended that the overall system will constitute a CGPS Station of the ESEAS (European Sea Level) and TIGA (GPS Tide Gauge Benchmark Monitoring) networks. At Barcelona harbour there is a MIROS radar tide gauge belonging to Puertos del Estado (Spanish Harbours).The radar sensor is over the water surface, on a L-shaped structure which elevates it a few meters above the quay shelf. 1-min data are transmitted to the ENAGAS Control Center by cable and then sent each 1 min to Puertos del Estado by e-mail. The information includes wave forescast (mean period, significant wave height, sea level, etc.This sensor also measures agitation and sends wave parameters each 20 min. There is a GPS station Leica Geosystems GRX1200 GG Pro and antenna AX 1202 GG. The Control Tower of the Port of Barcelona is situated in the North dike of the so-called Energy Pier in the Barcelona harbor (Spain). This tower has different kind of antennas for navigation monitoring and a GNSS permanent station. As the tower is founded in reclaimed land, and because its metallic structure, the 50 m building is subjected to diverse movements, including periodic fluctuations due to temperature changes. In this contribution the 2009, 2011, 2012, 2013 and 2014 the necessary monitoring campaigns are described. In the framework of a Spanish Space Project, the instrumentation of sea level measurements has been improved by providing the Barcelona site with a radar tide gauge Datamar 2000C from Geonica S.L. in June 2014 near an acoustic tide gauge from the Barcelona Harbour installed in 2013. Precision levelling has been made several times in the last two years because the tower is founded in reclaimed land and

Investigating Strain Transfer Along the Southern San Andreas Fault: A Geomorphic and Geodetic Study of Block Rotation in the Eastern Transverse Ranges, Joshua Tree National Park, CA

Science.gov (United States)

Guns, K. A.; Bennett, R. A.; Blisniuk, K.

2017-12-01

To better evaluate the distribution and transfer of strain and slip along the Southern San Andreas Fault (SSAF) zone in the northern Coachella valley in southern California, we integrate geological and geodetic observations to test whether strain is being transferred away from the SSAF system towards the Eastern California Shear Zone through microblock rotation of the Eastern Transverse Ranges (ETR). The faults of the ETR consist of five east-west trending left lateral strike slip faults that have measured cumulative offsets of up to 20 km and as low as 1 km. Present kinematic and block models present a variety of slip rate estimates, from as low as zero to as high as 7 mm/yr, suggesting a gap in our understanding of what role these faults play in the larger system. To determine whether present-day block rotation along these faults is contributing to strain transfer in the region, we are applying 10Be surface exposure dating methods to observed offset channel and alluvial fan deposits in order to estimate fault slip rates along two faults in the ETR. We present observations of offset geomorphic landforms using field mapping and LiDAR data at three sites along the Blue Cut Fault and one site along the Smoke Tree Wash Fault in Joshua Tree National Park which indicate recent Quaternary fault activity. Initial results of site mapping and clast count analyses reveal at least three stages of offset, including potential Holocene offsets, for one site along the Blue Cut Fault, while preliminary 10Be geochronology is in progress. This geologic slip rate data, combined with our new geodetic surface velocity field derived from updated campaign-based GPS measurements within Joshua Tree National Park will allow us to construct a suite of elastic fault block models to elucidate rates of strain transfer away from the SSAF and how that strain transfer may be affecting the length of the interseismic period along the SSAF.

Determination of recent horizontal crustal movements and deformations of African and Eurasian plates in western Mediterranean region using geodetic-GPS computations extended to 2006 (from 1997) related to NAFREF and AFREF frames.

Science.gov (United States)

Azzouzi, R.

2009-04-01

Determination of recent horizontal crustal movements and deformations of African and Eurasian plates in western Mediterranean region using geodetic-GPS computations extended to 2006 (from 1997) related to NAFREF and AFREF frames. By: R. Azzouzi*, M. Ettarid*, El H. Semlali*, et A. Rimi+ * Filière de Formation en Topographie Institut Agronomique et Vétérinaire Hassan II B.P. 6202 Rabat-Instituts MAROC + Département de la Physique du Globe Université Mohammed V Rabat MAROC This study focus on the use of the geodetic spatial technique GPS for geodynamic purposes generally in the Western Mediterranean area and particularly in Morocco. It aims to exploit this technique first to determine the geodetic coordinates on some western Mediterranean sites. And also this technique is used to detect and to determine movements cross the boundary line between the two African and Eurasian crustal plates on some well chosen GPS-Geodynamics sites. It will allow us also to estimate crustal dynamic parameters of tension that results. These parameters are linked to deformations of terrestrial crust in the region. They are also associated with tectonic constraints of the study area. The usefulness of repeated measurements of these elements, the estimate of displacements and the determination of their temporal rates is indisputable. Indeed, sismo-tectonique studies allow a good knowledge of the of earthquake processes, their frequency their amplitude and even of their prediction in the world in general and in Moroccan area especially. They allow also contributing to guarantee more security for all most important management projects, as projects of building great works (dams, bridges, nuclear centrals). And also as preliminary study, for the most important joint-project between Europe and Africa through the Strait of Gibraltar. For our application, 23 GPS monitoring stations under the ITRF2000 reference frame are chosen in Eurasian and African plates. The sites are located around the

A search for AGN activity in Infrared-Faint Radio Sources (IFRS)

Science.gov (United States)

Lenc, Emil; Middelberg, Enno; Norris, Ray; Mao, Minnie

2010-04-01

We propose to observe a large sample of radio sources from the ATLAS (Australia Telescope Large Area Survey) source catalogue with the LBA, to determine their compactness. The sample consists of 36 sources with no counterpart in the co-located SWIRE survey (3.6 um to 160 um), carried out with the Spitzer Space Telescope. This rare class of sources, dubber Infrared-Faint Radio Sources (IFRS), is inconsistent with current galaxy evolution models. VLBI observations are an essential way to obtain further clues on what these objects are and why they are hidden from infrared observations. We will measure the flux densities on long baselines to determine their compactness. Only five IFRS have been previously targeted with VLBI observations (resulting in two detections). We propose using single baseline (Parkes-ATCA) eVLBI observations with the LBA at 1 Gbps to maximise sensitivity. With the observations proposed here we will increase the number of VLBI-observed IFRS from 5 to 36, allowing us to draw statistical conclusions about this intriguing new class of objects.

Jet outflow and gamma-ray emission correlations in S5 0716+714

International Nuclear Information System (INIS)

Rani, B.; Krichbaum, T. P.; Marscher, A. P.

2014-01-01

Here, using millimeter very long baseline interferometry (VLBI) observations of the BL Lac object S5 0716+714 from August 2008 to September 2013, we investigate variations in the core flux density and orientation of the sub-parsec scale jet, i.e. position angle. The γ-ray data obtained by the Fermi Large Area Telescope are used to investigate the high-energy flux variations over the same time period. For the first time in any blazar, we report a significant correlation between the γ-ray flux variations and the position angle variations in the VLBI jet. The cross-correlation analysis also indicates a positive correlation such that the mm-VLBI core flux density variations are delayed with respect to the γ-ray flux by 82±32 days. This suggests that the high-energy emission is coming from a region located ≥(3.8±1.9) parsecs upstream of the mm-VLBI core (closer to the central black hole). Lastly, these results imply that the observed inner jet morphology has a strong connection with the observed γ-ray flares.

An accuracy assessment of realtime GNSS time series toward semi- real time seafloor geodetic observation

Science.gov (United States)

Osada, Y.; Ohta, Y.; Demachi, T.; Kido, M.; Fujimoto, H.; Azuma, R.; Hino, R.

2013-12-01

Large interplate earthquake repeatedly occurred in Japan Trench. Recently, the detail crustal deformation revealed by the nation-wide inland GPS network called as GEONET by GSI. However, the maximum displacement region for interplate earthquake is mainly located offshore region. GPS/Acoustic seafloor geodetic observation (hereafter GPS/A) is quite important and useful for understanding of shallower part of the interplate coupling between subducting and overriding plates. We typically conduct GPS/A in specific ocean area based on repeated campaign style using research vessel or buoy. Therefore, we cannot monitor the temporal variation of seafloor crustal deformation in real time. The one of technical issue on real time observation is kinematic GPS analysis because kinematic GPS analysis based on reference and rover data. If the precise kinematic GPS analysis will be possible in the offshore region, it should be promising method for real time GPS/A with USV (Unmanned Surface Vehicle) and a moored buoy. We assessed stability, precision and accuracy of StarFireTM global satellites based augmentation system. We primarily tested for StarFire in the static condition. In order to assess coordinate precision and accuracy, we compared 1Hz StarFire time series and post-processed precise point positioning (PPP) 1Hz time series by GIPSY-OASIS II processing software Ver. 6.1.2 with three difference product types (ultra-rapid, rapid, and final orbits). We also used difference interval clock information (30 and 300 seconds) for the post-processed PPP processing. The standard deviation of real time StarFire time series is less than 30 mm (horizontal components) and 60 mm (vertical component) based on 1 month continuous processing. We also assessed noise spectrum of the estimated time series by StarFire and post-processed GIPSY PPP results. We found that the noise spectrum of StarFire time series is similar pattern with GIPSY-OASIS II processing result based on JPL rapid orbit

A Study on the Development of Playback Control Software for Mark5B VSI System

Directory of Open Access Journals (Sweden)

S. J. Oh

2010-06-01

Full Text Available We developed the playback control software for a high-speed playback system which is a component of the Korea-Japan Joint VLBI Correlator (KJJVC. The Mark5B system, which is a recorder and playback system used in the Korean VLBI Network (KVN, has two kinds of operation mode. That is to say, the station unit (SU mode, which is for the present Mark4 system, and the VSI mode, which is for the new VLBI standard interface (VSI system. The software for SU is already developed and widely used in the Mark4 type VLBI system, but the software for VSI has only been developed for recording. The new VLBI system is designed with a VSI interface for compatibility between different systems. Therefore, the playback control software development of the VSI mode is needed for KVN. In this work, we developed the playback control software of the Mark5B VSI mode. The developed playback control software consists of an application part for data playing back, a data input/output part for the VSI board, a module for the StreamStor RAID board, and a user interface part, including an observation time control part. To verify the performance of developed playback control software, the playback and correlation experiments were performed using the real observation data in Mark5B system and KJJVC. To check the observation time control, the data playback experiment was performed between the Mark5B and Raw VLBI Data Buffer (RVDB systems. Through the experimental results, we confirmed the performance of developed playback control software in the Mark5B VSI mode.

Current Trends and Challenges in Satellite Laser Ranging

Science.gov (United States)

Appleby, Graham M.; Bianco, Giuseppe; Noll, Carey E.; Pavlis, Erricos C.; Pearlman, Michael R.

2016-12-01

Satellite Laser Ranging (SLR) is used to measure accurately the distance from ground stations to retro-reflectors on satellites and on the Moon. SLR is one of the fundamental space-geodetic techniques that define the International Terrestrial Reference Frame (ITRF), which is the basis upon which many aspects of global change over space, time, and evolving technology are measured; with VLBI the two techniques define the scale of the ITRF; alone the SLR technique defines its origin (geocenter). The importance of the reference frame has recently been recognized at the inter-governmental level through the United Nations, which adopted in February 2015 the Resolution "Global Geodetic Reference Frame for Sustainable Development." Laser Ranging provides precision orbit determination and instrument calibration and validation for satellite-borne altimeters for the better understanding of sea level change, ocean dynamics, ice mass-balance, and terrestrial topography. It is also a tool to study the dynamics of the Moon and fundamental constants and theories. With the exception of the currently in-orbit GPS constellation, all GNSS satellites now carry retro-reflectors for improved orbit determination, harmonization of reference frames, and in-orbit co-location and system performance validation; the next generation of GPS satellites due for launch from 2019 onwards will also carry retro-reflectors. The ILRS delivers weekly realizations that are accumulated sequentially to extend the ITRF and the Earth Orientation Parameter series with a daily resolution. SLR technology continues to evolve towards the next-generation laser ranging systems and it is expected to successfully meet the challenges of the GGOS2020 program for a future Global Space Geodetic Network. Ranging precision is improving as higher repetition rate, narrower pulse lasers, and faster detectors are implemented within the network. Automation and pass interleaving at some stations is expanding temporal coverage and

Metre-wavelength fine structure in 30 extragalactic radio sources with sizes of a few arcsec

International Nuclear Information System (INIS)

Banhatti, D.G.; Ananthakrishnan, S.; Pramesh Rao, A.

1983-01-01

Interplanetary scintillation (IPS) observations at 327 MHz of an unbiased sample of 30 extragalactic radio sources having overall sizes between 1 and 4 arcsec, and flux densities greater than 1 Jy at 327 MHz are reported. From VLBI observations, these sources have been reported to contain compact components of sizes < approx.= to 0.02 arcsec contributing on an average about 25 per cent of the total emission at 5 HGz. The IPS observations show that about 45 per cent of the total emission at 327 MHz arises from structures of sizes between 0.05 and 0.5 arcsec (corresponding typically to 0.5 to 5 kpc). A comparison of the VLBI and IPS results indicates that the VLBI and IPS components probably refer to the same physical features in these sources. (author)

Regional Crustal Deformation and Lithosphere Thickness Observed with Geodetic Techniques

Science.gov (United States)

Vermeer, M.; Poutanen, M.; Kollo, K.; Koivula, H.; Ahola, J.

2009-04-01

The solid Earth, including the lithosphere, interacts in many ways with other components of the Earth system, oceans, atmosphere and climate. Geodesy is a key provider of data needed for global and environmental research. Geodesy provides methods and accurate measurements of contemporary deformation, sea level and gravity change. The importance of the decades-long stability and availability of reference frames must be stressed for such studies. In the future, the need to accurately monitor 3-D crustal motions will grow, both together with increasingly precise GNSS (Global Navigation Satellite System) positioning, demands for better follow-up of global change, and local needs for crustal motions, especially in coastal areas. These demands cannot yet be satisfied. The project described here is a part of a larger entity: Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas, DynaQlim, an International Lithosphere Project (ILP) -sponsored initiative. The aims of DynaQlim are to understand the relations between upper mantle dynamics, mantle composition, physical properties, temperature and rheology, to study the postglacial uplift and ice thickness models, sea level change and isostatic response, Quaternary climate variations and Weichselian (Laurentian and other) glaciations during the late Quaternary. We aim at studying various aspects of lithospheric motion within the Finnish and Fennoscandian area, but within a global perspective, by the newest geodetic techniques in a multidisciplinary setting. The studies involve observations of three-dimensional motions and gravity change in a multidisciplinary context on a range of spatial scales: the whole of Fennoscandia, Finland, a regional test area of Satakunta, and the local test site Olkiluoto. Objectives of the research include improving our insight into the 3-D motion of a thick lithosphere, and into the gravity effect of the uplift, using novel approaches; improving the kinematic 3-D models in the

Geodetic data support trapping of ethane in Titan's polar crust

Science.gov (United States)

Sotin, Christophe; Rambaux, Nicolas

2016-04-01

Titan's surface is characterized by polar depressions that strongly influence interpretations of the gravity data. This study investigates several geodynamical models that can explain these depressions. For each model, the values of the three moments of inertia are computed numerically by discretizing the interior in spherical coordinates. The study shows that a Pratt model where the polar subsurface is made of ethane clathrates can explain the polar depression, the abrupt jump in altitude at about 60 degrees latitude, and the values of the degree 2 gravity coefficients. This model, proposed by Choukroun and Sotin [1], is based on the stability of ethane clathrate hydrates relative to methane clathrate hydrates. In addition to fitting the geodetic data, it explains the absence of ethane in Titan's atmosphere although ethane is the main product of the photolysis of methane. Other geophysical models based on latitudinal variations in the tidal heating production or in the heat flux at the base of the icy crust do not provide such a good match to the gravity and topographic observations. The ethane-clathrate model predicts that all the ethane produced by photolysis of methane at the present rate during the last billion years could be stored in the polar subsurface. It is consistent with the age of Titan's surface and that of Titan's atmospheric methane inferred from geological and geochemical observations by the Cassini/Huygens mission. The present study also emphasizes the role of mass anomalies on the interpretation of the degree 2 gravity coefficients. It shows that for Titan, a slow rotator, the values of the two equatorial moments of inertia (MoI) are largely affected by the polar depressions whereas the value of polar MoI is not. Therefore, as pointed out by previous calculations [2], calculating the moment of inertia (MoI) factor from the value of J2 could lead to major errors. This is not the case for our preferred Titan's model for which the negative polar

Combination of monthly gravity field solutions from different processing centers

Science.gov (United States)

Jean, Yoomin; Meyer, Ulrich; Jäggi, Adrian

2015-04-01

Currently, the official GRACE Science Data System (SDS) monthly gravity field solutions are generated independently by the Centre for Space Research (CSR) and the German Research Centre for Geosciences (GFZ). Additional GRACE SDS monthly fields are provided by the Jet Propulsion Laboratory (JPL) for validation and outside the SDS by a number of other institutions worldwide. Although the adopted background models and processing standards have been harmonized more and more by the various processing centers during the past years, notable differences still exist and the users are more or less left alone with a decision which model to choose for their individual applications. Combinations are well-established in the area of other space geodetic techniques, such as the Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI), where regular comparisons and combinations of space-geodetic products have tremendously increased the usefulness of the products in a wide range of disciplines and scientific applications. In the frame of the recently started Horizon 2020 project European Gravity Service for Improved Emergency Management (EGSIEM), a scientific combination service shall therefore be established to deliver the best gravity products for applications in Earth and environmental science research based on the unified knowledge of the European GRACE community. In a first step the large variety of available monthly GRACE gravity field solutions shall be mutually compared spatially and spectrally. We assess the noise of the raw as well as filtered solutions and compare the secular and seasonal periodic variations fitted to the monthly solutions. In a second step we will explore ways to generate combined solutions, e.g., based on a weighted average of the individual solutions using empirical weights derived from pair-wise comparisons. We will also assess the quality of such a combined solution and discuss the

Geodetic Networks, This is udated by the use of GPS and updated weekely. It consist of interstate highways, state highways, major roads and local roads as well as private streets with address range, speed limit and elevation data associated to each segement., Published in 2007, Johnson County Government.

Data.gov (United States)

NSGIC Local Govt | GIS Inventory — Geodetic Networks dataset current as of 2007. This is udated by the use of GPS and updated weekely. It consist of interstate highways, state highways, major roads...

Analytic-graphic testing of deformities at the waterworks Pod Bukovcom

Directory of Open Access Journals (Sweden)

Jeèný Miloš

2001-09-01

Full Text Available The paper presents some geodetic measurement results in a frame of deformity survey of the bulk dam at the waterworks Pod Bukovcom nearby Košice. Periodic geodetic position and levelling measurement are realized on the dam since 1999. Testing statistics are applied into the deformity survey. Geodetic data obtained from individual measurements in the geodetic network on the bulk dam at the waterworks Pod Bukovcom are adjusted using Gauss-Markov model. Accuracy analysis by means of using relative and confidence ellipses is complemented to geodetic measurements.

Monitoring deep geodynamic processes within Vrancea intermediate-depth seismic zone by geodetic means

Science.gov (United States)

Besutiu, Lucian; Zlagnean, Luminita

2015-04-01

Background Located in the bending zone of East Carpathians, the so-called Vrancea zone is one of the most active seismic regions in Europe. Despite many years of international research, its intermediate-depth seismicity within full intra-continental environment still represents a challenge of the 21st century. Infrastructure In the attempt to join the above-mentioned efforts, the Solid Earth Dynamics Department (SEDD) in the Institute of Geodynamics of the Romanian Academy has developed a special research infrastructure, mainly devoted to gravity and space geodesy observations. A geodetic network covering the epicentre area of the intermediate-depth earthquakes has been designed and implemented for monitoring deep geodynamic processes and their surface echoes. Within each base-station of the above-mentioned network, a still-reinforced concrete pillar allows for high accuracy repeated gravity and GPS determinations. Results Starting from some results of the previously run CERGOP and UNIGRACE European programmes, to which additional SEDD repeated field campaigns were added, an unusual geodynamic behaviour has been revealed in the area. 1) Crust deformation: unlike the overall uprising of East Carpathians, as a result of denudation followed by erosion, their SE bending zone, with Vrancea epicentre area exhibits a slight subsidence. 2) Gravity change: more than 200 microgals non-tidal gravity decrease over a 20 years time-span has been noticed within the subsiding area. Extended observations showed the gravity lowering as a nowadays continuing process. Interpretation This strange combination of topography subsidence and gravity lowering has been interpreted in terms of crust stretching in the Vrancea epicentre zone due to the gravity pull created by densification of the lower crust as a result of phase-transform processes taking place in the lithospheric compartment sunken into the upper mantle. The occurrence of crust earthquakes with vertical-extension focal

Geodetic Measurements and Numerical Modeling of the Deformation Cycle for Okmok Volcano, Alaska: 1993-2008

Science.gov (United States)

Ohlendorf, S. J.; Feigl, K.; Thurber, C. H.; Lu, Z.; Masterlark, T.

2011-12-01

Okmok Volcano is an active caldera located on Umnak Island in the Aleutian Island arc. Okmok, having recently erupted in 1997 and 2008, is well suited for multidisciplinary studies of magma migration and storage because it hosts a good seismic network and has been the subject of synthetic aperture radar (SAR) images that span the recent eruption cycle. Interferometric SAR can characterize surface deformation in space and time, while data from the seismic network provides important information about the interior processes and structure of the volcano. We conduct a complete time series analysis of deformation of Okmok with images collected by the ERS and Envisat satellites on more than 100 distinct epochs between 1993 and 2008. We look for changes in inter-eruption inflation rates, which may indicate inelastic rheologic effects. For the time series analysis, we analyze the gradient of phase directly, without unwrapping, using the General Inversion of Phase Technique (GIPhT) [Feigl and Thurber, 2009]. This approach accounts for orbital and atmospheric effects and provides realistic estimates of the uncertainties of the model parameters. We consider several models for the source, including the prolate spheroid model and the Mogi model, to explain the observed deformation. Using a medium that is a homogeneous half space, we estimate the source depth to be centered at about 4 km below sea level, consistent with the findings of Masterlark et al. [2010]. As in several other geodetic studies, we find the source to be approximately centered beneath the caldera. To account for rheologic complexity, we next apply the Finite Element Method to simulate a pressurized cavity embedded in a medium with material properties derived from body wave seismic tomography. This approach allows us to address the problem of unreasonably large pressure values implied by a Mogi source with a radius of about 1 km by experimenting with larger sources. We also compare the time dependence of the

Structural control on the Tohoku earthquake rupture process investigated by 3D FEM, tsunami and geodetic data.

Science.gov (United States)

Romano, F; Trasatti, E; Lorito, S; Piromallo, C; Piatanesi, A; Ito, Y; Zhao, D; Hirata, K; Lanucara, P; Cocco, M

2014-07-09

The 2011 Tohoku earthquake (Mw = 9.1) highlighted previously unobserved features for megathrust events, such as the large slip in a relatively limited area and the shallow rupture propagation. We use a Finite Element Model (FEM), taking into account the 3D geometrical and structural complexities up to the trench zone, and perform a joint inversion of tsunami and geodetic data to retrieve the earthquake slip distribution. We obtain a close spatial correlation between the main deep slip patch and the local seismic velocity anomalies, and large shallow slip extending also to the North coherently with a seismically observed low-frequency radiation. These observations suggest that the friction controlled the rupture, initially confining the deeper rupture and then driving its propagation up to the trench, where it spreads laterally. These findings are relevant to earthquake and tsunami hazard assessment because they may help to detect regions likely prone to rupture along the megathrust, and to constrain the probability of high slip near the trench. Our estimate of ~40 m slip value around the JFAST (Japan Trench Fast Drilling Project) drilling zone contributes to constrain the dynamic shear stress and friction coefficient of the fault obtained by temperature measurements to ~0.68 MPa and ~0.10, respectively.

Rapid Ice-Sheet Changes and Mechanical Coupling to Solid-Earth/Sea-Level and Space Geodetic Observation

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Adhikari, S.; Ivins, E. R.; Larour, E. Y.

2015-12-01

Perturbations in gravitational and rotational potentials caused by climate driven mass redistribution on the earth's surface, such as ice sheet melting and terrestrial water storage, affect the spatiotemporal variability in global and regional sea level. Here we present a numerically accurate, computationally efficient, high-resolution model for sea level. Unlike contemporary models that are based on spherical-harmonic formulation, the model can operate efficiently in a flexible embedded finite-element mesh system, thus capturing the physics operating at km-scale yet capable of simulating geophysical quantities that are inherently of global scale with minimal computational cost. One obvious application is to compute evolution of sea level fingerprints and associated geodetic and astronomical observables (e.g., geoid height, gravity anomaly, solid-earth deformation, polar motion, and geocentric motion) as a companion to a numerical 3-D thermo-mechanical ice sheet simulation, thus capturing global signatures of climate driven mass redistribution. We evaluate some important time-varying signatures of GRACE inferred ice sheet mass balance and continental hydrological budget; for example, we identify dominant sources of ongoing sea-level change at the selected tide gauge stations, and explain the relative contribution of different sources to the observed polar drift. We also report our progress on ice-sheet/solid-earth/sea-level model coupling efforts toward realistic simulation of Pine Island Glacier over the past several hundred years.

Report for 2012 from the Bordeaux IVS Analysis Center

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Charlot, Patrick; Bellanger, Antoine; Bouffet, Romuald; Bourda, Geraldine; Collioud, Arnaud; Baudry, Alain

2013-01-01

This report summarizes the activities of the Bordeaux IVS Analysis Center during the year 2012. The work focused on (i) regular analysis of the IVS-R1 and IVS-R4 sessions with the GINS software package; (ii) systematic VLBI imaging of the RDV sessions and calculation of the corresponding source structure index and compactness values; (iii) investigation of the correlation between astrometric position instabilities and source structure variations; and (iv) continuation of our VLBI observational program to identify optically-bright radio sources suitable for the link with the future Gaia frame. Also of importance is the 11th European VLBI Network Symposium, which we organized last October in Bordeaux and which drew much attention from the European and International VLBI communities.

On the assimilation of absolute geodetic dynamic topography in a global ocean model: impact on the deep ocean state

Science.gov (United States)

Androsov, Alexey; Nerger, Lars; Schnur, Reiner; Schröter, Jens; Albertella, Alberta; Rummel, Reiner; Savcenko, Roman; Bosch, Wolfgang; Skachko, Sergey; Danilov, Sergey

2018-05-01

General ocean circulation models are not perfect. Forced with observed atmospheric fluxes they gradually drift away from measured distributions of temperature and salinity. We suggest data assimilation of absolute dynamical ocean topography (DOT) observed from space geodetic missions as an option to reduce these differences. Sea surface information of DOT is transferred into the deep ocean by defining the analysed ocean state as a weighted average of an ensemble of fully consistent model solutions using an error-subspace ensemble Kalman filter technique. Success of the technique is demonstrated by assimilation into a global configuration of the ocean circulation model FESOM over 1 year. The dynamic ocean topography data are obtained from a combination of multi-satellite altimetry and geoid measurements. The assimilation result is assessed using independent temperature and salinity analysis derived from profiling buoys of the AGRO float data set. The largest impact of the assimilation occurs at the first few analysis steps where both the model ocean topography and the steric height (i.e. temperature and salinity) are improved. The continued data assimilation over 1 year further improves the model state gradually. Deep ocean fields quickly adjust in a sustained manner: A model forecast initialized from the model state estimated by the data assimilation after only 1 month shows that improvements induced by the data assimilation remain in the model state for a long time. Even after 11 months, the modelled ocean topography and temperature fields show smaller errors than the model forecast without any data assimilation.

Geodetic integration of Sentinel-1A IW data using PSInSAR in Hungary

Science.gov (United States)

Farkas, Péter; Hevér, Renáta; Grenerczy, Gyula

2015-04-01

ESA's latest Synthetic Aperture Radar (SAR) mission Sentinel-1 is a huge step forward in SAR interferometry. With its default acquisition mode called the Interferometric Wide Swath Mode (IW) areas through all scales can be mapped with an excellent return time of 12 days (while only the Sentinel-1A is in orbit). Its operational data policy is also a novelty, it allows scientific users free and unlimited access to data. It implements a new type of ScanSAR mode called Terrain Observation with Progressive Scan (TOPS) SAR. It has the same resolution as ScanSAR but with better signal-to-noise ratio distribution. The bigger coverage is achieved by rotation of the antenna in the azimuth direction, therefore it requires very precise co-registration because even errors under a pixel accuracy can introduce azimuth phase variations caused by differences in Doppler-centroids. In our work we will summarize the benefits and the drawbacks of the IW mode. We would like to implement the processing chain of GAMMA Remote Sensing of such data for mapping surface motion with special attention to the co-registration step. Not only traditional InSAR but the advanced method of Persistent Scatterer InSAR (PSInSAR) will be performed and presented as well. PS coverage, along with coherence, is expected to be good due to the small perpendicular and temporal baselines. We would also like to integrate these measurements into national geodetic networks using common reference points. We have installed trihedral corner reflectors at some selected sites to aid precise collocation. Thus, we aim to demonstrate that Sentinel-1 can be effectively used for surface movement detection and monitoring and it can also provide valuable information for the improvement of our networks.

VLBI observations of the quasars CTD20 (0234+285), OJ248 (0827+243), and 4C19.44 (1354+195), and the millimeter-x-ray connection

International Nuclear Information System (INIS)

Marscher, A.P.; Broderick, J.J.

1983-01-01

We have obtained limited VLBI data on the quasars CTD20, OJ248, and 4C19.44 at 2.8 cm. CTD20 was also observed at 6 and 18 cm. All three sources contain multicomponent structure, and rather large fractions of the 2.8-cm flux densities arise in unresolved regions. All of the radio flux density of CTD20 originates in compact components. 4C19.44 is dominated at low frequencies by a steep-spectrum component which exceeds about 7 mas in size. Above 2 GHz the spectrum is flat and variable owing to several compact components. CTD20 and OJ248 belong to a sample of millimeter-excess quasars which were shown by Owen, Helfand, and Spangler to have highly predictable ratios of 90 GHz to 2-keV flux densities. A self-Compton explanation of this relationship is supported by the existence of unresolved radio components. However, the rapid 90-GHz variability of OJ248 and other quasars with strong millimeter emission should destroy the observed tight correlation except under special circumstances. A synchrotron origin of the radio-to-x-ray emission requires that any variations in the radio should be time delayed relative to the x ray

Low degree Earth's gravity coefficients determined from different space geodetic observations and climate models

Science.gov (United States)

Wińska, Małgorzata; Nastula, Jolanta

2017-04-01

Large scale mass redistribution and its transport within the Earth system causes changes in the Earth's rotation in space, gravity field and Earth's ellipsoid shape. These changes are observed in the ΔC21, ΔS21, and ΔC20 spherical harmonics gravity coefficients, which are proportional to the mass load-induced Earth rotational excitations. In this study, linear trend, decadal, inter-annual, and seasonal variations of low degree spherical harmonics coefficients of Earth's gravity field, determined from different space geodetic techniques, Gravity Recovery and Climate Experiment (GRACE), satellite laser ranging (SLR), Global Navigation Satellite System (GNSS), Earth rotation, and climate models, are examined. In this way, the contribution of each measurement technique to interpreting the low degree surface mass density of the Earth is shown. Especially, we evaluate an usefulness of several climate models from the Coupled Model Intercomparison Project phase 5 (CMIP5) to determine the low degree Earth's gravity coefficients using GRACE satellite observations. To do that, Terrestrial Water Storage (TWS) changes from several CMIP5 climate models are determined and then these simulated data are compared with the GRACE observations. Spherical harmonics ΔC21, ΔS21, and ΔC20 changes are calculated as the sum of atmosphere and ocean mass effect (GAC values) taken from GRACE and a land surface hydrological estimate from the selected CMIP5 climate models. Low degree Stokes coefficients of the surface mass density determined from GRACE, SLR, GNSS, Earth rotation measurements and climate models are compared to each other in order to assess their consistency. The comparison is done by using different types of statistical and signal processing methods.

Pattern of seismic deformation in the Western Mediterranean

Directory of Open Access Journals (Sweden)

S. Pondrelli

1999-06-01

Full Text Available The seismic deformation of the Western Mediterranean was studied with the aim of defining the strain pattern that characterizes the Africa-Eurasia plate boundary in this area. Within different sections along the boundary the cumulative moment tensor was computed over 90 years of seismological data. The results were compared with NUVELlA plate motion model and geodetic data. A stable agreement was found along Northern Africa to Sicily, where only Africa and Eurasia plates are involved. In this zone it is evident that changes in the strike of the boundary correspond to variations in the prevailing geometry of deformation, tectonic features and in the percentage of seismic with respect to total expected deformation. The geometry of deformation of periadriatic sections (Central to Southern Apennines, Eastern Alps and the Eastern Adriatic area agrees well with VLBI measurements and with regional geological features. Seismicity seems to account for low rates, from 3% to 31%, of total expected deformation. Only in the Sicily Strait, characterized by extensional to strike slip deformation, does the ratio reach a higher value (79%. If the amount of deformation deduced from seismicity seems low, because 90 years are probably not representative of the recurrence seismic cycle of the Western Mediterranean, the strain pattern we obtain from cumulative moment tensors is more representative of the kinematics of this area than global plate motion models and better identifies lower scale geodynamic features.

CONSTRAINING THE STRUCTURE OF SAGITTARIUS A*'s ACCRETION FLOW WITH MILLIMETER VERY LONG BASELINE INTERFEROMETRY CLOSURE PHASES

Energy Technology Data Exchange (ETDEWEB)

Broderick, Avery E [Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Fish, Vincent L; Doeleman, Sheperd S [Massachusetts Institute of Technology, Haystack Observatory, Route 40, Westford, MA 01886 (United States); Loeb, Abraham [Institute for Theory and Computation, Harvard University, Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2011-09-01

Millimeter wave very long baseline interferometry (mm-VLBI) provides access to the emission region surrounding Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, on sub-horizon scales. Recently, a closure phase of 0{sup 0} {+-} 40{sup 0} was reported on a triangle of Earth-sized baselines (SMT-CARMA-JCMT) representing a new constraint upon the structure and orientation of the emission region, independent from those provided by the previously measured 1.3 mm-VLBI visibility amplitudes alone. Here, we compare this to the closure phases associated with a class of physically motivated, radiatively inefficient accretion flow models and present predictions for future mm-VLBI experiments with the developing Event Horizon Telescope (EHT). We find that the accretion flow models are capable of producing a wide variety of closure phases on the SMT-CARMA-JCMT triangle and thus not all models are consistent with the recent observations. However, those models that reproduce the 1.3 mm-VLBI visibility amplitudes overwhelmingly have SMT-CARMA-JCMT closure phases between {+-}30{sup 0}, and are therefore broadly consistent with all current mm-VLBI observations. Improving station sensitivity by factors of a few, achievable by increases in bandwidth and phasing together multiple antennas at individual sites, should result in physically relevant additional constraints upon the model parameters and eliminate the current 180{sup 0} ambiguity on the source orientation. When additional stations are included, closure phases of order 45{sup 0}-90{sup 0} are typical. In all cases, the EHT will be able to measure these with sufficient precision to produce dramatic improvements in the constraints upon the spin of Sgr A*.

Monitoring Global Geophysical Fluids by Space Geodesy

Science.gov (United States)

Chao, Benjamin F.; Dehant, V.; Gross, R. S.; Ray, R. D.; Salstein, D. A.; Watkins, M.

1999-01-01

Since its establishment on 1/1/1998 by the International Earth Rotation Service, the Coordinating Center for Monitoring Global Geophysical Fluids (MGGF) and its seven Special Bureaus have engaged in an effort to support and facilitate the understanding of the geophysical fluids in global geodynamics research. Mass transports in the atmosphere-hydrosphere-solid Earth-core system (the "global geophysical fluids") will cause the following geodynamic effects on a broad time scale: (1) variations in the solid Earth's rotation (in length-of-day and polar motion/nutation) via the conservation of angular momentum and effected by torques at the fluid-solid Earth interface; (2) changes in the global gravitational field according to Newton's gravitational law; and (3) motion in the center of mass of the solid Earth relative to that of the whole Earth ("geocenter") via the conservation of linear momentum. These minute signals have become observable by space geodetic techniques, primarily VLBI, SLR, GPS, and DORIS, with ever increasing precision/accuracy and temporal/spatial resolution. Each of the seven Special Bureaus within MGGF is responsible for calculations related to a specific Earth component or aspect -- Atmosphere, Ocean, Hydrology, Ocean Tides, Mantle, Core, and Gravity/Geocenter. Angular momenta and torques, gravitational coefficients, and geocenter shift will be computed for geophysical fluids based on global observational data, and from state-of-the-art models, some of which assimilate such data. The computed quantities, algorithm and data formats are standardized. The results are archived and made available to the scientific research community. This paper reports the status of the MGGF activities and current results.

The concept of estimation of elevator shaft control measurement results in the local 3D coordinate system

Directory of Open Access Journals (Sweden)

Filipiak-Kowszyk Daria

2018-01-01

Full Text Available Geodetic control measurements play an important part because they provide information about the current state of repair of the construction, which has a direct impact on the safety assessment of its exploitation. Authors in this paper have focused on control measurements of the elevator shaft. The article discusses the problem of determining the deviation of elevator shaft walls from the vertical plane in the local 3D coordinate system. It presents a concept of estimation of measurements results base on the parametric method with conditions on parameters. The simulated measurement results were used to verify the concept presented in the paper.

Geodetic glacier mass balances at the push of a button: application of Structure from Motion technology on aerial images in mountain regions

Science.gov (United States)

Bolch, T.; Mölg, N.

2017-12-01

The application of Structure-from-Motion (SfM) to generate digital terrain models (DTMs) derived out of images from various kinds of sources has strongly increased in recent years. The major reason for this is its easy-to-use handling in comparison to conventional photogrammetry. In glaciology, DTMs are intensely used, among others, to calculate the geodetic mass balances. Few studies investigated the application of SfM to aerial images in mountainous terrain and results look promising. We tested this technique in a demanding environment in the Swiss Alps including very steep slopes, snow and ice covered terrain. SfM (using the commercial software packages of Agisoft Photoscan and Pix4DMapper) and conventional photogrammetry (ERDAS Photogrammetry) were applied on archival aerial images for nine dates between 1946 and 2005 the results were compared regarding bundle adjustment and final DTM quality. The overall precision of the DTMs could be defined with the use of a modern, high-quality reference DTM by Swisstopo. Results suggest a high performance of SfM to produce DTMs of similar quality as conventional photogrammetry. A ground resolution of high quality (little noise and artefacts) can be up to 50% higher, with 3-6 times less user effort. However, the controls on the commercial SfM software packages are limited in comparison to ERDAS Photogrammetry. SfM performs less reliably when few images with little overlap are processed. Overall, the uncertainty of DTMs from the different software are comparable and mostly within the uncertainty range of the reference DTM, making them highly valuable for glaciological purposes. Even though SfM facilitates the largely automated production of high quality DTMs, the user is not exempt from a thorough quality check, at best with reference data where available.

4-D Visualization of Seismic and Geodetic Data of the Big Island of Hawai'i

Science.gov (United States)

Burstein, J. A.; Smith-Konter, B. R.; Aryal, A.

2017-12-01

For decades Hawai'i has served as a natural laboratory for studying complex interactions between magmatic and seismic processes. Investigating characteristics of these processes, as well as the crustal response to major Hawaiian earthquakes, requires a synthesis of seismic and geodetic data and models. Here, we present a 4-D visualization of the Big Island of Hawai'i that investigates geospatial and temporal relationships of seismicity, seismic velocity structure, and GPS crustal motions to known volcanic and seismically active features. Using the QPS Fledermaus visualization package, we compile 90 m resolution topographic data from NASA's Shuttle Radar Topography Mission (SRTM) and 50 m resolution bathymetric data from the Hawaiian Mapping Research Group (HMRG) with a high-precision earthquake catalog of more than 130,000 events from 1992-2009 [Matoza et al., 2013] and a 3-D seismic velocity model of Hawai'i [Lin et al., 2014] based on seismic data from the Hawaiian Volcano Observatory (HVO). Long-term crustal motion vectors are integrated into the visualization from HVO GPS time-series data. These interactive data sets reveal well-defined seismic structure near the summit areas of Mauna Loa and Kilauea volcanoes, where high Vp and high Vp/Vs anomalies at 5-12 km depth, as well as clusters of low magnitude (M data are also used to help identify seismic clusters associated with the steady crustal detachment of the south flank of Kilauea's East Rift Zone. We also investigate the fault geometry of the 2006 M6.7 Kiholo Bay earthquake event by analyzing elastic dislocation deformation modeling results [Okada, 1985] and HVO GPS and seismic data of this event. We demonstrate the 3-D fault mechanisms of the Kiholo Bay main shock as a combination of strike-slip and dip-slip components (net slip 0.55 m) delineating a 30 km east-west striking, southward-dipping fault plane, occurring at 39 km depth. This visualization serves as a resource for advancing scientific analyses of

Immersive Virtual Reality Field Trips in the Geosciences: Integrating Geodetic Data in Undergraduate Geoscience Courses

Science.gov (United States)

La Femina, P. C.; Klippel, A.; Zhao, J.; Walgruen, J. O.; Stubbs, C.; Jackson, K. L.; Wetzel, R.

2017-12-01

High-quality geodetic data and data products, including GPS-GNSS, InSAR, LiDAR, and Structure from Motion (SfM) are opening the doors to visualizing, quantifying, and modeling geologic, tectonic, geomorphic, and geodynamic processes. The integration of these data sets with other geophysical, geochemical and geologic data is providing opportunities for the development of immersive Virtual Reality (iVR) field trips in the geosciences. iVR fieldtrips increase accessibility in the geosciences, by providing experiences that allow for: 1) exploration of field locations that might not be tenable for introductory or majors courses; 2) accessibility to outcrops for students with physical disabilities; and 3) the development of online geosciences courses. We have developed a workflow for producing iVR fieldtrips and tools to make quantitative observations (e.g., distance, area, and volume) within the iVR environment. We use a combination of terrestrial LiDAR and SfM data, 360° photos and videos, and other geophysical, geochemical and geologic data to develop realistic experiences for students to be exposed to the geosciences from sedimentary geology to physical volcanology. We present two of our iVR field trips: 1) Inside the Volcano: Exploring monogenetic volcanism at Thrihnukagigar Iceland; and 2) Changes in Depositional Environment in a Sedimentary Sequence: The Reedsville and Bald Eagle Formations, Pennsylvania. The Thrihnukagigar experience provides the opportunity to investigate monogenetic volcanism through the exploration of the upper 125 m of a fissure-cinder cone eruptive system. Students start at the plate boundary scale, then zoom into a single volcano where they can view the 3D geometry from either terrestrial LiDAR or SfM point clouds, view geochemical data and petrologic thins sections of rock samples, and a presentation of data collection and analysis, results and interpretation. Our sedimentary geology experience is based on a field lab from our

THE OPTICS OF REFRACTIVE SUBSTRUCTURE

Energy Technology Data Exchange (ETDEWEB)

Johnson, Michael D.; Narayan, Ramesh, E-mail: mjohnson@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2016-08-01

Newly recognized effects of refractive scattering in the ionized interstellar medium have broad implications for very long baseline interferometry (VLBI) at extreme angular resolutions. Building upon work by Blandford and Narayan, we present a simplified, geometrical optics framework, which enables rapid, semi-analytic estimates of refractive scattering effects. We show that these estimates exactly reproduce previous results based on a more rigorous statistical formulation. We then derive new expressions for the scattering-induced fluctuations of VLBI observables such as closure phase, and we demonstrate how to calculate the fluctuations for arbitrary quantities of interest using a Monte Carlo technique.

Monitoring ground deformation of cultural heritage sites using UAVs and geodetic techniques: the case study of Choirokoitia, JPI PROTHEGO project

Science.gov (United States)

Themistocleous, Kyriacos; Danezis, Chris; Mendonidis, Evangelos; Lymperopoulou, Efstathia

2017-10-01

This paper presents the integrated methods using UAVs and geodetic techniques to monitor ground deformation within the Choirokoitia UNESCO World Heritage Site in Cyprus. The Neolithic settlement of Choirokoitia, occupied from the 7th to the 4th millennium B.C., is one of the most important prehistoric sites in the eastern Mediterranean. The study is conducted under the PROTHEGO (PROTection of European Cultural HEritage from GeO-hazards) project, which is a collaborative research project funded in the framework of the Joint Programming Initiative on Cultural Heritage and Global Change (JPICH) - Heritage Plus in 2015-2018 (www.prothego.eu) and through the Cyprus Research Promotion Foundation. PROTHEGO aims to make an innovative contribution towards the analysis of geo-hazards in areas of cultural heritage, and uses novel space technology based on radar interferometry to retrieve information on ground stability and motion in the 400+ UNESCO's World Heritage List monuments and sites of Europe. The field measurements collected at the Choirokoitia site will be later compared with SAR data to verify micro-movements in the area to monitor potential geo-hazards. The site is located on a steep hill, which makes it vulnerable to rock falls and landslides.

Software Correlator for Radioastron Mission

Science.gov (United States)

Likhachev, Sergey F.; Kostenko, Vladimir I.; Girin, Igor A.; Andrianov, Andrey S.; Rudnitskiy, Alexey G.; Zharov, Vladimir E.

In this paper, we discuss the characteristics and operation of Astro Space Center (ASC) software FX correlator that is an important component of space-ground interferometer for Radioastron project. This project performs joint observations of compact radio sources using 10m space radio telescope (SRT) together with ground radio telescopes at 92, 18, 6 and 1.3 cm wavelengths. In this paper, we describe the main features of space-ground VLBI data processing of Radioastron project using ASC correlator. Quality of implemented fringe search procedure provides positive results without significant losses in correlated amplitude. ASC Correlator has a computational power close to real time operation. The correlator has a number of processing modes: “Continuum”, “Spectral Line”, “Pulsars”, “Giant Pulses”,“Coherent”. Special attention is paid to peculiarities of Radioastron space-ground VLBI data processing. The algorithms of time delay and delay rate calculation are also discussed, which is a matter of principle for data correlation of space-ground interferometers. During five years of Radioastron SRT successful operation, ASC correlator showed high potential of satisfying steady growing needs of current and future ground and space VLBI science. Results of ASC software correlator operation are demonstrated.

Geodetic Insights into the Earthquake Cycle in a Fold and Thrust Belt

Science.gov (United States)

Ingleby, T. F.; Wright, T. J.; Butterworth, V.; Weiss, J. R.; Elliott, J.

2017-12-01

Geodetic measurements are often sparse in time (e.g. individual interferograms) and/or space (e.g. GNSS stations), adversely affecting our ability to capture the spatiotemporal detail required to study the earthquake cycle in complex tectonic systems such as subaerial fold and thrust belts. In an effort to overcome these limitations we combine 3 generations of SAR satellite data (ERS 1/2, Envisat & Sentinel-1a/b) to obtain a 25 year, high-resolution surface displacement time series over the frontal portion of an active fold and thrust belt near Quetta, Pakistan where a Mw 7.1 earthquake doublet occurred in 1997. With these data we capture a significant portion of the seismic cycle including the interseismic, coseismic and postseismic phases. Each satellite time series has been referenced to the first ERS-1 SAR epoch by fitting a ground deformation model to the data. This allows us to separate deformation associated with each phase and to examine their relative roles in accommodating strain and creating topography, and to explore the relationship between the earthquake cycle and critical taper wedge mechanics. Modeling of the coseismic deformation suggests a long, thin rupture with rupture length 7 times greater than rupture width. Rupture was confined to a 20-30 degree north-northeast dipping reverse fault or ramp at depth, which may be connecting two weak decollements at approximately 8 km and 13 km depth. Alternatively, intersections between the coseismic fault plane and pre-existing steeper splay faults underlying folds may have played a significant role in inhibiting rupture, as evidenced by intersection points bordering the rupture. These fault intersections effectively partition the fault system down-dip and enable long, thin ruptures. Postseismic deformation is manifest as uplift across short-wavelength folds at the thrust front, with displacement rates decreasing with time since the earthquake. Broader patterns of postseismic uplift are also observed

Geodetic Infrastructure in the Ibiza and Barcelona Harbours for Sea Level Monitoring

Science.gov (United States)

Martinez-Benjamin, J. J.; Gili, J.; Lopez, R.; Tapia, A.; Perez, B.; Pros, F.

2013-12-01

The presentation is directed to the description of the actual situation and relevant information of the geodetic infrastructure of Ibiza and Barcelona sites for sea level determination and contribution to regional sea level rise. Time series are being analysed for mean sea level variations www.puertos.es. .In the framework of a Spanish Space Project, the instrumentation of sea level measurements has been improved by providing the Barcelona site with a radar tide gauge Datamar 2000C from Geonica s.l. near an acoustic tide gauge. Puertos del Estado installed in 2007 a MIROS radar tide gauge and the Barcelona Harbour Authority a GPS referente station in the roof of the new Control Tower situated in the Energy Pier. The radar sensor is over the water surface, on a L-shaped structure which elevates it a few meters above the quay shelf. 1-min data are transmitted to the ENAGAS Control Center by cable and then sent each 1 min to Puertos del Estado by e-mail. There is a GPS station Leica Geosystems GRX1200 GG Pro and antenna 1202. Precision levelling has been made several times in the last two years because the tower is founded in reclaimed land. The measured settlement rate is about 1cm/year that may be could mask the values registered by the tide gauge. A description of the actual infrastructure at Ibiza harbour at Marina de Botafoch, is presented and its applications to sea level monitoring and altimeter calibration in support of the main CGPS at Ibiza harbour. It is described the geometrical precision levelling made in June 2013 between the radar tide gauge and the GPS station. In particular, the CGPS located at Ibiza harbour is essential for its application to the marine campaign Baleares 2013, near Ibiza island. The main objective is to determine the altimeter bias for Jason-2, about 9:09 UTC September 15, 2013, and Saral/AltiKa, about 05:30 UTC September 16, UTC. These activities has been received funding of the Ministerio de Ciencia e Innovacion under Spanish

Global deformation of the Earth, surface mass anomalies, and the geodetic infrastructure required to study these processes

Science.gov (United States)

Kusche, J.; Rietbroek, R.; Gunter, B.; Mark-Willem, J.

2008-12-01

Global deformation of the Earth can be linked to loading caused by mass changes in the atmosphere, the ocean and the terrestrial hydrosphere. World-wide geodetic observation systems like GPS, e.g., the global IGS network, can be used to study the global deformation of the Earth directly and, when other effects are properly modeled, provide information regarding the surface loading mass (e.g., to derive geo-center motion estimates). Vice versa, other observing systems that monitor mass change, either through gravitational changes (GRACE) or through a combination of in-situ and modeled quantities (e.g., the atmosphere, ocean or hydrosphere), can provide indirect information on global deformation. In the framework of the German 'Mass transport and mass distribution' program, we estimate surface mass anomalies at spherical harmonic resolution up to degree and order 30 by linking three complementary data sets in a least squares approach. Our estimates include geo-center motion and the thickness of a spatially uniform layer on top of the ocean surface (that is otherwise estimated from surface fluxes, evaporation and precipitation, and river run-off) as a time-series. As with all current Earth observing systems, each dataset has its own limitations and do not realize homogeneous coverage over the globe. To assess the impact that these limitations might have on current and future deformation and loading mass solutions, a sensitivity study was conducted. Simulated real-case and idealized solutions were explored in which the spatial distribution and quality of GPS, GRACE and OBP data sets were varied. The results show that significant improvements, e.g., over the current GRACE monthly gravity fields, in particular at the low degrees, can be achieved when these solutions are combined with present day GPS and OBP products. Our idealized scenarios also provide quantitative implications on how much surface mass change estimates may improve in the future when improved observing

The Gravity Probe B experiment and early results

Energy Technology Data Exchange (ETDEWEB)

Conklin, John W [Stanford University (United States)], E-mail: johnwc@stanford.edu

2008-11-01

The NASA Gravity Probe B orbiting gyroscope test of General Relativity, launched from Vandenberg Air Force Base on 20 April, 2004 tests two consequences of Einstein's theory: 1) the predicted 6.6 arcs/yr geodetic effect due to the motion of the gyroscope through the curved space-time around the Earth; 2) the predicted 0.039 arcs/yr frame-dragging effect due to the rotating Earth. The mission required the development of many technologies that did not exist when experiment was conceived in 1960. Cryogenic gyroscopes with drift-rates 7 orders of magnitude better than the best inertial navigation gyroscopes, a < 1 marcs star tracking telescope, and other essential technologies were developed as a result of an intensive collaboration between Stanford physicists and engineers, NASA and industry. Gravity Probe B collected science data from August 27, 2004 through September 29, 2005. Analysis of the data began during the mission and is on-going. This paper describes the main features and challenges of the experiment and presents the preliminary results to date.

The Gravity Probe B experiment and early results

International Nuclear Information System (INIS)

Conklin, John W

2008-01-01

The NASA Gravity Probe B orbiting gyroscope test of General Relativity, launched from Vandenberg Air Force Base on 20 April, 2004 tests two consequences of Einstein's theory: 1) the predicted 6.6 arcs/yr geodetic effect due to the motion of the gyroscope through the curved space-time around the Earth; 2) the predicted 0.039 arcs/yr frame-dragging effect due to the rotating Earth. The mission required the development of many technologies that did not exist when experiment was conceived in 1960. Cryogenic gyroscopes with drift-rates 7 orders of magnitude better than the best inertial navigation gyroscopes, a < 1 marcs star tracking telescope, and other essential technologies were developed as a result of an intensive collaboration between Stanford physicists and engineers, NASA and industry. Gravity Probe B collected science data from August 27, 2004 through September 29, 2005. Analysis of the data began during the mission and is on-going. This paper describes the main features and challenges of the experiment and presents the preliminary results to date.

An embedded circumnuclear disk in Mrk 273

NARCIS (Netherlands)

Klockner, HR; Baan, WA

Radio observations using very long baseline interferometry (VLBI) and the Westerbork interferometer have been carried out to study the hydroxyl Megamaser emission in Mrk 273 at different spatial resolutions. Line and continuum observations were carried out by the European VLBI network (EVN) at 1.6

Comparison of pulsar positions from timing and very long baseline astrometry

Science.gov (United States)

Wang, J. B.; Coles, W. A.; Hobbs, G.; Shannon, R. M.; Manchester, R. N.; Kerr, M.; Yuan, J. P.; Wang, N.; Bailes, M.; Bhat, N. D. R.; Dai, S.; Dempsey, J.; Keith, M. J.; Lasky, P. D.; Levin, Y.; Osłowski, S.; Ravi, V.; Reardon, D. J.; Rosado, P. A.; Russell, C. J.; Spiewak, R.; van Straten, W.; Toomey, L.; Wen, L.; You, X.-P.; Zhu, X.-J.

2017-07-01

Pulsar positions can be measured with high precision using both pulsar timing methods and very long baseline interferometry (VLBI). Pulsar timing positions are referenced to a solar-system ephemeris, whereas VLBI positions are referenced to distant quasars. Here, we compare pulsar positions from published VLBI measurements with those obtained from pulsar timing data from the Nanshan and Parkes radio telescopes in order to relate the two reference frames. We find that the timing positions differ significantly from the VLBI positions (and also differ between different ephemerides). A statistically significant change in the obliquity of the ecliptic of 2.16 ± 0.33 mas is found for the JPL ephemeris DE405, but no significant rotation is found in subsequent JPL ephemerides. The accuracy with which we can relate the two frames is limited by the current uncertainties in the VLBI reference source positions and in matching the pulsars to their reference source. Not only do the timing positions depend on the ephemeris used in computing them, but also different segments of the timing data lead to varying position estimates. These variations are mostly common to all ephemerides, but slight changes are seen at the 10 μas level between ephemerides.

Macro- and micro- geodynamic of Terebliya-Riksk geodetic man-caused polygon of Ukrainian Carpathians influenced by specificities of structure-geological and hydro-geological conditions

Science.gov (United States)

Kulchyzkyy, A.; Serebryannyy, Y.; Tretyak, K.; Trevogo, I.; Zadoroznnyy, V.

2009-04-01

Terebliya-Riksk diversion power station is located on two levels ( with difference of 180m ) of south mountainside of Ukrainian Carpathians and separate parts of this power station lie inside rock. Therefore influential parameters of it's stability are geological, tectonic and hydrogeological conditions in complex. Monitoring of intensity and nature of displacements of flow ( pressure) pipe and other objects of power station with geoditic methods indicates that fluctuations of water-level in reservoir caused bouth by natural and artificial efects are of great influence on objects mentioned. Based on geodetical high-precision observations made by LeicaTPS 1201 robotic total station short-periodic components of fundamental vibrations which result in their destructive deformation were determined. Mathematical apparatus ( which uses function of Fourie series and theory of cinematic coefficients ) for displacements determinations of pressure pipe was disigned. Complex of engineering-geological surveys gave an opportunity to define the origin of macro- and micro- geodynamics movements of Terebliya-Riksk diversion power station region. Engineering-geological conditions which influence on power station structure most of all were determined as following : small foldings and cleavage areas appearances, also fluctuations of level of underground water (refered to hydrogeological conditions). Periodic micro-displacemets appearances ( which operate on reducing-stretching scheme) fixed on power station structure are turned to be in direct relation on to what exend reservoir is filled up. Permanent macro- displacements appearances ( which operates in north-west direction ) fixed on pressure pipe are the result sum of residual micro-displacements caused by return periodic movements and are determined by structure-geological, engineering-geological and tectonic conditions.

Geodetic Imaging for Rapid Assessment of Earthquakes: Airborne Laser Scanning (ALS)

Science.gov (United States)

Carter, W. E.; Shrestha, R. L.; Glennie, C. L.; Sartori, M.; Fernandez-Diaz, J.; National CenterAirborne Laser Mapping Operational Center

2010-12-01

northwest, from the epicenter in Baja California through the US-Mexico border. The ALS observations were collected from an aircraft altitude of 600 m, flying at approximately 80 m/sec, using an Optech Inc. Gemini sensor, operating at 100 kHz, a scanning angle plus/minus 14 degrees and scan rate of 60 Hz. Some 24 lines, comprising a corridor 3 km wide and 106 km in length, were mapped, with a nominal point density of just over 10 points/m2. Total flight time for the project was just under 21 hours, but the laser on time was only 13 hours and 21 minutes. Preliminary versions of the observational data were delivered to the PIs (Michael Oskin, UC Davis, and Ramon Arrowsmith, ASU) within a few days of their collection. Geodetic imaging is still in its early stages of development, and ALS technology is progressing rapidly. The use of multiple channel (based on multiple lasers of the same or different colors and/or receivers operating in parallel) ALS units will result in contiguous sub-decimeter coverage, and deployment of ALS units in UAVs, with data transmitted to the operators in real time, will further reduce the turn-around time and enable more rapid assessment of earthquakes within the next decade.

VMF3/GPT3: refined discrete and empirical troposphere mapping functions

Science.gov (United States)

Landskron, Daniel; Böhm, Johannes

2018-04-01

Incorrect modeling of troposphere delays is one of the major error sources for space geodetic techniques such as Global Navigation Satellite Systems (GNSS) or Very Long Baseline Interferometry (VLBI). Over the years, many approaches have been devised which aim at mapping the delay of radio waves from zenith direction down to the observed elevation angle, so-called mapping functions. This paper contains a new approach intended to refine the currently most important discrete mapping function, the Vienna Mapping Functions 1 (VMF1), which is successively referred to as Vienna Mapping Functions 3 (VMF3). It is designed in such a way as to eliminate shortcomings in the empirical coefficients b and c and in the tuning for the specific elevation angle of 3°. Ray-traced delays of the ray-tracer RADIATE serve as the basis for the calculation of new mapping function coefficients. Comparisons of modeled slant delays demonstrate the ability of VMF3 to approximate the underlying ray-traced delays more accurately than VMF1 does, in particular at low elevation angles. In other words, when requiring highest precision, VMF3 is to be preferable to VMF1. Aside from revising the discrete form of mapping functions, we also present a new empirical model named Global Pressure and Temperature 3 (GPT3) on a 5°× 5° as well as a 1°× 1° global grid, which is generally based on the same data. Its main components are hydrostatic and wet empirical mapping function coefficients derived from special averaging techniques of the respective (discrete) VMF3 data. In addition, GPT3 also contains a set of meteorological quantities which are adopted as they stand from their predecessor, Global Pressure and Temperature 2 wet. Thus, GPT3 represents a very comprehensive troposphere model which can be used for a series of geodetic as well as meteorological and climatological purposes and is fully consistent with VMF3.

Towards combined global monthly gravity field solutions

Science.gov (United States)

Jaeggi, Adrian; Meyer, Ulrich; Beutler, Gerhard; Weigelt, Matthias; van Dam, Tonie; Mayer-Gürr, Torsten; Flury, Jakob; Flechtner, Frank; Dahle, Christoph; Lemoine, Jean-Michel; Bruinsma, Sean

2014-05-01

Currently, official GRACE Science Data System (SDS) monthly gravity field solutions are generated independently by the Centre for Space Research (CSR) and the German Research Centre for Geosciences (GFZ). Additional GRACE SDS monthly fields are provided by the Jet Propulsion Laboratory (JPL) for validation and outside the SDS by a number of other institutions worldwide. Although the adopted background models and processing standards have been harmonized more and more by the various processing centers during the past years, notable differences still exist and the users are more or less left alone with a decision which model to choose for their individual applications. This procedure seriously limits the accessibility of these valuable data. Combinations are well established in the area of other space geodetic techniques, such as the Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI). Regularly comparing and combining space-geodetic products has tremendously increased the usefulness of the products in a wide range of disciplines and scientific applications. Therefore, we propose in a first step to mutually compare the large variety of available monthly GRACE gravity field solutions, e.g., by assessing the signal content over selected regions, by estimating the noise over the oceans, and by performing significance tests. We make the attempt to assign different solution characteristics to different processing strategies in order to identify subsets of solutions, which are based on similar processing strategies. Using these subsets we will in a second step explore ways to generate combined solutions, e.g., based on a weighted average of the individual solutions using empirical weights derived from pair-wise comparisons. We will also assess the quality of such a combined solution and discuss the potential benefits for the GRACE and GRACE-FO user community, but also address minimum processing

Investigation of land subsidence due to climate changes in surrounding areas of Urmia Lake (located in northwest of Iran) using wavelet coherence analysis of geodetic measurements and methodological data

Science.gov (United States)

Moghtased-Azar, K.; Mirzaei, A.; Nankali, H. R.; Tavakoli, F.

2012-04-01

Urmia Lake (salt lake in northwest of Iran) plays a valuable role in environment, wildlife and economy of Iran and the region, and now faces great challenges for survival. The Lake is in immediate and great danger and rapidly going to become salty desert. During the recent years and new heat wave, Iran, like many other countries are experiencing, is faced with relativity reduced rain fall. From a few years ago environment activists warned about potential dangers. Geodetic measurements, e.g., repeated leveling measurements of first order leveling network of Iran and continuous GPS measurements of Iranian Permanent GPS network of Iran (IPGN) showed that there is subsidence in surrounding areas of the lake. This paper investigates the relation between subsidence and climate changing in the area, using the wavelet coherence of the data of permanent GPS stations and daily methodological data. The results show that there is strong coherence between the subsidence phenomena induced by GPS data and climate warming from January 2009 up to end of August 2009. However, relative lake height variations computed from altimetry observations (TOPEX/POSEIDON (T/P), Jason-1 and Jason-2/OSTM) confirms maximum evaporation rates of the lake in this period.

Review and comparison of recent methods in space geodesy

International Nuclear Information System (INIS)

Varga, M.

1983-01-01

The study of geodynamic processes requires the application of new space-born geodesic measuring methods. A terrestrial reference system (TRS) is required for describing geodynamic processes. For this purpose satisfactory knowledge of polar motions, Earth rotation and tidal forces determined by laser, global positioning system (GPS) and VLBI measurements are needed. In addition, gravity and magnetic field of the Earth have to be known, modelled by using satellite to satellite traching (SST), altimetry, gradiometry and magnetometry results. Motions of the Earth-Moon system, as well as the relation between the terrestrial reference system and the inertial system can be determined by means of VLBI measurements. (author)

Very Long Baseline Interferometry with the SKA

NARCIS (Netherlands)

Paragi, Z.; Godfrey, L.; Reynolds, C.; Rioja, M. J.; Deller, A.; Zhang, B.; Gurvits, L.; Bietenholz, M.; Szomoru, A.; Bignall, H. E.; Boven, P.; Charlot, P.; Dodson, R.; Frey, S.; Garrett, M. A.; Imai, H.; Lobanov, A.; Reid, M. J.; Ros, E.; van Langevelde, H. J.; Zensus, A. J.; Zheng, X. W.; Alberdi, A.; Agudo, I.; An, T.; Argo, M.; Beswick, R.; Biggs, A.; Brunthaler, A.; Campbell, B.; Cimo, G.; Colomer, F.; Corbel, S.; Conway, J. E.; Cseh, D.; Deane, R.; Falcke, H. D. E.; Gawronski, M.; Gaylard, M.; Giovannini, G.; Giroletti, M.; Goddi, C.; Goedhart, S.; Gómez, J. L.; Gunn, A.; Kharb, P.; Kloeckner, H. R.; Koerding, E.; Kovalev, Y.; Kunert-Bajraszewska, M.; Lindqvist, M.; Lister, M.; Mantovani, F.; Marti-Vidal, I.; Mezcua, M.; McKean, J.; Middelberg, E.; Miller-Jones, J. C. A.; Moldon, J.; Muxlow, T.; O'Brien, T.; Perez-Torres, M.; Pogrebenko, S. V.; Quick, J.; Rushton, A.; Schilizzi, R.; Smirnov, O.; Sohn, B. W.; Surcis, G.; Taylor, G. B.; Tingay, S.; Tudose, V. M.; van der Horst, A.; van Leeuwen, J.; Venturi, T.; Vermeulen, R.; Vlemmings, W. H. T.; de Witt, A.; Wucknitz, O.; Yang, J.; Gabänyi, K.; Jung, T.

2015-01-01

Adding VLBI capability to the SKA arrays will greatly broaden the science of the SKA, and is feasible within the current specifications. SKA-VLBI can be initially implemented by providing phased-array outputs for SKA1-MID and SKA1-SUR and using these extremely sensitive stations with other radio

From Geodetic Imaging of Seismic and Aseismic Fault Slip to Dynamic Modeling of the Seismic Cycle

Science.gov (United States)

Avouac, Jean-Philippe

2015-05-01

Understanding the partitioning of seismic and aseismic fault slip is central to seismotectonics as it ultimately determines the seismic potential of faults. Thanks to advances in tectonic geodesy, it is now possible to develop kinematic models of the spatiotemporal evolution of slip over the seismic cycle and to determine the budget of seismic and aseismic slip. Studies of subduction zones and continental faults have shown that aseismic creep is common and sometimes prevalent within the seismogenic depth range. Interseismic coupling is generally observed to be spatially heterogeneous, defining locked patches of stress accumulation, to be released in future earthquakes or aseismic transients, surrounded by creeping areas. Clay-rich tectonites, high temperature, and elevated pore-fluid pressure seem to be key factors promoting aseismic creep. The generally logarithmic time evolution of afterslip is a distinctive feature of creeping faults that suggests a logarithmic dependency of fault friction on slip rate, as observed in laboratory friction experiments. Most faults can be considered to be paved with interlaced patches where the friction law is either rate-strengthening, inhibiting seismic rupture propagation, or rate-weakening, allowing for earthquake nucleation. The rate-weakening patches act as asperities on which stress builds up in the interseismic period; they might rupture collectively in a variety of ways. The pattern of interseismic coupling can help constrain the return period of the maximum- magnitude earthquake based on the requirement that seismic and aseismic slip sum to match long-term slip. Dynamic models of the seismic cycle based on this conceptual model can be tuned to reproduce geodetic and seismological observations. The promise and pitfalls of using such models to assess seismic hazard are discussed.

Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis.

Science.gov (United States)

Rogers, A E; Cappallo, R J; Hinteregger, H F; Levine, J I; Nesman, E F; Webber, J C; Whitney, A R; Clark, T A; Ma, C; Ryan, J; Corey, B E; Counselman, C C; Herring, T A; Shapiro, I I; Knight, C A; Shaffer, D B; Vandenberg, N R; Lacasse, R; Mauzy, R; Rayhrer, B; Schupler, B R; Pigg, J C

1983-01-07

The Mark III very-long-baseline interferometry (VLBI) system allows recording and later processing of up to 112 megabits per second from each radio telescope of an interferometer array. For astrometric and geodetic measurements, signals from two radio-frequency bands (2.2 to 2.3 and 8.2 to 8.6 gigahertz) are sampled and recorded simultaneously at all antenna sites. From these dual-band recordings the relative group delays of signals arriving at each pair of sites can be corrected for the contributions due to the ionosphere. For many radio sources for which the signals are sufficiently intense, these group delays can be determined with uncertainties under 50 picoseconds. Relative positions of widely separated antennas and celestial coordinates of radio sources have been determined from such measurements with 1 standard deviation uncertainties of about 5 centimeters and 3 milliseconds of arc, respectively. Sample results are given for the lengths of baselines between three antennas in the United States and three in Europe as well as for the arc lengths between the positions of six extragalactic radio sources. There is no significant evidence of change in any of these quantities. For mapping the brightness distribution of such compact radio sources, signals of a given polarization, or of pairs of orthogonal polarizations, can be recorded in up to 28 contiguous bands each nearly 2 megahertz wide. The ability to record large bandwidths and to link together many large radio telescopes allows detection and study of compact sources with flux densities under 1 millijansky.

Active galactic nuclei cores in infrared-faint radio sources. Very long baseline interferometry observations using the Very Long Baseline Array

Science.gov (United States)

Herzog, A.; Middelberg, E.; Norris, R. P.; Spitler, L. R.; Deller, A. T.; Collier, J. D.; Parker, Q. A.

2015-06-01

Context. Infrared-faint radio sources (IFRS) form a new class of galaxies characterised by radio flux densities between tenths and tens of mJy and faint or absent infrared counterparts. It has been suggested that these objects are radio-loud active galactic nuclei (AGNs) at significant redshifts (z ≳ 2). Aims: Whereas the high redshifts of IFRS have been recently confirmed based on spectroscopic data, the evidence for the presence of AGNs in IFRS is mainly indirect. So far, only two AGNs have been unquestionably confirmed in IFRS based on very long baseline interferometry (VLBI) observations. In this work, we test the hypothesis that IFRS contain AGNs in a large sample of sources using VLBI. Methods: We observed 57 IFRS with the Very Long Baseline Array (VLBA) down to a detection sensitivity in the sub-mJy regime and detected compact cores in 35 sources. Results: Our VLBA detections increase the number of VLBI-detected IFRS from 2 to 37 and provide strong evidence that most - if not all - IFRS contain AGNs. We find that IFRS have a marginally higher VLBI detection fraction than randomly selected sources with mJy flux densities at arcsec-scales. Moreover, our data provide a positive correlation between compactness - defined as the ratio of milliarcsec- to arcsec-scale flux density - and redshift for IFRS, but suggest a decreasing mean compactness with increasing arcsec-scale radio flux density. Based on these findings, we suggest that IFRS tend to contain young AGNs whose jets have not formed yet or have not expanded, equivalent to very compact objects. We found two IFRS that are resolved into two components. The two components are spatially separated by a few hundred milliarcseconds in both cases. They might be components of one AGN, a binary black hole, or the result of gravitational lensing.

Geodetic Mass Balance of the Northern Patagonian Icefield from 2000 to 2012 Using Two Independent Methods

Directory of Open Access Journals (Sweden)

Inés Dussaillant

2018-02-01

Full Text Available We compare two independent estimates of the rate of elevation change and geodetic mass balance of the Northern Patagonian Icefield (NPI between 2000 (3,856 km2 and 2012 (3,740 km2 from space-borne data. The first is obtained by differencing the Shuttle Radar Topography Mission (SRTM digital elevation model (DEM from February 2000 and a Satellite pour l'Observation de la Terre 5 (SPOT5 DEM from March 2012. The second is deduced by fitting pixel-based linear elevation trends over 118 DEMs calculated from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER stereo images acquired between 2000 and 2012. Both methods lead to similar and strongly negative icefield-wide mass balance rates of −1.02 ± 0.21 and −1.06 ± 0.14 m w.e. yr−1 respectively, which is in agreement with earlier studies. Contrasting glacier responses are observed, with individual glacier mass balance rates ranging from −0.15 to −2.30 m w.e. yr−1 (standard deviation = 0.49 m w.e. yr−1; N = 38. For individual glaciers, the two methods agree within error bars, except for small glaciers poorly sampled in the SPOT5 DEM due to clouds. Importantly, our study confirms the lack of penetration of the C-band SRTM radar signal into the NPI snow and firn except for a region above 2,900 m a.s.l. covering <1% of the total area. Ignoring penetration would bias the mass balance by only 0.005 m w.e. yr−1. A strong advantage of the ASTER method is that it relies only on freely available data and can thus be extended to other glacierized areas.

First results of the Nordic and Baltic GNSS Analysis Centre

Science.gov (United States)

Lahtinen, Sonja; Pasi, Häkli; Jivall, Lotti; Kempe, Christina; Kollo, Karin; Kosenko, Ksenija; Pihlak, Priit; Prizginiene, Dalia; Tangen, Oddvar; Weber, Mette; Paršeliūnas, Eimuntas; Baniulis, Rimvydas; Galinauskas, Karolis

2018-03-01

The Nordic Geodetic Commission (NKG) has launched a joint NKG GNSS Analysis Centre that aims to routinely produce high qualityGNSS solutions for the common needs of the NKG and the Nordic and Baltic countries. A consistent and densified velocity field is needed for the constraining of the gla-cial isostatic adjustment (GIA) modelling that is a key component of maintaining the national reference frame realisations in the area. We described the methods of the NKG GNSS Analysis Centre including the defined processing setup for the local analysis centres (LAC) and for the combination centres.We analysed the results of the first 2.5 years (2014.5-2016). The results showed that different subnets were consistent with the combined solution within 1-2 mm level. We observed the so called network effect affecting our reference frame alignment. However, the accuracy of the reference frame alignment was on a few millimetre level in the area of the main interest (Nordic and Baltic Countries). TheNKGGNSS AC was declared fully operational in April 2017.

Twenty-five years of geodetic measurements along the Tadjoura-Asal rift system, Djibouti, East Africa

Science.gov (United States)

Vigny, Christophe; de Chabalier, Jean-Bernard; Ruegg, Jean-Claude; Huchon, Philippe; Feigl, Kurt L.; Cattin, Rodolphe; Asfaw, Laike; Kanbari, Khaled

2007-06-01

Since most of Tadjoura-Asal rift system sits on dry land in the Afar depression near the triple junction between the Arabia, Somalia, and Nubia plates, it is an ideal natural laboratory for studying rifting processes. We analyze these processes in light of a time series of geodetic measurements from 1978 through 2003. The surveys used triangulation (1973), trilateration (1973, 1979, and 1981-1986), leveling (1973, 1979, 1984-1985, and 2000), and the Global Positioning System (GPS, in 1991, 1993, 1995, 1997, 1999, 2001, and 2003). A network of about 30 GPS sites covers the Republic of Djibouti. Additional points were also measured in Yemen and Ethiopia. Stations lying in the Danakil block have almost the same velocity as Arabian plate, indicating that opening near the southern tip of the Red Sea is almost totally accommodated in the Afar depression. Inside Djibouti, the Asal-Ghoubbet rift system accommodates 16 ± 1 mm/yr of opening perpendicular to the rift axis and exhibits a pronounced asymmetry with essentially null deformation on its southwestern side and significant deformation on its northeastern side. This rate, slightly higher than the large-scale Arabia-Somalia motion (13 ± 1 mm/yr), suggests transient variations associated with relaxation processes following the Asal-Ghoubbet seismovolcanic sequence of 1978. Inside the rift, the deformation pattern exhibits a clear two-dimensional pattern. Along the rift axis, the rate decreases to the northwest, suggesting propagation in the same direction. Perpendicular to the rift axis, the focus of the opening is clearly shifted to the northeast, relative to the topographic rift axis, in the "Petit Rift," a rift-in-rift structure, containing most of the active faults and the seismicity. Vertical motions, measured by differential leveling, show the same asymmetric pattern with a bulge of the northeastern shoulder. Although the inner floor of the rift is subsiding with respect to the shoulders, all sites within the

Hα Intensity Oscillations in Large Flares Ram Ajor Maurya & Ashok ...

Indian Academy of Sciences (India)

) have recently used this method for spectral analysis of VLBI observational data, and investigated the problem of appearance of spurious signal in the data with unequally spaced sampling. 4. Results and conclusion. The Hα filtergrams for ...

A System to Produce Precise Global GPS Network Solutions for all Geodetic GPS Stations in the World

Science.gov (United States)

Blewitt, G.; Kreemer, C. W.

2010-12-01

We have developed an end-to-end system that automatically seeks and routinely retrieves geodetic GPS data from ~5000 stations (currently) around the globe, reduces the data into unique, daily global network solutions, and produces high precision time series for station coordinates ready for time-series analysis, geophysical modeling and interpretation. Moreover, “carrier range” data are produced for all stations, enabling epoch-by-epoch tracking of individual station motions by precise point positioning for investigation of sub-daily processes, such as post-seismic after-slip and ocean tidal loading. Solutions are computed in a global reference frame aligned to ITRF, and optionally in user-specified continental-scale reference frames that can filter out common-mode signals to enhance regional strain anomalies. We describe the elements of this system, the underlying signal processing theory, the products, operational statistics, and scientific applications of our system. The system is fundamentally based on precise point positioning using JPL's GIPSY OASIS II software, coupled with ambiguity resolution and a global network adjustment of ~300,000 parameters per day using our newly developed Ambizap3 software. The system is designed to easily and efficiently absorb stations that deliver data very late, by recycling prior computations in the network adjustment, such that the resulting network solution is identical to starting from scratch. Thus, it becomes possible to trawl continuously the Internet for late arriving data, or for newly discovered data, and seamlessly update all GPS station time series using the new information content. As new stations are added to the processing archive, automated e-mail requests are made to H.-G. Scherneck's server at Chalmers University to compute ocean loading coefficients used by the station motion model. Rinex file headers are parsed and compared with alias tables in order to infer the correct receiver type and antenna

Analysis of geodetic and legal documentation in the process of expropriation for roads. Krakow case study

Science.gov (United States)

Trembecka, Anna

2013-06-01

Amendment to the Act on special rules of preparation and implementation of investment in public roads resulted in an accelerated mode of acquisition of land for the development of roads. The decision to authorize the execution of road investment issued on its basis has several effects, i.e. determines the location of a road, approves surveying division, approves construction design and also results in acquisition of a real property by virtue of law by the State Treasury or local government unit, among others. The conducted study revealed that over 3 years, in this mode, the city of Krakow has acquired 31 hectares of land intended for the implementation of road investments. Compensation is determined in separate proceedings based on an appraisal study estimating property value, often at a distant time after the loss of land by the owner. One reason for the lengthy compensation proceedings is challenging the proposed amount of compensation, unregulated legal status of the property as well as imprecise legislation. It is important to properly develop geodetic and legal documentation which accompanies the application for issuance of the decision and is also used in compensation proceedings. Zmiana ustawy o szczególnych zasadach przygotowywania i realizacji inwestycji w zakresie dróg publicznych spowodowała przyspieszony tryb pozyskiwania gruntów przeznaczonych pod budowę dróg. Wydawana na jej podstawie decyzja o zezwoleniu na realizację inwestycji drogowej wywołuje szereg skutków, tj. m.in. ustala lokalizację drogi, zatwierdza podziały geodezyjne, zatwierdza projekt budowlany a także powoduje nabycie nieruchomości z mocy prawa, przez Skarb Państwa lub jednostki samorządu terytorialnego. Przeprowadzone badania wykazały iż w powyższym trybie miasto Kraków nabyło w okresie 3 lat ponad 31 ha gruntów przeznaczonych na realizację inwestycji drogowych. Odszkodowanie ustalane jest w drodze odrębnego postępowania w oparciu o operat szacunkowy okre

Collaboration and Development of Radio Astronomy in Australasia and South-Pacific Region: New Zealand Perspectives

Science.gov (United States)

Gulyaev, S.; Natusch, T.

2006-08-01

Radio telescopes in the Asia-Pacific region form a natural network for VLBI observations, similar to the very successful networks in North America (Network Users Group) and Europe (European VLBI Network). New Zealand's VLBI facility, which we are developing since 2005, has the potential to strengthen the Asian-Pacific VLBI network and its role in astronomy, geodesy and geoscience. It will positively influence regional and international activities in geoscience and geodesy that advance New Zealand's national interests. A self-contained radio astronomy system for VLBI, including a 1.658 GHz (centre frequency), 16 MHz bandwidth RF system (feed and downconversion system locked to a Rubidium maser and GPS clock), an 8-bit sampler/digitisation system, and a disk-based recording system built around a commodity PC was developed in New Zealand Centre for Radiophysics and Space Research. This was designed as a portable system for use on various radio telescopes. A number of Trans-Tasman tests has been conducted in 2005-2006 between the CRSR system installed on a 6 metre dish located in Auckland and the Australia Telescope Compact Array in Narrabri, Australia. This work has been successful, with fringes located from the recorded data and high resolution image of the quasar PKS1921-231 obtained. Experiments were recently conducted with Japan; new tests are planned with Korea and Fiji. Plans have been made to build a new 16.5 m antenna in New Zealand's North Island and to upgrade an 11 m dish in the South Island. A possible future of New Zealand's participation in the SKA is being discussed.

GRAVITY VARIATIONS AND RECENT GEODYNAMICS OF THE SOUTH-WESTERN PART OF THE BAIKAL REGION

Directory of Open Access Journals (Sweden)

V. Yu. Timofeev

2013-01-01

Full Text Available Modern methods for determination of gravity values make it possible to obtain measurements with the accuracy up to 10–9 from g0 of the normal value (up to 1 microgal = 10 m/sec2. While all the systematic and periodic effects are excluded, a question is raised about stability of the gravity field of the Earth over time. Changes of the altitude (the Earth’s radius with time can be estimated with an accuracy of 0.1 mm by modern space geodetic techniques, such as VLBI method. Our experiments for evaluation of stability of the gravity values over the past decades are based on the data obtained by Russian and foreign observatories using absolute ballistic laser gravimeters. The results put a limit of 10–10 per year to changes of the Earth’s radius. These estimations can be useful for testing hypotheses in tectonics.Measurements of non-tidal variations of gravity (Δg, which were obtained from 1992 to 2012 at the Talaya seismic station (located in the south-western part of the Baikal region, are interpreted together with GPS observation data. At the Talaya seismic station, the linear component of gravity variations corresponds to changes in the elevation of this site. The correlation coefficient is close to the normal value of the vertical gradient of gravity. At this site, coseismic gravity variations at the time of the Kultuk earthquake (27 August 2008, Mw=6.3 were caused by a combined effect of the change of the site’s elevation and deformation of the crust. Our estimations of the coseismic effects are consistent with results obtained by modeling based on the available seismic data.

High-resolution DEMs for High-mountain Asia: A systematic, region-wide assessment of geodetic glacier mass balance and dynamics

Science.gov (United States)

Shean, D. E.; Arendt, A. A.; Osmanoglu, B.; Montesano, P.

2017-12-01

High Mountain Asia (HMA) constitutes the largest glacierized region outside of the Earth's polar regions. Although available observations are limited, long-term records indicate sustained regional glacier mass loss since 1850, with increased loss in recent decades. Recent satellite data (e.g., GRACE, ICESat-1) show spatially variable glacier mass balance, with significant mass loss in the Himalaya and Hindu Kush and slight mass gain in the Karakoram. We generated 4000 high-resolution digital elevation models (DEMs) from sub-meter commercial stereo imagery (DigitalGlobe WorldView/GeoEye) acquired over glaciers in High-mountain Asia from 2002-present (mostly 2013-present). We produced a regional 8-m DEM mosaic for 2015 and estimated 15-year geodetic mass balance for 40000 glaciers larger than 0.1 km2. We are combining with other regional DEM sources to systematically document the spatiotemporal evolution of glacier mass balance for the entire HMA region. We also generated monthly to interannual DEM and velocity time series for high-priority sites distributed across the region, with >15-20 DEMs available for some locations from 2010-present. These records document glacier dynamics, seasonal snow accumulation/redistribution, and processes that affect glacier mass balance (e.g., ice-cliff retreat, debris cover evolution). These efforts will provide basin-scale assessments of snow/ice melt runoff contributions for model cal/val and downstream water resources applications. We will continue processing all archived and newly available commercial stereo imagery for HMA, and will release all DEMs through the HiMAT DAAC.

DiFX: A software correlator for very long baseline interferometry using multi-processor computing environments

OpenAIRE

Deller, A. T.; Tingay, S. J.; Bailes, M.; West, C.

2007-01-01

We describe the development of an FX style correlator for Very Long Baseline Interferometry (VLBI), implemented in software and intended to run in multi-processor computing environments, such as large clusters of commodity machines (Beowulf clusters) or computers specifically designed for high performance computing, such as multi-processor shared-memory machines. We outline the scientific and practical benefits for VLBI correlation, these chiefly being due to the inherent flexibility of softw...

Long-term monitoring of Sgr A* at 7 mm with VERA and KaVA

Science.gov (United States)

Akiyama, K.; Kino, M.; Sohn, B.; Lee, S.; Trippe, S.; Honma, M.

2014-05-01

We present the results of radio monitoring observations of Sgr A* at 7 mm (i.e. 43 GHz) with the VLBI Exploration of Radio Astrometry (VERA), which is a VLBI array in Japan. VERA provides angular resolution on millisecond scales, resolving structures within 100 Schwarzschild radii of Sgr A* , similar to the Very Large Baseline Array (VLBA). We performed multi-epoch observations of Sgr A* in 2005 - 2008, and started monitoring it again with VERA from 2013 January to trace the current G2 encounter event. Our preliminary results in 2013 show that Sgr A* on mas scales has been in an ordinary state as of August 2013, although some fraction of the G2 cloud already passed the pericenter of Sgr A* in April 2013. We will continue monitoring Sgr A* with VERA and the newly developed KaVA (KVN and VERA Array).

3 mm GMVA Observations of Total and Polarized Emission from Blazar and Radio Galaxy Core Regions

Directory of Open Access Journals (Sweden)

Carolina Casadio

2017-10-01

Full Text Available We present total and linearly polarized 3 mm Global mm-VLBI Array (GMVA; mm-VLBI: Very Long Baseline Interferometry observations at millimetre wavelengths images of a sample of blazars and radio galaxies from the VLBA-BU-BLAZAR 7 mm monitoring program designed to probe the innermost regions of active galactic nuclei (AGN jets and locate the sites of gamma-ray emission observed by the Fermi-LAT. The lower opacity at 3 mm and improved angular resolution—on the order of 50 microarcseconds—allow us to distinguish features in the jet not visible in the 7 mm VLBA data. We also compare two different methods used for the calibration of instrumental polarisation and we analyze the resulting images for some of the sources in the sample.

The activities of the 42nd Japanese Antarctic Research Expedition (JARE-42 wintering team 2001-2002

Directory of Open Access Journals (Sweden)

Yoichi Motoyoshi

2003-07-01

Full Text Available The 42nd Japanese Antarctic Research Expedition (JARE-42 wintering team has conducted the Vth five-year JARE program during the period of February 1st 2001 to January 31st 2002, in which 40 members were engaged in the various scientific activities and maintenance of Syowa Station. The major observation programs of JARE-42 were as follows : Upper Atmo-spheric Physics-observations using Fabry-Perot imager, sodium Lidar and HFMF radar; Atmospheric Sciences and Glaciology-aerosols and air sampling, and shallow ice core drilling; Geophysics-superconducting gravity measurement, geodetic VLBI observations, and natural earthquake monitoring; Biology and Medicine-photosynthesis under sea water, populations census of penguins, and physiological and psychological adaptation to Antarctic environment, etc. In addition, satellite data receiving from ERS-2 and NOAA were also performed by using multi-purpose antenna at Syowa Station. Field activities included air sampling by using an aircraft, biological and geophysical observations, and reconnaissance survey for a possible aircraft runway around Syowa Station. Three inland traverse parties were organized, in which fuel transportation, maintenance of Dome Fuji Station, and various glaciological and geophysical observations were performed. A great efforts were made to maintain the facilities at Syowa Station by logistic personnel including mechanical engineers, radio operators, chefs, medical doctors, aircraft pilots and an engineer, an environmental engineer, a carpenter, a field assistant, a cinematographer, a satellite engineer, and an administrative officer. They were also involved in the support of field activities.

DORIS and GNSS processing at CNES/CLS for the contribution to the next ITRF2013

Science.gov (United States)

Loyer, Sylvain; Capdeville, Hugues; Soudarin, Laurent; Mezerette, Adrien; Lemoine, Jean-Michel; Mercier, Flavien; Perosanz, Felix

2014-05-01

CNES serves as Analysis Center in the International DORIS Service (IDS) and the International GNSS Service (IGS). DORIS and GNSS data are processed by its subsidiary CLS with the GRGS package software GINS/DYNAMO. For the contribution to the next release of the International Terrestrial Reference Frame planned this year (ITRF2013), two decades of data were analyzed (1993-2013 for DORIS, 1998-2013 for GPS, and 2009-2013 for GLONASS). In this context, the CNES/CLS Analysis Centers provided SINEX solutions to the IDS and IGS Combination Centers, respectively multi-satellite weekly solutions and daily solutions. Normal equations derived from this analysis are also made available to the GRGS Combination Center for the combination at the observation level of the geodetic parameters measured by DORIS, GPS, SLR and VLBI techniques. The purpose of this presentation is to point out how the overall quality of the DORIS and GNSS data processing benefits from the use of the same software and a common basis of models. Here, we present the modeling standards, the networks and the processing strategies. Assessments of some models are also discussed. The quality and the homogeneity of the products (orbits, station coordinates and Earth Orientation Parameters) over the complete period are shown, as well as the temporal variations of some parameters (dynamical parameters, orbit residuals, internal orbit overlaps ...). Some examples of time series of DORIS and GNSS station positions at collocated sites complete this presentation.

The Water Maser in II Zw 96: Scientific Justification

Energy Technology Data Exchange (ETDEWEB)

Wiggins, Brandon Kerry [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2015-08-06

We propose a VLBI search to image and locate the water emission in II Zw 96. We propose 3 sites within II Zw 96 for VLBI followup (see the proposed target listing below). We request 2.5 hours of on-source integration time with the VLBA per source. The array will achieve ~ 65µJy sensitivity in K band in this time which will be sufficient to detect luminous water maser features.

Evidences of the expanding Earth from space-geodetic data over solid land and sea level rise in recent two decades

Directory of Open Access Journals (Sweden)

Wenbin Shen

2015-07-01

Full Text Available According to the space-geodetic data recorded at globally distributed stations over solid land spanning a period of more than 20-years under the International Terrestrial Reference Frame 2008, our previous estimate of the average-weighted vertical variation of the Earth's solid surface suggests that the Earth's solid part is expanding at a rate of 0.24 ± 0.05 mm/a in recent two decades. In another aspect, the satellite altimetry observations spanning recent two decades demonstrate the sea level rise (SLR rate 3.2 ± 0.4 mm/a, of which 1.8 ± 0.5 mm/a is contributed by the ice melting over land. This study shows that the oceanic thermal expansion is 1.0 ± 0.1 mm/a due to the temperature increase in recent half century, which coincides with the estimate provided by previous authors. The SLR observation by altimetry is not balanced by the ice melting and thermal expansion, which is an open problem before this study. However, in this study we infer that the oceanic part of the Earth is expanding at a rate about 0.4 mm/a. Combining the expansion rates of land part and oceanic part, we conclude that the Earth is expanding at a rate of 0.35 ± 0.47 mm/a in recent two decades. If the Earth expands at this rate, then the altimetry-observed SLR can be well explained.

There is no one-size-fits-all product for InSAR; on the inclusion of contextual information for geodetically-proof InSAR data products

Science.gov (United States)

Hanssen, R. F.

2017-12-01

In traditional geodesy, one is interested in determining the coordinates, or the change in coordinates, of predefined benchmarks. These benchmarks are clearly identifiable and are especially established to be representative of the signal of interest. This holds, e.g., for leveling benchmarks, for triangulation/trilateration benchmarks, and for GNSS benchmarks. The desired coordinates are not identical to the basic measurements, and need to be estimated using robust estimation procedures, where the stochastic nature of the measurements is taken into account. For InSAR, however, the `benchmarks' are not predefined. In fact, usually we do not know where an effective benchmark is located, even though we can determine its dynamic behavior pretty well. This poses several significant problems. First, we cannot describe the quality of the measurements, unless we already know the dynamic behavior of the benchmark. Second, if we don't know the quality of the measurements, we cannot compute the quality of the estimated parameters. Third, rather harsh assumptions need to be made to produce a result. These (usually implicit) assumptions differ between processing operators and the used software, and are severely affected by the amount of available data. Fourth, the `relative' nature of the final estimates is usually not explicitly stated, which is particularly problematic for non-expert users. Finally, whereas conventional geodesy applies rigorous testing to check for measurement or model errors, this is hardly ever done in InSAR-geodesy. These problems make it rather impossible to provide a precise, reliable, repeatable, and `universal' InSAR product or service. Here we evaluate the requirements and challenges to move towards InSAR as a geodetically-proof product. In particular this involves the explicit inclusion of contextual information, as well as InSAR procedures, standards and a technical protocol, supported by the International Association of Geodesy and the

Fourier plane modeling of the jet in the galaxy M81

Science.gov (United States)

Ramessur, Arvind; Bietenholz, Michael F.; Leeuw, Lerothodi L.; Bartel, Norbert

2015-03-01

The nearby spiral galaxy M81 has a low-luminosity Active Galactic Nucleus in its center with a core and a one-sided curved jet, dubbed M81*, that is barely resolved with VLBI. To derive basic parameters such as the length of the jet, its orientation and curvature, the usual method of model-fitting with point sources and elliptical Gaussians may not always be the most appropriate one. We are developing Fourier-plane models for such sources, in particular an asymmetric triangle model to fit the extensive set of VLBI data of M81* in the u-v plane. This method may have an advantage over conventional ones in extracting information close to the resolution limit to provide us with a more comprehensive picture of the structure and evolution of the jet. We report on preliminary results.

Russian State Time and Earth Rotation Service: Observations, Eop Series, Prediction

Science.gov (United States)

Kaufman, M.; Pasynok, S.

2010-01-01

Russian State Time, Frequency and Earth Rotation Service provides the official EOP data and time for use in scientific, technical and metrological works in Russia. The observations of GLONASS and GPS on 30 stations in Russia, and also the Russian and worldwide observations data of VLBI (35 stations) and SLR (20 stations) are used now. To these three series of EOP the data calculated in two other Russian analysis centers are added: IAA (VLBI, GPS and SLR series) and MCC (SLR). Joint processing of these 7 series is carried out every day (the operational EOP data for the last day and the predicted values for 50 days). The EOP values are weekly refined and systematic errors of every individual series are corrected. The combined results become accessible on the VNIIFTRI server (ftp.imvp.ru) approximately at 6h UT daily.

Insights into the 3D architecture of an active caldera ring-fault at Tendürek volcano through modeling of geodetic data

KAUST Repository

Vasyura-Bathke, Hannes

2015-04-28

The three-dimensional assessment of ring-fault geometries and kinematics at active caldera volcanoes is typically limited by sparse field, geodetic or seismological data, or by only partial ring-fault rupture or slip. Here we use a novel combination of spatially dense InSAR time-series data, numerical models and sand-box experiments to determine the three-dimensional geometry and kinematics of a sub-surface ring-fault at Tendürek volcano in Turkey. The InSAR data reveal that the area within the ring-fault not only subsides, but also shows substantial westward-directed lateral movement. The models and experiments explain this as a consequence of a ‘sliding-trapdoor’ ring-fault architecture that is mostly composed of outward-inclined reverse segments, most markedly so on the volcano\\'s western flanks but includes inward-inclined normal segments on its eastern flanks. Furthermore, the model ring-fault exhibits dextral and sinistral strike-slip components that are roughly bilaterally distributed onto its northern and southern segments, respectively. Our more complex numerical model describes the deformation at Tendürek better than an analytical solution for a single rectangular dislocation in a half-space. Comparison to ring-faults defined at Glen Coe, Fernandina and Bárðarbunga calderas suggests that ‘sliding-trapdoor’ ring-fault geometries may be common in nature and should therefore be considered in geological and geophysical interpretations of ring-faults at different scales worldwide.

Coseismic deformation of the 2001 El Salvador and 2002 Denali fault earthquakes from GPS geodetic measurements

Science.gov (United States)

Hreinsdottir, Sigrun

2005-07-01

GPS geodetic measurements are used to study two major earthquakes, the 2001 MW 7.7 El Salvador and 2002 MW 7.9 Denali Fault earthquakes. The 2001 MW 7.7 earthquake was a normal fault event in the subducting Cocos plate offshore El Salvador. Coseismic displacements of up to 15 mm were measured at permanent GPS stations in Central America. The GPS data were used to constrain the location of and slip on the normal fault. One month later a MW 6.6 strike-slip earthquake occurred in the overriding Caribbean plate. Coulomb stress changes estimated from the M W 7.7 earthquake suggest that it triggered the MW 6.6 earthquake. Coseismic displacement from the MW 6.6 earthquake, about 40 mm at a GPS station in El Salvador, indicates that the earthquake triggered additional slip on a fault close to the GPS station. The MW 6.6 earthquake further changed the stress field in the overriding Caribbean plate, with triggered seismic activity occurring west and possibly also to the east of the rupture in the days to months following the earthquake. The MW 7.9 Denali Fault earthquake ruptured three faults in the interior of Alaska. It initiated with a thrust motion on the Susitna Glacier fault but then ruptured the Denali and Totschunda faults with predominantly right-lateral strike-slip motion unilaterally from west to east. GPS data measured in the two weeks following the earthquake suggest a complex coseismic rupture along the faults with two main regions of moment release along the Denali fault. A large amount of additional data were collected in the year following the earthquake which greatly improved the resolution on the fault, revealing more details of the slip distribution. We estimate a total moment release of 6.81 x 1020 Nm in the earthquake with a M W 7.2 thrust subevent on Susitna Glacier fault. The slip on the Denali fault is highly variable, with 4 main pulses of moment release. The largest moment pulse corresponds to a MW 7.5 subevent, about 40 km west of the Denali

IVS contribution to the next ITRF

Science.gov (United States)

Bachmann, Sabine; Messerschmitt, Linda; Thaller, Daniela

2015-04-01

Generating the contribution of the International VLBI Service (IVS) to the next ITRF (ITRF2013 or ITRF2014) was the main task of the IVS Combination Center at the Federal Agency for Cartography and Geodesy (BKG, Germany) in 2014. Starting with the ITRF2005, the IVS contribution to the ITRF is an intra-technique combined solution using multiple individual contributions from different institutions. For the upcoming ITRF ten international institutions submitted data files for a combined solution. The data files contain 24h VLBI sessions from the late 1970s until the end of 2014 in SINEX file format containing datum free normal equations with station coordinates and Earth Orientation Parameters (EOP). All contributions have to meet the IVS standards for ITRF contribution in order to guarantee a consistent combined solution. In the course of the generation of the intra-technique combined solution, station coordinate time series for each station as well as a Terrestrial Reference Frame based on the contributed VLBI data (VTRF) were generated and analyzed. Preliminary results using data until the end of 2013 show a scaling factor of -0.47 ppb resulting from a 7-parameter Helmert transformation of the VTRF w.r.t. ITRF2008, which is comparable to the scaling factor that was determined in the precedent ITRF generation. An internal comparison of the EOPs between the combined solution and the individual contributions as well as external comparisons of the EOP series were carried out in order to assure a consistent quality of the EOPs. The data analyses, the combination procedure and results of the combined solution for station coordinates and EOP will be presented.