The limits of direct satellite tracking with the Global Positioning System (GPS)

Science.gov (United States)

Bertiger, W. I.; Yunck, T. P.

1988-01-01

Recent advances in high precision differential Global Positioning System-based satellite tracking can be applied to the more conventional direct tracking of low earth satellites. To properly evaluate the limiting accuracy of direct GPS-based tracking, it is necessary to account for the correlations between the a-priori errors in GPS states, Y-bias, and solar pressure parameters. These can be obtained by careful analysis of the GPS orbit determination process. The analysis indicates that sub-meter accuracy can be readily achieved for a user above 1000 km altitude, even when the user solution is obtained with data taken 12 hours after the data used in the GPS orbit solutions.

78 FR 67132 - GPS Satellite Simulator Control Working Group Meeting

Science.gov (United States)

2013-11-08

... DEPARTMENT OF DEFENSE Department of the Air Force GPS Satellite Simulator Control Working Group... simulator manufacturers, who supply products to the Department of Defense (DoD), and GPS simulator users..., and email address) to [email protected]us.af.mil and have your security personnel submit your VAR...

Coarse Initial Orbit Determination for a Geostationary Satellite Using Single-Epoch GPS Measurements

Directory of Open Access Journals (Sweden)

Ghangho Kim

2015-04-01

Full Text Available A practical algorithm is proposed for determining the orbit of a geostationary orbit (GEO satellite using single-epoch measurements from a Global Positioning System (GPS receiver under the sparse visibility of the GPS satellites. The algorithm uses three components of a state vector to determine the satellite’s state, even when it is impossible to apply the classical single-point solutions (SPS. Through consideration of the characteristics of the GEO orbital elements and GPS measurements, the components of the state vector are reduced to three. However, the algorithm remains sufficiently accurate for a GEO satellite. The developed algorithm was tested on simulated measurements from two or three GPS satellites, and the calculated maximum position error was found to be less than approximately 40 km or even several kilometers within the geometric range, even when the classical SPS solution was unattainable. In addition, extended Kalman filter (EKF tests of a GEO satellite with the estimated initial state were performed to validate the algorithm. In the EKF, a reliable dynamic model was adapted to reduce the probability of divergence that can be caused by large errors in the initial state.

Coarse Initial Orbit Determination for a Geostationary Satellite Using Single-Epoch GPS Measurements

Science.gov (United States)

Kim, Ghangho; Kim, Chongwon; Kee, Changdon

2015-01-01

A practical algorithm is proposed for determining the orbit of a geostationary orbit (GEO) satellite using single-epoch measurements from a Global Positioning System (GPS) receiver under the sparse visibility of the GPS satellites. The algorithm uses three components of a state vector to determine the satellite’s state, even when it is impossible to apply the classical single-point solutions (SPS). Through consideration of the characteristics of the GEO orbital elements and GPS measurements, the components of the state vector are reduced to three. However, the algorithm remains sufficiently accurate for a GEO satellite. The developed algorithm was tested on simulated measurements from two or three GPS satellites, and the calculated maximum position error was found to be less than approximately 40 km or even several kilometers within the geometric range, even when the classical SPS solution was unattainable. In addition, extended Kalman filter (EKF) tests of a GEO satellite with the estimated initial state were performed to validate the algorithm. In the EKF, a reliable dynamic model was adapted to reduce the probability of divergence that can be caused by large errors in the initial state. PMID:25835299

Multi-Band Multi-Tone Tunable Millimeter-Wave Frequency Synthesizer For Satellite Beacon Transmitter

Science.gov (United States)

Simons, Rainee N.; Wintucky, Edwin G.

2016-01-01

This paper presents the design and test results of a multi-band multi-tone tunable millimeter-wave frequency synthesizer, based on a solid-state frequency comb generator. The intended application of the synthesizer is in a satellite beacon transmitter for radio wave propagation studies at K-band (18 to 26.5 GHz), Q-band (37 to 42 GHz), and E-band (71 to 76 GHz). In addition, the architecture for a compact beacon transmitter, which includes the multi-tone synthesizer, polarizer, horn antenna, and power/control electronics, has been investigated for a notional space-to-ground radio wave propagation experiment payload on a small satellite. The above studies would enable the design of robust high throughput multi-Gbps data rate future space-to-ground satellite communication links.

Small satellite attitude determination based on GPS/IMU data fusion

Energy Technology Data Exchange (ETDEWEB)

Golovan, Andrey [Navigation and Control Laboratory, M.V. Lomonosov Moscow State University, GSP-1, Leninskie Gory, Moscow (Russian Federation); Cepe, Ali [Department of Applied Mechanics and Control, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2014-12-10

In this paper, we present the mathematical models and algorithms that describe the problem of attitude determination for a small satellite using measurements from three angular rate sensors (ARS) and aiding measurements from multiple GPS receivers/antennas rigidly attached to the platform of the satellite.

GPS/Loran-C interoperability for time and frequency applications: A survey of the times of arrival of Loran-C transmissions via GPS common mode/common view satellite observations

Science.gov (United States)

Penrod, Bruce; Funderburk, Richard; Dana, Peter

1990-01-01

The results from this survey clearly indicate that the Global Positioning System (GPS) time transfer capability is superior to that of the Loran-C system for absolute timing accuracy, and that even with the most careful calibration of the Loran-C receiver delay and propagation path, inexplicable time of arrival (TOA) biases remain which are larger than the variations across all of the transmitters. Much more data covering years would be needed to show that these biases were stable enough to be removed with a one time site calibration. The synchronization of the transmissions is excellent, all showing low parts in 10(exp 13) offsets versus the United States Naval Observatory (USNO) master clock. With the exception of the Searchlight transmitter, all of the transmissions exhibit timing stabilities over the entire period of less than 300 ns RMS which is at the observed levels of GPS under selective availability (SA). The Loran-C phase instabilities take place over a much greater time interval than those being forced onto the GPS signals under SA, providing for better medium to short term frequency stability. Data show that all but the most distant transmitters offer better than three parts in 10(exp 11) stability at this averaging time. It is in the frequency control area where GPS/Loran-C interoperation will offer some synergistic advantages over GPS alone under SA.

A GPS measurement system for precise satellite tracking and geodesy

Science.gov (United States)

Yunck, T. P.; Wu, S.-C.; Lichten, S. M.

1985-01-01

NASA is pursuing two key applications of differential positioning with the Global Positioning System (GPS): sub-decimeter tracking of earth satellites and few-centimeter determination of ground-fixed baselines. Key requirements of the two applications include the use of dual-frequency carrier phase data, multiple ground receivers to serve as reference points, simultaneous solution for use position and GPS orbits, and calibration of atmospheric delays using water vapor radiometers. Sub-decimeter tracking will be first demonstrated on the TOPEX oceanographic satellite to be launched in 1991. A GPS flight receiver together with at least six ground receivers will acquire delta range data from the GPS carriers for non-real-time analysis. Altitude accuracies of 5 to 10 cm are expected. For baseline measurements, efforts will be made to obtain precise differential pseudorange by resolving the cycle ambiguity in differential carrier phase. This could lead to accuracies of 2 or 3 cm over a few thousand kilometers. To achieve this, a high-performance receiver is being developed, along with improved calibration and data processing techniques. Demonstrations may begin in 1986.

Climatology of GPS signal loss observed by Swarm satellites

Directory of Open Access Journals (Sweden)

C. Xiong

2018-04-01

Full Text Available By using 3-year global positioning system (GPS measurements from December 2013 to November 2016, we provide in this study a detailed survey on the climatology of the GPS signal loss of Swarm onboard receivers. Our results show that the GPS signal losses prefer to occur at both low latitudes between ±5 and ±20° magnetic latitude (MLAT and high latitudes above 60° MLAT in both hemispheres. These events at all latitudes are observed mainly during equinoxes and December solstice months, while totally absent during June solstice months. At low latitudes the GPS signal losses are caused by the equatorial plasma irregularities shortly after sunset, and at high latitude they are also highly related to the large density gradients associated with ionospheric irregularities. Additionally, the high-latitude events are more often observed in the Southern Hemisphere, occurring mainly at the cusp region and along nightside auroral latitudes. The signal losses mainly happen for those GPS rays with elevation angles less than 20°, and more commonly occur when the line of sight between GPS and Swarm satellites is aligned with the shell structure of plasma irregularities. Our results also confirm that the capability of the Swarm receiver has been improved after the bandwidth of the phase-locked loop (PLL widened, but the updates cannot radically avoid the interruption in tracking GPS satellites caused by the ionospheric plasma irregularities. Additionally, after the PLL bandwidth increased larger than 0.5 Hz, some unexpected signal losses are observed even at middle latitudes, which are not related to the ionospheric plasma irregularities. Our results suggest that rather than 1.0 Hz, a PLL bandwidth of 0.5 Hz is a more suitable value for the Swarm receiver.

Climatology of GPS signal loss observed by Swarm satellites

Science.gov (United States)

Xiong, Chao; Stolle, Claudia; Park, Jaeheung

2018-04-01

By using 3-year global positioning system (GPS) measurements from December 2013 to November 2016, we provide in this study a detailed survey on the climatology of the GPS signal loss of Swarm onboard receivers. Our results show that the GPS signal losses prefer to occur at both low latitudes between ±5 and ±20° magnetic latitude (MLAT) and high latitudes above 60° MLAT in both hemispheres. These events at all latitudes are observed mainly during equinoxes and December solstice months, while totally absent during June solstice months. At low latitudes the GPS signal losses are caused by the equatorial plasma irregularities shortly after sunset, and at high latitude they are also highly related to the large density gradients associated with ionospheric irregularities. Additionally, the high-latitude events are more often observed in the Southern Hemisphere, occurring mainly at the cusp region and along nightside auroral latitudes. The signal losses mainly happen for those GPS rays with elevation angles less than 20°, and more commonly occur when the line of sight between GPS and Swarm satellites is aligned with the shell structure of plasma irregularities. Our results also confirm that the capability of the Swarm receiver has been improved after the bandwidth of the phase-locked loop (PLL) widened, but the updates cannot radically avoid the interruption in tracking GPS satellites caused by the ionospheric plasma irregularities. Additionally, after the PLL bandwidth increased larger than 0.5 Hz, some unexpected signal losses are observed even at middle latitudes, which are not related to the ionospheric plasma irregularities. Our results suggest that rather than 1.0 Hz, a PLL bandwidth of 0.5 Hz is a more suitable value for the Swarm receiver.

Simultaneous ground-satellite observations of daytime traveling ionospheric disturbances over Japan using the GPS-TEC network and the CHAMP satellite

Science.gov (United States)

Moral, A. C.; Shiokawa, K.; Otsuka, Y.; Liu, H.; Nishioka, M.; Tsugawa, T.

2017-12-01

We report results of simultaneous ground-satellite measurements of daytime travelling ionospheric disturbances (TIDs) over Japan by using the GEONET GPS receiver network and the CHAMP satellite. For the two years of 2002 and 2008, we examined GPS measurements of TEC (Total Electron Content) and neutral and electron densities measured by CHAMP satellite. Total of fifteen TID events with clear southward moving structures in the GPS-TEC measurements are found by simultaneous ground-satellite measurements. On 2002, simultaneous events are only observed in January (1 event) and February (4 events). On 2008, ten events are observed around winter months (January (3 events), February (5), March (1), and October (1)). Neutral and electron densities measured by CHAMP show quasi-periodic fluctuations throughout the passages for all events. The CHAMP satellite crossed at least one clear TID phase front for all the events. We fitted a sinusoidal function to both ground and satellite data to obtain the frequencies and phase of the observed variations. We calculated the corresponding phase relationships between TEC variations and neutral and electron densities measured by CHAMP to categorize the events. In the presentations we report correspondence of these TID structures seen in the simultaneous ground-satellite observations by GPS-TEC and CHAMP, and discuss their phase relationship to identify the source of the daytime TIDs and specify how much of the observed variations are showing clear frequencies/or not in the nature at middle latitudes.

Improved Solar-Radiation-Pressure Models for GPS Satellites

Science.gov (United States)

Bar-Sever, Yoaz; Kuang, Da

2006-01-01

A report describes a series of computational models conceived as an improvement over prior models for determining effects of solar-radiation pressure on orbits of Global Positioning System (GPS) satellites. These models are based on fitting coefficients of Fourier functions of Sun-spacecraft- Earth angles to observed spacecraft orbital motions.

Analysis of GPS Satellite Allocation for the United States Nuclear Detonation Detection System (USNDS)

National Research Council Canada - National Science Library

Bell, Aaron

2002-01-01

...) satellites to detect atmospheric nuclear detonations. Though there are currently over 24 operational GPS satellites, USNDS ground based antennas are only capable of actively monitoring 24 satellites at a time...

GNSS global navigation satellite systems : GPS, GLONASS, Galileo, and more

CERN Document Server

Hofmann-Wellenhof, Bernhard; Wasle, Elmar

2008-01-01

This book is an extension to the acclaimed scientific bestseller "GPS - Theory and Practice". It covers Global Navigation Satellite Systems (GNSS) and includes the Russian GLONASS, the European system Galileo, and additional systems.

Where on Earth am I? Don't Worry,. GPS Satellites will Guide you ...

Indian Academy of Sciences (India)

ordinate frame shown is the reference frame used by GPS, it is called earth .... the satellite clock offsets five monitoring stations are spread over the earth ..... (P 2) GPS receiver for armoured vehicles (on the right is auxiliary display). ( P 3) GPS ...

Radiotracking large wilderness mammals: Integration of GPS and Argos technology

Science.gov (United States)

Schwartz, Charles C.; Arthur, Steve M.

1999-01-01

We tested 30 prototype global positioning system (GPS) radiocollars on brown bears (Ursus arctos) over a 3-year period on the Kenai Peninsula, Alaska. Collars were of 2 design types: GPS with an Argos (Argos Data collection and Location System) satellite uplink (n=19) and GPS unites where the data were stored on board (n=10) for retrieval at a later date. All units also contained a conventional VHF (very high frequency) transmitter and weighed 1.7 kg. GPS-Argos united obtained 10-82% of expected GPS fixes, and fix rate declined significantly (Pbears varied more and were lower than fix rates for stationary collars placed in various vegetation types, suggesting that the bear, terrain, and movement all influence both fix and uplink success rate. Application of this new technology to grizzly and brown bear research and comparisons to studies with moose (Alces alces) are discussed.

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.

Sea level change along the Black Sea coast from satellite altimetry, tide gauge and GPS observations

Directory of Open Access Journals (Sweden)

Nevin B. Avsar

2016-01-01

Full Text Available Sea level change affects human living conditions, particularly ocean coasts. However, sea level change is still unclear along the Black Sea coast due to lack of in-situ measurements and low resolution satellite data. In this paper, sea level change along the Black Sea coast is investigated from joint satellite altimetry, tide gauge (TG and Global Positioning System (GPS observations. The linear trend and seasonal components of sea level change are estimated at 8 TG stations (Amasra, Igneada, Trabzon-II, Sinop, Sile, Poti, Tuapse, and Batumi located along the Black Sea coast, which are compared with Satellite Altimetry and GPS. At the tide gauge stations with long-term records such as Poti (about 21 years and Tuapse (about 19 years, the results obtained from the satellite altimetry and tide gauge observations show a remarkably good agreement. While some big differences are existed between Satellite Altimetry and TG at other stations, after adding vertical motion from GPS, correlation coefficients of the trend have been greatly improved from 0.37 to 0.99 at 3 co-located GPS and TG stations (Trabzon-II, Sinop and Sile.

Handbook of satellite orbits from Kepler to GPS

CERN Document Server

Capderou, Michel

2014-01-01

Fifty years after Sputnik, artificial satellites have become indispensable monitors in many areas, such as economics, meteorology, telecommunications, navigation and remote sensing. The specific orbits are important for the proper functioning of the satellites. This book discusses the great variety of satellite orbits, both in shape (circular to highly elliptical) and properties (geostationary, Sun-synchronous, etc.). This volume starts with an introduction into geodesy. This is followed by a presentation of the fundamental equations of mechanics to explain and demonstrate the properties for all types of orbits. Numerous examples are included, obtained through IXION software developed by the author. The book also includes an exposition of the historical background that is necessary to help the reader understand the main stages of scientific thought from Kepler to GPS. This book is intended for researchers, teachers and students working in the field of satellite technology. Engineers, geographers and all those...

Comparison of mapped and measured total ionospheric electron content using global positioning system and beacon satellite observations

International Nuclear Information System (INIS)

Lanyi, G.E.; Roth, T.

1988-01-01

Total ionospheric electron contents (TEC) were measured by global positioning system (GPS) dual-frequency receivers developed by the Jet Propulsion Laboratory. The measurements included P-code (precise ranging code) and carrier phase data for six GPS satellites during multiple five-hour observing sessions. A set of these GPS TEC measurements were mapped from the GPS lines of sight to the line of sight of a Faraday beacon satellite by statistically fitting the TEC data to a simple model of the ionosphere. The mapped GPS TEC values were compared with the Faraday rotation measurements. Because GPS transmitter offsets are different for each satellite and because some GPS receiver offsets were uncalibrated, the sums of the satellite and receiver offsets were estimated simultaneously with the TEC in a least squares procedure. The accuracy of this estimation procedure is evaluated indicating that the error of the GPS-determined line of sight TEC can be at or below 1 x 10 to the 16th el/sq cm. Consequently, the current level of accuracy is comparable to the Faraday rotation technique; however, GPS provides superior sky coverage. 15 references

Long-term GPS tracking of ocean sunfish Mola mola offers a new direction in fish monitoring.

Directory of Open Access Journals (Sweden)

David W Sims

Full Text Available Satellite tracking of large pelagic fish provides insights on free-ranging behaviour, distributions and population structuring. Up to now, such fish have been tracked remotely using two principal methods: direct positioning of transmitters by Argos polar-orbiting satellites, and satellite relay of tag-derived light-level data for post hoc track reconstruction. Error fields associated with positions determined by these methods range from hundreds of metres to hundreds of kilometres. However, low spatial accuracy of tracks masks important details, such as foraging patterns. Here we use a fast-acquisition global positioning system (Fastloc GPS tag with remote data retrieval to track long-term movements, in near real time and position accuracy of <70 m, of the world's largest bony fish, the ocean sunfish Mola mola. Search-like movements occurred over at least three distinct spatial scales. At fine scales, sunfish spent longer in highly localised areas with faster, straighter excursions between them. These 'stopovers' during long-distance movement appear consistent with finding and exploiting food patches. This demonstrates the feasibility of GPS tagging to provide tracks of unparalleled accuracy for monitoring movements of large pelagic fish, and with nearly four times as many locations obtained by the GPS tag than by a conventional Argos transmitter. The results signal the potential of GPS-tagged pelagic fish that surface regularly to be detectors of resource 'hotspots' in the blue ocean and provides a new capability for understanding large pelagic fish behaviour and habitat use that is relevant to ocean management and species conservation.

Radio-tracking large wilderness mammals: integration of GPS and Argos technologies

Science.gov (United States)

Schwartz, Charles C.; Arthur, Steve M.

1999-01-01

We tested 30 prototype global positioning system (GPS) radiocollars on brown bears (Ursus arctos) over a 3-year period on the Kenai Peninsula, Alaska. Collars were of 2 design types: GPS units with an Argos (Argos Data collection and Location System) satellite uplink (n = 19) and GPS units where the data were stored on board (n = 10) for retrieval at a later date. All units also contained a conventional VHF (very high frequency) transmitter and weighed 1.7 kg. GPS-Argos units obtained 10-82% of expected GPS fixes, and fix rate declined significantly (P bears varied more and were lower than fix rates for stationary collars placed in various vegetation types, suggesting that the bear, terrain, and movement all influence both fix and uplink success rate. Application of this new technology to grizzly and brown bear research and comparisons to studies with moose (Alces alces) are discussed.

An improved grey model for the prediction of real-time GPS satellite clock bias

Science.gov (United States)

Zheng, Z. Y.; Chen, Y. Q.; Lu, X. S.

2008-07-01

In real-time GPS precise point positioning (PPP), real-time and reliable satellite clock bias (SCB) prediction is a key to implement real-time GPS PPP. It is difficult to hold the nuisance and inenarrable performance of space-borne GPS satellite atomic clock because of its high-frequency, sensitivity and impressionable, it accords with the property of grey model (GM) theory, i. e. we can look on the variable process of SCB as grey system. Firstly, based on limits of quadratic polynomial (QP) and traditional GM to predict SCB, a modified GM (1,1) is put forward to predict GPS SCB in this paper; and then, taking GPS SCB data for example, we analyzed clock bias prediction with different sample interval, the relationship between GM exponent and prediction accuracy, precision comparison of GM to QP, and concluded the general rule of different type SCB and GM exponent; finally, to test the reliability and validation of the modified GM what we put forward, taking IGS clock bias ephemeris product as reference, we analyzed the prediction precision with the modified GM, It is showed that the modified GM is reliable and validation to predict GPS SCB and can offer high precise SCB prediction for real-time GPS PPP.

Improved GPS-based Satellite Relative Navigation Using Femtosecond Laser Relative Distance Measurements

Directory of Open Access Journals (Sweden)

Hyungjik Oh

2016-03-01

Full Text Available This study developed an approach for improving Carrier-phase Differential Global Positioning System (CDGPS based realtime satellite relative navigation by applying laser baseline measurement data. The robustness against the space operational environment was considered, and a Synthetic Wavelength Interferometer (SWI algorithm based on a femtosecond laser measurement model was developed. The phase differences between two laser wavelengths were combined to measure precise distance. Generated laser data were used to improve estimation accuracy for the float ambiguity of CDGPS data. Relative navigation simulations in real-time were performed using the extended Kalman filter algorithm. The GPS and laser-combined relative navigation accuracy was compared with GPS-only relative navigation solutions to determine the impact of laser data on relative navigation. In numerical simulations, the success rate of integer ambiguity resolution increased when laser data was added to GPS data. The relative navigational errors also improved five-fold and two-fold, relative to the GPS-only error, for 250 m and 5 km initial relative distances, respectively. The methodology developed in this study is suitable for application to future satellite formation-flying missions.

Measurements of ionospheric TEC in the direction of GPS satellites and comparison with three ionospheric models

Directory of Open Access Journals (Sweden)

E. Zuccheretti

1997-06-01

Full Text Available The IEN Galileo Ferraris uses GPS for time and frequency synchronization. To obtain high performance it is important to reduce the error due to the ionospheric time-delay in GPS measurements. Evaluations of TEC in the direction of GPS satellites, obtained from three different ionospheric models, have been compared with corresponding measurements by GPS signal.

Comparison of two-way satellite time transfer and GPS common-view time transfer between OCA and TUG

Science.gov (United States)

Kirchner, Dieter; Thyr, U.; Ressler, H.; Robnik, R.; Grudler, P.; Baumont, Francoise S.; Veillet, Christian; Lewandowski, Wlodzimierz W.; Hanson, W.; Clements, A.

1992-01-01

For about one year the time scales UTC(OCA) and UTC(TUG) were compared by means of GPS and two-way satellite time transfer. At the end of the experiment both links were independently 'calibrated' by measuring the differential delays of the GPS receivers and of the satellite earth stations by transportation of a GPS receiver and of one of the satellite terminals. The results obtained by both methods differ by about 3 ns, but reveal a seasonal variation of about 8 ns peak-to-peak which is likely the result of a temperature-dependence of the delays of the GPS receivers used. For the comparison of both methods the stabilities of the timescales are of great importance. Unfortunately, during the last three months of the experiment a less stable clock had to be used for the generation of UTC(TUG).

Hydrodynamic effect of a satellite transmitter on a juvenile green turtle (Chelonia mydas)

Science.gov (United States)

Watson; Granger

1998-09-01

Wind tunnel tests were performed to measure the effect of a satellite transmitter on a juvenile green turtle (Chelonia mydas). A full-scale turtle model was constructed from an 11.5 kg specimen with a 48 cm carapace length, and a transmitter model was constructed from a Telonics ST-6. The turtle model was tested in a wind tunnel with and without the transmitter, which was mounted on the forward, topmost part of the carapace. Drag, lift and pitch moment were measured for several speeds and flow angles, and the data were scaled for application to the marine environment. At small flow angles representative of straight-line swimming, the transmitter increased drag by 27-30 %, reduced lift by less than 10 % and increased the pitch moment by 11-42 %. On the basis of the drag data at zero angle of attack, it is estimated that the backpack will reduce swimming speed by 11 %, assuming that the turtle produces the same thrust with the unit attached. The drag data are also used to estimate the effect of a transmitter on the swimming energetics of an adult green turtle. Design guidelines are included to minimize the adverse forces and moments caused by the transmitter.

Features of High-Latitude Ionospheric Irregularities Development as Revealed by Ground-Based GPS Observations, Satellite-Borne GPS Observations and Satellite In Situ Measurements over the Territory of Russia during the Geomagnetic Storm on March 17-18, 2015

Science.gov (United States)

Zakharenkova, I. E.; Cherniak, Iu. V.; Shagimuratov, I. I.; Klimenko, M. V.

2018-01-01

The dynamic picture of the response of the high- and mid-latitude ionosphere to the strong geomagnetic disturbances on March 17-18, 2015, has been studied with ground-based and satellite observations, mainly, by transionospheric measurements of delays of GPS (Global Positioning System) signals. The advantages of the joint use of ground-based GPS measurements and GPS measurements on board of the Swarm Low-Earth-Orbit satellite mission for monitoring of the appearance of ionospheric irregularities over the territory of Russia are shown for the first time. The results of analysis of ground-based and space-borne GPS observations, as well as satellite, in situ measurements, revealed large-scale ionospheric plasma irregularities observed over the territory of Russia in the latitude range of 50°-85° N during the main phase of the geomagnetic storm. The most intense ionospheric irregularities were detected in the auroral zone and in the region of the main ionospheric trough (MIT). It has been found that sharp changes in the phase of the carrier frequency of the navigation signal from all tracked satellites were recorded at all GPS stations located to the North from 55° MLAT. The development of a deep MIT was related to dynamic processes in the subauroral ionosphere, in particular, with electric fields of the intense subauroral polarization stream. Analysis of the electron and ion density values obtained by instruments on board of the Swarm and DMSP satellites showed that the zone of highly structured auroral ionosphere extended at least to heights of 850-900 km.

Link establishment criterion and topology optimization for hybrid GPS satellite communications with laser crosslinks

Science.gov (United States)

Li, Lun; Wei, Sixiao; Tian, Xin; Hsieh, Li-Tse; Chen, Zhijiang; Pham, Khanh; Lyke, James; Chen, Genshe

2018-05-01

In the current global positioning system (GPS), the reliability of information transmissions can be enhanced with the aid of inter-satellite links (ISLs) or crosslinks between satellites. Instead of only using conventional radio frequency (RF) crosslinks, the laser crosslinks provide an option to significantly increase the data throughput. The connectivity and robustness of ISL are needed for analysis, especially for GPS constellations with laser crosslinks. In this paper, we first propose a hybrid GPS communication architecture in which uplinks and downlinks are established via RF signals and crosslinks are established via laser links. Then, we design an optical crosslink assignment criteria considering the practical optical communication factors such as optical line- of-sight (LOS) range, link distance, and angular velocity, etc. After that, to further improve the rationality of establishing crosslinks, a topology control algorithm is formulated to optimize GPS crosslink networks at both physical and network layers. The RF transmission features for uplink and downlink and optical transmission features for crosslinks are taken into account as constraints for the optimization problem. Finally, the proposed link establishment criteria are implemented for GPS communication with optical crosslinks. The designs of this paper provide a potential crosslink establishment and topology control algorithm for the next generation GPS.

The NASA CYGNSS Small Satellite Constellation

Science.gov (United States)

Ruf, C. S.; Gleason, S.; McKague, D. S.; Rose, R.; Scherrer, J.

2017-12-01

The NASA Cyclone Global Navigation Satellite System (CYGNSS) is a constellation of eight microsatellite observatories that was launched into a low (35°) inclination, low Earth orbit on 15 December 2016. Each observatory carries a 4-channel GNSS-R bistatic radar receiver. The radars are tuned to receive the L1 signals transmitted by GPS satellites, from which near-surface ocean wind speed is estimated. The mission architecture is designed to improve the temporal sampling of winds in tropical cyclones (TCs). The 32 receive channels of the complete CYGNSS constellation, combined with the 30 GPS satellite transmitters, results in a revisit time for sampling of the wind of 2.8 hours (median) and 7.2 hours (mean) at all locations between 38 deg North and 38 deg South latitude. Operation at the GPS L1 frequency of 1575 MHz allows for wind measurements in the TC inner core that are often obscured from other spaceborne remote sensing instruments by intense precipitation in the eye wall and inner rain bands. An overview of the CYGNSS mission wil be presented, followed by early on-orbit status and results.

Satellite tracking of a young Steppe Eagle from the United Arab ...

African Journals Online (AJOL)

Following recovery and successful rehabilitation, a young Steppe Eagle Aquila nipalensis was tagged with a 45 g GPS satellite transmitter to track its migration and identify potential wintering and summering areas of the species passing through the United Arab Emirates (UAE). The study is part of a larger study on ...

Abdominally implanted satellite transmitters affect reproduction and survival rather than migration of large shorebirds

Science.gov (United States)

Hooijmeijer, Jos C. E. W.; Gill, Robert E.; Mulcahy, Daniel M.; Tibbitts, T. Lee; Kentie, Rosemarie; Gerritsen, Gerrit J.; Bruinzeel, Leo W.; Tijssen, David C.; Harwood, Christopher M.; Piersma, Theunis

2014-01-01

Satellite telemetry has become a common technique to investigate avian life-histories, but whether such tagging will affect fitness is a critical unknown. In this study, we evaluate multi-year effects of implanted transmitters on migratory timing and reproductive performance in shorebirds. Shorebirds increasingly are recognized as good models in ecology and evolution. That many of them are of conservation concern adds to the research responsibilities. In May 2009, we captured 56 female Black-tailed Godwits Limosa limosa limosa during late incubation in The Netherlands. Of these, 15 birds were equipped with 26-g satellite transmitters with a percutaneous antenna (7.8 % ± 0.2 SD of body mass), surgically implanted in the coelom. We compared immediate nest survival, timing of migration, subsequent nest site fidelity and reproductive behaviour including egg laying with those of the remaining birds, a comparison group of 41 females. We found no effects on immediate nest survival. Fledging success and subsequent southward and northward migration patterns of the implanted birds conformed to the expectations, and arrival time on the breeding grounds in 2010–2012 did not differ from the comparison group. Compared with the comparison group, in the year after implantation, implanted birds were equally faithful to the nest site and showed equal territorial behaviour, but a paucity of behaviours indicating nests or clutches. In the 3 years after implantation, the yearly apparent survival of implanted birds was 16 % points lower. Despite intense searching, we found only three eggs of two implanted birds; all were deformed. A similarly deformed egg was reported in a similarly implanted Whimbrel Numenius phaeopus returning to breed in central Alaska. The presence in the body cavity of an object slightly smaller than a normal egg may thus lead to egg malformation and, likely, reduced egg viability. That the use of implanted satellite transmitters in these large shorebirds

Impacts of Satellite Orbit and Clock on Real-Time GPS Point and Relative Positioning.

Science.gov (United States)

Shi, Junbo; Wang, Gaojing; Han, Xianquan; Guo, Jiming

2017-06-12

Satellite orbit and clock corrections are always treated as known quantities in GPS positioning models. Therefore, any error in the satellite orbit and clock products will probably cause significant consequences for GPS positioning, especially for real-time applications. Currently three types of satellite products have been made available for real-time positioning, including the broadcast ephemeris, the International GNSS Service (IGS) predicted ultra-rapid product, and the real-time product. In this study, these three predicted/real-time satellite orbit and clock products are first evaluated with respect to the post-mission IGS final product, which demonstrates cm to m level orbit accuracies and sub-ns to ns level clock accuracies. Impacts of real-time satellite orbit and clock products on GPS point and relative positioning are then investigated using the P3 and GAMIT software packages, respectively. Numerical results show that the real-time satellite clock corrections affect the point positioning more significantly than the orbit corrections. On the contrary, only the real-time orbit corrections impact the relative positioning. Compared with the positioning solution using the IGS final product with the nominal orbit accuracy of ~2.5 cm, the real-time broadcast ephemeris with ~2 m orbit accuracy provided <2 cm relative positioning error for baselines no longer than 216 km. As for the baselines ranging from 574 to 2982 km, the cm-dm level positioning error was identified for the relative positioning solution using the broadcast ephemeris. The real-time product could result in <5 mm relative positioning accuracy for baselines within 2982 km, slightly better than the predicted ultra-rapid product.

Impacts of Satellite Orbit and Clock on Real-Time GPS Point and Relative Positioning

Directory of Open Access Journals (Sweden)

Junbo Shi

2017-06-01

Full Text Available Satellite orbit and clock corrections are always treated as known quantities in GPS positioning models. Therefore, any error in the satellite orbit and clock products will probably cause significant consequences for GPS positioning, especially for real-time applications. Currently three types of satellite products have been made available for real-time positioning, including the broadcast ephemeris, the International GNSS Service (IGS predicted ultra-rapid product, and the real-time product. In this study, these three predicted/real-time satellite orbit and clock products are first evaluated with respect to the post-mission IGS final product, which demonstrates cm to m level orbit accuracies and sub-ns to ns level clock accuracies. Impacts of real-time satellite orbit and clock products on GPS point and relative positioning are then investigated using the P3 and GAMIT software packages, respectively. Numerical results show that the real-time satellite clock corrections affect the point positioning more significantly than the orbit corrections. On the contrary, only the real-time orbit corrections impact the relative positioning. Compared with the positioning solution using the IGS final product with the nominal orbit accuracy of ~2.5 cm, the real-time broadcast ephemeris with ~2 m orbit accuracy provided <2 cm relative positioning error for baselines no longer than 216 km. As for the baselines ranging from 574 to 2982 km, the cm–dm level positioning error was identified for the relative positioning solution using the broadcast ephemeris. The real-time product could result in <5 mm relative positioning accuracy for baselines within 2982 km, slightly better than the predicted ultra-rapid product.

Comparing land surface phenology derived from satellite and GPS network microwave remote sensing.

Science.gov (United States)

Jones, Matthew O; Kimball, John S; Small, Eric E; Larson, Kristine M

2014-08-01

The land surface phenology (LSP) start of season (SOS) metric signals the seasonal onset of vegetation activity, including canopy growth and associated increases in land-atmosphere water, energy and carbon (CO2) exchanges influencing weather and climate variability. The vegetation optical depth (VOD) parameter determined from satellite passive microwave remote sensing provides for global LSP monitoring that is sensitive to changes in vegetation canopy water content and biomass, and insensitive to atmosphere and solar illumination constraints. Direct field measures of canopy water content and biomass changes desired for LSP validation are generally lacking due to the prohibitive costs of maintaining regional monitoring networks. Alternatively, a normalized microwave reflectance index (NMRI) derived from GPS base station measurements is sensitive to daily vegetation water content changes and may provide for effective microwave LSP validation. We compared multiyear (2007-2011) NMRI and satellite VOD records at over 300 GPS sites in North America, and their derived SOS metrics for a subset of 24 homogenous land cover sites to investigate VOD and NMRI correspondence, and potential NMRI utility for LSP validation. Significant correlations (P<0.05) were found at 276 of 305 sites (90.5 %), with generally favorable correspondence in the resulting SOS metrics (r (2)=0.73, P<0.001, RMSE=36.8 days). This study is the first attempt to compare satellite microwave LSP metrics to a GPS network derived reflectance index and highlights both the utility and limitations of the NMRI data for LSP validation, including spatial scale discrepancies between local NMRI measurements and relatively coarse satellite VOD retrievals.

In-flight performance analysis of MEMS GPS receiver and its application to precise orbit determination of APOD-A satellite

Science.gov (United States)

Gu, Defeng; Liu, Ye; Yi, Bin; Cao, Jianfeng; Li, Xie

2017-12-01

An experimental satellite mission termed atmospheric density detection and precise orbit determination (APOD) was developed by China and launched on 20 September 2015. The micro-electro-mechanical system (MEMS) GPS receiver provides the basis for precise orbit determination (POD) within the range of a few decimetres. The in-flight performance of the MEMS GPS receiver was assessed. The average number of tracked GPS satellites is 10.7. However, only 5.1 GPS satellites are available for dual-frequency navigation because of the loss of many L2 observations at low elevations. The variations in the multipath error for C1 and P2 were estimated, and the maximum multipath error could reach up to 0.8 m. The average code noises are 0.28 m (C1) and 0.69 m (P2). Using the MEMS GPS receiver, the orbit of the APOD nanosatellite (APOD-A) was precisely determined. Two types of orbit solutions are proposed: a dual-frequency solution and a single-frequency solution. The antenna phase center variations (PCVs) and code residual variations (CRVs) were estimated, and the maximum value of the PCVs is 4.0 cm. After correcting the antenna PCVs and CRVs, the final orbit precision for the dual-frequency and single-frequency solutions were 7.71 cm and 12.91 cm, respectively, validated using the satellite laser ranging (SLR) data, which were significantly improved by 3.35 cm and 25.25 cm. The average RMS of the 6-h overlap differences in the dual-frequency solution between two consecutive days in three dimensions (3D) is 4.59 cm. The MEMS GPS receiver is the Chinese indigenous onboard receiver, which was successfully used in the POD of a nanosatellite. This study has important reference value for improving the MEMS GPS receiver and its application in other low Earth orbit (LEO) nanosatellites.

Geodynamics implication of GPS and satellite altimeter and gravity observations to the Eastern Mediterranean

Directory of Open Access Journals (Sweden)

Khaled H. Zahran

2012-06-01

Results show important zones of mass discontinuity in this region correlated with the seismological activities and temporal gravity variations agree with the crustal deformation obtained from GPS observations. The current study indicates that satellite gravity data is a valuable source of data in understanding the geodynamical behavior of the studied region and that satellite gravity data is an important contemporary source of data in the geodynamical studies.

COSMIC Payload in NCAR-NASPO GPS Satellite System for Severe Weather Prediction

Science.gov (United States)

Lai-Chen, C.

Severe weather, such as cyclones, heavy rainfall, outburst of cold air, etc., results in great disaster all the world. It is the mission for the scientists to design a warning system, to predict the severe weather systems and to reduce the damage of the society. In Taiwan, National Satellite Project Office (NSPO) initiated ROCSAT-3 program at 1997. She scheduled the Phase I conceptual design to determine the mission for observation weather system. Cooperating with National Center of Atmospheric Research (NCAR), NSPO involved an international cooperation research and operation program to build a 32 GPS satellites system. NCAR will offer 24 GPS satellites. The total expanse will be US 100 millions. NSPO also provide US 80 millions for launching and system engineering operation. And NCAR will be responsible for Payload Control Center and Fiducial Network. The cooperative program contract has been signed by Taiwan National Science Council, Taipei Economic Cultural Office of United States and American Institute in Taiwan. One of the payload is COSMIC, Constellation Observation System for Meteorology, Ionosphere and Climate. It is a GPS meteorology instrument system. The system will observe the weather information, e. g. electron density profiles, horizontal and vertical TEC and CFT scintillation and communication outage maps. The mission is to obtain the weather data such as vertical temperature profiles, water vapor distribution and pressure distribution over the world for global weather forecasting, especially during the severe weather period. The COSMIC Conference held on November, 1998. The export license was also issued by Department of Commerce of Unites States at November, 1998. Recently, NSPO begun to train their scientists to investigate the system. Scientists simulate the observation data to combine the existing routine satellite infrared cloud maps, radar echo and synoptic weather analysis for severe weather forecasting. It is hopeful to provide more accurate

Detection of ionospheric perturbations associated with Japanese earthquakes on the basis of reception of LF transmitter signals on the satellite DEMETER

Directory of Open Access Journals (Sweden)

F. Muto

2008-02-01

Full Text Available There have been recently reported a lot of electromagnetic phenomena associated with earthquakes (EQs. Among these, the ground-based reception of subionospheric waves from VLF/LF transmitters, is recognized as a promising tool to investigate the ionospheric perturbations associated with EQs. This paper deals with the corresponding whistler-mode signals in the upper ionosphere from those VLF/LF transmitters, which is the counterpart of subionospheric signals. The whistler-mode VLF/LF transmitter signals are detected on board the French satellite, DEMETER launched on 29 June 2004. We have chosen several large Japanese EQs including the Miyagi-oki EQ (16 August 2005; M=7.2, depth=36 km, and the target transmitter is a Japanese LF transmitter (JJY whose transmitter frequency is 40 kHz. Due to large longitudinal separation of each satellite orbit (2500 km, we have to adopt a statistical analysis over a rather long period (such as 3 weeks or one month to have reliable data set. By analyzing the spatial distribution of JJY signal intensity (in the form of signal to noise ratio SNR during a period of 4 months including the Miyagi-oki EQ, we have found significant changes in the intensity; generally the SNR is significantly depleted before the EQ, which is considered to be a precursory ionospheric signature of the EQ. This abnormal effect is reasonably explained in terms of either (1 enhanced absorption of whistler-mode LF signals in the lower ionosphere due to the lowering of the lower ionosphere, or (2 nonlinear wave-wave scattering. Finally, this analysis suggests an important role of satellite observation in the study of lithosphere-atmosphere-ionosphere coupling.

The Effect of high temperature plasma on GPS satellite signals

International Nuclear Information System (INIS)

Aghanajafi, C.; Alizadeh, M.M.

2002-01-01

Ionospheric disturbances caused by pulses of electromagnetic radiation are observed in the propagation of radio signals. Specific events affecting particular aspects of radio propagation are sudden phase anomaly; sudden frequency deviation, sudden cosmic noise and short wave fade out. Global positioning System (GPS) is a space-based navigation system, developed by the United States, to satisfy the requirements for the military forces and the civilians to determine their position, velocity and time in a common reference system anywhere on or near the earth. The purpose of this paper is to calculate the effect of ionosphere on GPS satellite signals. In order to find this effects, calculation of the total column electron content is needed. The lack of data necessary to generate real Electron Density Profile versus altitude, latitude, time, season and solar activity; causes the introduction of a new method to reproduce the topside and bottom side component of the peak electron density. Electron density profiles computed in this method are compared with GPS derived profiles, which use observations of dual frequency receivers. Ionospheric range corrections, for signal point positioning, using two methods have also been discussed

Thermal imbalance force modelling for a GPS satellite using the finite element method

Science.gov (United States)

Vigue, Yvonne; Schutz, Bob E.

1991-01-01

Methods of analyzing the perturbation due to thermal radiation and determining its effects on the orbits of GPS satellites are presented, with emphasis on the FEM technique to calculate satellite solar panel temperatures which are used to determine the magnitude and direction of the thermal imbalance force. Although this force may not be responsible for all of the force mismodeling, conditions may work in combination with the thermal imbalance force to produce such accelerations on the order of 1.e-9 m/sq s. If submeter accurate orbits and centimeter-level accuracy for geophysical applications are desired, a time-dependent model of the thermal imbalance force should be used, especially when satellites are eclipsing, where the observed errors are larger than for satellites in noneclipsing orbits.

A design proposal of a certain missile tactical command system based on Beidou satellite communication and GPS positioning techniques

Science.gov (United States)

Ma, Jian; Hao, Yongsheng; Miao, Jian; Zhang, Jianmao

2007-11-01

This paper introduced a design proposal of tactical command system that applied to a kind of anti-tank missile carriers. The tactical command system was made up of embedded computer system based on PC104 bus, Linux operating system, digital military map, Beidou satellite communication equipments and GPS positioning equipments. The geographic coordinates was measured by the GPS receiver, the positioning data, commands and information were transmitted real-time between tactical command systems, tactical command systems and command center, by the Beidou satellite communication systems. The Beidou satellite communication equipments and GPS positioning equipments were integrated to an independent module, exchanging data with embedded computer through RS232 serial ports and USB ports. The decision support system software based on information fusion, calculates positioning data, geography information and battle field information synthetically, shows the position of allies and the position of enemy on the military map, and assesses the various threats of different enemy objects, educes a situation assessment and threat assessment.

Ground-Based Global Navigation Satellite System (GNSS) GPS Broadcast Ephemeris Data (daily files) from NASA CDDIS

Data.gov (United States)

National Aeronautics and Space Administration — This dataset consists of ground-based Global Navigation Satellite System (GNSS) GPS Broadcast Ephemeris Data (daily files) from the NASA Crustal Dynamics Data...

Low-degree gravity change from GPS data of COSMIC and GRACE satellite missions

Science.gov (United States)

Lin, Tingjung; Hwang, Cheinway; Tseng, Tzu-Pang; Chao, B. F.

2012-01-01

This paper demonstrates estimation of time-varying gravity harmonic coefficients from GPS data of COSMIC and GRACE satellite missions. The kinematic orbits of COSMIC and GRACE are determined to the cm-level accuracy. The NASA Goddard's GEODYN II software is used to model the orbit dynamics of COSMIC and GRACE, including the effect of a static gravity field. The surface forces are estimated per one orbital period. Residual orbits generated from kinematic and reference orbits serve as observables to determine the harmonic coefficients in the weighted-constraint least-squares. The monthly COSMIC and GRACE GPS data from September 2006 to December 2007 (16 months) are processed to estimate harmonic coefficients to degree 5. The geoid variations from the GPS and CSR RL04 (GRACE) solutions show consistent patterns over space and time, especially in regions of active hydrological changes. The monthly GPS-derived second zonal coefficient closely resembles the SLR-derived and CSR RL04 values, and third and fourth zonal coefficients resemble the CSR RL04 values.

PDOP values for simulated GPS/Galileo positioning

DEFF Research Database (Denmark)

Cederholm, Jens Peter

2005-01-01

The paper illustrates satellite coverage and PDOP values for a simulated combined GPS/Galileo system. The designed GPS satellite constellation and the planned Galileo satellite constellation are presented. The combined system is simulated and the number of visible satellites and PDOP values...

The GPS Laser Retroreflector Array Project

Science.gov (United States)

Merkowitz, Stephen M.

2012-01-01

Systematic co-location in space through the precision orbit determination of GPS satellites via satellite laser ranging will contribute significantly towards improving the accuracy and stability of the international terrestrial reference frame. NASA recently formed the GPS Laser Retroreflector Array Project to develop and deliver retroreflectors for integration on the next generation of GPS satellites. These retroreflectors will be an important contributor to achieving a global accuracy of 1.0 mm and 0.1 mm/year stability in the international terrestrial reference frame. We report here the current status of the GPS Laser Retroreflector Array Project.

Single-Receiver GPS Phase Bias Resolution

Science.gov (United States)

Bertiger, William I.; Haines, Bruce J.; Weiss, Jan P.; Harvey, Nathaniel E.

2010-01-01

Existing software has been modified to yield the benefits of integer fixed double-differenced GPS-phased ambiguities when processing data from a single GPS receiver with no access to any other GPS receiver data. When the double-differenced combination of phase biases can be fixed reliably, a significant improvement in solution accuracy is obtained. This innovation uses a large global set of GPS receivers (40 to 80 receivers) to solve for the GPS satellite orbits and clocks (along with any other parameters). In this process, integer ambiguities are fixed and information on the ambiguity constraints is saved. For each GPS transmitter/receiver pair, the process saves the arc start and stop times, the wide-lane average value for the arc, the standard deviation of the wide lane, and the dual-frequency phase bias after bias fixing for the arc. The second step of the process uses the orbit and clock information, the bias information from the global solution, and only data from the single receiver to resolve double-differenced phase combinations. It is called "resolved" instead of "fixed" because constraints are introduced into the problem with a finite data weight to better account for possible errors. A receiver in orbit has much shorter continuous passes of data than a receiver fixed to the Earth. The method has parameters to account for this. In particular, differences in drifting wide-lane values must be handled differently. The first step of the process is automated, using two JPL software sets, Longarc and Gipsy-Oasis. The resulting orbit/clock and bias information files are posted on anonymous ftp for use by any licensed Gipsy-Oasis user. The second step is implemented in the Gipsy-Oasis executable, gd2p.pl, which automates the entire process, including fetching the information from anonymous ftp

Validation of GPS atmospheric water vapor with WVR data in satellite tracking mode

Science.gov (United States)

Shangguan, M.; Heise, S.; Bender, M.; Dick, G.; Ramatschi, M.; Wickert, J.

2015-01-01

Slant-integrated water vapor (SIWV) data derived from GPS STDs (slant total delays), which provide the spatial information on tropospheric water vapor, have a high potential for assimilation to weather models or for nowcasting or reconstruction of the 3-D humidity field with tomographic techniques. Therefore, the accuracy of GPS STD is important, and independent observations are needed to estimate the quality of GPS STD. In 2012 the GFZ (German Research Centre for Geosciences) started to operate a microwave radiometer in the vicinity of the Potsdam GPS station. The water vapor content along the line of sight between a ground station and a GPS satellite can be derived from GPS data and directly measured by a water vapor radiometer (WVR) at the same time. In this study we present the validation results of SIWV observed by a ground-based GPS receiver and a WVR. The validation covers 184 days of data with dry and wet humidity conditions. SIWV data from GPS and WVR generally show good agreement with a mean bias of -0.4 kg m-2 and an rms (root mean square) of 3.15 kg m-2. The differences in SIWV show an elevation dependent on an rms of 7.13 kg m-2 below 15° but of 1.76 kg m-2 above 15°. Nevertheless, this elevation dependence is not observed regarding relative deviations. The relation between the differences and possible influencing factors (elevation angles, pressure, temperature and relative humidity) are analyzed in this study. Besides the elevation, dependencies between the atmospheric humidity conditions, temperature and the differences in SIWV are found.

Terrestrial VLF transmitter injection into the magnetosphere

Science.gov (United States)

Cohen, M. B.; Inan, U. S.

2012-08-01

Very Low Frequency (VLF, 3-30 kHz) radio waves emitted from ground sources (transmitters and lightning) strongly impact the radiation belts, driving electron precipitation via whistler-electron gyroresonance, and contributing to the formation of the slot region. However, calculations of the global impacts of VLF waves are based on models of trans-ionospheric propagation to calculate the VLF energy reaching the magnetosphere. Limited comparisons of these models to individual satellite passes have found that the models may significantly (by >20 dB) overestimate amplitudes of ground based VLF transmitters in the magnetosphere. To form a much more complete empirical picture of VLF transmitter energy reaching the magnetosphere, we present observations of the radiation pattern from a number of ground-based VLF transmitters by averaging six years of data from the DEMETER satellite. We divide the slice at ˜700 km altitude above a transmitter into pixels and calculate the average field for all satellite passes through each pixel. There are enough data to see 25 km features in the radiation pattern, including the modal interference of the subionospheric signal mapped upwards. Using these data, we deduce the first empirical measure of the radiated power into the magnetosphere from these transmitters, for both daytime and nighttime, and at both the overhead and geomagnetically conjugate region. We find no detectable variation of signal intensity with geomagnetic conditions at low and mid latitudes (L ionospheric heating by one VLF transmitter which modifies the trans-ionospheric absorption of signals from other transmitters passing through the heated region.

Precise orbit determination of the Sentinel-3A altimetry satellite using ambiguity-fixed GPS carrier phase observations

Science.gov (United States)

Montenbruck, Oliver; Hackel, Stefan; Jäggi, Adrian

2017-11-01

The Sentinel-3 mission takes routine measurements of sea surface heights and depends crucially on accurate and precise knowledge of the spacecraft. Orbit determination with a targeted uncertainty of less than 2 cm in radial direction is supported through an onboard Global Positioning System (GPS) receiver, a Doppler Orbitography and Radiopositioning Integrated by Satellite instrument, and a complementary laser retroreflector for satellite laser ranging. Within this study, the potential of ambiguity fixing for GPS-only precise orbit determination (POD) of the Sentinel-3 spacecraft is assessed. A refined strategy for carrier phase generation out of low-level measurements is employed to cope with half-cycle ambiguities in the tracking of the Sentinel-3 GPS receiver that have so far inhibited ambiguity-fixed POD solutions. Rather than explicitly fixing double-difference phase ambiguities with respect to a network of terrestrial reference stations, a single-receiver ambiguity resolution concept is employed that builds on dedicated GPS orbit, clock, and wide-lane bias products provided by the CNES/CLS (Centre National d'Études Spatiales/Collecte Localisation Satellites) analysis center of the International GNSS Service. Compared to float ambiguity solutions, a notably improved precision can be inferred from laser ranging residuals. These decrease from roughly 9 mm down to 5 mm standard deviation for high-grade stations on average over low and high elevations. Furthermore, the ambiguity-fixed orbits offer a substantially improved cross-track accuracy and help to identify lateral offsets in the GPS antenna or center-of-mass (CoM) location. With respect to altimetry, the improved orbit precision also benefits the global consistency of sea surface measurements. However, modeling of the absolute height continues to rely on proper dynamical models for the spacecraft motion as well as ground calibrations for the relative position of the altimeter reference point and the CoM.

A New Position Location System Using DTV Transmitter Identification Watermark Signals

Directory of Open Access Journals (Sweden)

Chouinard Jean-Yves

2006-01-01

Full Text Available A new position location technique using the transmitter identification (TxID RF watermark in the digital TV (DTV signals is proposed in this paper. Conventional global positioning system (GPS usually does not work well inside buildings due to the high frequency and weak field strength of the signal. In contrast to the GPS, the DTV signals are received from transmitters at relatively short distance, while the broadcast transmitters operate at levels up to the megawatts effective radiated power (ERP. Also the RF frequency of the DTV signal is much lower than the GPS, which makes it easier for the signal to penetrate buildings and other objects. The proposed position location system based on DTV TxID signal is presented in this paper. Practical receiver implementation issues including nonideal correlation and synchronization are analyzed and discussed. Performance of the proposed technique is evaluated through Monte Carlo simulations and compared with other existing position location systems. Possible ways to improve the accuracy of the new position location system is discussed.

Contents of GPS Data Files

Energy Technology Data Exchange (ETDEWEB)

Sullivan, John P. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Carver, Matthew Robert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Norman, Benjamin [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2016-12-09

There are no very detailed descriptions of most of these instruments in the literature – we will attempt to fix that problem in the future. The BDD instruments are described in [1]. One of the dosimeter instruments on CXD boxes is described in [2]. These documents (or web links to them) and a few others are in this directory tree. The cross calibration of the CXD electron data with RBSP is described in [3]. Each row in the data file contains the data from one time bin from a CXD or BDD instrument along with a variety of parameters derived from the data. Time steps are commandable but 4 minutes is a typical setting. These instruments are on many (but not all) GPS satellites which are currently in operation. The data come from either BDD instruments on GPS Block IIR satellites (SVN41 and 48), or else CXD-IIR instruments on GPS Block IIR and IIR-M satellites (SVN53-61) or CXD-IIF instruments on GPS block IIF satellites (SVN62-73). The CXD-IIR instruments on block IIR and IIR(M) satellites use the same design.

Precise positioning with current multi-constellation Global Navigation Satellite Systems: GPS, GLONASS, Galileo and BeiDou.

Science.gov (United States)

Li, Xingxing; Zhang, Xiaohong; Ren, Xiaodong; Fritsche, Mathias; Wickert, Jens; Schuh, Harald

2015-02-09

The world of satellite navigation is undergoing dramatic changes with the rapid development of multi-constellation Global Navigation Satellite Systems (GNSSs). At the moment more than 70 satellites are already in view, and about 120 satellites will be available once all four systems (BeiDou + Galileo + GLONASS + GPS) are fully deployed in the next few years. This will bring great opportunities and challenges for both scientific and engineering applications. In this paper we develop a four-system positioning model to make full use of all available observations from different GNSSs. The significant improvement of satellite visibility, spatial geometry, dilution of precision, convergence, accuracy, continuity and reliability that a combining utilization of multi-GNSS brings to precise positioning are carefully analyzed and evaluated, especially in constrained environments.

Global Surface Mass Variations from Continuous GPS Observations and Satellite Altimetry Data

Directory of Open Access Journals (Sweden)

Xinggang Zhang

2017-09-01

Full Text Available The Gravity Recovery and Climate Experiment (GRACE mission is able to observe the global large-scale mass and water cycle for the first time with unprecedented spatial and temporal resolution. However, no other time-varying gravity fields validate GRACE. Furthermore, the C20 of GRACE is poor, and no GRACE data are available before 2002 and there will likely be a gap between the GRACE and GRACE-FOLLOW-ON mission. To compensate for GRACE’s shortcomings, in this paper, we provide an alternative way to invert Earth’s time-varying gravity field, using a priori degree variance as a constraint on amplitudes of Stoke’s coefficients up to degree and order 60, by combining continuous GPS coordinate time series and satellite altimetry (SA mean sea level anomaly data from January 2003 to December 2012. Analysis results show that our estimated zonal low-degree gravity coefficients agree well with those of GRACE, and large-scale mass distributions are also investigated and assessed. It was clear that our method effectively detected global large-scale mass changes, which is consistent with GRACE observations and the GLDAS model, revealing the minimums of annual water cycle in the Amazon in September and October. The global mean mass uncertainty of our solution is about two times larger than that of GRACE after applying a Gaussian spatial filter with a half wavelength at 500 km. The sensitivity analysis further shows that ground GPS observations dominate the lower-degree coefficients but fail to contribute to the higher-degree coefficients, while SA plays a complementary role at higher-degree coefficients. Consequently, a comparison in both the spherical harmonic and geographic domain confirms our global inversion for the time-varying gravity field from GPS and Satellite Altimetry.

Atmospheric density determination using high-accuracy satellite GPS data

Science.gov (United States)

Tingling, R.; Miao, J.; Liu, S.

2017-12-01

Atmospheric drag is the main error source in the orbit determination and prediction of low Earth orbit (LEO) satellites, however, empirical models which are used to account for atmosphere often exhibit density errors around 15 30%. Atmospheric density determination thus become an important topic for atmospheric researchers. Based on the relation between atmospheric drag force and the decay of orbit semi-major axis, we derived atmospheric density along the trajectory of CHAMP with its Rapid Science Orbit (RSO) data. Three primary parameters are calculated, including the ratio of cross sectional area to mass, drag coefficient, and the decay of semi-major axis caused by atmospheric drag. We also analyzed the source of error and made a comparison between GPS-derived and reference density. Result on 2 Dec 2008 shows that the mean error of GPS-derived density can decrease from 29.21% to 9.20% when time span adopted on the process of computation increase from 10min to 50min. Result for the whole December indicates that when the time span meet the condition that the amplitude of the decay of semi-major axis is much greater than its standard deviation, then density precision of 10% can be achieved.

Assessment of long-range kinematic GPS positioning errors by comparison with airborne laser altimetry and satellite altimetry

DEFF Research Database (Denmark)

Zhang, X.H.; Forsberg, René

2007-01-01

Long-range airborne laser altimetry and laser scanning (LIDAR) or airborne gravity surveys in, for example, polar or oceanic areas require airborne kinematic GPS baselines of many hundreds of kilometers in length. In such instances, with the complications of ionospheric biases, it can be a real...... challenge for traditional differential kinematic GPS software to obtain reasonable solutions. In this paper, we will describe attempts to validate an implementation of the precise point positioning (PPP) technique on an aircraft without the use of a local GPS reference station. We will compare PPP solutions...... of the Arctic Ocean north of Greenland, near-coincident in time and space with the ICESat satellite laser altimeter. Both of these flights were more than 800 km long. Comparisons between different GPS methods and four different software packages do not suggest a clear preference for any one, with the heights...

Spectral broadening of VLF transmitter signals and sideband structure observed on Aureol 3 satellite at middle latitudes

International Nuclear Information System (INIS)

Tanaka, Y.; Hayakawa, M.; Lagoutte, D.; Lefeuvre, F.; Tajima, S.

1987-01-01

Electric and magnetic field wave data acquired on Aureol 3 satellite demonstrate the existence of a spectral broadening effect in which VLF transmitter signals from Alpha station (geographic coordinates, 50.5 degree N, 137 degree E) in USSR undergo a significant spectral broadening on electric fields as they propagate through the ionosphere up to the spacecraft in the altitude range of 500-2,000 km at middle latitudes (L ∼ 2). The spectral broadening phenomena may be divided into two types: (1) spectrally broadened components occurring without any association with ELF/VLF emissions under disturbed ionospheric conditions and (2) spectrally broadened components with predominant sideband structure in association with ELF emissions. Bicoherence computation results suggest a nonlinear mode coupling between the transmitter signal and ELF emission which produces sidebands that are quasi-electrostatic in nature. However, faint spectral broadened components in both types 1 and 2 may be connected with Doppler shift of quasi-electrostatic whistler mode waves with a broad spectrum of k near the resonance cone, due to scattering of the transmitter signals from ionospheric irregularities in the F region

Accuracy of WAAS-Enabled GPS-RF Warning Signals When Crossing a Terrestrial Geofence

Directory of Open Access Journals (Sweden)

Lindsay M. Grayson

2016-06-01

Full Text Available Geofences are virtual boundaries based on geographic coordinates. When combined with global position system (GPS, or more generally global navigation satellite system (GNSS transmitters, geofences provide a powerful tool for monitoring the location and movements of objects of interest through proximity alarms. However, the accuracy of geofence alarms in GNSS-radio frequency (GNSS-RF transmitter receiver systems has not been tested. To achieve these goals, a cart with a GNSS-RF locator was run on a straight path in a balanced factorial experiment with three levels of cart speed, three angles of geofence intersection, three receiver distances from the track, and three replicates. Locator speed, receiver distance and geofence intersection angle all affected geofence alarm accuracy in an analysis of variance (p = 0.013, p = 2.58 × 10−8, and p = 0.0006, respectively, as did all treatment interactions (p < 0.0001. Slower locator speed, acute geofence intersection angle, and closest receiver distance were associated with reduced accuracy of geofence alerts.

GPS Ephemeris Message Broadcast Simulation

National Research Council Canada - National Science Library

Browne, Nathan J; Light, James J

2005-01-01

The warfighter constantly needs increased accuracy from GPS and a means to increasing this accuracy to the decimeter level is a broadcast ephemeris message containing GPS satellite orbit and clock corrections...

RAPID COMMUNICATION: Improving prediction accuracy of GPS satellite clocks with periodic variation behaviour

Science.gov (United States)

Heo, Youn Jeong; Cho, Jeongho; Heo, Moon Beom

2010-07-01

The broadcast ephemeris and IGS ultra-rapid predicted (IGU-P) products are primarily available for use in real-time GPS applications. The IGU orbit precision has been remarkably improved since late 2007, but its clock products have not shown acceptably high-quality prediction performance. One reason for this fact is that satellite atomic clocks in space can be easily influenced by various factors such as temperature and environment and this leads to complicated aspects like periodic variations, which are not sufficiently described by conventional models. A more reliable prediction model is thus proposed in this paper in order to be utilized particularly in describing the periodic variation behaviour satisfactorily. The proposed prediction model for satellite clocks adds cyclic terms to overcome the periodic effects and adopts delay coordinate embedding, which offers the possibility of accessing linear or nonlinear coupling characteristics like satellite behaviour. The simulation results have shown that the proposed prediction model outperforms the IGU-P solutions at least on a daily basis.

Performance Analysis of Several GPS/Galileo Precise Point Positioning Models.

Science.gov (United States)

Afifi, Akram; El-Rabbany, Ahmed

2015-06-19

This paper examines the performance of several precise point positioning (PPP) models, which combine dual-frequency GPS/Galileo observations in the un-differenced and between-satellite single-difference (BSSD) modes. These include the traditional un-differenced model, the decoupled clock model, the semi-decoupled clock model, and the between-satellite single-difference model. We take advantage of the IGS-MGEX network products to correct for the satellite differential code biases and the orbital and satellite clock errors. Natural Resources Canada's GPSPace PPP software is modified to handle the various GPS/Galileo PPP models. A total of six data sets of GPS and Galileo observations at six IGS stations are processed to examine the performance of the various PPP models. It is shown that the traditional un-differenced GPS/Galileo PPP model, the GPS decoupled clock model, and the semi-decoupled clock GPS/Galileo PPP model improve the convergence time by about 25% in comparison with the un-differenced GPS-only model. In addition, the semi-decoupled GPS/Galileo PPP model improves the solution precision by about 25% compared to the traditional un-differenced GPS/Galileo PPP model. Moreover, the BSSD GPS/Galileo PPP model improves the solution convergence time by about 50%, in comparison with the un-differenced GPS PPP model, regardless of the type of BSSD combination used. As well, the BSSD model improves the precision of the estimated parameters by about 50% and 25% when the loose and the tight combinations are used, respectively, in comparison with the un-differenced GPS-only model. Comparable results are obtained through the tight combination when either a GPS or a Galileo satellite is selected as a reference.

GPS satellite clock determination in case of inter-frequency clock biases for triple-frequency precise point positioning

Science.gov (United States)

Guo, Jiang; Geng, Jianghui

2017-12-01

Significant time-varying inter-frequency clock biases (IFCBs) within GPS observations prevent the application of the legacy L1/L2 ionosphere-free clock products on L5 signals. Conventional approaches overcoming this problem are to estimate L1/L5 ionosphere-free clocks in addition to their L1/L2 counterparts or to compute IFCBs between the L1/L2 and L1/L5 clocks which are later modeled through a harmonic analysis. In contrast, we start from the undifferenced uncombined GNSS model and propose an alternative approach where a second satellite clock parameter dedicated to the L5 signals is estimated along with the legacy L1/L2 clock. In this manner, we do not need to rely on the correlated L1/L2 and L1/L5 ionosphere-free observables which complicates triple-frequency GPS stochastic models, or account for the unfavorable time-varying hardware biases in undifferenced GPS functional models since they can be absorbed by the L5 clocks. An extra advantage over the ionosphere-free model is that external ionosphere constraints can potentially be introduced to improve PPP. With 27 days of triple-frequency GPS data from globally distributed stations, we find that the RMS of the positioning differences between our GPS model and all conventional models is below 1 mm for all east, north and up components, demonstrating the effectiveness of our model in addressing triple-frequency observations and time-varying IFCBs. Moreover, we can combine the L1/L2 and L5 clocks derived from our model to calculate precisely the L1/L5 clocks which in practice only depart from their legacy counterparts by less than 0.006 ns in RMS. Our triple-frequency GPS model proves convenient and efficient in combating time-varying IFCBs and can be generalized to more than three frequency signals for satellite clock determination.

47 CFR 25.281 - Automatic Transmitter Identification System (ATIS).

Science.gov (United States)

2010-10-01

... 47 Telecommunication 2 2010-10-01 2010-10-01 false Automatic Transmitter Identification System (ATIS). 25.281 Section 25.281 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES SATELLITE COMMUNICATIONS Technical Operations § 25.281 Automatic Transmitter...

Ionospheric turbulence from ground-based and satellite VLF/LF transmitter signal observations for the Simushir earthquake (November 15, 2006

Directory of Open Access Journals (Sweden)

Pier Francesco Biagi

2012-04-01

Full Text Available

Signals from very low frequency (VLF/ low frequency (LF transmitters recorded on the ground station at Petropavlovsk-Kamchatsky and on board the French DEMETER satellite were analyzed for the Simushir earthquake (M 8.3; November 15, 2006. The period of analysis was from October 1, 2006, to January 31, 2007. The ground and satellite data were processed by a method based on the difference between the real signal at night-time and the model signal. The model for the ground observations was the monthly averaged signal amplitudes and phases, as calculated for the quiet days of every month. For the satellite data, a two-dimensional model of the signal distribution over the selected area was constructed. Preseismic effects were found several days before the earthquake, in both the ground and satellite observations.

Inversion of GPS meteorology data

Directory of Open Access Journals (Sweden)

K. Hocke

Full Text Available The GPS meteorology (GPS/MET experiment, led by the Universities Corporation for Atmospheric Research (UCAR, consists of a GPS receiver aboard a low earth orbit (LEO satellite which was launched on 3 April 1995. During a radio occultation the LEO satellite rises or sets relative to one of the 24 GPS satellites at the Earth's horizon. Thereby the atmospheric layers are successively sounded by radio waves which propagate from the GPS satellite to the LEO satellite. From the observed phase path increases, which are due to refraction of the radio waves by the ionosphere and the neutral atmosphere, the atmospheric parameter refractivity, density, pressure and temperature are calculated with high accuracy and resolution (0.5–1.5 km. In the present study, practical aspects of the GPS/MET data analysis are discussed. The retrieval is based on the Abelian integral inversion of the atmospheric bending angle profile into the refractivity index profile. The problem of the upper boundary condition of the Abelian integral is described by examples. The statistical optimization approach which is applied to the data above 40 km and the use of topside bending angle profiles from model atmospheres stabilize the inversion. The retrieved temperature profiles are compared with corresponding profiles which have already been calculated by scientists of UCAR and Jet Propulsion Laboratory (JPL, using Abelian integral inversion too. The comparison shows that in some cases large differences occur (5 K and more. This is probably due to different treatment of the upper boundary condition, data runaways and noise. Several temperature profiles with wavelike structures at tropospheric and stratospheric heights are shown. While the periodic structures at upper stratospheric heights could be caused by residual errors of the ionospheric correction method, the periodic temperature fluctuations at heights below 30 km are most likely caused by atmospheric waves (vertically

How and Why to Do VLBI on GPS

Science.gov (United States)

Dickey, J. M.

2010-01-01

In order to establish the position of the center of mass of the Earth in the International Celestial Reference Frame, observations of the Global Positioning Satellite (GPS) constellation using the IVS network are important. With a good frame-tie between the coordinates of the IVS telescopes and nearby GPS receivers, plus a common local oscillator reference signal, it should be possible to observe and record simultaneously signals from the astrometric calibration sources and the GPS satellites. The standard IVS solution would give the atmospheric delay and clock offsets to use in analysis of the GPS data. Correlation of the GPS signals would then give accurate orbital parameters of the satellites in the ICRF reference frame, i.e., relative to the positions of the astrometric sources. This is particularly needed to determine motion of the center of mass of the earth along the rotation axis.

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

High Gain Advanced GPS Receiver

National Research Council Canada - National Science Library

Brown, Alison; Zhang, Gengsheng

2006-01-01

NAVSYS High Gain Advanced GPS Receiver (HAGR) uses a digital beam-steering antenna array to enable up to eight GPS satellites to be tracked, each with up to 10 dBi of additional antenna gain over a conventional receiver solution...

Indoor Positioning Using GPS Revisited

DEFF Research Database (Denmark)

Kjærgaard, Mikkel Baun; Blunck, Henrik; Godsk, Torben

2010-01-01

It has been considered a fact that GPS performs too poorly inside buildings to provide usable indoor positioning. We analyze results of a measurement campaign to improve on the understanding of indoor GPS reception characteristics. The results show that using state-of-the-art receivers GPS...... low signal-to-noise ratios, multipath phenomena or bad satellite constellation geometry. We have also measured the indoor performance of embedded GPS receivers in mobile phones which provided lower availability and accuracy than state-of-the-art ones. Finally, we consider how the GPS performance...

The use of the AOA TTR-4P GPS receiver in operation at the BIPM for real-time restitution of GPS time

Science.gov (United States)

Thomas, Claudine

1994-01-01

The Global Positioning System is an outstanding tool for the dissemination of time. Using mono-channel C/A-code GPS time receivers, the restitution of GPS time through the satellite constellation presents a peak-to-peak discrepancy of several tens of nanoseconds without SA but may be as high as several hundreds of nanoseconds with SA. As a consequence, civil users are more and more interested in implementing hardware and software methods for efficient restitution of GPS time, especially in the framework of the project of a real-time prediction of UTC (UTCp) which could be available in the form of time differences (UTCp - GPS time). Previous work, for improving the real-time restitution of GPS time with SA, to the level obtained without SA, focused on the implementation of a Kalman filter based on past data and updated at each new observation. An alternative solution relies upon the statistical features of the noise brought about by SA; it has already been shown that the SA noise is efficiently reduced by averaging data from numerous satellites observed simultaneously over a sufficiently long time. This method was successfully applied to data from a GPS time receiver, model AOA TTR-4P, connected to the cesium clock kept at the BIPM. This device, a multi-channel, dual frequency, P-code GPS time receiver, is one of the first TTR-4P units in operation in a civil laboratory. Preliminary comparative studies of this new equipment with conventional GPS time receivers are described in this paper. The results of an experimental restitution of GPS time, obtained in June 1993, are also detailed: 3 to 6 satellites were observed simultaneously with a sample interval of 15 s, an efficient smoothing of SA noise was realized by averaging data on all observed satellites over more than 1 hour. When the GPS system is complete in 1994, 8 satellites will be observable continuously from anywhere in the world and the same level of uncertainty will be obtained using a shorter averaging

Observability of satellite launcher navigation with INS, GPS, attitude sensors and reference trajectory

Science.gov (United States)

Beaudoin, Yanick; Desbiens, André; Gagnon, Eric; Landry, René

2018-01-01

The navigation system of a satellite launcher is of paramount importance. In order to correct the trajectory of the launcher, the position, velocity and attitude must be known with the best possible precision. In this paper, the observability of four navigation solutions is investigated. The first one is the INS/GPS couple. Then, attitude reference sensors, such as magnetometers, are added to the INS/GPS solution. The authors have already demonstrated that the reference trajectory could be used to improve the navigation performance. This approach is added to the two previously mentioned navigation systems. For each navigation solution, the observability is analyzed with different sensor error models. First, sensor biases are neglected. Then, sensor biases are modelled as random walks and as first order Markov processes. The observability is tested with the rank and condition number of the observability matrix, the time evolution of the covariance matrix and sensitivity to measurement outlier tests. The covariance matrix is exploited to evaluate the correlation between states in order to detect structural unobservability problems. Finally, when an unobservable subspace is detected, the result is verified with theoretical analysis of the navigation equations. The results show that evaluating only the observability of a model does not guarantee the ability of the aiding sensors to correct the INS estimates within the mission time. The analysis of the covariance matrix time evolution could be a powerful tool to detect this situation, however in some cases, the problem is only revealed with a sensitivity to measurement outlier test. None of the tested solutions provide GPS position bias observability. For the considered mission, the modelling of the sensor biases as random walks or Markov processes gives equivalent results. Relying on the reference trajectory can improve the precision of the roll estimates. But, in the context of a satellite launcher, the roll

Vertical land motion along the coast of Louisiana: Integrating satellite altimetry, tide gauge and GPS

Science.gov (United States)

Dixon, T. H.; A Karegar, M.; Uebbing, B.; Kusche, J.; Fenoglio-Marc, L.

2017-12-01

Coastal Louisiana is experiencing the highest rate of relative sea-level rise in North America due to the combination of sea-level rise and subsidence of the deltaic plain. The land subsidence in this region is studied using various techniques, with continuous GPS site providing high temporal resolution. Here, we use high resolution tide-gauge data and advanced processing of satellite altimetry to derive vertical displacements time series at NOAA tide-gauge stations along the coast (Figure 1). We apply state-of-the-art retracking techniques to process raw altimetry data, allowing high accuracy on range measurements close to the coast. Data from Jason-1, -2 and -3, Envisat, Saral and Cryosat-2 are used, corrected for solid Earth tide, pole tide and tidal ocean loading, using background models consistent with the GPS processing technique. We reprocess the available GPS data using precise point positioning and estimate the rate uncertainty accounting for correlated noise. The displacement time series are derived by directly subtracting tide-gauge data from the altimetry sea-level anomaly data. The quality of the derived displacement rates is evaluated in Grand Isle, Amerada Pass and Shell Beach where GPS data are available adjacent to the tide gauges. We use this technique to infer vertical displacement at tide gauges in New Orleans (New Canal Station) and Port Fourchon and Southwest Pass along the coastline.

Robust GPS autonomous signal quality monitoring

Science.gov (United States)

Ndili, Awele Nnaemeka

The Global Positioning System (GPS), introduced by the U.S. Department of Defense in 1973, provides unprecedented world-wide navigation capabilities through a constellation of 24 satellites in global orbit, each emitting a low-power radio-frequency signal for ranging. GPS receivers track these transmitted signals, computing position to within 30 meters from range measurements made to four satellites. GPS has a wide range of applications, including aircraft, marine and land vehicle navigation. Each application places demands on GPS for various levels of accuracy, integrity, system availability and continuity of service. Radio frequency interference (RFI), which results from natural sources such as TV/FM harmonics, radar or Mobile Satellite Systems (MSS), presents a challenge in the use of GPS, by posing a threat to the accuracy, integrity and availability of the GPS navigation solution. In order to use GPS for integrity-sensitive applications, it is therefore necessary to monitor the quality of the received signal, with the objective of promptly detecting the presence of RFI, and thus provide a timely warning of degradation of system accuracy. This presents a challenge, since the myriad kinds of RFI affect the GPS receiver in different ways. What is required then, is a robust method of detecting GPS accuracy degradation, which is effective regardless of the origin of the threat. This dissertation presents a new method of robust signal quality monitoring for GPS. Algorithms for receiver autonomous interference detection and integrity monitoring are demonstrated. Candidate test statistics are derived from fundamental receiver measurements of in-phase and quadrature correlation outputs, and the gain of the Active Gain Controller (AGC). Performance of selected test statistics are evaluated in the presence of RFI: broadband interference, pulsed and non-pulsed interference, coherent CW at different frequencies; and non-RFI: GPS signal fading due to physical blockage and

Greenland ice mass balance from GPS, GRACE and ICESat

DEFF Research Database (Denmark)

Khan, Shfaqat Abbas; Kjær, Kurt H.; Korsgaard, Niels Jákup

Greenland, using stereoscopic coverage by aerial photographs recorded in 1985, and subsequent comparative surface elevation data from ICESat (Ice, Cloud and land Elevation Satellite) and ATM (Airborne Topographic Mapper) supplemented with measurements from GPS and the Gravity Recovery and Climate Experiment...... (GRACE) satellite gravity mission, launched in March, 2002. The GRACE results provide a direct measure of mass loss, while the GPS data are used to monitor crustal uplift caused by ice mass loss close to the GPS sites....

New method of GPS orbit determination from GCPS network for the purpose of DOP calculations

Directory of Open Access Journals (Sweden)

Aly M. El-naggar

2012-06-01

Full Text Available The accuracy of GPS measurement satisfies the requirements of some applications, but many applications require an improvement of GPS measurement accuracy. For precise positioning by GPS, it is necessary to perform GPS mission planning. The GPS mission planning is a pre-survey task in which the values of Dilution Of Precision (DOP should be predicted for the observation points, this task should determine the best observation periods which meet the project requirements. The main purpose of this work is to study a rather simple but still fairly accurate algorithm to determine the artificial satellite orbits for the purpose of DOP calculation. The orbit determination algorithm proposed in this paper is implemented by using several reference stations and calculated the orbits by new algorithm; inverse GPS. Inverse GPS means that reference stations are considered as satellites and satellite as receiver. This new algorithm used to calculate the satellite orbit which is mainly used to calculate the DOP. A comparison is done between the estimated PDOP by using satellite coordinates from new method and from the SP3 (Standard Product # 3 file.

Co-location satellite GPS and SLR geodetic techniques at the Felix Aguilar Astronomical Observatory of San Juan, Argentina

Science.gov (United States)

Podestá, R.; Pacheco, A. M.; Alvis Rojas, H.; Quinteros, J.; Podestá, F.; Albornoz, E.; Navarro, A.; Luna, M.

2018-01-01

This work shows the strategy followed for the co-location of the Satellite Laser Ranging (SLR) ILRS 7406 telescope and the antenna of the permanent Global Positioning System (GPS) station, located at the Félix Aguilar Astronomical Observatory (OAFA) in San Juan, Argentina. The accomplishment of the co-location consisted in the design, construction, measurement, adjustment and compensation of a geodesic net between the stations SLR and GPS, securing support points solidly built in the soil. The co-location allows the coordinates of the station to be obtained by combining the data of both SLR and GPS techniques, achieving a greater degree of accuracy than individually. The International Earth Rotation and Reference Systems Service (IERS) considers the co-located stations as the most valuable and important points for the maintenance of terrestrial reference systems and their connection with the celestial ones. The 3 mm precision required by the IERS has been successfully achieved.

Influence of Ephemeris Error on GPS Single Point Positioning Accuracy

Science.gov (United States)

Lihua, Ma; Wang, Meng

2013-09-01

The Global Positioning System (GPS) user makes use of the navigation message transmitted from GPS satellites to achieve its location. Because the receiver uses the satellite's location in position calculations, an ephemeris error, a difference between the expected and actual orbital position of a GPS satellite, reduces user accuracy. The influence extent is decided by the precision of broadcast ephemeris from the control station upload. Simulation analysis with the Yuma almanac show that maximum positioning error exists in the case where the ephemeris error is along the line-of-sight (LOS) direction. Meanwhile, the error is dependent on the relationship between the observer and spatial constellation at some time period.

The Evolution of Global Positioning System (GPS) Technology.

Science.gov (United States)

Kumar, Sameer; Moore, Kevin B.

2002-01-01

Describes technological advances in the Global Positioning System (GPS), which is also known as the NAVSTAR GPS satellite constellation program developed in 1937, and changes in the nature of our world by GPS in the areas of agriculture, health, military, transportation, environment, wildlife biology, surveying and mapping, space applications, and…

GPS/INS Sensor Fusion Using GPS Wind up Model

Science.gov (United States)

Williamson, Walton R. (Inventor)

2013-01-01

A method of stabilizing an inertial navigation system (INS), includes the steps of: receiving data from an inertial navigation system; and receiving a finite number of carrier phase observables using at least one GPS receiver from a plurality of GPS satellites; calculating a phase wind up correction; correcting at least one of the finite number of carrier phase observables using the phase wind up correction; and calculating a corrected IMU attitude or velocity or position using the corrected at least one of the finite number of carrier phase observables; and performing a step selected from the steps consisting of recording, reporting, or providing the corrected IMU attitude or velocity or position to another process that uses the corrected IMU attitude or velocity or position. A GPS stabilized inertial navigation system apparatus is also described.

Observations on the Reliability of Rubidium Frequency Standards on Block 2/2A GPS Satellites

Science.gov (United States)

Dieter, Gary L.

1996-01-01

Currently, the block 2/2A Global Positioning System (GPS) satellites are equipped with two rubidium frequency standards. These frequency standards were originally intended to serve as the back-ups to two cesium frequency standards. As the constellation ages, the master Control Station is forced to initialize and increasing number or rubidium frequency standards. Unfortunately the operational use of these frequency standards has not lived up to initial expectations. Although the performance of these rubidium frequency standards has met and even exceeded GPS requirements, their reliability has not. The number of unscheduled outage times and the short operational lifetimes of the rubidium frequency standards compare poorly to the track record of the cesium frequency standards. Only a small number of rubidium frequency standards have actually been made operational. Of these, a large percentage have exhibited poor reliability. If this trend continues, it is unlikely that the rubidium frequency standards will help contribute to the navigation payload meeting program specification.

GPS-based tracking system for TOPEX orbit determination

Science.gov (United States)

Melbourne, W. G.

1984-01-01

A tracking system concept is discussed that is based on the utilization of the constellation of Navstar satellites in the Global Positioning System (GPS). The concept involves simultaneous and continuous metric tracking of the signals from all visible Navstar satellites by approximately six globally distributed ground terminals and by the TOPEX spacecraft at 1300-km altitude. Error studies indicate that this system could be capable of obtaining decimeter position accuracies and, most importantly, around 5 cm in the radial component which is key to exploiting the full accuracy potential of the altimetric measurements for ocean topography. Topics covered include: background of the GPS, the precision mode for utilization of the system, past JPL research for using the GPS in precision applications, the present tracking system concept for high accuracy satellite positioning, and results from a proof-of-concept demonstration.

The Statistics of GPS

National Research Council Canada - National Science Library

Matsakis, Demetrios

2007-01-01

The Global Positioning System (GPS) is an extremely effective satellite-based system that broadcasts sufficient information for a user to determine time and position from any location on or near the Earth...

Precise GPS orbits for geodesy

Science.gov (United States)

Colombo, Oscar L.

1994-01-01

The Global Positioning System (GPS) has become, in recent years, the main space-based system for surveying and navigation in many military, commercial, cadastral, mapping, and scientific applications. Better receivers, interferometric techniques (DGPS), and advances in post-processing methods have made possible to position fixed or moving receivers with sub-decimeter accuracies in a global reference frame. Improved methods for obtaining the orbits of the GPS satellites have played a major role in these achievements; this paper gives a personal view of the main developments in GPS orbit determination.

Thermal structure of intense convective clouds derived from GPS radio occultations

DEFF Research Database (Denmark)

Biondi, Riccardo; Randel, W. J.; Ho, S. -P.

2012-01-01

Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature...... behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS...

Thermal structure of intense convective clouds derived from GPS radio occultations

DEFF Research Database (Denmark)

Biondi, Riccardo; Randel, W. J.; Ho, S.-P.

2011-01-01

Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature...... behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS...

Perturbations of ionosphere-magnetosphere coupling by powerful VLF emissions from ground-based transmitters

International Nuclear Information System (INIS)

Belov, A. S.; Markov, G. A.; Ryabov, A. O.; Parrot, M.

2012-01-01

The characteristics of the plasma-wave disturbances stimulated in the near-Earth plasma by powerful VLF radiation from ground-based transmitters are investigated. Radio communication VLF transmitters of about 1 MW in power are shown to produce artificial plasma-wave channels (density ducts) in the near-Earth space that originate in the lower ionosphere above the disturbing emission source and extend through the entire ionosphere and magnetosphere of the Earth along the magnetic field lines. Measurements with the onboard equipment of the DEMETER satellite have revealed that under the action of emission from the NWC transmitter, which is one of the most powerful VLF radio transmitters, the generation of quasi-electrostatic (plasma) waves is observed on most of the satellite trajectory along the disturbed magnetic flux tube. This may probably be indicative of stimulated emission of a magnetospheric maser.

Advantages of Hybrid Global Navigation Satellite Systems

Directory of Open Access Journals (Sweden)

Asim Bilajbegović

2007-05-01

Full Text Available In a decision-making situation, what kind of GPS equipment to purchase, one always has a dilemma, tobuy hybrid (GPS+GLONASS or only GPS receivers? In the case of completeness of the GLONASS satellite system, this dilemma probably would not have existed. The answer to this dilemma is given in the present paper, but for the constellation of the GLONASS satellites in summer 2006 (14 satellites operational. Due to the short operational period of these satellites (for example GLONASS-M, 5 years, and not launching new ones, at this moment (February 25, 2007, only 10 satellites are operational. For the sake of research and giving answers to these questions, about 252 RTK measurements have been done using (GPS and GNSS receivers, on points with different obstructions of horizon. Besides that, initialisation time has been investigated for both systems from about 480 measurements, using rover's antenna with metal cover, during a time interval of 0.5, 2 and 5 seconds. Moreover, accuracy, firmware declared accuracy and redundancy of GPS and GNSS RTK measurements have been investigating.  

Intraperitoneal implantation of life-long telemetry transmitters in otariids

Directory of Open Access Journals (Sweden)

Haulena Martin

2008-12-01

Full Text Available Abstract Background Pinnipeds, including many endangered and declining species, are inaccessible and difficult to monitor for extended periods using externally attached telemetry devices that are shed during the annual molt. Archival satellite transmitters were implanted intraperitoneally into four rehabilitated California sea lions (Zalophus californianus and 15 wild juvenile Steller sea lions (Eumetopias jubatus to determine the viability of this surgical technique for the deployment of long-term telemetry devices in otariids. The life history transmitters record information throughout the life of the host and transmit data to orbiting satellites after extrusion following death of the host. Results Surgeries were performed under isoflurane anesthesia and single (n = 4 or dual (n = 15 transmitters were inserted into the ventrocaudal abdominal cavity via an 8.5 to 12 cm incision along the ventral midline between the umbilicus and pubic symphysis or preputial opening. Surgeries lasted 90 minutes (SD = 8 for the 19 sea lions. All animals recovered well and were released into the wild after extended monitoring periods from 27 to 69 days at two captive animal facilities. Minimum post-implant survival was determined via post-release tracking using externally attached satellite transmitters or via opportunistic re-sighting for mean durations of 73.7 days (SE = 9.0, Z. californianus and 223.6 days (SE = 71.5, E. jubatus. Conclusion The low morbidity and zero mortality encountered during captive observation and post-release tracking periods confirm the viability of this surgical technique for the implantation of long-term telemetry devices in otariids.

Ionospheric irregularities at Antarctic using GPS measurements

Indian Academy of Sciences (India)

Scintillation is a major problem in navigation application using GPS and in satellite ... ground ionization which leads to phase as well as amplitude scintillation as reported by ..... in satellite sig- nals which arise from the scattering of radio waves.

Timing Comparisons for GLEs and High-energy Proton Events using GPS Proton Measurements

Science.gov (United States)

Bernstein, V.; Winter, L. M.; Carver, M.; Morley, S.

2017-12-01

The newly released LANL GPS particle sensor data offers a unique snapshot of access of relativistic particles into the geomagnetic field. Currently, 23 of the 31 operational GPS satellites host energetic particle detectors which can detect the arrival of high-energy solar protons associated with Ground Level Enhancements (GLEs). We compare the timing profiles of solar energetic proton detections from GPS satellites as well as from ground-based Neutron Monitors and GOES spacecraft at geostationary orbit in order to understand how high-energy protons from the Sun enter the geomagnetic field and investigate potential differences in arrival time of energetic protons at GPS satellites as a function of location. Previous studies could only use one or two spacecraft at a similar altitude to track the arrival of energetic particles. With GPS data, we can now test whether the particles arrive isotropically, as assumed, or whether there exist differences in the timing and energetics viewed by each of the individual satellites. Extensions of this work could lead to improvements in space weather forecasting that predict more localized risk estimates for space-based technology.

Mobile satellite communications in the 1990's

Science.gov (United States)

Singh, Jai

1992-07-01

The evolution of Inmarsat global services from a single market and single service of the 1980's to all of the key mobile markets and a wide range of new terminals and services in the 1990's is described. An overview of existing mobile satellite services, as well as new services under implementation for introduction in the near and longer term, including a handheld satellite phone (Inmarsat-P), is provided. The initiative taken by Inmarsat in the integration of its global mobile satellite services with global navigation capability derived from GPS (Global Positioning System) and the GLONASS (Russian GPS) navigation satellite systems and the provision of an international civil overlay for GPS/GLONASS integrity and augmentation is highlighted. To complete the overview of the development of mobile satellite services in the 1990's, the known national and regional mobile satellite system plans and the various recent proposals for both orbiting and geostationary satellite systems for proving handheld satellite phone and/or data messaging services are described.

Combined Global Navigation Satellite Systems in the Space Service Volume

Science.gov (United States)

Force, Dale A.; Miller, James J.

2013-01-01

Besides providing position, velocity, and timing (PVT) for terrestrial users, the Global Positioning System (GPS) is also being used to provide PVT information for earth orbiting satellites. In 2006, F. H. Bauer, et. al., defined the Space Service Volume in the paper GPS in the Space Service Volume , presented at ION s 19th international Technical Meeting of the Satellite Division, and looked at GPS coverage for orbiting satellites. With GLONASS already operational, and the first satellites of the Galileo and Beidou/COMPASS constellations already in orbit, it is time to look at the use of the new Global Navigation Satellite Systems (GNSS) coming into service to provide PVT information for earth orbiting satellites. This presentation extends GPS in the Space Service Volume by examining the coverage capability of combinations of the new constellations with GPS GPS was first explored as a system for refining the position, velocity, and timing of other spacecraft equipped with GPS receivers in the early eighties. Because of this, a new GPS utility developed beyond the original purpose of providing position, velocity, and timing services for land, maritime, and aerial applications. GPS signals are now received and processed by spacecraft both above and below the GPS constellation, including signals that spill over the limb of the earth. Support of GPS space applications is now part of the system plan for GPS, and support of the Space Service Volume by other GNSS providers has been proposed to the UN International Committee on GNSS (ICG). GPS has been demonstrated to provide decimeter level position accuracy in real-time for satellites in low Earth orbit (centimeter level in non-real-time applications). GPS has been proven useful for satellites in geosynchronous orbit, and also for satellites in highly elliptical orbits. Depending on how many satellites are in view, one can keep time locked to the GNSS standard, and through that to Universal Time as long as at least one

GPS Navigation and Tracking Device

Directory of Open Access Journals (Sweden)

Yahya Salameh Khraisat

2011-10-01

Full Text Available Since the introduction of GPS Navigation systems in the marketplace, consumers and businesses have been coming up with innovative ways to use the technology in their everyday life. GPS Navigation and Tracking systems keep us from getting lost when we are in strange locations, they monitor children when they are away from home, keep track of business vehicles and can even let us know where a philandering partner is at all times. Because of this we attend to build a GPS tracking device to solve the mentioned problems. Our work consists of the GPS module that collects data from satellites and calculates the position information before transmitting them to the user’s PC (of Navigation system or observers (of Tracking System using wireless technology (GSM.

A Terrestrial Reference Frame realised on the observation level using a GPS-LEO satellite constellation

Science.gov (United States)

Koenig, Daniel

2018-02-01

Applying a one-step integrated process, i.e. by simultaneously processing all data and determining all satellite orbits involved, a Terrestrial Reference Frame (TRF) consisting of a geometric as well as a dynamic part has been determined at the observation level using the EPOS-OC software of Deutsches GeoForschungsZentrum. The satellite systems involved comprise the Global Positioning System (GPS) as well as the twin GRACE spacecrafts. Applying a novel approach, the inherent datum defect has been overcome empirically. In order not to rely on theoretical assumptions this is done by carrying out the TRF estimation based on simulated observations and using the associated satellite orbits as background truth. The datum defect is identified here as the total of all three translations as well as the rotation about the z-axis of the ground station network leading to a rank-deficient estimation problem. To rectify this singularity, datum constraints comprising no-net translation (NNT) conditions in x, y, and z as well as a no-net rotation (NNR) condition about the z-axis are imposed. Thus minimally constrained, the TRF solution covers a time span of roughly a year with daily resolution. For the geometric part the focus is put on Helmert transformations between the a priori and the estimated sets of ground station positions, and the dynamic part is represented by gravity field coefficients of degree one and two. The results of a reference solution reveal the TRF parameters to be estimated reliably with high precision. Moreover, carrying out a comparable two-step approach using the same data and models leads to parameters and observational residuals of worse quality. A validation w.r.t. external sources shows the dynamic origin to coincide at a level of 5 mm or better in x and y, and mostly better than 15 mm in z. Comparing the derived GPS orbits to IGS final orbits as well as analysing the SLR residuals for the GRACE satellites reveals an orbit quality on the few cm level

A Geometry-Based Cycle Slip Detection and Repair Method with Time-Differenced Carrier Phase (TDCP for a Single Frequency Global Position System (GPS + BeiDou Navigation Satellite System (BDS Receiver

Directory of Open Access Journals (Sweden)

Chuang Qian

2016-12-01

Full Text Available As the field of high-precision applications based on carriers continues to expand, the development of low-cost, small, modular receivers and their application in diverse scenarios and situations with complex data quality has increased the requirements of carrier-phase data preprocessing. A new geometry-based cycle slip detection and repair method based on Global Position System (GPS + BeiDou Navigation Satellite System (BDS is proposed. The method uses a Time-differenced Carrier Phase (TDCP model, which eliminates the Inner-System Bias (ISB between GPS and BDS, and it is conducive to the effective combination of GPS and BDS. It avoids the interference of the noise of the pseudo-range with cycle slip detection, while the cycle slips are preserved as integers. This method does not limit the receiver frequency number, and it is applicable to single-frequency data. The process is divided into two steps to detect and repair cycle slip. The first step is cycle slip detection, using the Improved Local Analysis Method (ILAM to find satellites that have cycle slips; The second step is to repair the cycle slips, including estimating the float solution of changes in ambiguities at the satellites that have cycle slips with the least squares method and the integer solution of the cycle slips by rounding. In the process of rounding, in addition to the success probability, a decimal test is carried out to validate the result. Finally, experiments with filed test data are carried out to prove the effectiveness of this method. The results show that the detectable cycle slips number with GPS + BDS is much greater than that with GPS. The method can also detect the non-integer outliers while fixing the cycle slip. The maximum decimal bias in repair is less than that with GPS. It implies that this method takes full advantages of multi-system.

On the Realistic Stochastic Model of GPS Observables: Implementation and Performance

Science.gov (United States)

Zangeneh-Nejad, F.; Amiri-Simkooei, A. R.; Sharifi, M. A.; Asgari, J.

2015-12-01

High-precision GPS positioning requires a realistic stochastic model of observables. A realistic GPS stochastic model of observables should take into account different variances for different observation types, correlations among different observables, the satellite elevation dependence of observables precision, and the temporal correlation of observables. Least-squares variance component estimation (LS-VCE) is applied to GPS observables using the geometry-based observation model (GBOM). To model the satellite elevation dependent of GPS observables precision, an exponential model depending on the elevation angles of the satellites are also employed. Temporal correlation of the GPS observables is modelled by using a first-order autoregressive noise model. An important step in the high-precision GPS positioning is double difference integer ambiguity resolution (IAR). The fraction or percentage of success among a number of integer ambiguity fixing is called the success rate. A realistic estimation of the GNSS observables covariance matrix plays an important role in the IAR. We consider the ambiguity resolution success rate for two cases, namely a nominal and a realistic stochastic model of the GPS observables using two GPS data sets collected by the Trimble R8 receiver. The results confirm that applying a more realistic stochastic model can significantly improve the IAR success rate on individual frequencies, either on L1 or on L2. An improvement of 20% was achieved to the empirical success rate results. The results also indicate that introducing the realistic stochastic model leads to a larger standard deviation for the baseline components by a factor of about 2.6 on the data sets considered.

Use of the North Sea by harbour seal with special emphasis on the Horns Reef area. Test of prototype GPS/GSM-transmitter on harbour seals in the Sealarium Esbjerg

International Nuclear Information System (INIS)

Tougaard, S.; Tougaard, J.

2004-04-01

A combined GPS-receiver and GSM mobile phone transmitter designed for deployment on wild seals was tested on a captive harbour seal. The unit has been under development in recent years and consists of a GPS-unit for positioning and a GSM mobile phone unit for transmission of logged positions to land. The test took place in the Sealarium at the Fisheries and Maritime Museum, Esbjerg. The unit was glued onto the fur on the head of the seal, where it stayed on for 13 days. Only one position was acquired by the unit and it failed to connect to the GSM-net during the test. Technical information from the constructor of the unit is not available and it is thus not possible to conclude on the reasons why the unit did not function as intended. The behaviour of the seal can however, be ruled out, as close observation and registration of the seals dive behaviour during the first days of deployment showed that the unit was free of the water for sufficiently long periods for positions to be acquired. (au)

A GPS Satellite Clock Offset Prediction Method Based on Fitting Clock Offset Rates Data

Directory of Open Access Journals (Sweden)

WANG Fuhong

2016-12-01

Full Text Available It is proposed that a satellite atomic clock offset prediction method based on fitting and modeling clock offset rates data. This method builds quadratic model or linear model combined with periodic terms to fit the time series of clock offset rates, and computes the model coefficients of trend with the best estimation. The clock offset precisely estimated at the initial prediction epoch is directly adopted to calculate the model coefficient of constant. The clock offsets in the rapid ephemeris (IGR provided by IGS are used as modeling data sets to perform certain experiments for different types of GPS satellite clocks. The results show that the clock prediction accuracies of the proposed method for 3, 6, 12 and 24 h achieve 0.43, 0.58, 0.90 and 1.47 ns respectively, which outperform the traditional prediction method based on fitting original clock offsets by 69.3%, 61.8%, 50.5% and 37.2%. Compared with the IGU real-time clock products provided by IGS, the prediction accuracies of the new method have improved about 15.7%, 23.7%, 27.4% and 34.4% respectively.

A Navigation/Positioning Service Based on Pseudolites Installed on Stratospheric Airships

OpenAIRE

辻井, 利昭; TSUJII, Toshiaki; 張替, 正敏; HARIGAE, Masatoshi

2002-01-01

Transmitters of GPS-like signals, called pseudolites (PL) or "pseudo-satellites" have been widely investigated as an additional ranging source for performance enhancement of GPS. Ground-based GPS augmentation systems using pseudolites have been investigated for several applications such as vehicle navigation in downtown urban canyons, positioning in deep open-cut pits and mines and precision landing of aircraft. The concept of an innovative GPS navigation/ positioning system augmented by airs...

Soil Moisture Retrieval Based on GPS Signal Strength Attenuation

Directory of Open Access Journals (Sweden)

Franziska Koch

2016-07-01

Full Text Available Soil moisture (SM is a highly relevant variable for agriculture, the emergence of floods and a key variable in the global energy and water cycle. In the last years, several satellite missions have been launched especially to derive large-scale products of the SM dynamics on the Earth. However, in situ validation data are often scarce. We developed a new method to retrieve SM of bare soil from measurements of low-cost GPS (Global Positioning System sensors that receive the freely available GPS L1-band signals. The experimental setup of three GPS sensors was installed at a bare soil field at the German Weather Service (DWD in Munich for almost 1.5 years. Two GPS antennas were installed within the soil column at a depth of 10 cm and one above the soil. SM was successfully retrieved based on GPS signal strength losses through the integral soil volume. The results show high agreement with measured and modelled SM validation data. Due to its non-destructive, cheap and low power setup, GPS sensor networks could also be used for potential applications in remote areas, aiming to serve as satellite validation data and to support the fields of agriculture, water supply, flood forecasting and climate change.

Use of the North Sea by harbour seal with special emphasis on the Horns Reef area. Test of prototype GPS/GSM-transmitter on harbour seals in the Sealarium Esbjerg[Denmark

Energy Technology Data Exchange (ETDEWEB)

Tougaard, S.; Tougaard, J.

2004-04-15

A combined GPS-receiver and GSM mobile phone transmitter designed for deployment on wild seals was tested on a captive harbour seal. The unit has been under development in recent years and consists of a GPS-unit for positioning and a GSM mobile phone unit for transmission of logged positions to land. The test took place in the Sealarium at the Fisheries and Maritime Museum, Esbjerg. The unit was glued onto the fur on the head of the seal, where it stayed on for 13 days. Only one position was acquired by the unit and it failed to connect to the GSM-net during the test. Technical information from the constructor of the unit is not available and it is thus not possible to conclude on the reasons why the unit did not function as intended. The behaviour of the seal can however, be ruled out, as close observation and registration of the seals dive behaviour during the first days of deployment showed that the unit was free of the water for sufficiently long periods for positions to be acquired. (au)

Directional Networking in GPS Denied Environments - Time Synchronization

Science.gov (United States)

2016-03-14

RF-based measurements to synchronize time and measure node range.  Satellite Doppler: Using Doppler measurements from multiple satellites along...with satellite catalog data to determine time and position.  LTE : Use existing LTE base-stations for time and position.  Differential GPS: A...Opportunistic Signals: Opportunistically take advantage of existing RF signals (i.e., FM radio, DTV, LTE , etc.) transmitted from known locations

Comprehensive Comparisons of Satellite Data, Signals, and Measurements between the BeiDou Navigation Satellite System and the Global Positioning System †

Science.gov (United States)

Jan, Shau-Shiun; Tao, An-Lin

2016-01-01

The Chinese BeiDou navigation satellite system (BDS) aims to provide global positioning service by 2020. The combined use of BDS and Global Positioning System (GPS) is proposed to provide navigation service with more stringent requirements. Actual satellite data, signals and measurements were collected for more than one month to analyze the positioning service qualities from both BDS and GPS. In addition to the conversions of coordinate and timing system, five data quality analysis (DQA) methods, three signal quality analysis (SQA) methods, and four measurement quality analysis (MQA) methods are proposed in this paper to improve the integrated positioning performance of BDS and GPS. As shown in the experiment results, issues related to BDS and GPS are resolved by the above proposed quality analysis methods. Thus, the anomalies in satellite data, signals and measurements can be detected by following the suggested resolutions to enhance the positioning performance of the combined use of BDS and GPS in the Asia Pacific region. PMID:27187403

Jason-1 and Jason-2 POD Using GPS

Science.gov (United States)

Melachroinos, Stavros; Lemoine, Frank G.; Zelensky, Nikita P.; Rowlands, David D.; Luthcke, Scott B.; Beckley, Brian D.

2012-01-01

The Jason-2 satellite, launched in June 2008, is the latest follow-on to the successful Jason-1 altimetry satellite mission launched in December 7, 2001. Both, Jason-2 and Jason-1 are equipped with a GPS dual-frequency receiver, a laser retroreflector array, and a DORIS receiver for precise orbit determination (POD). A series of dynamic and reduced-dynamic Jason-2 orbits computed at NASA GSFC, based on GPS-only data and the std0905 standards, have been completed till cy74through cycle 74 using the IGS05 framework. These orbits, now publicly available, have been shown to agree radially at 1 cm RMS with the GSFC std0905 SLR/DORIS orbits and in comparison with orbits produced by JPL, ESA and CNES. In this paper, we describe the implementation of the IGS08 and repro1 framework for the Jason-2 and Jason-1 GPS POD processing with the NASA GSFC GEODYN software. . In our updated GPS POD, ambiguity fixing and updated time variable and static gravity fields. We also evaluate the implementation of non-tidal and degree-1 loading displacement as forward modeling to the tracking stations. Reduced-dynamic versus dynamic orbit differences are used to characterize the remaining force model errors and TRF instability. In particular, we assess their consistency radially and the stability of the altimeter satellite reference frame in the North/South direction as a proxy to assess the consistency of the reference frame.

Seasonal and circadian biases in bird tracking with solar GPS-tags

OpenAIRE

Silva, Rafa; Afán, Isabel; Gil, Juan A.; Bustamante, Javier

2017-01-01

Global Positioning System (GPS) tags are nowadays widely used in wildlife tracking. This geolocation technique can suffer from fix loss biases due to poor satellite GPS geometry, that result in tracking data gaps leading to wrong research conclusions. In addition, new solar-powered GPS tags deployed on birds can suffer from a new "battery drain bias" currently ignored in movement ecology analyses. We use a GPS tracking dataset of bearded vultures (Gypaetus barbatus), tracked for several years...

Remote reference processing in MT survey using GPS clock; MT ho ni okeru GPS wo mochiita jikoku doki system

Energy Technology Data Exchange (ETDEWEB)

Yamane, K; Inoue, J; Takasugi, S [Geothermal Energy Research and Development Co. Ltd., Tokyo (Japan); Kosuge, S [DRICO Co. Ltd., Tokyo (Japan)

1996-05-01

A report is given about the application of a synchronizing system using clock signals from GPS satellites to a remote reference method which is a technique to reject noise from the MT method. This system uses the C/A code out of the L1 band waves from NAVSTAR/GPS satellites. The new system was operated in MT method-using investigations conducted at China Peninsula, Aichi Prefecture, and Izu Peninsula, Shizuoka Prefecture, with the reference points placed several 100km away in Iwate Prefecture on both occasions. It was found as the result that it is basically possible to catch signals from the GPS at any place, that the signals are accurate enough to be applied to time synchronization for the MT method, and that the signals assure a far remote reference method with a separation of several 100km between the sites involved. The referencing process at high frequencies whose feasibility had been doubted proved a success when highly correlated signals were exchanged between two stations over a distance of several 100km. 5 refs., 9 figs.

Design of an adaptive CubeSat transmitter for achieving optimum signal-to-noise ratio (SNR)

Science.gov (United States)

Jaswar, F. D.; Rahman, T. A.; Hindia, M. N.; Ahmad, Y. A.

2017-12-01

CubeSat technology has opened the opportunity to conduct space-related researches at a relatively low cost. Typical approach to maintain an affordable cubeSat mission is to use a simple communication system, which is based on UHF link with fixed-transmit power and data rate. However, CubeSat in the Low Earth Orbit (LEO) does not have relative motion with the earth rotation, resulting in variable propagation path length that affects the transmission signal. A transmitter with adaptive capability to select multiple sets of data rate and radio frequency (RF) transmit power is proposed to improve and optimise the link. This paper presents the adaptive UHF transmitter design as a solution to overcome the variability of the propagation path. The transmitter output power is adjustable from 0.5W to 2W according to the mode of operations and satellite power limitations. The transmitter is designed to have four selectable modes to achieve the optimum signal-to-noise ratio (SNR) and efficient power consumption based on the link budget analysis and satellite requirement. Three prototypes are developed and tested for space-environment conditions such as the radiation test. The Total Ionizing Dose measurements are conducted in the radiation test done at Malaysia Nuclear Agency Laboratory. The results from this test have proven that the adaptive transmitter can perform its operation with estimated more than seven months in orbit. This radiation test using gamma source with 1.5krad exposure is the first one conducted for a satellite program in Malaysia.

BDS/GPS Dual Systems Positioning Based on the Modified SR-UKF Algorithm

Directory of Open Access Journals (Sweden)

JaeHyok Kong

2016-05-01

Full Text Available The Global Navigation Satellite System can provide all-day three-dimensional position and speed information. Currently, only using the single navigation system cannot satisfy the requirements of the system’s reliability and integrity. In order to improve the reliability and stability of the satellite navigation system, the positioning method by BDS and GPS navigation system is presented, the measurement model and the state model are described. Furthermore, the modified square-root Unscented Kalman Filter (SR-UKF algorithm is employed in BDS and GPS conditions, and analysis of single system/multi-system positioning has been carried out, respectively. The experimental results are compared with the traditional estimation results, which show that the proposed method can perform highly-precise positioning. Especially when the number of satellites is not adequate enough, the proposed method combine BDS and GPS systems to achieve a higher positioning precision.

GPS radio collar 3D performance as influenced by forest structure and topography

Science.gov (United States)

R. Scott Gamo; Mark A. Rumble; Fred Lindzey; Matt Stefanich

2000-01-01

Global Positioning System (GPS) telemetry enables biologists to obtain accurate and systematic locations of animals. Vegetation can block signals from satellites to GPS radio collars. Therefore, a vegetation dependent bias to telemetry data may occur which if quantified, could be accounted for. We evaluated the performance of GPS collars in 6 structural stage...

Real Time Monitoring of GPS-IGU orbits and clocks as a tool to disseminate corrections to GPS-Broadcast Ephemerides

Science.gov (United States)

Thaler, G.; Opitz, M.; Weber, R.

2009-04-01

Nowadays RTIGS and NTRIP have become standards for real time GNSS based positioning applications. The IGS (International GNSS Service) Real-Time Working Group disseminates via Internet (RTIGS) raw observation data of a subset of stations of the IGS network. This observation data can be used to establish a real-time integrity monitoring of the IGS predicted orbits (Ultra Rapid (IGU-) Orbits) and clocks, according to the recommendations of the IGS Workshop 2004 in Bern and in a further step correction terms for improving the accuracy of the GPS broadcast ephemerides can be calculated. The Institute for "Geodesy and Geophysics" of the TU-Vienna develops in cooperation with the IGS Real-Time Working Group the software "RTR- Control", which currently provides a real-time integrity monitoring of predicted IGU Satellite Clock Corrections to GPS Time. The real-time orbit calculation and monitoring of the predicted IGU satellite orbits is currently in a testing phase and will be operable in the near future. A kinematic model and calculated ranges to the satellites are combined in a KALMAN-Filter approach. Currently the most recent GPS- Satellite Clock Corrections are published in Real Time via Internet. A 24 - hour clock RINEX file and the IGU SP3 files modified for the associated clock corrections are stored on the ftp-server of the institute. To perform the task of calculating corrections to the broadcast ephemerides three programs are used, which are BNC (BKG Ntrip Client) and BNS (BKG Ntrip State Space Server) from BKG (Bundesamt für Kartographie und Geoinformation) as well as RTR-Control. BNC receives the GPS-broadcast ephemerides from the Ntrip-Caster and forwards them to BNS. RTR-Control calculates the satellite clocks and in future also the satellite orbits and forwards them in SP3-format to BNS. BNS calculates the correction terms to the broadcast ephemerides and delivers it in RTCM 3.x format (proprietary message 4056) back to the Ntrip-caster. Subsequently

The impact of GPS receiver modifications and ionospheric activity on Swarm baseline determination

Science.gov (United States)

Mao, X.; Visser, P. N. A. M.; van den IJssel, J.

2018-05-01

The European Space Agency (ESA) Swarm mission is a satellite constellation launched on 22 November 2013 aiming at observing the Earth geomagnetic field and its temporal variations. The three identical satellites are equipped with high-precision dual-frequency Global Positioning System (GPS) receivers, which make the constellation an ideal test bed for baseline determination. From October 2014 to August 2016, a number of GPS receiver modifications and a new GPS Receiver Independent Exchange Format (RINEX) converter were implemented. Moreover, the on-board GPS receiver performance has been influenced by the ionospheric scintillations. The impact of these factors is assessed for baseline determination of the pendulum formation flying Swarm-A and -C satellites. In total 30 months of data - from 15 July 2014 to the end of 2016 - is analyzed. The assessment includes analysis of observation residuals, success rate of GPS carrier phase ambiguity fixing, a consistency check between the so-called kinematic and reduced-dynamic baseline solution, and validations of orbits by comparing with Satellite Laser Ranging (SLR) observations. External baseline solutions from The German Space Operations Center (GSOC) and Astronomisches Institut - Universität Bern (AIUB) are also included in the comparison. Results indicate that the GPS receiver modifications and RINEX converter changes are effective to improve the baseline determination. This research eventually shows a consistency level of 9.3/4.9/3.0 mm between kinematic and reduced-dynamic baselines in the radial/along-track/cross-track directions. On average 98.3% of the epochs have kinematic solutions. Consistency between TU Delft and external reduced-dynamic baseline solutions is at a level of 1 mm level in all directions.

Pre- and post-flight radiation performance evaluation of the space GPS receiver (SGR)

International Nuclear Information System (INIS)

Oldfield, M.K.; Underwood, C.I.; Unwin, M.J.; Asenek, V.; Harboe-Sorensen, R.

1999-01-01

SSTL (Survey Satellite Technology Ltd), in collaboration with ESA/ESTEC, recently developed a state-of-the-art low cost GPS (Global Positioning System) receiver payload for use on small satellites. The space GPS Receiver (SGR), will be flown on the TiungSAT-1 micro-satellite, UoSAT-12 mini-satellite and ESA's PROBA satellite. The SGR payload is currently flying on the TMSAT micro-satellite in low Earth orbit (LEO) and has carried out autonomous on-board positioning whilst also providing an experimental test-bed for evaluating spacecraft attitude determination algorithms. In order to reduce development time and costs, the SGR consists solely of industry standard COTS (commercial off-the-shelf) devices. This paper describes the ground-based radiation testing of several payload-critical COTS devices used in the SGR payload and describes its on-orbit performance. (authors)

The use of ionospheric tomography and elevation masks to reduce the overall error in single-frequency GPS timing applications

Science.gov (United States)

Rose, Julian A. R.; Tong, Jenna R.; Allain, Damien J.; Mitchell, Cathryn N.

2011-01-01

Signals from Global Positioning System (GPS) satellites at the horizon or at low elevations are often excluded from a GPS solution because they experience considerable ionospheric delays and multipath effects. Their exclusion can degrade the overall satellite geometry for the calculations, resulting in greater errors; an effect known as the Dilution of Precision (DOP). In contrast, signals from high elevation satellites experience less ionospheric delays and multipath effects. The aim is to find a balance in the choice of elevation mask, to reduce the propagation delays and multipath whilst maintaining good satellite geometry, and to use tomography to correct for the ionosphere and thus improve single-frequency GPS timing accuracy. GPS data, collected from a global network of dual-frequency GPS receivers, have been used to produce four GPS timing solutions, each with a different ionospheric compensation technique. One solution uses a 4D tomographic algorithm, Multi-Instrument Data Analysis System (MIDAS), to compensate for the ionospheric delay. Maps of ionospheric electron density are produced and used to correct the single-frequency pseudorange observations. This method is compared to a dual-frequency solution and two other single-frequency solutions: one does not include any ionospheric compensation and the other uses the broadcast Klobuchar model. Data from the solar maximum year 2002 and October 2003 have been investigated to display results when the ionospheric delays are large and variable. The study focuses on Europe and results are produced for the chosen test site, VILL (Villafranca, Spain). The effects of excluding all of the GPS satellites below various elevation masks, ranging from 5° to 40°, on timing solutions for fixed (static) and mobile (moving) situations are presented. The greatest timing accuracies when using the fixed GPS receiver technique are obtained by using a 40° mask, rather than a 5° mask. The mobile GPS timing solutions are most

GPS antenna designs

Science.gov (United States)

Laube, Samuel J. P.

1987-05-01

Application of the current GPS NAVSTAR system to civilian service requires that a right hand, circularly polarized, -160 dBW spread spectrum signal be received from an orbiting satellite, where the antenna environment is also moving. This presents a design challenge when inexpensive antennas are desired. The intent of this survey is to provide information on the antennas mentioned and to construct and test prototypes to determine whether the choice made by the industry, the quadrifilar helix, is the best. The helix antenna is currently the low cost standard for GPS. Prototype versions were constructed using 12 gauge wire and subminiature coaxial hardline. The constructed antennas were tested using a signal generator and a reference turnstile. A spectrum analyzer was used to measure the level of the received signal.

Design and implementation of the GPS subsystem for the Radio Aurora eXplorer

Science.gov (United States)

Spangelo, Sara C.; Bennett, Matthew W.; Meinzer, Daniel C.; Klesh, Andrew T.; Arlas, Jessica A.; Cutler, James W.

2013-06-01

This paper presents the design and implementation of the Global Positioning System (GPS) subsystem for the Radio Aurora eXplorer (RAX) CubeSat. The GPS subsystem provides accurate temporal and spatial information necessary to satisfy the science objectives of the RAX mission. There are many challenges in the successful design and implementation of a GPS subsystem for a CubeSat-based mission, including power, size, mass, and financial constraints. This paper presents an approach for selecting and testing the individual and integrated GPS subsystem components, including the receiver, antenna, low noise amplifier, and supporting circuitry. The procedures to numerically evaluate the GPS link budget and test the subsystem components at various stages of system integration are described. Performance results for simulated tests in the terrestrial and orbital environments are provided, including start-up times, carrier-to-noise ratios, and orbital position accuracy. Preliminary on-orbit GPS results from the RAX-1 and RAX-2 spacecraft are presented to validate the design process and pre-flight simulations. Overall, this paper provides a systematic approach to aid future satellite designers in implementing and verifying GPS subsystems for resource-constrained small satellites.

Physical applications of GPS geodesy: a review.

Science.gov (United States)

Bock, Yehuda; Melgar, Diego

2016-10-01

Geodesy, the oldest science, has become an important discipline in the geosciences, in large part by enhancing Global Positioning System (GPS) capabilities over the last 35 years well beyond the satellite constellation's original design. The ability of GPS geodesy to estimate 3D positions with millimeter-level precision with respect to a global terrestrial reference frame has contributed to significant advances in geophysics, seismology, atmospheric science, hydrology, and natural hazard science. Monitoring the changes in the positions or trajectories of GPS instruments on the Earth's land and water surfaces, in the atmosphere, or in space, is important for both theory and applications, from an improved understanding of tectonic and magmatic processes to developing systems for mitigating the impact of natural hazards on society and the environment. Besides accurate positioning, all disturbances in the propagation of the transmitted GPS radio signals from satellite to receiver are mined for information, from troposphere and ionosphere delays for weather, climate, and natural hazard applications, to disturbances in the signals due to multipath reflections from the solid ground, water, and ice for environmental applications. We review the relevant concepts of geodetic theory, data analysis, and physical modeling for a myriad of processes at multiple spatial and temporal scales, and discuss the extensive global infrastructure that has been built to support GPS geodesy consisting of thousands of continuously operating stations. We also discuss the integration of heterogeneous and complementary data sets from geodesy, seismology, and geology, focusing on crustal deformation applications and early warning systems for natural hazards.

A different approach to the analysis of GPS scintillations data

International Nuclear Information System (INIS)

Forte, B.; Radicella, S.M.; Ezquer, R.G.

2001-09-01

Amplitude scintillations data from GPS have been analyzed. The objective is to estimate the impact of ionospheric scintillations at Satellite-Based Augmentation System (SBAS) Ranging and Integrity Monitoring Station (RIMS) level and at GPS user level. For this purpose a new approach to the problem has been considered. Data have been studied from the point of view of the impact of scintillations on the calculation of VTEC at pierce points and ionospheric grid points. An ionospheric grid of 5 deg. by 5 deg. surface squares has been assumed. From geometrical considerations and taking into account the basic principle to compute VTEC at grid points, with the data analyzed it is shown that very seldom scintillations can affect the calculation of a grid point VTEC. Data from all the RIMS and for the entire GPS satellites network must be analyzed simultaneously to describe a realistic scenario for the impact of scintillations on SBAS. Finally, GPS scintillation data have been analyzed at user level: service availability problems have been encountered. (author)

Satellite telemetry: A new tool for wildlife research and management

Science.gov (United States)

Fancy, Steven G.; Pank, Larry F.; Douglas, David C.; Curby, Catherine H.; Garner, Gerald W.; Amstrup, Steven C.; Regelin, Wayne L.

1998-01-01

The U.S. Fish and Wildlife Service and the Alaska Department of Fish and Game have cooperated since 1984 to develop and evaluate satellite telemetry as a means of overcoming the high costs and logistical problems of conventional VHF (very high frequency) radiotelemetry systems. Detailed locational and behavioral data on caribou (Rangifer tarandus), polar bears (Ursus maritimus), and other large mammals in Alaska have been obtained using the Argos Data Collection and Location System (DCLS). The Argos system, a cooperative project of the Centre National d'Études Spatiales of France, the National Oceanic and Atmospheric Administration, and the National Aeronautics and Space Administration, is designed to acquire environmental data on a routine basis from anywhere on earth. Transmitters weighing 1.6-2.0 kg and functioning approximately 12-18 months operated on a frequency of 401.650 MHz. Signals from the transmitters were received by Argos DCLS instruments aboard two Tiros-N weather satellites in sun-synchronous, nearpolar orbits. Data from the satellites were received at tracking stations, transferred to processing centers in Maryland and France, and made available to users via computer tape, printouts, or telephone links.During 1985 and 1986, more than 25,000 locations and an additional 28,000 sets of sensor data (transmitter temperature and short-term and long-term indices of animal activity) were acquired for caribou and polar bears. Locations were calculated from the Doppler shift in the transmitted signal as the satellite approached and then moved away from the transmitter. The mean locational error for transmitters at known locations (n - 1,265) was 829 m; 90% of the calculated locations were within 1,700 m of the true location. Caribou transmitters provided a mean of 3.1 (+5.0. SD) locations per day during 6h of daily operation, and polar bear transmitters provided 1.7 (+6.9SD) locations during 12h of operation every third day. During the first 6 months of

Kinematic-PPP using Single/Dual Frequency Observations from (GPS, GLONASS and GPS/GLONASS) Constellations for Hydrography

Science.gov (United States)

Farah, Ashraf

2018-03-01

Global Positioning System (GPS) technology is ideally suited for inshore and offshore positioning because of its high accuracy and the short observation time required for a position fix. Precise point positioning (PPP) is a technique used for position computation with a high accuracy using a single GNSS receiver. It relies on highly accurate satellite position and clock data that can be acquired from different sources such as the International GNSS Service (IGS). PPP precision varies based on positioning technique (static or kinematic), observations type (single or dual frequency) and the duration of observations among other factors. PPP offers comparable accuracy to differential GPS with safe in cost and time. For many years, PPP users depended on GPS (American system) which considered the solely reliable system. GLONASS's contribution in PPP techniques was limited due to fail in maintaining full constellation. Yet, GLONASS limited observations could be integrated into GPS-based PPP to improve availability and precision. As GLONASS reached its full constellation early 2013, there is a wide interest in PPP systems based on GLONASS only and independent of GPS. This paper investigates the performance of kinematic PPP solution for the hydrographic applications in the Nile river (Aswan, Egypt) based on GPS, GLONASS and GPS/GLONASS constellations. The study investigates also the effect of using two different observation types; single-frequency and dual frequency observations from the tested constellations.

Analysis of the altitudinal structure of Storm-enhanced density using Total Electron Content data of space-borne and ground-based GPS receivers

Directory of Open Access Journals (Sweden)

Yukari Goi

2013-11-01

Full Text Available The altitudinal structure of Storm-enhanced density (SED was studied using the Total Electron Content (TEC data of the GPS receiver on the Gravity Recovery and Climate Experiment (GRACE satellite and the ground-based GPS receivers. The GRACETEC-data are derived from the GPS receiver on the GRACE satellite. A SED is a high-electron density phenomenon that extends from the Equatorial Ionization Anomaly (EIA toward the north-west in the northern hemisphere during geomagnetic disturbed time. TwoSEDs were observed as TEC variations in the GRACE-TEC data and in the ground-GPS TEC data. The ground-GPS TEC data is the TEC data between the ground GPS receiver and the GPS satellites. The SED observed in the GRACE-TEC data appeared at higher latitudes than that in the ground-GPS TEC data. We concluded detected that the altitudinal structure of the SED would be different between at lower than at higher latitudes due to the effects of the eastward E×B drift.

Satellite and acoustic tracking device

KAUST Repository

Berumen, Michael L.

2014-02-20

The present invention relates a method and device for tracking movements of marine animals or objects in large bodies of water and across significant distances. The method and device can track an acoustic transmitter attached to an animal or object beneath the ocean surface by employing an unmanned surface vessel equipped with a hydrophone array and GPS receiver.

Satellite and acoustic tracking device

KAUST Repository

Berumen, Michael L.; De la Torre, Pedro

2014-01-01

The present invention relates a method and device for tracking movements of marine animals or objects in large bodies of water and across significant distances. The method and device can track an acoustic transmitter attached to an animal or object beneath the ocean surface by employing an unmanned surface vessel equipped with a hydrophone array and GPS receiver.

Status of Precise Orbit Determination for Jason-2 Using GPS

Science.gov (United States)

Melachroinos, S.; Lemoine, F. G.; Zelensky, N. P.; Rowlands, D. D.; Pavlis, D. E.

2011-01-01

The JASON-2 satellite, launched in June 2008, is the latest follow-on to the successful TOPEX/Poseidon (T/P) and JASON-I altimetry missions. JASON-2 is equipped with a TRSR Blackjack GPS dual-frequency receiver, a laser retroreflector array, and a DORIS receiver for precise orbit determination (POD). The most recent time series of orbits computed at NASA GSFC, based on SLR/DORIS data have been completed using both ITRF2005 and ITRF2008. These orbits have been shown to agree radially at 1 cm RMS for dynamic vs SLRlDORIS reduced-dynamic orbits and in comparison with orbits produced by other analysis centers (Lemoine et al., 2010; Zelensky et al., 2010; Cerri et al., 2010). We have recently upgraded the GEODYN software to implement model improvements for GPS processing. We describe the implementation of IGS standards to the Jason2 GEODYN GPS processing, and other dynamical and measurement model improvements. Our GPS-only JASON-2 orbit accuracy is assessed using a number of tests including analysis of independent SLR and altimeter crossover residuals, orbit overlap differences, and direct comparison to orbits generated at GSFC using SLR and DORIS tracking, and to orbits generated externally at other centers. Tests based on SLR and the altimeter crossover residuals provide the best performance indicator for independent validation of the NASAlGSFC GPS-only reduced dynamic orbits. For the ITRF2005 and ITRF2008 implementation of our GPS-only obits we are using the IGS05 and IGS08 standards. Reduced dynamic versus dynamic orbit differences are used to characterize the remaining force model error and TRF instability. We evaluate the GPS vs SLR & DORIS orbits produced using the GEODYN software and assess in particular their consistency radially and the stability of the altimeter satellite reference frame in the Z direction for both ITRF2005 and ITRF2008 as a proxy to assess the consistency of the reference frame for altimeter satellite POD.

Fiber-Based, Trace-Gas, Laser Transmitter Technology Development for Space

Science.gov (United States)

Stephen, Mark; Yu, Anthony; Chen, Jeffrey; Nicholson, Jeffrey; Engin, Doruk; Mathason, Brian; Wu, Stewart; Allan, Graham; Hasselbrack, William; Gonzalez, Brayler;

Suomi NPP VIIRS solar diffuser screen transmittance model and its applications.

Science.gov (United States)

Lei, Ning; Xiong, Xiaoxiong; Mcintire, Jeff

2017-11-01

The visible infrared imaging radiometer suite on the Suomi National Polar-orbiting Partnership satellite calibrates its reflective solar bands through observations of a sunlit solar diffuser (SD) panel. Sunlight passes through a perforated plate, referred to as the SD screen, before reaching the SD. It is critical to know whether the SD screen transmittance measured prelaunch is accurate. Several factors such as misalignments of the SD panel and the measurement apparatus could lead to errors in the measured transmittance and thus adversely impact on-orbit calibration quality through the SD. We develop a mathematical model to describe the transmittance as a function of the angles that incident light makes with the SD screen, and apply the model to fit the prelaunch measured transmittance. The results reveal that the model does not reproduce the measured transmittance unless the size of the apertures in the SD screen is quite different from the design value. We attribute the difference to the orientation alignment errors for the SD panel and the measurement apparatus. We model the alignment errors and apply our transmittance model to fit the prelaunch transmittance to retrieve the "true" transmittance. To use this model correctly, we also examine the finite source size effect on the transmittance. Furthermore, we compare the product of the retrieved "true" transmittance and the prelaunch SD bidirectional reflectance distribution function (BRDF) value to the value derived from on-orbit data to determine whether the prelaunch SD BRDF value is relatively accurate. The model is significant in that it can evaluate whether the SD screen transmittance measured prelaunch is accurate and help retrieve the true transmittance from the transmittance with measurement errors, consequently resulting in a more accurate sensor data product by the same amount.

Precise Point Positioning with the BeiDou Navigation Satellite System

Directory of Open Access Journals (Sweden)

Min Li

2014-01-01

Full Text Available By the end of 2012, China had launched 16 BeiDou-2 navigation satellites that include six GEOs, five IGSOs and five MEOs. This has provided initial navigation and precise pointing services ability in the Asia-Pacific regions. In order to assess the navigation and positioning performance of the BeiDou-2 system, Wuhan University has built up a network of BeiDou Experimental Tracking Stations (BETS around the World. The Position and Navigation Data Analyst (PANDA software was modified to determine the orbits of BeiDou satellites and provide precise orbit and satellite clock bias products from the BeiDou satellite system for user applications. This article uses the BeiDou/GPS observations of the BeiDou Experimental Tracking Stations to realize the BeiDou and BeiDou/GPS static and kinematic precise point positioning (PPP. The result indicates that the precision of BeiDou static and kinematic PPP reaches centimeter level. The precision of BeiDou/GPS kinematic PPP solutions is improved significantly compared to that of BeiDou-only or GPS-only kinematic PPP solutions. The PPP convergence time also decreases with the use of combined BeiDou/GPS systems.

Precise point positioning with the BeiDou navigation satellite system.

Science.gov (United States)

Li, Min; Qu, Lizhong; Zhao, Qile; Guo, Jing; Su, Xing; Li, Xiaotao

2014-01-08

By the end of 2012, China had launched 16 BeiDou-2 navigation satellites that include six GEOs, five IGSOs and five MEOs. This has provided initial navigation and precise pointing services ability in the Asia-Pacific regions. In order to assess the navigation and positioning performance of the BeiDou-2 system, Wuhan University has built up a network of BeiDou Experimental Tracking Stations (BETS) around the World. The Position and Navigation Data Analyst (PANDA) software was modified to determine the orbits of BeiDou satellites and provide precise orbit and satellite clock bias products from the BeiDou satellite system for user applications. This article uses the BeiDou/GPS observations of the BeiDou Experimental Tracking Stations to realize the BeiDou and BeiDou/GPS static and kinematic precise point positioning (PPP). The result indicates that the precision of BeiDou static and kinematic PPP reaches centimeter level. The precision of BeiDou/GPS kinematic PPP solutions is improved significantly compared to that of BeiDou-only or GPS-only kinematic PPP solutions. The PPP convergence time also decreases with the use of combined BeiDou/GPS systems.

Relationships between GPS-signal propagation errors and EISCAT observations

Directory of Open Access Journals (Sweden)

N. Jakowski

1996-12-01

Full Text Available When travelling through the ionosphere the signals of space-based radio navigation systems such as the Global Positioning System (GPS are subject to modifications in amplitude, phase and polarization. In particular, phase changes due to refraction lead to propagation errors of up to 50 m for single-frequency GPS users. If both the L1 and the L2 frequencies transmitted by the GPS satellites are measured, first-order range error contributions of the ionosphere can be determined and removed by difference methods. The ionospheric contribution is proportional to the total electron content (TEC along the ray path between satellite and receiver. Using about ten European GPS receiving stations of the International GPS Service for Geodynamics (IGS, the TEC over Europe is estimated within the geographic ranges -20°≤ λ ≤40°E and 32.5°≤ Φ ≤70°N in longitude and latitude, respectively. The derived TEC maps over Europe contribute to the study of horizontal coupling and transport proces- ses during significant ionospheric events. Due to their comprehensive information about the high-latitude ionosphere, EISCAT observations may help to study the influence of ionospheric phenomena upon propagation errors in GPS navigation systems. Since there are still some accuracy limiting problems to be solved in TEC determination using GPS, data comparison of TEC with vertical electron density profiles derived from EISCAT observations is valuable to enhance the accuracy of propagation-error estimations. This is evident both for absolute TEC calibration as well as for the conversion of ray-path-related observations to vertical TEC. The combination of EISCAT data and GPS-derived TEC data enables a better understanding of large-scale ionospheric processes.

Localization system for use in GPS denied environments

Energy Technology Data Exchange (ETDEWEB)

Trueblood, J. J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2017-02-01

The military uses to autonomous platforms to complete missions to provide standoff for the warfighters. However autonomous platforms rely on GPS to provide their global position. In many missions spaces the autonomous platforms may encounter GPS denied environments which limits where the platform operates and requires the warfighters to takes its place. GPS denied environments can occur due to tall building, trees, canyon wall blocking the GPS satellite signals or a lack of coverage. An Inertial Navigation System (INS) uses sensors to detect the vehicle movement and direction its traveling to calculate the vehicle. One of biggest challenges with an INS system is the accuracy and accumulation of errors over time of the sensors. If these challenges can be overcome the INS would provide accurate positioning information to the autonomous vehicle in GPS denied environments and allow them to provide the desired standoff for the warfighters.

High-energy, 2µm laser transmitter for coherent wind LIDAR

Science.gov (United States)

Singh, Upendra N.; Yu, Jirong; Kavaya, Michael J.; Koch, Grady J.

2017-11-01

A coherent Doppler lidar at 2μm wavelength has been built with higher output energy (300 mJ) than previously available. The laser transmitter is based on the solid-state Ho:Tm:LuLiF, a NASA Langley Research Center invented laser material for higher extraction efficiency. This diode pumped injection seeded MOPA has a transform limited line width and diffraction limited beam quality. NASA Langley Research Center is developing coherent wind lidar transmitter technology at eye-safe wavelength for satellite-based observation of wind on a global scale. The ability to profile wind is a key measurement for understanding and predicting atmospheric dynamics and is a critical measurement for improving weather forecasting and climate modeling. We would describe the development and performance of an engineering hardened 2μm laser transmitter for coherent Doppler wind measurement from ground/aircraft/space platform.

Indoor/Outdoor Seamless Positioning Using Lighting Tags and GPS Cellular Phones for Personal Navigation

Science.gov (United States)

Namie, Hiromune; Morishita, Hisashi

The authors focused on the development of an indoor positioning system which is easy to use, portable and available for everyone. This system is capable of providing the correct position anywhere indoors, including onboard ships, and was invented in order to evaluate the availability of GPS indoors. Although the performance of GPS is superior outdoors, there has been considerable research regarding indoor GPS involving sensitive GPS, pseudolites (GPS pseudo satellite), RFID (Radio Frequency IDentification) tags, and wireless LAN .However, the positioning rate and the precision are not high enough for general use, which is the reason why these technologies have not yet spread to personal navigation systems. In this regard, the authors attempted to implement an indoor positioning system using cellular phones with built-in GPS and infrared light data communication functionality, which are widely used in Japan. GPS is becoming increasingly popular, where GPGGS sentences of the NMEA outputted from the GPS receiver provide spatiotemporal information including latitude, longitude, altitude, and time or ECEF xyz coordinates. As GPS applications grow rapidly, spatiotemporal data becomes key to the ubiquitous outdoor and indoor seamless positioning services at least for the entire area of Japan, as well as to becoming familiar with satellite positioning systems (e.g. GPS). Furthermore, the authors are also working on the idea of using PDAs (Personal Digital Assistants), as cellular phones with built-in GPS and PDA functionality are also becoming increasingly popular.

High-precision coseismic displacement estimation with a single-frequency GPS receiver

Science.gov (United States)

Guo, Bofeng; Zhang, Xiaohong; Ren, Xiaodong; Li, Xingxing

2015-07-01

To improve the performance of Global Positioning System (GPS) in the earthquake/tsunami early warning and rapid response applications, minimizing the blind zone and increasing the stability and accuracy of both the rapid source and rupture inversion, the density of existing GPS networks must be increased in the areas at risk. For economic reasons, low-cost single-frequency receivers would be preferable to make the sparse dual-frequency GPS networks denser. When using single-frequency GPS receivers, the main problem that must be solved is the ionospheric delay, which is a critical factor when determining accurate coseismic displacements. In this study, we introduce a modified Satellite-specific Epoch-differenced Ionospheric Delay (MSEID) model to compensate for the effect of ionospheric error on single-frequency GPS receivers. In the MSEID model, the time-differenced ionospheric delays observed from a regional dual-frequency GPS network to a common satellite are fitted to a plane rather than part of a sphere, and the parameters of this plane are determined by using the coordinates of the stations. When the parameters are known, time-differenced ionospheric delays for a single-frequency GPS receiver could be derived from the observations of those dual-frequency receivers. Using these ionospheric delay corrections, coseismic displacements of a single-frequency GPS receiver can be accurately calculated based on time-differenced carrier-phase measurements in real time. The performance of the proposed approach is validated using 5 Hz GPS data collected during the 2012 Nicoya Peninsula Earthquake (Mw 7.6, 2012 September 5) in Costa Rica. This shows that the proposed approach improves the accuracy of the displacement of a single-frequency GPS station, and coseismic displacements with an accuracy of a few centimetres are achieved over a 10-min interval.

Performance characteristics of the 12 GHz, 200 watt Transmitter Experiment Package for CTS. [Communication Technology Satellite

Science.gov (United States)

Miller, E. F.; Fiala, J. L.; Hansen, I. G.

1975-01-01

Measured performance characteristics from ground test of the Transmitter Experiment Package (TEP) for the Communications Technology Satellite are presented. The experiment package consists of a 200 W Output Stage Tube (OST) powered by a Power Processing System (PPS). Descriptions of both the PPS and OST are given. The PPS provides the necessary voltages with a measured dc/dc conversion efficiency of 89 per cent. The OST, a traveling wave tube with multiple collectors, has a saturated rf output power of 224 W and operates at an overall efficiency exceeding 40 per cent over an 85 MHz bandwidth at 12 GHz. OST performance given includes frequency response, saturation characteristics, group delay, AM to PM conversion, intermodulation distortion, and two channel gain suppression. Single and dual channel FM video performance is presented. It was determined that for 12 MHz peak to peak frequency deviation on each channel, dual channel FM television signals can be transmitted through the TEP at 60 W, each channel, with 40 MHz channel spacing (center to center).

Clock Management Data Analysis for Satellite Communications

National Research Council Canada - National Science Library

Gross, Rachel; Melkers, Raimond

2005-01-01

The U.S. Naval Research Laboratory has installed GPS-based timing systems in several Defense Satellite Communication System "DSCS-III" satellite communication facilities to support the Single Channel Transponder "SCT" program...

GPS satellite and receiver instrumental biases estimation using least ...

Indian Academy of Sciences (India)

PA) landings. Therefore, GPS augmentation sys- tem is required to provide users with orbit, clock, and ionosphere corrections. The first space-based augmentation system .... detailed structure of the transversal filter consists of 3 basic weight ...

Probability of detecting marine predator-prey and species interactions using novel hybrid acoustic transmitter-receiver tags.

Directory of Open Access Journals (Sweden)

Laurie L Baker

Full Text Available Understanding the nature of inter-specific and conspecific interactions in the ocean is challenging because direct observation is usually impossible. The development of dual transmitter/receivers, Vemco Mobile Transceivers (VMT, and satellite-linked (e.g. GPS tags provides a unique opportunity to better understand between and within species interactions in space and time. Quantifying the uncertainty associated with detecting a tagged animal, particularly under varying field conditions, is vital for making accurate biological inferences when using VMTs. We evaluated the detection efficiency of VMTs deployed on grey seals, Halichoerus grypus, off Sable Island (NS, Canada in relation to environmental characteristics and seal behaviour using generalized linear models (GLM to explore both post-processed detection data and summarized raw VMT data. When considering only post-processed detection data, only about half of expected detections were recorded at best even when two VMT-tagged seals were estimated to be within 50-200 m of one another. At a separation of 400 m, only about 15% of expected detections were recorded. In contrast, when incomplete transmissions from the summarized raw data were also considered, the ratio of complete transmission to complete and incomplete transmissions was about 70% for distances ranging from 50-1000 m, with a minimum of around 40% at 600 m and a maximum of about 85% at 50 m. Distance between seals, wind stress, and depth were the most important predictors of detection efficiency. Access to the raw VMT data allowed us to focus on the physical and environmental factors that limit a transceiver's ability to resolve a transmitter's identity.

A Kalman filter-based short baseline RTK algorithm for single-frequency combination of GPS and BDS.

Science.gov (United States)

Zhao, Sihao; Cui, Xiaowei; Guan, Feng; Lu, Mingquan

2014-08-20

The emerging Global Navigation Satellite Systems (GNSS) including the BeiDou Navigation Satellite System (BDS) offer more visible satellites for positioning users. To employ those new satellites in a real-time kinematic (RTK) algorithm to enhance positioning precision and availability, a data processing model for the dual constellation of GPS and BDS is proposed and analyzed. A Kalman filter-based algorithm is developed to estimate the float ambiguities for short baseline scenarios. The entire work process of the high-precision algorithm based on the proposed model is deeply investigated in detail. The model is validated with real GPS and BDS data recorded from one zero and two short baseline experiments. Results show that the proposed algorithm can generate fixed baseline output with the same precision level as that of either a single GPS or BDS RTK algorithm. The significantly improved fixed rate and time to first fix of the proposed method demonstrates a better availability and effectiveness on processing multi-GNSSs.

A Kalman Filter-Based Short Baseline RTK Algorithm for Single-Frequency Combination of GPS and BDS

Directory of Open Access Journals (Sweden)

Sihao Zhao

2014-08-01

Full Text Available The emerging Global Navigation Satellite Systems (GNSS including the BeiDou Navigation Satellite System (BDS offer more visible satellites for positioning users. To employ those new satellites in a real-time kinematic (RTK algorithm to enhance positioning precision and availability, a data processing model for the dual constellation of GPS and BDS is proposed and analyzed. A Kalman filter-based algorithm is developed to estimate the float ambiguities for short baseline scenarios. The entire work process of the high-precision algorithm based on the proposed model is deeply investigated in detail. The model is validated with real GPS and BDS data recorded from one zero and two short baseline experiments. Results show that the proposed algorithm can generate fixed baseline output with the same precision level as that of either a single GPS or BDS RTK algorithm. The significantly improved fixed rate and time to first fix of the proposed method demonstrates a better availability and effectiveness on processing multi-GNSSs.

Determination of the SNPP VIIRS SDSM Screen Relative Transmittance From Both Yaw Maneuver and Regular On-Orbit Data

Science.gov (United States)

Lei, Ning; Chen, Xuexia; Xiong, Xiaoxiong

2015-01-01

The Visible Infrared Imaging Radiometer Suiteaboard the Suomi National Polar-orbiting Partnership (SNPP) satellite performs radiometric calibration of its reflective solar bands primarily through observing a sunlit onboard solar diffuser (SD). The SD bidirectional reflectance distribution function(BRDF) degradation factor is determined by an onboard SD stability monitor (SDSM), which observes the Sun through a pinhole screen and the sunlit SD. The transmittance of the SDSM pinhole screen over a range of solar angles was determined prelaunch and used initially to determine the BRDF degradation factor.The degradation-factor-versus-time curves were found to have a number of very large unphysical undulations likely due to the inaccuracy in the prelaunch determined SDSM screen transmittance.To refine the SDSM screen transmittance, satellite yaw maneuvers were carried out. With the SDSM screen relative transmittance determined from the yaw maneuver data, the computed BRDFdegradation factor curves still have large unphysical ripples, indicating that the projected solar horizontal angular step size in the yaw maneuver data is too large to resolve the transmittance at a fine angular scale. We develop a methodology to use both the yaw maneuver and a small portion of regular on-orbit data to determine the SDSM screen relative transmittance at a fine angular scale. We determine that the error standard deviation of the calculated relative transmittance ranges from 0.00030 (672 nm) to 0.00092 (926 nm). With the newly determined SDSM screen relative transmittance, the computed BRDF degradation factor behaves much more smoothly over time.

WGS 84 Coordinate Validation and Improvement for the NIMA and Air Force GPS Tracking Stations

National Research Council Canada - National Science Library

Cunningham, James

1996-01-01

Using 10 days of Global Positioning System (GPS) pseudorange and carrier phase data collected in 1995 from 31 stations and 24 Block II/IIA satellites, estimates of GPS clocks, orbits, and tracking station coordinates were generated...

Movements of the reef manta ray (Manta alfredi) in the Red Sea using satellite and acoustic telemetry

KAUST Repository

Braun, Camrin D.

2015-10-27

Populations of mobulid rays are declining globally through a combination of directed fisheries and indirect anthropogenic threats. Understanding the movement ecology of these rays remains an important priority for devising appropriate conservation measures throughout the world’s oceans. We sought to determine manta movements across several temporal and spatial scales with a focus on quantifying site fidelity and seasonality in the northern Farasan Banks, Red Sea. We fitted manta rays with acoustic transmitters (n = 9) and pop-up satellite archival transmitting (PSAT) tags (n = 9), including four with GPS capability (Fastloc), during spring 2011 and 2012. We deployed an extensive array of acoustic receivers (n = 67) to record movements of tagged mantas in the study area. All acoustically tagged individuals traveled frequently among high-use receiver locations and reefs and demonstrated fidelity to specific sites within the array. Estimated and realized satellite tag data indicated regional movements <200 km from the tagging location, largely coastal residency, and high surface occupation. GPS-tagged individuals regularly moved within the coastal reef matrix up to ~70 km to the south but continued to return to the tagging area near the high-occupancy sites identified in the acoustic array. We also tested the accuracy of several geolocation models to determine the best approach to analyze our light-based satellite tag data. We documented significant errors in light-based movement estimates that should be considered when interpreting tracks derived from light-level geolocation, especially for animals with restricted movements through a homogenous temperature field. Despite some error in satellite tag positions, combining results from PSAT and acoustic tags in this study yielded a comprehensive representation of manta spatial ecology across several scales, and such approaches will, in the future, inform the design of appropriate management strategies for manta

Tightly coupled low cost 3D RISS/GPS integration using a mixture particle filter for vehicular navigation.

Science.gov (United States)

Georgy, Jacques; Noureldin, Aboelmagd

2011-01-01

Satellite navigation systems such as the global positioning system (GPS) are currently the most common technique used for land vehicle positioning. However, in GPS-denied environments, there is an interruption in the positioning information. Low-cost micro-electro mechanical system (MEMS)-based inertial sensors can be integrated with GPS and enhance the performance in denied GPS environments. The traditional technique for this integration problem is Kalman filtering (KF). Due to the inherent errors of low-cost MEMS inertial sensors and their large stochastic drifts, KF, with its linearized models, has limited capabilities in providing accurate positioning. Particle filtering (PF) was recently suggested as a nonlinear filtering technique to accommodate for arbitrary inertial sensor characteristics, motion dynamics and noise distributions. An enhanced version of PF called the Mixture PF is utilized in this study to perform tightly coupled integration of a three dimensional (3D) reduced inertial sensors system (RISS) with GPS. In this work, the RISS consists of one single-axis gyroscope and a two-axis accelerometer used together with the vehicle's odometer to obtain 3D navigation states. These sensors are then integrated with GPS in a tightly coupled scheme. In loosely-coupled integration, at least four satellites are needed to provide acceptable GPS position and velocity updates for the integration filter. The advantage of the tightly-coupled integration is that it can provide GPS measurement update(s) even when the number of visible satellites is three or lower, thereby improving the operation of the navigation system in environments with partial blockages by providing continuous aiding to the inertial sensors even during limited GPS satellite availability. To effectively exploit the capabilities of PF, advanced modeling for the stochastic drift of the vertically aligned gyroscope is used. In order to benefit from measurement updates for such drift, which are

Tightly Coupled Low Cost 3D RISS/GPS Integration Using a Mixture Particle Filter for Vehicular Navigation

Directory of Open Access Journals (Sweden)

Jacques Georgy

2011-04-01

Full Text Available Satellite navigation systems such as the global positioning system (GPS are currently the most common technique used for land vehicle positioning. However, in GPS-denied environments, there is an interruption in the positioning information. Low-cost micro-electro mechanical system (MEMS-based inertial sensors can be integrated with GPS and enhance the performance in denied GPS environments. The traditional technique for this integration problem is Kalman filtering (KF. Due to the inherent errors of low-cost MEMS inertial sensors and their large stochastic drifts, KF, with its linearized models, has limited capabilities in providing accurate positioning. Particle filtering (PF was recently suggested as a nonlinear filtering technique to accommodate for arbitrary inertial sensor characteristics, motion dynamics and noise distributions. An enhanced version of PF called the Mixture PF is utilized in this study to perform tightly coupled integration of a three dimensional (3D reduced inertial sensors system (RISS with GPS. In this work, the RISS consists of one single-axis gyroscope and a two-axis accelerometer used together with the vehicle’s odometer to obtain 3D navigation states. These sensors are then integrated with GPS in a tightly coupled scheme. In loosely-coupled integration, at least four satellites are needed to provide acceptable GPS position and velocity updates for the integration filter. The advantage of the tightly-coupled integration is that it can provide GPS measurement update(s even when the number of visible satellites is three or lower, thereby improving the operation of the navigation system in environments with partial blockages by providing continuous aiding to the inertial sensors even during limited GPS satellite availability. To effectively exploit the capabilities of PF, advanced modeling for the stochastic drift of the vertically aligned gyroscope is used. In order to benefit from measurement updates for such drift

Satellite myths

Science.gov (United States)

Easton, Roger L.; Hall, David

2008-01-01

Richard Corfield's article “Sputnik's legacy” (October 2007 pp23-27) states that the satellite on board the US Vanguard rocket, which exploded during launch on 6 December 1957 two months after Sputnik's successful take-off, was “a hastily put together contraption of wires and circuitry designed only to send a radio signal back to Earth”. In fact, the Vanguard satellite was developed over a period of several years and put together carefully using the best techniques and equipment available at the time - such as transistors from Bell Laboratories/Western Electric. The satellite contained not one but two transmitters, in which the crystal-controlled oscillators had been designed to measure both the temperature of the satellite shell and of the internal package.

Orbit Determination of GPS and Koreasat 2 Satellite Using Angle-Only Data and Requirements for Optical Tracking System

Directory of Open Access Journals (Sweden)

Woo-Kyoung Lee

2004-09-01

Full Text Available Gauss method for the initial orbit determination was tested using angle-only data obtained by orbit propagation using TLE and SGP4/SDP4 orbit propagation model. As the analysis of this simulation, a feasible time span between observation time of satellite resulting the minimum error to the true orbit was found. Initial orbit determination is performed using observational data of GPS 26 and Koreasat 2 from 0.6m telescope of KAO(Korea Astronomy Observatory and precise orbit determination is also performed using simulated data. The result of precise orbit determination shows that the accuracy of resulting orbit is related to the accuracy of the observations and the number of data.

GTAG: architecture and design of miniature transmitter with position logging for radio telemetry

Science.gov (United States)

Řeřucha, Šimon; Bartonička, Tomáš; Jedlička, Petr

2011-10-01

The radio telemetry is a well-known technique used within zoological research to exploit the behaviour of animal species. A usage of GPS for a frequent and precise position recording gives interesting possibility for a further enhancement of this method. We present our proposal of an architecture and design concepts of telemetry transmitter with GPS module, called GTAG, that is suited for study of the Egyptian fruit bat (Rousettus aegyptiacus). The model group we study set particular constrains, especially the weight limit (9 g) and prevention of any power resources recharging technique. We discuss the aspect of physical realization and the energyconsumption issues. We have developed a reference implementation that has been already deployed during telemetry sessions and we evaluate the experience and compare the estimated performance of our device to a real data.

Using GPS for studying pastoral mobility

DEFF Research Database (Denmark)

Adriansen, Hanne Kirstine

2017-01-01

geographer familiar with satellite remote sensing and GIS, I pondered how these relatively new technologies could be combined with classic ethnographic fieldwork, which we also use in human geography. I decided to use handheld GPS devices for tracking the pastoralists and their herds. My study was, as far...... the interviewee’s point of view....

GPS & Galileo. Friendly Foes?

Science.gov (United States)

2007-04-01

some of their data, others employ different techniques. United States defense contractor Lockheed Martin developed an anti-jam GPS receiver in 2000 for...Europe in a New Generation of Satellite Navigation Services,” European Commission (9 Feb 1999): 16. 25. Ibid. 26. Anne Jolis , “Problems Run Rampant...European Outer Space,” Euro Topics (19 March 2007), found at http://www.eurotopics.net/en/presseschau/archiv/archiv_dossier/DOSSIER15435. 40. Jolis

Handbook of satellite applications

CERN Document Server

Madry, Scott; Camacho-Lara, Sergio

2017-01-01

The first edition of this ground breaking reference work was the most comprehensive reference source available about the key aspects of the satellite applications field. This updated second edition covers the technology, the markets, applications and regulations related to satellite telecommunications, broadcasting and networking—including civilian and military systems; precise satellite navigation and timing networks (i.e. GPS and others); remote sensing and meteorological satellite systems. Created under the auspices of the International Space University based in France, this brand new edition is now expanded to cover new innovative small satellite constellations, new commercial launching systems, innovation in military application satellites and their acquisition, updated appendices, a useful glossary and more.

Assessing performance of Bayesian state-space models fit to Argos satellite telemetry locations processed with Kalman filtering.

Directory of Open Access Journals (Sweden)

Mónica A Silva

Full Text Available Argos recently implemented a new algorithm to calculate locations of satellite-tracked animals that uses a Kalman filter (KF. The KF algorithm is reported to increase the number and accuracy of estimated positions over the traditional Least Squares (LS algorithm, with potential advantages to the application of state-space methods to model animal movement data. We tested the performance of two Bayesian state-space models (SSMs fitted to satellite tracking data processed with KF algorithm. Tracks from 7 harbour seals (Phoca vitulina tagged with ARGOS satellite transmitters equipped with Fastloc GPS loggers were used to calculate the error of locations estimated from SSMs fitted to KF and LS data, by comparing those to "true" GPS locations. Data on 6 fin whales (Balaenoptera physalus were used to investigate consistency in movement parameters, location and behavioural states estimated by switching state-space models (SSSM fitted to data derived from KF and LS methods. The model fit to KF locations improved the accuracy of seal trips by 27% over the LS model. 82% of locations predicted from the KF model and 73% of locations from the LS model were <5 km from the corresponding interpolated GPS position. Uncertainty in KF model estimates (5.6 ± 5.6 km was nearly half that of LS estimates (11.6 ± 8.4 km. Accuracy of KF and LS modelled locations was sensitive to precision but not to observation frequency or temporal resolution of raw Argos data. On average, 88% of whale locations estimated by KF models fell within the 95% probability ellipse of paired locations from LS models. Precision of KF locations for whales was generally higher. Whales' behavioural mode inferred by KF models matched the classification from LS models in 94% of the cases. State-space models fit to KF data can improve spatial accuracy of location estimates over LS models and produce equally reliable behavioural estimates.

Detection test of wireless network signal strength and GPS positioning signal in underground pipeline

Science.gov (United States)

Li, Li; Zhang, Yunwei; Chen, Ling

2018-03-01

In order to solve the problem of selecting positioning technology for inspection robot in underground pipeline environment, the wireless network signal strength and GPS positioning signal testing are carried out in the actual underground pipeline environment. Firstly, the strength variation of the 3G wireless network signal and Wi-Fi wireless signal provided by China Telecom and China Unicom ground base stations are tested, and the attenuation law of these wireless signals along the pipeline is analyzed quantitatively and described. Then, the receiving data of the GPS satellite signal in the pipeline are tested, and the attenuation of GPS satellite signal under underground pipeline is analyzed. The testing results may be reference for other related research which need to consider positioning in pipeline.

DOTD standards for GPS data collection accuracy : research project capsule.

Science.gov (United States)

2013-12-01

Global Navigational Satellite Systems (GNSS), which includes GPS technologies : maintained by the United States, are used extensively throughout government : and industry. These technologies continue to revolutionize positional data : collection acti...

Satellite telemetry of Afrotropical ducks: methodological details and ...

African Journals Online (AJOL)

Despite widespread and increasing use of solarpowered satellite transmitters to tag wild birds, there are few published articles that detail how transmitters should be attached to different species and even fewer assessments of the overall field success of telemetry projects. The scarcity of this information makes it difficult to ...

Retrieval of Electron Density Profile for KOMPSAT-5 GPS Radio Occultation

Directory of Open Access Journals (Sweden)

Woo-Kyoung Lee

2007-12-01

Full Text Available The AOPOD (Atmosphere Occultation and Precision Orbit Determination system, the secondary payload of KOMPSAT (KOrea Multi-Purpose SATellite-5 scheduled to be launched in 2010, shall provide GPS radio occultation data. In this paper, we simulated the GPS radio occultation characteristic of KOMPSAT-5 and retrieved electron density profiles using KROPS (KASI Radio Occultation Processing Software. The electron density retrieved from CHAMP (CHAllenging Minisatellite Payload GPS radio occultation data on June 20, 2004 was compared with IRI (International Reference Ionosphere - 2001, PLP (Planar Langmuir Probe, and ionosonde measurements. When the result was compared with ionosonde measurements, the discrepancies were 5 km on the F_2 peak height (hmF_2 and 3×10^{10} el/m^3 on the electron density of the F_2 peak height (NmF_2. By comparing with the Langmuir Probe measurements of CHAMP satellite (PLP, both agrees with 1.6×10^{11} el/m^3 at the height of 365.6 km.

Radiation-resistant composite scintillators based on GSO and GPS grains

Energy Technology Data Exchange (ETDEWEB)

Boyarintsev, A.Yu. [Institute for Scintillation Materials, National Academy of Sciences of Ukraine, 60 Nauki Avenue, 61001 Kharkiv (Ukraine); Galunov, N.Z. [Institute for Scintillation Materials, National Academy of Sciences of Ukraine, 60 Nauki Avenue, 61001 Kharkiv (Ukraine); V.N. Karasin Kharkov National University, 4 Svobody Sq., 61022 Kharkiv (Ukraine); Gerasymov, Ia.V.; Karavaeva, N.L. [Institute for Scintillation Materials, National Academy of Sciences of Ukraine, 60 Nauki Avenue, 61001 Kharkiv (Ukraine); Krech, A.V., E-mail: AntonKrech@gmail.com [Institute for Scintillation Materials, National Academy of Sciences of Ukraine, 60 Nauki Avenue, 61001 Kharkiv (Ukraine); Levchuk, L.G.; Popov, V.F. [National Science Center, Kharkov Institute of Physics and Technology, 1 Akademicheskaya Str., 61108 Kharkiv (Ukraine); Sidletskiy, O.Ts. [Institute for Scintillation Materials, National Academy of Sciences of Ukraine, 60 Nauki Avenue, 61001 Kharkiv (Ukraine); Sorokin, P.V. [National Science Center, Kharkov Institute of Physics and Technology, 1 Akademicheskaya Str., 61108 Kharkiv (Ukraine); Tarasenko, O.A. [Institute for Scintillation Materials, National Academy of Sciences of Ukraine, 60 Nauki Avenue, 61001 Kharkiv (Ukraine)

2017-01-01

The effect of irradiation on the scintillation light output, optical transmittance, and luminescent spectra of composite scintillators based on grains of single crystals Gd{sub 2}SiO{sub 5}:Ce (GSO) and Gd{sub 2}Si{sub 2}O{sub 7}:Ce (GPS) is studied. The dielectric gel Sylgard-184 is the base and the binder for the grains inside the composite scintillator. The paper presents and analyzes the results obtained for the scintillators exposed by 10 MeV electrons from the linear electron accelerator at room temperature. The exposure doses D≤250 Mrad. The dose rate is 0.2 or 1500 Mrad/h. The study has shown that the composite scintillators based on the grains of GSO and GPS are radiation-resistant over the range of the irradiation.

Study on index system of GPS interference effect evaluation

Science.gov (United States)

Zhang, Kun; Zeng, Fangling; Zhao, Yuan; Zeng, Ruiqi

2018-05-01

Satellite navigation interference effect evaluation is the key technology to break through the research of Navigation countermeasure. To evaluate accurately the interference degree and Anti-jamming ability of GPS receiver, this text based on the existing research results of Navigation interference effect evaluation, build the index system of GPS receiver effectiveness evaluation from four levels of signal acquisition, tracking, demodulation and positioning/timing and establish the model for each index. These indexes can accurately and quantitatively describe the interference effect at all levels.

Assessing GPS Constellation Resiliency in an Urban Canyon Environment

Science.gov (United States)

2015-03-26

ABMS ) is used to model complex adaptive systems (CAS) potentially made up of many different types of agents. North & Macal [25] state that, “Agent-based...modeling and simulation ( ABMS ) is founded on the notion that the whole of many systems or organizations is greater than the simple sum of its...satellite systems is challenging the capabilities provided by space assets. More specifically, the global positioning system (GPS) satellite

GPS Navigation for the Magnetospheric Multi-Scale Mission

Science.gov (United States)

Bamford, William; Mitchell, Jason; Southward, Michael; Baldwin, Philip; Winternitz, Luke; Heckler, Gregory; Kurichh, Rishi; Sirotzky, Steve

2009-01-01

In 2014. NASA is scheduled to launch the Magnetospheric Multiscale Mission (MMS), a four-satellite formation designed to monitor fluctuations in the Earth's magnetosphere. This mission has two planned phases with different orbits (1? x 12Re and 1.2 x 25Re) to allow for varying science regions of interest. To minimize ground resources and to mitigate the probability of collisions between formation members, an on-board orbit determination system consisting of a Global Positioning System (GPS) receiver and crosslink transceiver was desired. Candidate sensors would be required to acquire GPS signals both below and above the constellation while spinning at three revolutions-per-minute (RPM) and exchanging state and science information among the constellation. The Intersatellite Ranging and Alarm System (IRAS), developed by Goddard Space Flight Center (GSFC) was selected to meet this challenge. IRAS leverages the eight years of development GSFC has invested in the Navigator GPS receiver and its spacecraft communication expertise, culminating in a sensor capable of absolute and relative navigation as well as intersatellite communication. The Navigator is a state-of-the-art receiver designed to acquire and track weak GPS signals down to -147dBm. This innovation allows the receiver to track both the main lobe and the much weaker side lobe signals. The Navigator's four antenna inputs and 24 tracking channels, together with customized hardware and software, allow it to seamlessly maintain visibility while rotating. Additionally, an extended Kalman filter provides autonomous, near real-time, absolute state and time estimates. The Navigator made its maiden voyage on the Space Shuttle during the Hubble Servicing Mission, and is scheduled to fly on MMS as well as the Global Precipitation Measurement Mission (GPM). Additionally, Navigator's acquisition engine will be featured in the receiver being developed for the Orion vehicle. The crosslink transceiver is a 1/4 Watt transmitter

Absolute GPS Positioning Using Genetic Algorithms

Science.gov (United States)

Ramillien, G.

A new inverse approach for restoring the absolute coordinates of a ground -based station from three or four observed GPS pseudo-ranges is proposed. This stochastic method is based on simulations of natural evolution named genetic algorithms (GA). These iterative procedures provide fairly good and robust estimates of the absolute positions in the Earth's geocentric reference system. For comparison/validation, GA results are compared to the ones obtained using the classical linearized least-square scheme for the determination of the XYZ location proposed by Bancroft (1985) which is strongly limited by the number of available observations (i.e. here, the number of input pseudo-ranges must be four). The r.m.s. accuracy of the non -linear cost function reached by this latter method is typically ~10-4 m2 corresponding to ~300-500-m accuracies for each geocentric coordinate. However, GA can provide more acceptable solutions (r.m.s. errors < 10-5 m2), even when only three instantaneous pseudo-ranges are used, such as a lost of lock during a GPS survey. Tuned GA parameters used in different simulations are N=1000 starting individuals, as well as Pc=60-70% and Pm=30-40% for the crossover probability and mutation rate, respectively. Statistical tests on the ability of GA to recover acceptable coordinates in presence of important levels of noise are made simulating nearly 3000 random samples of erroneous pseudo-ranges. Here, two main sources of measurement errors are considered in the inversion: (1) typical satellite-clock errors and/or 300-metre variance atmospheric delays, and (2) Geometrical Dilution of Precision (GDOP) due to the particular GPS satellite configuration at the time of acquisition. Extracting valuable information and even from low-quality starting range observations, GA offer an interesting alternative for high -precision GPS positioning.

Two laboratory methods for the calibration of GPS speed meters

International Nuclear Information System (INIS)

Bai, Yin; Sun, Qiao; Du, Lei; Yu, Mei; Bai, Jie

2015-01-01

The set-ups of two calibration systems are presented to investigate calibration methods of GPS speed meters. The GPS speed meter calibrated is a special type of high accuracy speed meter for vehicles which uses Doppler demodulation of GPS signals to calculate the measured speed of a moving target. Three experiments are performed: including simulated calibration, field-test signal replay calibration, and in-field test comparison with an optical speed meter. The experiments are conducted at specific speeds in the range of 40–180 km h −1 with the same GPS speed meter as the device under calibration. The evaluation of measurement results validates both methods for calibrating GPS speed meters. The relative deviations between the measurement results of the GPS-based high accuracy speed meter and those of the optical speed meter are analyzed, and the equivalent uncertainty of the comparison is evaluated. The comparison results justify the utilization of GPS speed meters as reference equipment if no fewer than seven satellites are available. This study contributes to the widespread use of GPS-based high accuracy speed meters as legal reference equipment in traffic speed metrology. (paper)

TerraSAR-X precise orbit determination with real-time GPS ephemerides

Science.gov (United States)

Wermuth, Martin; Hauschild, Andre; Montenbruck, Oliver; Kahle, Ralph

TerraSAR-X is a German Synthetic Aperture Radar (SAR) satellite, which was launched in June 2007 from Baikonour. Its task is to acquire radar images of the Earth's surface. In order to locate the radar data takes precisely, the satellite is equipped with a high-quality dual-frequency GPS receiver -the Integrated Geodetic and Occultation Receiver (IGOR) provided by the GeoForschungsZentrum Potsdam (GFZ). Using GPS observations from the IGOR instrument in a reduced dynamic precise orbit determination (POD), the German Space Operations Center (DLR/GSOC) is computing rapid and science orbit products on a routine basis. The rapid orbit products arrive with a latency of about one hour after data reception with an accuracy of 10-20 cm. Science orbit products are computed with a latency of five days achieving an accuracy of about 5cm (3D-RMS). For active and future Earth observation missions, the availability of near real-time precise orbit information is becoming more and more important. Other applications of near real-time orbit products include the processing of GNSS radio occulation measurements for atmospheric sounding as well as altimeter measurements of ocean surface heights, which are nowadays employed in global weather and ocean circulation models with short latencies. For example after natural disasters it is necessary to evaluate the damage by satellite images as soon as possible. The latency and quality of POD results is mainly driven by the availability of precise GPS ephemerides. In order to have high-quality GPS ephemerides available at real-time, GSOC has developed the real-time clock estimation system RETICLE. The system receives NTRIP-data streams with GNSS observations from the global tracking network of IGS in real-time. Using the known station position, RETICLE estimates precise GPS satellite clock offsets and drifts based on the most recent available IGU predicted orbits. The clock offset estimates have an accuracy of better than 0.3 ns and are

Sea Turtle Satellite Telemetry Data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Sea turtles captured in various fishing gear (pound nets, long haul seines, gill nets) were outfitted with satellite transmitters so that their movements, migratory...

Toward Continuous GPS Carrier-Phase Time Transfer: Eliminating the Time Discontinuity at an Anomaly.

Science.gov (United States)

Yao, Jian; Levine, Judah; Weiss, Marc

2015-01-01

The wide application of Global Positioning System (GPS) carrier-phase (CP) time transfer is limited by the problem of boundary discontinuity (BD). The discontinuity has two categories. One is "day boundary discontinuity," which has been studied extensively and can be solved by multiple methods [1-8]. The other category of discontinuity, called "anomaly boundary discontinuity (anomaly-BD)," comes from a GPS data anomaly. The anomaly can be a data gap (i.e., missing data), a GPS measurement error (i.e., bad data), or a cycle slip. Initial study of the anomaly-BD shows that we can fix the discontinuity if the anomaly lasts no more than 20 min, using the polynomial curve-fitting strategy to repair the anomaly [9]. However, sometimes, the data anomaly lasts longer than 20 min. Thus, a better curve-fitting strategy is in need. Besides, a cycle slip, as another type of data anomaly, can occur and lead to an anomaly-BD. To solve these problems, this paper proposes a new strategy, i.e., the satellite-clock-aided curve fitting strategy with the function of cycle slip detection. Basically, this new strategy applies the satellite clock correction to the GPS data. After that, we do the polynomial curve fitting for the code and phase data, as before. Our study shows that the phase-data residual is only ~3 mm for all GPS satellites. The new strategy also detects and finds the number of cycle slips by searching the minimum curve-fitting residual. Extensive examples show that this new strategy enables us to repair up to a 40-min GPS data anomaly, regardless of whether the anomaly is due to a data gap, a cycle slip, or a combination of the two. We also find that interference of the GPS signal, known as "jamming", can possibly lead to a time-transfer error, and that this new strategy can compensate for jamming outages. Thus, the new strategy can eliminate the impact of jamming on time transfer. As a whole, we greatly improve the robustness of the GPS CP time transfer.

Information content in reflected global navigation satellite system signals

DEFF Research Database (Denmark)

Høeg, Per; Carlstrom, Anders

2011-01-01

The direct signals from satellites in global satellite navigation satellites systems (GNSS) as, GPS, GLONASS and GALILEO, constitute the primary source for positioning, navigation and timing from space. But also the reflected GNSS signals contain an important information content of signal travel...

High accuracy autonomous navigation using the global positioning system (GPS)

Science.gov (United States)

Truong, Son H.; Hart, Roger C.; Shoan, Wendy C.; Wood, Terri; Long, Anne C.; Oza, Dipak H.; Lee, Taesul

1997-01-01

The application of global positioning system (GPS) technology to the improvement of the accuracy and economy of spacecraft navigation, is reported. High-accuracy autonomous navigation algorithms are currently being qualified in conjunction with the GPS attitude determination flyer (GADFLY) experiment for the small satellite technology initiative Lewis spacecraft. Preflight performance assessments indicated that these algorithms are able to provide a real time total position accuracy of better than 10 m and a velocity accuracy of better than 0.01 m/s, with selective availability at typical levels. It is expected that the position accuracy will be increased to 2 m if corrections are provided by the GPS wide area augmentation system.

Geomagnetic storm effects on GPS based navigation

Directory of Open Access Journals (Sweden)

P. V. S. Rama Rao

2009-05-01

Full Text Available The energetic events on the sun, solar wind and subsequent effects on the Earth's geomagnetic field and upper atmosphere (ionosphere comprise space weather. Modern navigation systems that use radio-wave signals, reflecting from or propagating through the ionosphere as a means of determining range or distance, are vulnerable to a variety of effects that can degrade the performance of the navigational systems. In particular, the Global Positioning System (GPS that uses a constellation of earth orbiting satellites are affected due to the space weather phenomena.

Studies made during two successive geomagnetic storms that occurred during the period from 8 to 12 November 2004, have clearly revealed the adverse affects on the GPS range delay as inferred from the Total Electron Content (TEC measurements made from a chain of seven dual frequency GPS receivers installed in the Indian sector. Significant increases in TEC at the Equatorial Ionization anomaly crest region are observed, resulting in increased range delay during the periods of the storm activity. Further, the storm time rapid changes occurring in TEC resulted in a number of phase slips in the GPS signal compared to those on quiet days. These phase slips often result in the loss of lock of the GPS receivers, similar to those that occur during strong(>10 dB L-band scintillation events, adversely affecting the GPS based navigation.

Seasonal and circadian biases in bird tracking with solar GPS-tags.

Directory of Open Access Journals (Sweden)

Rafa Silva

Full Text Available Global Positioning System (GPS tags are nowadays widely used in wildlife tracking. This geolocation technique can suffer from fix loss biases due to poor satellite GPS geometry, that result in tracking data gaps leading to wrong research conclusions. In addition, new solar-powered GPS tags deployed on birds can suffer from a new "battery drain bias" currently ignored in movement ecology analyses. We use a GPS tracking dataset of bearded vultures (Gypaetus barbatus, tracked for several years with solar GPS tags, to evaluate the causes and triggers of fix and data retrieval loss biases. We compare two models of solar GPS tags using different data retrieval systems (Argos vs GSM-GPRS, and programmed with different duty cycles. Neither of the models was able to accomplish the duty cycle programed initially. Fix and data retrieval loss rates were always greater than expected, and showed non-random gaps in GPS locations. Number of fixes per month of tracking was a bad criterion to identify tags with smaller biases. Fix-loss rates were four times higher due to battery drain than due to poor GPS satellite geometry. Both tag models were biased due to the uneven solar energy available for the recharge of the tag throughout the annual cycle, resulting in greater fix-loss rates in winter compared to summer. In addition, we suggest that the bias found along the diurnal cycle is linked to a complex three-factor interaction of bird flight behavior, topography and fix interval. More fixes were lost when vultures were perching compared to flying, in rugged versus flat topography. But long fix-intervals caused greater loss of fixes in dynamic (flying versus static situations (perching. To conclude, we emphasize the importance of evaluating fix-loss bias in current tracking projects, and deploying GPS tags that allow remote duty cycle updates so that the most appropriate fix and data retrieval intervals can be selected.

Estimating the contribution from different ionospheric regions to the TEC response to the solar flares using data from the international GPS network

Directory of Open Access Journals (Sweden)

L. A. Leonovich

Full Text Available This paper proposes a new method for estimating the contribution from different ionospheric regions to the response of total electron content variations to the solar flare, based on data from the international network of two-frequency multichannel receivers of the navigation GPS system. The method uses the effect of partial "shadowing" of the atmosphere by the terrestrial globe. The study of the solar flare influence on the atmosphere uses GPS stations located near the boundary of the shadow on the ground in the nightside hemisphere. The beams between the satellite-borne transmitter and the receiver on the ground for these stations pass partially through the atmosphere lying in the region of total shadow, and partially through the illuminated atmosphere. The analysis of the ionospheric effect of a powerful solar flare of class X5.7/3B that was recorded on 14 July 2000 (10:24 UT, N22 W07 in quiet geomagnetic conditions (D_st = -10 nT has shown that about 75% of the TEC increase corresponds to the ionospheric region lying below 300 km and about 25% to regions lying above 300 km.

Key words. Ionosphere (solar radiation and cosmic ray effects; instruments and techniques – Solar physics, astrophysics and astronomy (ultraviolet emissions

Ionosphere Delay Calibration and Calibration Errors for Satellite Navigation of Aircraft

Science.gov (United States)

Harris, Ian; Manucci, Anthony; Iijima, Byron; Lindqwister, Ulf; Muna, Demitri; Pi, Xiaoqing; Wilson, Brian

2000-01-01

The Federal Aviation Administration (FAA) is implementing a satellite-based navigation system for aircraft using the Global Positioning System (GPS). Positioning accuracy of a few meters will be achieved by broadcasting corrections to the direct GPS signal. These corrections are derived using the wide-area augmentation system (WAAS), which includes a ground network of at least 24 GPS receivers across the Continental US (CONUS). WAAS will provide real-time total electron content (TEC) measurements that can be mapped to fixed grid points using a real-time mapping algorithm. These TECs will be converted into vertical delay corrections for the GPS L1 frequency and broadcast to users every five minutes via geosynchronous satellite. Users will convert these delays to slant calibrations along their own lines-of-sight (LOS) to GPS satellites. Uncertainties in the delay calibrations will also be broadcast, allowing users to estimate the uncertainty of their position. To maintain user safety without reverting to excessive safety margins an empirical model of user calibration errors has been developed. WAAS performance depends on factors that include geographic location (errors increase near WAAS borders), and ionospheric conditions, such as the enhanced spatial electron density gradients found during ionospheric storms.

Coelomic implantation of satellite transmitters in the bar-tailed godwit (Limosa lapponica) and the bristle-thighed curlew (Numenius tahitiensis) using propofol, bupivacaine, and lidocaine

Science.gov (United States)

Mulcahy, Daniel M.; Gartrell, Brett D.; Gill, Robert E.; Tibbitts, T. Lee; Ruthrauff, Daniel R.

2011-01-01

Intravenous propofol was used as a general anesthetic with a 2∶1 (mg∶mg) adjunctive mixture of lidocaine and bupivacaine as local anesthetics infiltrated into the surgical sites for implantation of satellite transmitters into the right abdominal air sac of 39 female and 4 male bar-tailed godwits (Limosa lapponica baueri and Limosa lapponica menzbeiri) and 11 female and 12 male bristle-thighed curlews (Numenius tahitiensis). The birds were captured on nesting grounds in Alaska, USA, and on overwintering areas in New Zealand and Australia from 2005 through 2008. As it was developed, the mass of the transmitter used changed yearly from a low of 22.4 ± 0.2 g to a high of 27.1 ± 0.2 g and weighed 25.1 ± 0.2 g in the final year. The mean load ratios ranged from 5.2% to 7.7% for godwits and from 5.7% to 7.5% for curlews and exceeded 5% for all years, locations, and genders of both species. The maximum load ratio was 8.3% for a female bar-tailed godwit implanted in Australia in 2008. Three godwits and no curlews died during surgery. Most birds were hyperthermic upon induction but improved during surgery. Two godwits (one in New Zealand and one in Australia) could not stand upon release, likely due to capture myopathy. These birds failed to respond to treatment and were euthanized. The implanted transmitters were used to follow godwits through their southern and northern migrations, and curlews were followed on their southern migration.

Identification of high-risk areas for harbour porpoise Phocoena phocoena bycatch using remote electronic monitoring and satellite telemetry data

DEFF Research Database (Denmark)

Kindt-Larsen, Lotte; Berg, Casper Willestofte; Tougaard, J.

2016-01-01

grounds, quantify fishing effort and document harbour porpoise bycatch. Movement data from 66 harbour porpoises equipped with satellite transmitters from 1997 to 2012 were used to model population density. A simple model was constructed to investigate the relationship between the response (number...... telemetry or REM data allow for identification of areas of potential high and low bycatch risk, and better predictions are obtained when combining the 2 sources of data. The final model can thus be used as a tool to identify areas of bycatch risk...... and lower risk of porpoise bycatch. From May 2010 to April 2011, 4 commercial gillnet vessels were equipped with remote electronic monitoring (REM) systems. The REM system recorded time, GPS position and closed-circuit television (CCTV) footage of all gillnet hauls. REM data were used to identify fishing...

Using GPS RO L1 data for calibration of the atmospheric path delay model for data reduction of the satellite altimetery observations.

Science.gov (United States)

Petrov, L.

2017-12-01

Processing satellite altimetry data requires the computation of path delayin the neutral atmosphere that is used for correcting ranges. The path delayis computed using numerical weather models and the accuracy of its computationdepends on the accuracy of numerical weather models. Accuracy of numerical modelsof numerical weather models over Antarctica and Greenland where there is a very sparse network of ground stations, is not well known. I used the dataset of GPS RO L1 data, computed predicted path delay for ROobservations using the numerical whether model GEOS-FPIT, formed the differences with observed path delay and used these differences for computationof the corrections to the a priori refractivity profile. These profiles wereused for computing corrections to the a priori zenith path delay. The systematic patter of these corrections are used for de-biasing of the the satellite altimetry results and for characterization of the systematic errorscaused by mismodeling atmosphere.

Testing an attachment method for solar-powered tracking devices on a long-distance migrating shorebird

NARCIS (Netherlands)

Chan, Y.-C; Brugge, M.; Tibbitts, T.L.; Dekinga, A.; Porter, R.; Klaassen, R.H.G.; Piersma, T.

2016-01-01

Small solar-powered satellite transmitters andGPS data loggers enable continuous, multi-year, and globaltracking of birds. What is lacking, however, are reliablemethods to attach these tracking devices to small migratorybirds so that (1) flight performance is not impacted and (2)tags are retained

VELOCITY AND GRAVITATIONAL EFFECTS ON GPS SATELLITES: AN OUTLINE OF EARLY PREDICTION AND DETECTION OF STRONG EARTHQUAKES EFECTOS DE VELOCIDAD Y DE GRAVITACIÓN EN GPS SATELITALES: UN ESQUEMA PARA LA PREDICCIÓN Y DETECCIÓN TEMPRANA DE FUERTES TERREMOTOS

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H Torres-Silva

2010-12-01

Full Text Available Today, the global navigation satellite systems, GPS used as global positioning systems, are based on a gravitational model and hence they are only operative when several relativistic effects are taken into account. The most important relativistic effects (to order 1/c² are: the Doppler red shift of second order, due to the motion of the satellite (special relativity and the Einstein gravitational blue shift effect of the satellite clock frequency (equivalence principle of general relativity. Both of these effects can be treated at a basic level, making for an appealing application of relativity to every life. This paper examines the significant effects that must be taken into account in the design and operation of systems GPS without resorting to the theory of special and general relativity, yielding the same results for these systems, where one of the effects can be treated with the time contraction approach proposed here and the other using the Newton's theory as an approximation of the General Relativity. This approach allow us to propose an outline of early prediction and detection on strong earthquake phenomena.Hoy en día, los sistemas de navegación global por satélite, GPS utilizados como sistemas de posicionamiento global, se basan en un modelo gravitacional y por lo tanto solo son operativos cuando varios efectos relativistas son tenidos en cuenta. Los efectos relativistas más importantes (hasta el orden 1/c² son: el desplazamiento Doppler al rojo de segundo orden, debido al movimiento del satélite (la relatividad especial y el efecto gravitacional de Einstein corrimiento al azul de la frecuencia de reloj del satélite (principio de equivalencia de la relatividad general. Ambos efectos pueden ser tratados en un nivel básico, apelando a la relatividad del día a día. Este artículo examina los efectos significativos que deben tenerse en cuenta en la operación de sistemas de GPS sin tener que recurrir a las teorías de la

Interaction between subdaily Earth rotation parameters and GPS orbits

Science.gov (United States)

Panafidina, Natalia; Seitz, Manuela; Hugentobler, Urs

2013-04-01

In processing GPS observations the geodetic parameters like station coordinates and ERPs (Earth rotation parameters) are estimated w.r.t. the celestial reference system realized by the satellite orbits. The interactions/correlations between estimated GPS orbis and other parameters may lead to numerical problems with the solution and introduce systematic errors in the computed values: the well known correlations comprise 1) the correlation between the orbital parameters determining the orientation of the orbital plane in inertial space and the nutation and 2) in the case of estimating ERPs with subdaily resolution the correlation between retrograde diurnal polar motion and nutation (and so the respective orbital elements). In this contribution we study the interaction between the GPS orbits and subdaily model for the ERPs. Existing subdaily ERP model recommended by the IERS comprises ~100 terms in polar motion and ~70 terms in Universal Time at diurnal and semidiurnal tidal periods. We use a long time series of daily normal equation systems (NEQ) obtaine from GPS observations from 1994 till 2007 where the ERPs with 1-hour resolution are transformed into tidal terms and the influence of the tidal terms with different frequencies on the estimated orbital parameters is considered. We found that although there is no algebraic correlation in the NEQ between the individual orbital parameters and the tidal terms, the changes in the amplitudes of tidal terms with periods close to 24 hours can be better accmodated by systematic changes in the orbital parameters than for tidal terms with other periods. Since the variation in Earth rotation with the period of siderial day (23.93h, tide K1) in terrestrial frame has in inertial space the same period as the period of revolution of GPS satellites, the K1 tidal term in polar motion is seen by the satellites as a permanent shift. The tidal terms with close periods (from ~24.13h to ~23.80h) are seen as a slow rotation of the

GPS Based Reduced-Dynamic Orbit Determination for Low Earth Orbiters with Ambiguity Fixing

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Yang Yang

2015-01-01

Full Text Available With the ever-increasing number of satellites in Low Earth Orbit (LEO for scientific missions, the precise determination of the position and velocity of the satellite is a necessity. GPS (Global Positioning System based reduced-dynamic orbit determination (RPOD method is commonly used in the post processing with high precision. This paper presents a sequential RPOD strategy for LEO satellite in the framework of Extended Kalman Filter (EKF. Precise Point Positioning (PPP technique is used to process the GPS observations, with carrier phase ambiguity resolution using Integer Phase Clocks (IPCs products. A set of GRACE (Gravity Recovery And Climate Experiment mission data is used to test and validate the RPOD performance. Results indicate that orbit determination accuracy could be improved by 15% in terms of 3D RMS error in comparison with traditional RPOD method with float ambiguity solutions.

Data Integration from GPS and Inertial Navigation Systems for Pedestrians in Urban Area

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Krzysztof Bikonis

2013-09-01

Full Text Available The GPS system is widely used in navigation and the GPS receiver can offer long-term stable absolute positioning information. The overall system performance depends largely on the signal environments. The position obtained from GPS is often degraded due to obstruction and multipath effect caused by buildings, city infrastructure and vegetation, whereas, the current performance achieved by inertial navigation systems (INS is still relatively poor due to the large inertial sensor errors. The complementary features of GPS and INS are the main reasons why integrated GPS/INS systems are becoming increasingly popular. GPS/INS systems offer a high data rate, high accuracy position and orientation that can work in all environments, particularly those where satellite availability is restricted. In the paper integration algorithm of GPS and INS systems data for pedestrians in urban area is presented. For data integration an Extended Kalman Filter (EKF algorithm is proposed. Complementary characteristics of GPS and INS with EKF can overcome the problem of huge INS drifts, GPS outages, dense multipath effect and other individual problems associated with these sensors.

An alternative ionospheric correction model for global navigation satellite systems

Science.gov (United States)

Hoque, M. M.; Jakowski, N.

2015-04-01

The ionosphere is recognized as a major error source for single-frequency operations of global navigation satellite systems (GNSS). To enhance single-frequency operations the global positioning system (GPS) uses an ionospheric correction algorithm (ICA) driven by 8 coefficients broadcasted in the navigation message every 24 h. Similarly, the global navigation satellite system Galileo uses the electron density NeQuick model for ionospheric correction. The Galileo satellite vehicles (SVs) transmit 3 ionospheric correction coefficients as driver parameters of the NeQuick model. In the present work, we propose an alternative ionospheric correction algorithm called Neustrelitz TEC broadcast model NTCM-BC that is also applicable for global satellite navigation systems. Like the GPS ICA or Galileo NeQuick, the NTCM-BC can be optimized on a daily basis by utilizing GNSS data obtained at the previous day at monitor stations. To drive the NTCM-BC, 9 ionospheric correction coefficients need to be uploaded to the SVs for broadcasting in the navigation message. Our investigation using GPS data of about 200 worldwide ground stations shows that the 24-h-ahead prediction performance of the NTCM-BC is better than the GPS ICA and comparable to the Galileo NeQuick model. We have found that the 95 percentiles of the prediction error are about 16.1, 16.1 and 13.4 TECU for the GPS ICA, Galileo NeQuick and NTCM-BC, respectively, during a selected quiet ionospheric period, whereas the corresponding numbers are found about 40.5, 28.2 and 26.5 TECU during a selected geomagnetic perturbed period. However, in terms of complexity the NTCM-BC is easier to handle than the Galileo NeQuick and in this respect comparable to the GPS ICA.

Software Defined GPS Receiver for International Space Station

Science.gov (United States)

Duncan, Courtney B.; Robison, David E.; Koelewyn, Cynthia Lee

2011-01-01

JPL is providing a software defined radio (SDR) that will fly on the International Space Station (ISS) as part of the CoNNeCT project under NASA's SCaN program. The SDR consists of several modules including a Baseband Processor Module (BPM) and a GPS Module (GPSM). The BPM executes applications (waveforms) consisting of software components for the embedded SPARC processor and logic for two Virtex II Field Programmable Gate Arrays (FPGAs) that operate on data received from the GPSM. GPS waveforms on the SDR are enabled by an L-Band antenna, low noise amplifier (LNA), and the GPSM that performs quadrature downconversion at L1, L2, and L5. The GPS waveform for the JPL SDR will acquire and track L1 C/A, L2C, and L5 GPS signals from a CoNNeCT platform on ISS, providing the best GPS-based positioning of ISS achieved to date, the first use of multiple frequency GPS on ISS, and potentially the first L5 signal tracking from space. The system will also enable various radiometric investigations on ISS such as local multipath or ISS dynamic behavior characterization. In following the software-defined model, this work will create a highly portable GPS software and firmware package that can be adapted to another platform with the necessary processor and FPGA capability. This paper also describes ISS applications for the JPL CoNNeCT SDR GPS waveform, possibilities for future global navigation satellite system (GNSS) tracking development, and the applicability of the waveform components to other space navigation applications.

Why GPS makes distances bigger than they are.

Science.gov (United States)

Ranacher, Peter; Brunauer, Richard; Trutschnig, Wolfgang; Van der Spek, Stefan; Reich, Siegfried

2016-02-01

Global navigation satellite systems such as the Global Positioning System (GPS) is one of the most important sensors for movement analysis. GPS is widely used to record the trajectories of vehicles, animals and human beings. However, all GPS movement data are affected by both measurement and interpolation errors. In this article we show that measurement error causes a systematic bias in distances recorded with a GPS; the distance between two points recorded with a GPS is - on average - bigger than the true distance between these points. This systematic 'overestimation of distance' becomes relevant if the influence of interpolation error can be neglected, which in practice is the case for movement sampled at high frequencies. We provide a mathematical explanation of this phenomenon and illustrate that it functionally depends on the autocorrelation of GPS measurement error ( C ). We argue that C can be interpreted as a quality measure for movement data recorded with a GPS. If there is a strong autocorrelation between any two consecutive position estimates, they have very similar error. This error cancels out when average speed, distance or direction is calculated along the trajectory. Based on our theoretical findings we introduce a novel approach to determine C in real-world GPS movement data sampled at high frequencies. We apply our approach to pedestrian trajectories and car trajectories. We found that the measurement error in the data was strongly spatially and temporally autocorrelated and give a quality estimate of the data. Most importantly, our findings are not limited to GPS alone. The systematic bias and its implications are bound to occur in any movement data collected with absolute positioning if interpolation error can be neglected.

A New Indoor Positioning System Architecture Using GPS Signals.

Science.gov (United States)

Xu, Rui; Chen, Wu; Xu, Ying; Ji, Shengyue

2015-04-29

The pseudolite system is a good alternative for indoor positioning systems due to its large coverage area and accurate positioning solution. However, for common Global Positioning System (GPS) receivers, the pseudolite system requires some modifications of the user terminals. To solve the problem, this paper proposes a new pseudolite-based indoor positioning system architecture. The main idea is to receive real-world GPS signals, repeat each satellite signal and transmit those using indoor transmitting antennas. The transmitted GPS-like signal can be processed (signal acquisition and tracking, navigation data decoding) by the general receiver and thus no hardware-level modification on the receiver is required. In addition, all Tx can be synchronized with each other since one single clock is used in Rx/Tx. The proposed system is simulated using a software GPS receiver. The simulation results show the indoor positioning system is able to provide high accurate horizontal positioning in both static and dynamic situations.

First results from the GPS atmosphere sounding experiment TOR aboard the TerraSAR-X satellite

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G. Beyerle

2011-07-01

Full Text Available GPS radio occultation events observed between 24 July and 17 November 2008 by the IGOR occultation receiver aboard the TerraSAR-X satellite are processed and analyzed. The comparison of 15 327 refractivity profiles with collocated ECMWF data yield a mean bias between zero and −0.30 % at altitudes between 5 and 30 km. Standard deviations decrease from about 1.4 % at 5 km to about 0.6 % at 10 km altitude, however, increase significantly in the upper stratosphere. At low latitudes mean biases and standard deviations are larger, in particular in the lower troposphere. The results are consistent with 15 159 refractivity observations collected during the same time period by the BlackJack receiver aboard GRACE-A and processed by GFZ's operational processing system. The main difference between the two occultation instruments is the implementation of open-loop signal tracking in the IGOR (TerraSAR-X receiver which improves the tropospheric penetration depth in terms of ray height by about 2 km compared to the conventional closed-loop data acquired by BlackJack (GRACE-A.

Water vapour tomography using GPS phase observations: Results from the ESCOMPTE experiment

Science.gov (United States)

Nilsson, T.; Gradinarsky, L.; Elgered, G.

2007-10-01

Global Positioning System (GPS) tomography is a technique for estimating the 3-D structure of the atmospheric water vapour using data from a dense local network of GPS receivers. Several current methods utilize estimates of slant wet delays between the GPS satellites and the receivers on the ground, which are difficult to obtain with millimetre accuracy from the GPS observations. We present results of applying a new tomographic method to GPS data from the Expériance sur site pour contraindre les modèles de pollution atmosphérique et de transport d'emissions (ESCOMPTE) experiment in southern France. This method does not rely on any slant wet delay estimates, instead it uses the GPS phase observations directly. We show that the estimated wet refractivity profiles estimated by this method is on the same accuracy level or better compared to other tomographic methods. The results are in agreement with earlier simulations, for example the profile information is limited above 4 km.

Enhancing the accuracy of GPS point positioning by converting the single frequency data to dual frequency data

Directory of Open Access Journals (Sweden)

Aly M. El-naggar

2011-09-01

Full Text Available The global positioning system (GPS has been used to support a wide variety of applications, such as high-accuracy positioning and navigation. Differential GPS techniques can largely eliminate common-mode errors between the reference and the rover GPS stations resulting from ionospheric and tropospheric refraction and delays, satellite and receiver clock biases, and orbital errors [1]. The ionospheric delay in the propagation of global positioning system (GPS signals is one of the main sources of error in GPS precise positioning and navigation. A dual-frequency GPS receiver can eliminate (to the first order the ionospheric delay through a linear combination of the L1 and L2 observations [2]. The most significant effect of ionospheric delay appear in case of using single frequency data. In this paper the single frequency data of concerned station are converted to dual frequency data by employing dual frequency data from 11 regional GPS stations distributed around it. Total electron content (TEC was calculated at every GPS station to produce the mathematical model of TEC which is a function of latitude (Φ and longitude (λ. By using this mathematical model the values of TEC and L2 can be predicted at the single frequency GPS station for each satellite, after that the comparison between predicted and observation values of TEC and L2 was performed. The estimation method and test results of the proposed method indicates that the difference between predicted and observation values is very small.

Fisheye-Based Method for GPS Localization Improvement in Unknown Semi-Obstructed Areas

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Julien Moreau

2017-01-01

Full Text Available A precise GNSS (Global Navigation Satellite System localization is vital for autonomous road vehicles, especially in cluttered or urban environments where satellites are occluded, preventing accurate positioning. We propose to fuse GPS (Global Positioning System data with fisheye stereovision to face this problem independently to additional data, possibly outdated, unavailable, and needing correlation with reality. Our stereoscope is sky-facing with 360° × 180° fisheye cameras to observe surrounding obstacles. We propose a 3D modelling and plane extraction through following steps: stereoscope self-calibration for decalibration robustness, stereo matching considering neighbours epipolar curves to compute 3D, and robust plane fitting based on generated cartography and Hough transform. We use these 3D data with GPS raw data to estimate NLOS (Non Line Of Sight reflected signals pseudorange delay. We exploit extracted planes to build a visibility mask for NLOS detection. A simplified 3D canyon model allows to compute reflections pseudorange delays. In the end, GPS positioning is computed considering corrected pseudoranges. With experimentations on real fixed scenes, we show generated 3D models reaching metric accuracy and improvement of horizontal GPS positioning accuracy by more than 50%. The proposed procedure is effective, and the proposed NLOS detection outperforms CN0-based methods (Carrier-to-receiver Noise density.

GPS Estimates of Integrated Precipitable Water Aid Weather Forecasters

Science.gov (United States)

Moore, Angelyn W.; Gutman, Seth I.; Holub, Kirk; Bock, Yehuda; Danielson, David; Laber, Jayme; Small, Ivory

2013-01-01

Global Positioning System (GPS) meteorology provides enhanced density, low-latency (30-min resolution), integrated precipitable water (IPW) estimates to NOAA NWS (National Oceanic and Atmospheric Adminis tration Nat ional Weather Service) Weather Forecast Offices (WFOs) to provide improved model and satellite data verification capability and more accurate forecasts of extreme weather such as flooding. An early activity of this project was to increase the number of stations contributing to the NOAA Earth System Research Laboratory (ESRL) GPS meteorology observing network in Southern California by about 27 stations. Following this, the Los Angeles/Oxnard and San Diego WFOs began using the enhanced GPS-based IPW measurements provided by ESRL in the 2012 and 2013 monsoon seasons. Forecasters found GPS IPW to be an effective tool in evaluating model performance, and in monitoring monsoon development between weather model runs for improved flood forecasting. GPS stations are multi-purpose, and routine processing for position solutions also yields estimates of tropospheric zenith delays, which can be converted into mm-accuracy PWV (precipitable water vapor) using in situ pressure and temperature measurements, the basis for GPS meteorology. NOAA ESRL has implemented this concept with a nationwide distribution of more than 300 "GPSMet" stations providing IPW estimates at sub-hourly resolution currently used in operational weather models in the U.S.

SLR and GPS spatial techniques in ITRF. Argentine results.

Science.gov (United States)

Actis, Eloy Vicente; Huang, Dongping; Márquez, Raúl; Adarvez, Sonia; Flores, Matías; Brizuela, Diego; Nievas, Jesica; Podestá, Ricardo; Pacheco, Ana M.; Rojas, Hernán Alvis; Yin, Zhiqiang; Li, Jinzeng; Han, Yanben; Liu, Weidong; Wang, Rui

2012-08-01

Along the late 30 years spatial geodetic techniques enable us to measure horizontal and vertical deformations of the Earth’s surface with a very high precision. Performing this task we made Satellite Laser Ranging (SLR), and Global Positioning System (GPS) observations in South America ILRS 7406 Station placed at Observatorio Astronómico Félix Aguilar (OAFA) in San Juan, Argentina, accomplishing a Cooperation Agreement between CAS - NAOC and OAFA - UNSJ. Trough LAGEOS II Satellite observations we obtain rectangular coordinates of San Juan ILRS Station in the Terrestrial Reference Frame (ITR 2000), standing out that Argentine Station data were included in the late arrangements ITRF given by International Earth Rotation and Reference System Service (IERS). Spatial and temporary variations of the epoch 2010 - 2011 were evaluated finding out remarkable displacements, of about a half meter, related with seismic events on the region. We confirm these deformations by means of GP S determinations referred to Permanent GPS Station placed nearby the SLR Station.

Improving Ambiguity Resolution for Medium Baselines Using Combined GPS and BDS Dual/Triple-Frequency Observations.

Science.gov (United States)

Gao, Wang; Gao, Chengfa; Pan, Shuguo; Wang, Denghui; Deng, Jiadong

2015-10-30

The regional constellation of the BeiDou navigation satellite system (BDS) has been providing continuous positioning, navigation and timing services since 27 December 2012, covering China and the surrounding area. Real-time kinematic (RTK) positioning with combined BDS and GPS observations is feasible. Besides, all satellites of BDS can transmit triple-frequency signals. Using the advantages of multi-pseudorange and carrier observations from multi-systems and multi-frequencies is expected to be of much benefit for ambiguity resolution (AR). We propose an integrated AR strategy for medium baselines by using the combined GPS and BDS dual/triple-frequency observations. In the method, firstly the extra-wide-lane (EWL) ambiguities of triple-frequency system, i.e., BDS, are determined first. Then the dual-frequency WL ambiguities of BDS and GPS were resolved with the geometry-based model by using the BDS ambiguity-fixed EWL observations. After that, basic (i.e., L1/L2 or B1/B2) ambiguities of BDS and GPS are estimated together with the so-called ionosphere-constrained model, where the ambiguity-fixed WL observations are added to enhance the model strength. During both of the WL and basic AR, a partial ambiguity fixing (PAF) strategy is adopted to weaken the negative influence of new-rising or low-elevation satellites. Experiments were conducted and presented, in which the GPS/BDS dual/triple-frequency data were collected in Nanjing and Zhengzhou of China, with the baseline distance varying from about 28.6 to 51.9 km. The results indicate that, compared to the single triple-frequency BDS system, the combined system can significantly enhance the AR model strength, and thus improve AR performance for medium baselines with a 75.7% reduction of initialization time on average. Besides, more accurate and stable positioning results can also be derived by using the combined GPS/BDS system.

Improvement of tsunami detection in timeseries data of GPS buoys with the Continuous Wavelet Transform

Science.gov (United States)

Chida, Y.; Takagawa, T.

2017-12-01

The observation data of GPS buoys which are installed in the offshore of Japan are used for monitoring not only waves but also tsunamis in Japan. The real-time data was successfully used to upgrade the tsunami warnings just after the 2011 Tohoku earthquake. Huge tsunamis can be easily detected because the signal-noise ratio is high enough, but moderate tsunami is not. GPS data sometimes include the error waveforms like tsunamis because of changing accuracy by the number and the position of GPS satellites. To distinguish the true tsunami waveforms from pseudo-tsunami ones is important for tsunami detection. In this research, a method to reduce misdetections of tsunami in the observation data of GPS buoys and to increase the efficiency of tsunami detection was developed.Firstly, the error waveforms were extracted by using the indexes of position dilution of precision, reliability of GPS satellite positioning and satellite number for calculation. Then, the output from this procedure was used for the Continuous Wavelet Transform (CWT) to analyze the time-frequency characteristics of error waveforms and real tsunami waveforms.We found that the error waveforms tended to appear when the accuracy of GPS buoys positioning was low. By extracting these waveforms, it was possible to decrease about 43% error waveforms without the reduction of the tsunami detection rate. Moreover, we found that the amplitudes of power spectra obtained from the error waveforms and real tsunamis were similar in the component of long period (4-65 minutes), on the other hand, the amplitude in the component of short period (< 1 minute) obtained from the error waveforms was significantly larger than that of the real tsunami waveforms. By thresholding of the short-period component, further extraction of error waveforms became possible without a significant reduction of tsunami detection rate.

The use of civilian-type GPS receivers by the military and their vulnerability to jamming

Directory of Open Access Journals (Sweden)

Ludwig Combrinck

2012-05-01

Full Text Available We considered the impact of external influences on a GPS receiver and how these influences affect the capabilities of civilian-type GPS receivers. A standard commercial radio frequency signal generator and passive GPS antenna were used to test the sensitivity of GPS to intentional jamming; the possible effects of the terrain on the propagation of the jamming signal were also tested. It was found that the high sensitivity of GPS receivers and the low strength level of GPS satellite signals combine to make GPS receivers very vulnerable to intentional jamming or unintentional radio frequency interference. Terrain undulation was used to shield GPS antennas from the direct line-of-sight of the jamming antenna and this indicated that terrain characteristics can be used to mitigate the effects of jamming. These results illuminate the vulnerability of civilian-type GPS receivers to the possibility and the ease of disablement and establish the foundation for future work.

An Extended ADOP for Performance Evaluation of Single-Frequency Single-Epoch Positioning by BDS/GPS in Asia-Pacific Region

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Xin Liu

2017-09-01

Full Text Available Single-Frequency Single-Epoch (SFSE high-precision positioning has always been the hot spot of Global Navigation Satellite System (GNSS, and ambiguity dilution of precision (ADOP is a well-known scalar measure for success rate of ambiguity resolution. Traditional ADOP expression is complicated, thus the SFSE extended ADOP (E-ADOP, with the newly defined Summation-Multiplication Ratio of Weight (SMRW and two theorems for short baseline, was developed. This simplifies the ADOP expression; gives a clearer insight into the influences of SMRW and number of satellites on E-ADOP; and makes theoretical analysis of E-ADOP more convenient than that of ADOP, and through that the E-ADOP value can be predicted more accurately than through the ADOP expression for ADOP value. E-ADOP reveals that number of satellites and SMRW or high-elevation satellite are important for ADOP and, through E-ADOP, we studied which factor is dominant to control ADOP in different conditions and make ADOP different between BeiDou Navigation Satellite System (BDS, Global Positioning System (GPS, and BDS/GPS. Based on experimental results of SFSE positioning with different baselines, some conclusions are made: (1 ADOP decreases when new satellites are added mainly because the number of satellites becomes larger; (2 when the number of satellites is constant, ADOP is mainly affected by SMRW; (3 in contrast to systems where the satellites with low-elevation are the majority or where low- and high-elevation satellites are equally distributed, in systems where the high-elevation satellites are the majority, the SMRW mainly makes ADOP smaller, even if there are fewer satellites than in the two previous cases, and the difference in numbers of satellites can be expanded as the proportion of high-elevation satellites becomes larger; and (4 ADOP of BDS is smaller than ADOP of GPS mainly because of its SMRW.

Air traffic management system design using satellite based geo-positioning and communications assets

Science.gov (United States)

Horkin, Phil

1995-01-01

The current FAA and ICAO FANS vision of Air Traffic Management will transition the functions of Communications, Navigation, and Surveillance to satellite based assets in the 21st century. Fundamental to widespread acceptance of this vision is a geo-positioning system that can provide worldwide access with best case differential GPS performance, but without the associated problems. A robust communications capability linking-up aircraft and towers to meet the voice and data requirements is also essential. The current GPS constellation does not provide continuous global coverage with a sufficient number of satellites to meet the precision landing requirements as set by the world community. Periodic loss of the minimum number of satellites in view creates an integrity problem, which prevents GPS from becoming the primary system for navigation. Furthermore, there is reluctance on the part of many countries to depend on assets like GPS and GLONASS which are controlled by military communities. This paper addresses these concerns and provides a system solving the key issues associated with navigation, automatic dependent surveillance, and flexible communications. It contains an independent GPS-like navigation system with 27 satellites providing global coverage with a minimum of six in view at all times. Robust communications is provided by a network of TDMA/FDMA communications payloads contained on these satellites. This network can support simultaneous communications for up to 30,000 links, nearly enough to simultaneously support three times the current global fleet of jumbo air passenger aircraft. All of the required hardware is directly traceable to existing designs.

Assessment of NASA airborne laser altimetry data using ground-based GPS data near Summit Station, Greenland

Science.gov (United States)

Brunt, Kelly M.; Hawley, Robert L.; Lutz, Eric R.; Studinger, Michael; Sonntag, John G.; Hofton, Michelle A.; Andrews, Lauren C.; Neumann, Thomas A.

2017-03-01

A series of NASA airborne lidars have been used in support of satellite laser altimetry missions. These airborne laser altimeters have been deployed for satellite instrument development, for spaceborne data validation, and to bridge the data gap between satellite missions. We used data from ground-based Global Positioning System (GPS) surveys of an 11 km long track near Summit Station, Greenland, to assess the surface-elevation bias and measurement precision of three airborne laser altimeters including the Airborne Topographic Mapper (ATM), the Land, Vegetation, and Ice Sensor (LVIS), and the Multiple Altimeter Beam Experimental Lidar (MABEL). Ground-based GPS data from the monthly ground-based traverses, which commenced in 2006, allowed for the assessment of nine airborne lidar surveys associated with ATM and LVIS between 2007 and 2016. Surface-elevation biases for these altimeters - over the flat, ice-sheet interior - are less than 0.12 m, while assessments of measurement precision are 0.09 m or better. Ground-based GPS positions determined both with and without differential post-processing techniques provided internally consistent solutions. Results from the analyses of ground-based and airborne data provide validation strategy guidance for the Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) elevation and elevation-change data products.

Analyzing the Impact of Different Pcv Calibration Models on Height Determination Using Gps/Glonass Observations from Asg-Eupos Network

Science.gov (United States)

Dawidowicz, Karol

2014-12-01

The integration of GPS with GLONASS is very important in satellite-based positioning because it can clearly improve reliability and availability. However, unlike GPS, GLONASS satellites transmit signals at different frequencies. This results in significant difficulties in modeling and ambiguity resolution for integrated GNSS positioning. There are also some difficulties related to the antenna Phase Center Variations (PCV) problem because, as is well known, the PCV is dependent on the received signal frequency dependent. Thus, processing simultaneous observations from different positioning systems, e.g. GPS and GLONASS, we can expect complications resulting from the different structure of signals and differences in satellite constellations. The ASG-EUPOS multifunctional system for precise satellite positioning is a part of the EUPOS project involving countries of Central and Eastern Europe. The number of its users is increasing rapidly. Currently 31 of 101 reference stations are equipped with GPS/GLONASS receivers and the number is still increasing. The aim of this paper is to study the height solution differences caused by using different PCV calibration models in integrated GPS/GLONASS observation processing. Studies were conducted based on the datasets from the ASG-EUPOS network. Since the study was intended to evaluate the impact on height determination from the users' point of view, a so-called "commercial" software was chosen for post-processing. The analysis was done in a baseline mode: 3 days of GNSS data collected with three different receivers and antennas were used. For the purposes of research the daily observations were divided into different sessions with a session length of one hour. The results show that switching between relative and absolute PCV models may cause an obvious effect on height determination. This issue is particularly important when mixed GPS/GLONASS observations are post-processed.

Combining GPS measurements and IRI model predictions

International Nuclear Information System (INIS)

Hernandez-Pajares, M.; Juan, J.M.; Sanz, J.; Bilitza, D.

2002-01-01

The free electrons distributed in the ionosphere (between one hundred and thousands of km in height) produce a frequency-dependent effect on Global Positioning System (GPS) signals: a delay in the pseudo-orange and an advance in the carrier phase. These effects are proportional to the columnar electron density between the satellite and receiver, i.e. the integrated electron density along the ray path. Global ionospheric TEC (total electron content) maps can be obtained with GPS data from a network of ground IGS (international GPS service) reference stations with an accuracy of few TEC units. The comparison with the TOPEX TEC, mainly measured over the oceans far from the IGS stations, shows a mean bias and standard deviation of about 2 and 5 TECUs respectively. The discrepancies between the STEC predictions and the observed values show an RMS typically below 5 TECUs (which also includes the alignment code noise). he existence of a growing database 2-hourly global TEC maps and with resolution of 5x2.5 degrees in longitude and latitude can be used to improve the IRI prediction capability of the TEC. When the IRI predictions and the GPS estimations are compared for a three month period around the Solar Maximum, they are in good agreement for middle latitudes. An over-determination of IRI TEC has been found at the extreme latitudes, the IRI predictions being, typically two times higher than the GPS estimations. Finally, local fits of the IRI model can be done by tuning the SSN from STEC GPS observations

GPS Tomography: Water Vapour Monitoring for Germany

Science.gov (United States)

Bender, Michael; Dick, Galina; Wickert, Jens; Raabe, Armin

2010-05-01

Ground based GPS atmosphere sounding provides numerous atmospheric quantities with a high temporal resolution for all weather conditions. The spatial resolution of the GPS observations is mainly given by the number of GNSS satellites and GPS ground stations. The latter could considerably be increased in the last few years leading to more reliable and better resolved GPS products. New techniques such as the GPS water vapour tomography gain increased significance as data from large and dense GPS networks become available. The GPS tomography has the potential to provide spatially resolved fields of different quantities operationally, i. e. the humidity or wet refractivity as required for meteorological applications or the refraction index which is important for several space based observations or for precise positioning. The number of German GPS stations operationally processed by the GFZ in Potsdam was recently enlarged to more than 300. About 28000 IWV observations and more than 1.4 millions of slant total delay data are now available per day with a temporal resolution of 15 min and 2.5 min, respectively. The extended network leads not only to a higher spatial resolution of the tomographically reconstructed 3D fields but also to a much higher stability of the inversion process and with that to an increased quality of the results. Under these improved conditions the GPS tomography can operate continuously over several days or weeks without applying too tight constraints. Time series of tomographically reconstructed humidity fields will be shown and different initialisation strategies will be discussed: Initialisation with a simple exponential profile, with a 3D humidity field extrapolated from synoptic observations and with the result of the preceeding reconstruction. The results are compared to tomographic reconstructions initialised with COSMO-DE analyses and to the corresponding model fields. The inversion can be further stabilised by making use of independent

The Mean Sea Surface DTU10mss - Comparison With Gps And Tide Gauges

DEFF Research Database (Denmark)

Andersen, Ole Baltazar; Knudsen, Per; Bondo, Torsten

2010-01-01

Satellite altimetry and the Global Position System (GPS) are conveniently given in the same reference frame and can therefore be used to construct a vertical reference surface for offshore navigation. Here a new Mean Sea Surface DTU10MSS is presented with a vertical accuracy better than 10 cm...... in most areas of the world confirmed by extensive comparison with GPS leveled tide gauges around Britain and Norway. It is proposed that this model is used as a global vertical reference. This paper briefly outlines the update of the previous DTU model to DTU10MSS and presents comparisons on GPS positions...

Multiscale GPS tomography during COPS: validation and applications

Science.gov (United States)

Champollion, Cédric; Flamant, Cyrille; Masson, Frédéric; Gégout, Pascal; Boniface, Karen; Richard, Evelyne

2010-05-01

Accurate 3D description of the water vapour field is of interest for process studies such as convection initiation. None of the current techniques (LIDAR, satellite, radio soundings, GPS) can provide an all weather continuous 3D field of moisture. The combination of GPS tomography with radio-soundings (and/or LIDAR) has been used for such process studies using both advantages of vertically resolved soundings and high temporal density of GPS measurements. GPS tomography has been used at short scale (10 km horizontal resolution but in a 50 km² area) for process studies such as the ESCOMPTE experiment (Bastin et al., 2005) and at larger scale (50 km horizontal resolution) during IHOP_2002. But no extensive statistical validation has been done so far. The overarching goal of the COPS field experiment is to advance the quality of forecasts of orographically induced convective precipitation by four-dimensional observations and modeling of its life cycle for identifying the physical and chemical processes responsible for deficiencies in QPF over low-mountain regions. During the COPS field experiment, a GPS network of about 100 GPS stations has been continuously operating during three months in an area of 500 km² in the East of France (Vosges Mountains) and West of Germany (Black Forest). If the mean spacing between the GPS is about 50 km, an East-West GPS profile with a density of about 10 km is dedicated to high resolution tomography. One major goal of the GPS COPS experiment is to validate the GPS tomography with different spatial resolutions. Validation is based on additional radio-soundings and airborne / ground-based LIDAR measurement. The number and the high quality of vertically resolved water vapor observations give an unique data set for GPS tomography validation. Numerous tests have been done on real data to show the type water vapor structures that can be imaging by GPS tomography depending of the assimilation of additional data (radio soundings), the

Development And Test of A Digitally Steered Antenna Array for The Navigator GPS Receiver

Science.gov (United States)

Pinto, Heitor David; Valdez, Jennifer E.; Winternitz, Luke M. B.; Hassouneh, Munther A.; Price, Samuel R.

2012-01-01

Global Positioning System (GPS)-based navigation has become common for low-Earth orbit spacecraft as the signal environment is similar to that on the Earth s surface. The situation changes abruptly, however, for spacecraft whose orbital altitudes exceed that of the GPS constellation. Visibility is dramatically reduced and signals that are present may be very weak and more susceptible to interference. GPS receivers effective at these altitudes require increased sensitivity, which often requires a high-gain antenna. Pointing such an antenna can pose a challenge. One efficient approach to mitigate these problems is the use of a digitally steered antenna array. Such an antenna can optimally allocate gain toward desired signal sources and away from interferers. This paper presents preliminary results in the development and test of a digitally steered antenna array for the Navigator GPS research program at NASA s Goddard Space Flight Center. In particular, this paper highlights the development of an array and front-end electronics, the development and test of a real-time software GPS receiver, and implementation of three beamforming methods for combining the signals from the array. Additionally, this paper discusses the development of a GPS signal simulator which produces digital samples of the GPS L1C/A signals as they would be received by an arbitrary antenna array configuration. The simulator models transmitter and receiver dynamics, near-far and multipath interference, and has been a critical component in both the development and test of the GPS receiver. The GPS receiver system was tested with real and simulated GPS signals. Preliminary results show that performance improvement was achieved in both the weak signal and interference environments, matching analytical predictions. This paper summarizes our initial findings and discusses the advantages and limitations of the antenna array and the various beamforming methods.

Seismo-Ionospheric Coupling as Intensified EIA Observed by Satellite Electron Density and GPS-TEC Data

Science.gov (United States)

Ryu, K.; Jangsoo, C.; Kim, S. G.; Jeong, K. S.; Parrot, M.; Pulinets, S. A.; Oyama, K. I.

2014-12-01

Examples of intensified EIA features temporally and spatially related to large earthquakes observed by satellites and GPS-TEC are introduced. The precursory, concurrent, and ex-post enhancements of EIA represented by the equatorial electron density, which are thought to be related to the M8.7 Northern Sumatra earthquake of March 2005, the M8.0 Pisco earthquake of August 2007, and the M7.9 Wenchuan Earthquake of 12 May 2008, are shown with space weather condition. Based on the case studies, statistical analysis on the ionospheric electron density data measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions satellite (DEMETER) over a period of 2005-2010 was executed in order to investigate the correlation between seismic activity and equatorial plasma density variations. To simplify the analysis, three equatorial regions with frequent earthquakes were selected and then one-dimensional time series analysis between the daily seismic activity indices and the EIA intensity indices were performed for each region with excluding the possible effects from the geomagnetic and solar activity. The statistically significant values of the lagged cross-correlation function, particularly in the region with minimal effects of longitudinal asymmetry, indicate that some of the very large earthquakes with M > 7.0 in the low latitude region can accompany observable seismo-ionospheric coupling phenomena in the form of EIA enhancements, even though the seismic activity is not the most significant driver of the equatorial ionospheric evolution. The physical mechanisms of the seismo-ionospheric coupling to explain the observation and the possibility of earthquake prediction using the EIA intensity variation are discussed.

Operational aspects of CASA UNO '88-The first large scale international GPS geodetic network

Science.gov (United States)

Neilan, Ruth E.; Dixon, T. H.; Meehan, Thomas K.; Melbourne, William G.; Scheid, John A.; Kellogg, J. N.; Stowell, J. L.

1989-01-01

For three weeks, from January 18 to February 5, 1988, scientists and engineers from 13 countries and 30 international agencies and institutions cooperated in the most extensive GPS (Global Positioning System) field campaign, and the largest geodynamics experiment, in the world to date. This collaborative eperiment concentrated GPS receivers in Central and South America. The predicted rates of motions are on the order of 5-10 cm/yr. Global coverage of GPS observations spanned 220 deg of longitude and 125 deg of latitude using a total of 43 GPS receivers. The experiment was the first civilian effort at implementing an extended international GPS satellite tracking network. Covariance analyses incorporating the extended tracking network predicted significant improvement in precise orbit determination, allowing accurate long-baseline geodesy in the science areas.

Estimating maneuvers for precise relative orbit determination using GPS

Science.gov (United States)

Allende-Alba, Gerardo; Montenbruck, Oliver; Ardaens, Jean-Sébastien; Wermuth, Martin; Hugentobler, Urs

2017-01-01

Precise relative orbit determination is an essential element for the generation of science products from distributed instrumentation of formation flying satellites in low Earth orbit. According to the mission profile, the required formation is typically maintained and/or controlled by executing maneuvers. In order to generate consistent and precise orbit products, a strategy for maneuver handling is mandatory in order to avoid discontinuities or precision degradation before, after and during maneuver execution. Precise orbit determination offers the possibility of maneuver estimation in an adjustment of single-satellite trajectories using GPS measurements. However, a consistent formulation of a precise relative orbit determination scheme requires the implementation of a maneuver estimation strategy which can be used, in addition, to improve the precision of maneuver estimates by drawing upon the use of differential GPS measurements. The present study introduces a method for precise relative orbit determination based on a reduced-dynamic batch processing of differential GPS pseudorange and carrier phase measurements, which includes maneuver estimation as part of the relative orbit adjustment. The proposed method has been validated using flight data from space missions with different rates of maneuvering activity, including the GRACE, TanDEM-X and PRISMA missions. The results show the feasibility of obtaining precise relative orbits without degradation in the vicinity of maneuvers as well as improved maneuver estimates that can be used for better maneuver planning in flight dynamics operations.

Migration patterns of the Osprey Pandion haliaetus on the Eastern ...

African Journals Online (AJOL)

We analysed migration strategies of the Osprey Pandion haliaetus on the poorly studied Eastern European– East African flyway. Four adult birds were equipped with GPS-based satellite-transmitters or data-loggers in their breeding sites in Estonia (north-eastern Europe) and tracked to their wintering grounds in Africa and ...

Global Ionospheric Modelling using Multi-GNSS: BeiDou, Galileo, GLONASS and GPS.

Science.gov (United States)

Ren, Xiaodong; Zhang, Xiaohong; Xie, Weiliang; Zhang, Keke; Yuan, Yongqiang; Li, Xingxing

2016-09-15

The emergence of China's Beidou, Europe's Galileo and Russia's GLONASS satellites has multiplied the number of ionospheric piercing points (IPP) offered by GPS alone. This provides great opportunities for deriving precise global ionospheric maps (GIMs) with high resolution to improve positioning accuracy and ionospheric monitoring capabilities. In this paper, the GIM is developed based on multi-GNSS (GPS, GLONASS, BeiDou and Galileo) observations in the current multi-constellation condition. The performance and contribution of multi-GNSS for ionospheric modelling are carefully analysed and evaluated. Multi-GNSS observations of over 300 stations from the Multi-GNSS Experiment (MGEX) and International GNSS Service (IGS) networks for two months are processed. The results show that the multi-GNSS GIM products are better than those of GIM products based on GPS-only. Differential code biases (DCB) are by-products of the multi-GNSS ionosphere modelling, the corresponding standard deviations (STDs) are 0.06 ns, 0.10 ns, 0.18 ns and 0.15 ns for GPS, GLONASS, BeiDou and Galileo, respectively in satellite, and the STDs for the receiver are approximately 0.2~0.4 ns. The single-frequency precise point positioning (SF-PPP) results indicate that the ionospheric modelling accuracy of the proposed method based on multi-GNSS observations is better than that of the current dual-system GIM in specific areas.

Exploring the Limits of High Altitude GPS for Future Lunar Missions

Science.gov (United States)

Ashman, Benjamin W.; Parker, Joel J. K.; Bauer, Frank H.; Esswein, Michael

2018-01-01

An increasing number of spacecraft are relying on the Global Positioning System (GPS) for navigation at altitudes near or above the GPS constellation itself - the region known as the Space Service Volume (SSV). While the formal definition of the SSV ends at geostationary altitude, the practical limit of high-altitude space usage is not known, and recent missions have demonstrated that signal availability is sufficient for operational navigation at altitudes halfway to the moon. This paper presents simulation results based on a high-fidelity model of the GPS constellation, calibrated and validated through comparisons of simulated GPS signal availability and strength with flight data from recent high-altitude missions including the Geostationary Operational Environmental Satellite 16 (GOES-16) and the Magnetospheric Multiscale (MMS) mission. This improved model is applied to the transfer to a lunar near-rectilinear halo orbit (NRHO) of the class being considered for the international Deep Space Gateway concept. The number of GPS signals visible and their received signal strengths are presented as a function of receiver altitude in order to explore the practical upper limit of high-altitude space usage of GPS.

A New Algorithm for ABS/GPS Integration Based on Fuzzy-Logic in Vehicle Navigation System

Directory of Open Access Journals (Sweden)

Ali Amin Zadeh

2011-10-01

Full Text Available GPS based vehicle navigation systems have difficulties in tracking vehicles in urban canyons due to poor satellite availability. ABS (Antilock Brake System Navigation System consists of self-contained optical encoders mounted on vehicle wheels that can continuously provide accurate short-term positioning information. In this paper, a new concept regarding GPS/ABS integration, based on Fuzzy Logic is presented. The proposed algorithm is used to identify GPS position accuracy based on environment and vehicle dynamic knowledge. The GPS is used as reference during the time it is in a good condition and replaced by ABS positioning system when GPS information is unreliable. We compare our proposed algorithm with other common algorithm in real environment. Our results show that the proposed algorithm can significantly improve the stability and reliability of ABS/GPS navigation system.

Forecasting Space Weather-Induced GPS Performance Degradation Using Random Forest

Science.gov (United States)

Filjar, R.; Filic, M.; Milinkovic, F.

2017-12-01

Space weather and ionospheric dynamics have a profound effect on positioning performance of the Global Satellite Navigation System (GNSS). However, the quantification of that effect is still the subject of scientific activities around the world. In the latest contribution to the understanding of the space weather and ionospheric effects on satellite-based positioning performance, we conducted a study of several candidates for forecasting method for space weather-induced GPS positioning performance deterioration. First, a 5-days set of experimentally collected data was established, encompassing the space weather and ionospheric activity indices (including: the readings of the Sudden Ionospheric Disturbance (SID) monitors, components of geomagnetic field strength, global Kp index, Dst index, GPS-derived Total Electron Content (TEC) samples, standard deviation of TEC samples, and sunspot number) and observations of GPS positioning error components (northing, easting, and height positioning error) derived from the Adriatic Sea IGS reference stations' RINEX raw pseudorange files in quiet space weather periods. This data set was split into the training and test sub-sets. Then, a selected set of supervised machine learning methods based on Random Forest was applied to the experimentally collected data set in order to establish the appropriate regional (the Adriatic Sea) forecasting models for space weather-induced GPS positioning performance deterioration. The forecasting models were developed in the R/rattle statistical programming environment. The forecasting quality of the regional forecasting models developed was assessed, and the conclusions drawn on the advantages and shortcomings of the regional forecasting models for space weather-caused GNSS positioning performance deterioration.

IMPLEMENTATION OF AERONAUTICAL LOCAL SATELLITE AUGMENTATION SYSTEM

Directory of Open Access Journals (Sweden)

Stojce Ilcev

2011-03-01

Full Text Available Abstract. This paper introduces development and implementation of new Local Satellite AugmentationSystem as an integration component of the Regional Satellite Augmentation System (RSAS employingcurrent and new Satellite Communications, Navigation and Surveillance (CNS for improvement of the AirTraffic Control (ATC and Air Traffic Management (ATM and for enhancement safety systems includingtransport security and control of flights in all stages, airport approaching, landing, departures and allmovements over airport surface areas. The current first generation of the Global Navigation Satellite SystemGNSS-1 applications are represented by fundamental military solutions for Position, Velocity and Time ofthe satellite navigation and determination systems such as the US GPS and Russian GLONASS (Former-USSR requirements, respectively. The establishment of Aeronautical CNS is also discussed as a part ofGlobal Satellite Augmentation Systems of GPS and GLONASS systems integrated with existing and futureRSAS and LSAS in airports areas. Specific influence and factors related to the Comparison of the Currentand New Aeronautical CNS System including the Integration of RSAS and GNSS solutions are discussedand packet of facts is determined to maximize the new satellite Automatic Dependent Surveillance System(ADSS and Special Effects of the RSAS Networks. The possible future integration of RSAS and GNSS andthe common proposal of the satellite Surface Movement Guidance and Control are presented in thechangeless ways as of importance for future enfacements of ATC and ATM for any hypothetical airportinfrastructure.Keywords: ADSS, ATC, ATM, CNS, GSAS, LRAS, RSAS, SMGC, Special Effects of RSAS.

Lightweight GPS-tags, one giant leap for wildlife tracking? An assessment approach.

Directory of Open Access Journals (Sweden)

Mariano R Recio

Full Text Available Recent technological improvements have made possible the development of lightweight GPS-tagging devices suitable to track medium-to-small sized animals. However, current inferences concerning GPS performance are based on heavier designs, suitable only for large mammals. Lightweight GPS-units are deployed close to the ground, on species selecting micro-topographical features and with different behavioural patterns in comparison to larger mammal species. We assessed the effects of vegetation, topography, motion, and behaviour on the fix success rate for lightweight GPS-collar across a range of natural environments, and at the scale of perception of feral cats (Felis catus. Units deployed at 20 cm above the ground in sites of varied vegetation and topography showed that trees (native forest and shrub cover had the largest influence on fix success rate (89% on average; whereas tree cover, sky availability, number of satellites and horizontal dilution of position (HDOP were the main variables affecting location error (±39.5 m and ±27.6 m before and after filtering outlier fixes. Tests on HDOP or number of satellites-based screening methods to remove inaccurate locations achieved only a small reduction of error and discarded many accurate locations. Mobility tests were used to simulate cats' motion, revealing a slightly lower performance as compared to the fixed sites. GPS-collars deployed on 43 cats showed no difference in fix success rate by sex or season. Overall, fix success rate and location error values were within the range of previous tests carried out with collars designed for larger species. Lightweight GPS-tags are a suitable method to track medium to small size species, hence increasing the range of opportunities for spatial ecology research. However, the effects of vegetation, topography and behaviour on location error and fix success rate need to be evaluated prior to deployment, for the particular study species and their habitats.

Nonbreeding home‐range size and survival of lesser prairie‐chickens

Science.gov (United States)

Robinson, Samantha G.; Haukos, David A.; Plumb, Reid T.; Lautenbach, Joseph M.; Sullins, Daniel S.; Kraft, John D.; Lautenbach, Jonathan D.; Hagen, Christian A.; Pitman, James C.

2018-01-01

The lesser prairie‐chicken (Tympanuchus pallidicinctus), a species of conservation concern with uncertain regulatory status, has experienced population declines over the past century. Most research on lesser prairie‐chickens has focused on the breeding season, with little research conducted during the nonbreeding season, a period that exerts a strong influence on demography in other upland game birds. We trapped lesser prairie‐chickens on leks and marked them with either global positioning system (GPS) satellite or very high frequency (VHF) transmitters to estimate survival and home‐range size during the nonbreeding season. We monitored 119 marked lesser prairie‐chickens in 3 study areas in Kansas, USA, from 16 September to 14 March in 2013, 2014, and 2015. We estimated home‐range size using Brownian Bridge movement models (GPS transmitters) and fixed kernel density estimators (VHF transmitters), and female survival using Kaplan–Meier known‐fate models. Average home‐range size did not differ between sexes. Estimated home‐range size was 3 times greater for individuals fitted with GPS satellite transmitters ( = 997 ha) than those with VHF transmitters ( = 286 ha), likely a result of the temporal resolution of the different transmitters. Home‐range size of GPS‐marked birds increased 2.8 times relative to the breeding season and varied by study area and year. Home‐range size was smaller in the 2013–2014 nonbreeding season ( = 495 ha) than the following 2 nonbreeding seasons ( = 1,290 ha and  = 1,158 ha), corresponding with drought conditions of 2013, which were alleviated in following years. Female survival () was high relative to breeding season estimates, and did not differ by study area or year ( = 0.73 ± 0.04 [SE]). Future management could remain focused on the breeding season because nonbreeding survival was 39–44% greater than the previous breeding season; however, considerations of total space

Fuzzy Logic Controller for Small Satellites Navigation

National Research Council Canada - National Science Library

Della Pietra, G; Falzini, S; Colzi, E; Crisconio, M

2005-01-01

.... The navigator aims at operating satellites in orbit with a minimum ground support and very good performances, by the adoption of innovative technologies, such as attitude observation GPS, attitude...

Individual Global Navigation Satellite Systems in the Space Service Volume

Science.gov (United States)

Force, Dale A.

2015-01-01

Besides providing position, navigation, and timing (PNT) to terrestrial users, GPS is currently used to provide for precision orbit determination, precise time synchronization, real-time spacecraft navigation, and three-axis control of Earth orbiting satellites. With additional Global Navigation Satellite Systems (GNSS) coming into service (GLONASS, Beidou, and Galileo), it will be possible to provide these services by using other GNSS constellations. The paper, "GPS in the Space Service Volume," presented at the ION GNSS 19th International Technical Meeting in 2006 (Ref. 1), defined the Space Service Volume, and analyzed the performance of GPS out to 70,000 km. This paper will report a similar analysis of the performance of each of the additional GNSS and compare them with GPS alone. The Space Service Volume, defined as the volume between 3,000 km altitude and geosynchronous altitude, as compared with the Terrestrial Service Volume between the surface and 3,000 km. In the Terrestrial Service Volume, GNSS performance will be similar to performance on the Earth's surface. The GPS system has established signal requirements for the Space Service Volume. A separate paper presented at the conference covers the use of multiple GNSS in the Space Service Volume.

Saved by Iridium? An Alternative to GPS

Science.gov (United States)

2012-05-17

know this. The enemy presents itself at any time, at any place, in many shapes and forms, often for no apparent reason. As Ecclesiastes 9:18 states...These physical architectures correspond to ground operations in scenarios ranging from complete air superiority to completely denied airspace.”86 A...not interfere with today’s GPS architectures .88 The second developed alternative from Dr. Asher’s group is the Rapidly Deployable Satellite

Attitude determination for small satellites using GPS signal-to-noise ratio

Science.gov (United States)

Peters, Daniel

An embedded system for GPS-based attitude determination (AD) using signal-to-noise (SNR) measurements was developed for CubeSat applications. The design serves as an evaluation testbed for conducting ground based experiments using various computational methods and antenna types to determine the optimum AD accuracy. Raw GPS data is also stored to non-volatile memory for downloading and post analysis. Two low-power microcontrollers are used for processing and to display information on a graphic screen for real-time performance evaluations. A new parallel inter-processor communication protocol was developed that is faster and uses less power than existing standard protocols. A shorted annular patch (SAP) antenna was fabricated for the initial ground-based AD experiments with the testbed. Static AD estimations with RMS errors in the range of 2.5° to 4.8° were achieved over a range of off-zenith attitudes.

GPS-Based Highway Performance Monitoring Performance Monitoring Using GPS: Characterization of Travel Speeds on any Roadway Segment

OpenAIRE

Kornhauser, Alain L.

2012-01-01

Presented is a characterization of travel speed on any roadway segment based on probe vehicle position data. Most of the characterization is based position data obtained from GPS receivers because of their high precision and their increasing availability. Comparison is also made to Qualcomm’s Automatic Satellite Position Reporting (QASPR) system because of its long history (10+ years) of extensive use by the long-haul trucking industry. Described is the use of these data in conjunction with d...

Comparing Global Positioning System (GPS) and Global Navigation Satellite System (GNSS) Measures of Team Sport Movements.

Science.gov (United States)

Jackson, Benjamin M; Polglaze, Ted; Dawson, Brian; King, Trish; Peeling, Peter

2018-02-21

To compare data from conventional GPS and new GNSS-enabled tracking devices, and to examine the inter-unit reliability of GNSS devices. Inter-device differences between 10 Hz GPS and GNSS devices were examined during laps (n=40) of a simulated game circuit (SGC) and during elite hockey matches (n=21); GNSS inter-unit reliability was also examined during the SGC laps. Differences in distance values and measures in three velocity categories (low 5 m.s -1 ) and acceleration/deceleration counts (>1.46 m.s -2 and GPS devices in all conditions. These findings suggest that GNSS devices may be more sensitive than GPS in quantifying the physical demands of team sport movements, but further study into the accuracy of GNSS devices is required.

Application and Limitations of GPS Radio Occultation (GPS-RO) Data for Atmospheric Boundary Layer Height Detection over the Arctic.

Science.gov (United States)

Ganeshan, M.; Wu, D. L.

2014-12-01

Due to recent changes in the Arctic environment, it is important to monitor the atmospheric boundary layer (ABL) properties over the Arctic Ocean, especially to explore the variability in ABL clouds (such as sensitivity and feedback to sea ice loss). For example, radiosonde and satellite observations of the Arctic ABL height (and low-cloud cover) have recently suggested a positive response to sea ice loss during October that may not occur during the melt season (June-September). Owing to its high vertical and spatiotemporal resolution, an independent ABL height detection algorithm using GPS Radio Occultation (GPS-RO) refractivity in the Arctic is explored. Similar GPS-RO algorithms developed previously typically define the level of the most negative moisture gradient as the ABL height. This definition is favorable for subtropical oceans where a stratocumulus-topped ABL is often capped by a layer of sharp moisture lapse rate (coincident with the temperature inversion). The Arctic Ocean is also characterized by stratocumulus cloud cover, however, the specific humidity does not frequently decrease in the ABL capping inversion. The use of GPS-RO refractivity for ABL height retrieval therefore becomes more complex. During winter months (December-February), when the total precipitable water in the troposphere is a minimum, a fairly straightforward algorithm for ABL height retrieval is developed. The applicability and limitations of this method for other seasons (Spring, Summer, Fall) is determined. The seasonal, interannual and spatial variability in the GPS-derived ABL height over the Arctic Ocean, as well as its relation to the underlying surface (ice vs. water), is investigated. The GPS-RO profiles are also explored for the evidence of low-level moisture transport in the cold Arctic environment.

Accuracy assessment of high-rate GPS measurements for seismology

Science.gov (United States)

Elosegui, P.; Davis, J. L.; Ekström, G.

2007-12-01

Analysis of GPS measurements with a controlled laboratory system, built to simulate the ground motions caused by tectonic earthquakes and other transient geophysical signals such as glacial earthquakes, enables us to assess the technique of high-rate GPS. The root-mean-square (rms) position error of this system when undergoing realistic simulated seismic motions is 0.05~mm, with maximum position errors of 0.1~mm, thus providing "ground truth" GPS displacements. We have acquired an extensive set of high-rate GPS measurements while inducing seismic motions on a GPS antenna mounted on this system with a temporal spectrum similar to real seismic events. We found that, for a particular 15-min-long test event, the rms error of the 1-Hz GPS position estimates was 2.5~mm, with maximum position errors of 10~mm, and the error spectrum of the GPS estimates was approximately flicker noise. These results may however represent a best-case scenario since they were obtained over a short (~10~m) baseline, thereby greatly mitigating baseline-dependent errors, and when the number and distribution of satellites on the sky was good. For example, we have determined that the rms error can increase by a factor of 2--3 as the GPS constellation changes throughout the day, with an average value of 3.5~mm for eight identical, hourly-spaced, consecutive test events. The rms error also increases with increasing baseline, as one would expect, with an average rms error for a ~1400~km baseline of 9~mm. We will present an assessment of the accuracy of high-rate GPS based on these measurements, discuss the implications of this study for seismology, and describe new applications in glaciology.

Chang?E-5T Orbit Determination Using Onboard GPS Observations

OpenAIRE

Su, Xing; Geng, Tao; Li, Wenwen; Zhao, Qile; Xie, Xin

2017-01-01

In recent years, Global Navigation Satellite System (GNSS) has played an important role in Space Service Volume, the region enclosing the altitudes above 3000 km up to 36,000 km. As an in-flight test for the feasibility as well as for the performance of GNSS-based satellite orbit determination (OD), the Chinese experimental lunar mission Chang?E-5T had been equipped with an onboard high-sensitivity GNSS receiver with GPS and GLONASS tracking capability. In this contribution, the 2-h onboard G...

Benefits of Combined GPS/GLONASS with Low-Cost MEMS IMUs for Vehicular Urban Navigation

Directory of Open Access Journals (Sweden)

Giovanni Pugliano

2012-04-01

Full Text Available The integration of Global Navigation Satellite Systems (GNSS with Inertial Navigation Systems (INS has been very actively researched for many years due to the complementary nature of the two systems. In particular, during the last few years the integration with micro-electromechanical system (MEMS inertial measurement units (IMUs has been investigated. In fact, recent advances in MEMS technology have made possible the development of a new generation of low cost inertial sensors characterized by small size and light weight, which represents an attractive option for mass-market applications such as vehicular and pedestrian navigation. However, whereas there has been much interest in the integration of GPS with a MEMS-based INS, few research studies have been conducted on expanding this application to the revitalized GLONASS system. This paper looks at the benefits of adding GLONASS to existing GPS/INS(MEMS systems using loose and tight integration strategies. The relative benefits of various constraints are also assessed. Results show that when satellite visibility is poor (approximately 50% solution availability the benefits of GLONASS are only seen with tight integration algorithms. For more benign environments, a loosely coupled GPS/GLONASS/INS system offers performance comparable to that of a tightly coupled GPS/INS system, but with reduced complexity and development time.

Benefits of combined GPS/GLONASS with low-cost MEMS IMUs for vehicular urban navigation.

Science.gov (United States)

Angrisano, Antonio; Petovello, Mark; Pugliano, Giovanni

2012-01-01

The integration of Global Navigation Satellite Systems (GNSS) with Inertial Navigation Systems (INS) has been very actively researched for many years due to the complementary nature of the two systems. In particular, during the last few years the integration with micro-electromechanical system (MEMS) inertial measurement units (IMUs) has been investigated. In fact, recent advances in MEMS technology have made possible the development of a new generation of low cost inertial sensors characterized by small size and light weight, which represents an attractive option for mass-market applications such as vehicular and pedestrian navigation. However, whereas there has been much interest in the integration of GPS with a MEMS-based INS, few research studies have been conducted on expanding this application to the revitalized GLONASS system. This paper looks at the benefits of adding GLONASS to existing GPS/INS(MEMS) systems using loose and tight integration strategies. The relative benefits of various constraints are also assessed. Results show that when satellite visibility is poor (approximately 50% solution availability) the benefits of GLONASS are only seen with tight integration algorithms. For more benign environments, a loosely coupled GPS/GLONASS/INS system offers performance comparable to that of a tightly coupled GPS/INS system, but with reduced complexity and development time.

A method of estimating GPS instrumental biases with a convolution algorithm

Science.gov (United States)

Li, Qi; Ma, Guanyi; Lu, Weijun; Wan, Qingtao; Fan, Jiangtao; Wang, Xiaolan; Li, Jinghua; Li, Changhua

2018-03-01

This paper presents a method of deriving the instrumental differential code biases (DCBs) of GPS satellites and dual frequency receivers. Considering that the total electron content (TEC) varies smoothly over a small area, one ionospheric pierce point (IPP) and four more nearby IPPs were selected to build an equation with a convolution algorithm. In addition, unknown DCB parameters were arranged into a set of equations with GPS observations in a day unit by assuming that DCBs do not vary within a day. Then, the DCBs of satellites and receivers were determined by solving the equation set with the least-squares fitting technique. The performance of this method is examined by applying it to 361 days in 2014 using the observation data from 1311 GPS Earth Observation Network (GEONET) receivers. The result was crosswise-compared with the DCB estimated by the mesh method and the IONEX products from the Center for Orbit Determination in Europe (CODE). The DCB values derived by this method agree with those of the mesh method and the CODE products, with biases of 0.091 ns and 0.321 ns, respectively. The convolution method's accuracy and stability were quite good and showed improvements over the mesh method.

Current Direction and Velocity Measurements Using GPS Receivers Mounted on Floats at Tom Bevill Lock and Dam

Science.gov (United States)

2002-12-01

radio and batteries. The procedures outlined in this CHETN will concentrate on the Magellan GPS ProMARK X-CP receiver as it was used to collect...The Magellan GPS ProMARK X-CP is a small robust light receiver that can log 9 hr of both pseudorange and carrier phase satellite data for post...post- processing software, pseudorange GPS data recorded by the ProMARK X-CP can be post-processed differential to achieve 1-3 m (3.3-9.8 ft) horizontal

Navigation GPS/GLONASS in the Arctic and aurora

Directory of Open Access Journals (Sweden)

Chernouss S. A.

2016-12-01

Full Text Available The correspondence of the time-spatial distribution of the radiances of the aurora oval and time-spatial changes in the parameters of the navigation satellites' signal has been shown. For this aim the experimental data on the regional and local heterogeneities of the Total Electron Content (or TEC and the data on the signal delays in the polar ionosphere have been analyzed. Using the data concerning aurora as the indicator of disturbances in the work of the GPS/GLONASS systems can give the opportunity to increase considerably the accuracy of positioning in the Arctic with the help of satellite navigation systems (SNS.

Transmitter Spatial Diversity for FSO Uplink in Presence of Atmospheric Turbulence and Weather Conditions for Different IM Schemes

Science.gov (United States)

Viswanath, Anjitha; Kumar Jain, Virander; Kar, Subrat

2017-12-01

We investigate the error performance of an earth-to-satellite free space optical uplink using transmitter spatial diversity in presence of turbulence and weather conditions, using gamma-gamma distribution and Beer-Lambert law, respectively, for on-off keying (OOK), M-ary pulse position modulation (M-PPM) and M-ary differential PPM (M-DPPM) schemes. Weather conditions such as moderate, light and thin fog cause additional degradation, while dense or thick fog and clouds may lead to link failure. The bit error rate reduces with increase in the number of transmitters for all the schemes. However, beyond a certain number of transmitters, the reduction becomes marginal. Diversity gain remains almost constant for various weather conditions but increases with increase in ground-level turbulence or zenith angle. Further, the number of transmitters required to improve the performance to a desired level is less for M-PPM scheme than M-DPPM and OOK schemes.

Communication plan of GPS monitoring system based on the Internet

Science.gov (United States)

Xing, Xiangpeng; Liu, Zhenan; Bao, Yuanlu

2005-11-01

In GPS monitoring system, wireless communications network is necessary to keep base station in contact with mobile stations. Public communications network and personal communications network can't work well all the time. In this article, an economical communications network that can be competent for communication of GPS monitoring system is introduced. Personal communications network is used in this GPS monitoring system. In order to enlarge the coverage area and to expand the capacity of the personal communications network, the concept of cellular radio system is introduced. Because only the non-adjacent cells can use the same frequency channel, handoff of mobile station is extremely important when it goes in another cell. The mobile station of the system will know its own longitude and latitude by receiving data from GPS satellites all the time, so it can change its working frequency channel according to its position. Internet, instead of personal communication cable, is used to connect the base stations. So the communications network has the advantage of public communications network and personal one.

GNSS satellite transmit power and its impact on orbit determination

Science.gov (United States)

Steigenberger, Peter; Thoelert, Steffen; Montenbruck, Oliver

2018-06-01

Antenna thrust is a small acceleration acting on Global Navigation Satellite System satellites caused by the transmission of radio navigation signals. Knowledge about the transmit power and the mass of the satellites is required for the computation of this effect. The actual transmit power can be obtained from measurements with a high-gain antenna and knowledge about the properties of the transmit and receive antennas as well as losses along the propagation path. Transmit power measurements for different types of GPS, GLONASS, Galileo, and BeiDou-2 satellites were taken with a 30-m dish antenna of the German Aerospace Center (DLR) located at its ground station in Weilheim. For GPS, total L-band transmit power levels of 50-240 W were obtained, 20-135 W for GLONASS, 95-265 W for Galileo, and 130-185 W for BeiDou-2. The transmit power differs usually only slightly for individual spacecraft within one satellite block. An exception are the GLONASS-M satellites where six subgroups with different transmit power levels could be identified. Considering the antenna thrust in precise orbit determination of GNSS satellites decreases the orbital radius by 1-27 mm depending on the transmit power, the satellite mass, and the orbital period.

Application of GPS in a high precision engineering survey network

International Nuclear Information System (INIS)

Ruland, R.; Leick, A.

1985-04-01

A GPS satellite survey was carried out with the Macrometer to support construction at the Stanford Linear Accelerator Center (SLAC). The network consists of 16 stations of which 9 stations were part of the Macrometer network. The horizontal and vertical accuracy of the GPS survey is estimated to be 1 to 2 mm and 2 to 3 mm respectively. The horizontal accuracy of the terrestrial survey, consisting of angles and distances, equals that of the GPS survey only in the ''loop'' portion of the network. All stations are part of a precise level network. The ellipsoidal heights obtained from the GPS survey and the orthometric heights of the level network are used to compute geoid undulations. A geoid profile along the linac was computed by the National Geodetic Survey in 1963. This profile agreed with the observed geoid within the standard deviation of the GPS survey. Angles and distances were adjusted together (TERRA), and all terrestrial observations were combined with the GPS vector observations in a combination adjustment (COMB). A comparison of COMB and TERRA revealed systematic errors in the terrestrial solution. A scale factor of 1.5 ppM +- .8 ppM was estimated. This value is of the same magnitude as the over-all horizontal accuracy of both networks. 10 refs., 3 figs., 5 tabs

Multi-GNSS phase delay estimation and PPP ambiguity resolution: GPS, BDS, GLONASS, Galileo

Science.gov (United States)

Li, Xingxing; Li, Xin; Yuan, Yongqiang; Zhang, Keke; Zhang, Xiaohong; Wickert, Jens

2018-06-01

This paper focuses on the precise point positioning (PPP) ambiguity resolution (AR) using the observations acquired from four systems: GPS, BDS, GLONASS, and Galileo (GCRE). A GCRE four-system uncalibrated phase delay (UPD) estimation model and multi-GNSS undifferenced PPP AR method were developed in order to utilize the observations from all systems. For UPD estimation, the GCRE-combined PPP solutions of the globally distributed MGEX and IGS stations are performed to obtain four-system float ambiguities and then UPDs of GCRE satellites can be precisely estimated from these ambiguities. The quality of UPD products in terms of temporal stability and residual distributions is investigated for GPS, BDS, GLONASS, and Galileo satellites, respectively. The BDS satellite-induced code biases were corrected for GEO, IGSO, and MEO satellites before the UPD estimation. The UPD results of global and regional networks were also evaluated for Galileo and BDS, respectively. As a result of the frequency-division multiple-access strategy of GLONASS, the UPD estimation was performed using a network of homogeneous receivers including three commonly used GNSS receivers (TRIMBLE NETR9, JAVAD TRE_G3TH DELTA, and LEICA). Data recorded from 140 MGEX and IGS stations for a 30-day period in January in 2017 were used to validate the proposed GCRE UPD estimation and multi-GNSS dual-frequency PPP AR. Our results show that GCRE four-system PPP AR enables the fastest time to first fix (TTFF) solutions and the highest accuracy for all three coordinate components compared to the single and dual system. An average TTFF of 9.21 min with 7{°} cutoff elevation angle can be achieved for GCRE PPP AR, which is much shorter than that of GPS (18.07 min), GR (12.10 min), GE (15.36 min) and GC (13.21 min). With observations length of 10 min, the positioning accuracy of the GCRE fixed solution is 1.84, 1.11, and 1.53 cm, while the GPS-only result is 2.25, 1.29, and 9.73 cm for the east, north, and vertical

47 CFR 74.461 - Transmitter power.

Science.gov (United States)

2010-10-01

... 47 Telecommunication 4 2010-10-01 2010-10-01 false Transmitter power. 74.461 Section 74.461....461 Transmitter power. (a) Transmitter power is the power at the transmitter output terminals and.... For the purpose of this Subpart, the transmitter power is the carrier power. (b) The authorized...

Ionospheric Tomography from a Reference GPS/MET Experiment Through the IRI Model

Directory of Open Access Journals (Sweden)

Lung-Chih Tsai

2006-01-01

Full Text Available In earlier studies, we implemented the Multiplicative Algebraic Reconstruction Technique (MART to reconstruct two-dimensional ionospheric structures from measured TECs through the receptions of the GPS-to-LEO signals and/or the NNSS-to-ground beacon signals. To examine the accuracy of the reconstructed image we need ground-based validation systems which are difficult to obtain. However, such comparative investigation is needed if one aims to improve tomography inverse techniques and algorithms. In this study, we propose a simulation scheme to carry out this task. We first simulate the GPS-to-LEO TEC measurements through the IRI model by integrating electron densities along the ¡§straight¡¨ ray occultation paths between the GPS and LEO satellite obtained from the real GPS/MET experiment. Contiguous tomographic images are then derived by the MART algorithm within the ¡§reference¡¨ GPS/MET experiment. They are verified by comparison with the ¡§true¡¨ IRI-modelled ionosphere. We show that simulation/reference results can be used to find the optimal reconstruction strategy in space-based ionospheric tomography.

Continental-scale water fluxes from continuous GPS observations of Earth surface loading

Science.gov (United States)

Borsa, A. A.; Agnew, D. C.; Cayan, D. R.

2015-12-01

After more than a decade of observing annual oscillations of Earth's surface from seasonal snow and water loading, continuous GPS is now being used to model time-varying terrestrial water fluxes on the local and regional scale. Although the largest signal is typically due to the seasonal hydrological cycle, GPS can also measure subtle surface deformation caused by sustained wet and dry periods, and to estimate the spatial distribution of the underlying terrestrial water storage changes. The next frontier is expanding this analysis to the continental scale and paving the way for incorporating GPS models into the National Climate Assessment and into the observational infrastructure for national water resource management. This will require reconciling GPS observations with predictions from hydrological models and with remote sensing observations from a suite of satellite instruments (e.g. GRACE, SMAP, SWOT). The elastic Earth response which transforms surface loads into vertical and horizontal displacements is also responsible for the contamination of loading observations by tectonic and anthropogenic transients, and we discuss these and other challenges to this new application of GPS.

75 FR 8928 - Announcement of IS-GPS-200, IS-GPS-705, IS-GPS-800 Interface Control Working Group (ICWG...

Science.gov (United States)

2010-02-26

... DEPARTMENT OF DEFENSE Department of the Air Force Announcement of IS-GPS-200, IS-GPS-705, IS-GPS... document/s IS-GPS-200E (NAVSTAR GPS Space Segment/Navigation User Interfaces), IS-GPS-705A (NAVSTAR GPS Space Segment/User Segment L5 Interfaces), and IS-GPS-800A (NAVSTAR GPS Space Segment/User Segment L1C...

Contribution of BeiDou satellite system for long baseline GNSS measurement in Indonesia

Science.gov (United States)

Gumilar, I.; Bramanto, B.; Kuntjoro, W.; Abidin, H. Z.; Trihantoro, N. F.

2018-05-01

The demand for more precise positioning method using GNSS (Global Navigation Satellite System) in Indonesia continue to rise. The accuracy of GNSS positioning depends on the length of baseline and the distribution of observed satellites. BeiDou Navigation Satellite System (BDS) is a positioning system owned by China that operating in Asia-Pacific region, including Indonesia. This research aims to find out the contribution of BDS in increasing the accuracy of long baseline static positioning in Indonesia. The contributions are assessed by comparing the accuracy of measurement using only GPS (Global Positioning System) and measurement using the combination of GPS and BDS. The data used is 5 days of GPS and BDS measurement data for baseline with 120 km in length. The software used is open-source RTKLIB and commercial software Compass Solution. This research will explain in detail the contribution of BDS to the accuracy of position in long baseline static GNSS measurement.

High-precision GPS autonomous platforms for sea ice dynamics and physical oceanography

Science.gov (United States)

Elosegui, P.; Wilkinson, J.; Olsson, M.; Rodwell, S.; James, A.; Hagan, B.; Hwang, B.; Forsberg, R.; Gerdes, R.; Johannessen, J.; Wadhams, P.; Nettles, M.; Padman, L.

2012-12-01

Project "Arctic Ocean sea ice and ocean circulation using satellite methods" (SATICE), is the first high-rate, high-precision, continuous GPS positioning experiment on sea ice in the Arctic Ocean. The SATICE systems collect continuous, dual-frequency carrier-phase GPS data while drifting on sea ice. Additional geophysical measurements also collected include ocean water pressure, ocean surface salinity, atmospheric pressure, snow-depth, air-ice-ocean temperature profiles, photographic imagery, and others, enabling sea ice drift, freeboard, weather, ice mass balance, and sea-level height determination. Relatively large volumes of data from each buoy are streamed over a satellite link to a central computer on the Internet in near real time, where they are processed to estimate the time-varying buoy positions. SATICE system obtains continuous GPS data at sub-minute intervals with a positioning precision of a few centimetres in all three dimensions. Although monitoring of sea ice motions goes back to the early days of satellite observations, these autonomous platforms bring out a level of spatio-temporal detail that has never been seen before, especially in the vertical axis. These high-resolution data allows us to address new polar science questions and challenge our present understanding of both sea ice dynamics and Arctic oceanography. We will describe the technology behind this new autonomous platform, which could also be adapted to other applications that require high resolution positioning information with sustained operations and observations in the polar marine environment, and present results pertaining to sea ice dynamics and physical oceanography.

Fiber-based laser MOPA transmitter packaging for space environment

Science.gov (United States)

Stephen, Mark; Yu, Anthony; Chen, Jeffrey; Numata, Kenji; Wu, Stewart; Gonzales, Brayler; Han, Lawrence; Fahey, Molly; Plants, Michael; Rodriguez, Michael; Allan, Graham; Abshire, James; Nicholson, Jeffrey; Hariharan, Anand; Mamakos, William; Bean, Brian

2018-02-01

NASA's Goddard Space Flight Center has been developing lidar to remotely measure CO2 and CH4 in the Earth's atmosphere. The ultimate goal is to make space-based satellite measurements with global coverage. We are working on maturing the technology readiness of a fiber-based, 1.57-micron wavelength laser transmitter designed for use in atmospheric CO2 remote-sensing. To this end, we are building a ruggedized prototype to demonstrate the required power and performance and survive the required environment. We are building a fiber-based master oscillator power amplifier (MOPA) laser transmitter architecture. The laser is a wavelength-locked, single frequency, externally modulated DBR operating at 1.57-micron followed by erbium-doped fiber amplifiers. The last amplifier stage is a polarization-maintaining, very-large-mode-area fiber with 1000 μm2 effective area pumped by a Raman fiber laser. The optical output is single-frequency, one microsecond pulses with >450 μJ pulse energy, 7.5 KHz repetition rate, single spatial mode, and < 20 dB polarization extinction.

Space industrialization - Education. [via communication satellites

Science.gov (United States)

Joels, K. M.

1978-01-01

The components of an educational system based on, and perhaps enhanced by, space industrialization communications technology are considered. Satellite technology has introduced a synoptic distribution system for various transmittable educational media. The cost of communications satellite distribution for educational programming has been high. It has, therefore, been proposed to utilize Space Shuttle related technology and Large Space Structures (LSS) to construct a system with a quantum advancement in communication capability and a quantum reduction in user cost. LSS for communications purposes have three basic advantages for both developed and emerging nations, including the ability to distribute signals over wide geographic areas, the reduced cost of satellite communications systems versus installation of land based systems, and the ability of a communication satellite system to create instant educational networks.

Hacking GPS

CERN Document Server

Kingsley-Hughes, Kathie

2005-01-01

* This is the "user manual" that didn't come with any of the 30 million GPS receivers currently in use, showing readers how to modify, tweak, and hack their GPS to take it to new levels!* Crazy-cool modifications include exploiting secret keycodes, revealing hidden features, building power cords and cables, hacking the battery and antenna, protecting a GPS from impact and falls, making a screen protector, and solar-powering a GPS* Potential power users will take the function and performance of their GPS to a whole new level by hacking into the firmware and hacking into a PC connection with a GPS* Fear not! Any potentially dangerous mod (to the device) is clearly labeled, with precautions listed that should be taken* Game time! Readers can check out GPS games, check into hacking geocaching, and even use a GPS as a metal detector

Statistical correlation of spectral broadening in VLF transmitter signal and low-frequency ionospheric turbulence from observation on DEMETER satellite

Directory of Open Access Journals (Sweden)

A. Rozhnoi

2008-10-01

Full Text Available In our earlier papers we have found the effect of VLF transmitter signal depression over epicenters of the large earthquakes from observation on the French DEMETER satellite that can be considered as new method of global diagnostics of seismic influence on the ionosphere. At present paper we investigate a possibility VLF signal-ionospheric turbulence interaction using additional characteristic of VLF signal-spectrum broadening. This characteristic is important for estimation of the interaction type: linear or nonlinear scattering. Our main results are the following:
– There are two zones of increased spectrum broadening, which are centered near magnetic latitudes Φ=±10° and Φ=±40°. Basing on the previous case study research and ground ionosonde registrations, probably it is evidence of nonlinear (active scattering of VLF signal on the ionospheric turbulence. However occurrence rate of spectrum broadening in the middle-latitude area is higher than in the near-equatorial zone (~15–20% in comparison with ~100% in former area that is probably coincides with the rate of ionospheric turbulence.
– From two years statistics of observation in the selected 3 low-latitude regions and 1 middle-latitude region inside reception area of VLF signal from NWC transmitter we find a correlation of spectrum broadening neither with ion-cyclotron noise (f=150–500 Hz, which possibly means poor representation of the turbulence by the noise due to its mixture with natural ELF emission (which correlates with whistler, nor with magnetic storm activity.
– We find rather evident correlation of ion-cyclotron frequency noise, VLF signal depression and weak correlation of spectrum broadening with seismicity in the middle-latitude region over Japan. But in the low-latitude regions we do not find such a correlation. Statistical decrease of VLF signal supports our previous case study results. However rather weak spectrum broadening

Plan of Time Management of Satellite Positioning System using Quasi-zenith Satellite

Science.gov (United States)

Takahashi, Yasuhiro; Fujieda, Miho; Amagai, Jun; Yokota, Shoichiro; Kimura, Kazuhiro; Ito, Hiroyuki; Hama, Shin'ichi; Morikawa, Takao; Kawano, Isao; Kogure, Satoshi

The Quasi-Zenith satellites System (QZSS) is developed as an integrated satellite service system of communication, broadcasting and positioning for mobile users in specified regions of Japan from high elevation angle. Purposes of the satellite positioning system using Quasi-Zenith satellite (QZS) are to complement and augment the GPS. The national institutes concerned have been developing the positioning system using QZS since 2003 and will carry out experiments and researches in three years after the launch. In this system, National Institute of Information and Communications Technology (NICT) is mainly in charge of timing system for the satellite positioning system using QZS, such as onboard hydrogen maser atomic clock and precise time management system of the QZSS. We started to develop the engineering model of the time management system for the QZSS. The time management system for the QZSS will be used to compare time differences between QZS and earth station as well as to compare between three onboard atomic clocks. This paper introduces time management of satellite positioning system using the QZSS.

Real-Time Vehicle Data Logging System Using GPS And GSM

Directory of Open Access Journals (Sweden)

Win Minn Thet

2015-07-01

Full Text Available Abstract This paper proposes and implements a low cost Vehicle Data Logging System using GPS and GSM. This system allows a user to trace the present and past positions recorded in SD card. This system also reads the current position of the vehicle using GPS the data is sent via GSM service from the GSM network. The vehicles position including the driving speed the UTC time and data are stored in the SD card for live and past tracking. All of that GPS data is sent to PIC 18F4520 by the Universal Asynchronous ReceiverTransmitter UART and also store in SD card. GSM also uses UART to transmit. To know the position of the vehicle the owner sends a request through a SMS. The SMS sends to the authorized person through the GSM network. The travel history of the vehicle are stored in a file on an SD card in FAT format.This system is very useful for car tracking for adolescent driver being checked by parent speed limit exceeding leaving a specific area. V The developed system is easy to use requires no additional hardware and permits the selection of the amount of data and the time intervals between the data recordings. In addition the collected data can easily be transferred to a computer via a connected serial port.

Water vapor transmittance models for narrow bands in the 13 to 19 μm spectral region

International Nuclear Information System (INIS)

Weichel, R.L.

1983-10-01

The purpose of this report is to document the development of water vapor transmittance models for narrow bands (satellite sensor channels) in the 13 to 19 μm spectral region. The models are the result of research efforts of the author in 1971-1972 while on active duty with the US Air Force at the Air Force Global Weather Central (AFGWC). The models were developed for application in studies involving a temperature profiling sensor system carried aboard the satellites of the Defense Meteorological Satellite Program (DMSP), formerly DAPP. Recently, (Lovill et al., 1978; Luther et al., 1981) the models were implemented for studies concerned with methodologies to retrieve total atmospheric column ozone from measurements of newer DMSP Block 5D series satellite sensors with similar channels (see Nichols, 1975)

Upper Troposphere Lower Stratosphere structure during convective systems using GPS radio occultations

DEFF Research Database (Denmark)

Biondi, Riccardo

The deep convective systems play a fundamental role in atmospheric circulation and climate. Thunderstorms and meso-scale convective systems produce fast vertical transport, redistributing water vapor and trace gases and influencing the thermal structure of the upper troposphere and lower...... stratosphere (UTLS) contributing to the troposphere-stratosphere transport and affecting the Earth global circulation and the climate changes. The Global Positioning System (GPS) Radio Occultation (RO) technique enables measurement of atmospheric density structure in any meteorological condition...... to the analysis of tropical storms for the future mission ACES will also be evaluated. Using data from the past and ongoing GPS RO missions we have defined an algorithm to detect the clouds top of the convective systems and their thermal structure. Other satellite and in-situ measurements co-located with GPS ROs...

Special Features in the Structure of Resonant Perturbations of Uncontrollable Objects of Glonass and GPS Navigating Systems. Influence on the Orbital Evolution

Science.gov (United States)

Tomilova, I. V.; Bordovitsyna, T. V.

2017-08-01

Results of investigation into the resonant structure of perturbations and long-term orbital evolution of space vehicles of GLONASS and GPS global navigating satellite systems (GNSS) under assumption that all of them have lost control on 08/01/2015 are presented. It is demonstrated that the majority of the examined objects are in the range of action of the secular resonances of various types. In addition, practically all satellites of the GPS system are within the scope of the 2:1 orbital resonance with rotation of the Earth. Results of the MEGNO analysis demonstrate that the motion of all objects of the GLONASS system during the 100-year period is regular, whereas the motion of the majority of objects of the GPS system is subject to chaotization.

Impact of GPS antenna phase center and code residual variation maps on orbit and baseline determination of GRACE

Science.gov (United States)

Mao, X.; Visser, P. N. A. M.; van den IJssel, J.

2017-06-01

Precision Orbit Determination (POD) is a prerequisite for the success of many Low Earth Orbiting (LEO) satellite missions. With high-quality, dual-frequency Global Positioning System (GPS) receivers, typically precisions of the order of a few cm are possible for single-satellite POD, and of a few mm for relative POD of formation flying spacecraft with baselines up to hundreds of km. To achieve the best precision, the use of Phase Center Variation (PCV) maps is indispensable. For LEO GPS receivers, often a-priori PCV maps are obtained by a pre-launch ground campaign, which is not able to represent the real space-borne environment of satellites. Therefore, in-flight calibration of the GPS antenna is more widely conducted. This paper shows that a further improvement is possible by including the so-called Code Residual Variation (CRV) maps in absolute/undifferenced and relative/Double-differenced (DD) POD schemes. Orbit solutions are produced for the GRACE satellite formation for a four months test period (August-November, 2014), demonstrating enhanced orbit precision after first using the in-flight PCV maps and a further improvement after including the CRV maps. The application of antenna maps leads to a better consistency with independent Satellite Laser Ranging (SLR) and K-band Ranging (KBR) low-low Satellite-to-Satellite Tracking (ll-SST) observations. The inclusion of the CRV maps results also in a much better consistency between reduced-dynamic and kinematic orbit solutions for especially the cross-track direction. The improvements are largest for GRACE-B, where a cross-talk between the GPS main antenna and the occultation antenna yields higher systematic observation residuals. For high-precision relative POD which necessitates DD carrier-phase ambiguity fixing, in principle frequency-dependent PCV maps would be required. To this aim, use is made of an Extended Kalman Filter (EKF) that is capable of optimizing relative spacecraft dynamics and iteratively fixing

Comparison of observed and modeled seasonal crustal vertical displacements derived from multi-institution GPS and GRACE solutions

Science.gov (United States)

Gu, Yanchao; Fan, Dongming; You, Wei

2017-07-01

Eleven GPS crustal vertical displacement (CVD) solutions for 110 IGS08/IGS14 core stations provided by the International Global Navigation Satellite Systems Service Analysis Centers are compared with seven Gravity Recovery and Climate Experiment (GRACE)-modeled CVD solutions. The results of the internal comparison of the GPS solutions from multiple institutions imply large uncertainty in the GPS postprocessing. There is also evidence that GRACE solutions from both different institutions and different processing approaches (mascon and traditional spherical harmonic coefficients) show similar results, suggesting that GRACE can provide CVD results of good internal consistency. When the uncertainty of the GPS data is accounted for, the GRACE data can explain as much as 50% of the actual signals and more than 80% of the GPS annual signals. Our study strongly indicates that GRACE data have great potential to correct the nontidal loading in GPS time series.

47 CFR 80.959 - Radiotelephone transmitter.

Science.gov (United States)

2010-10-01

... watts into 50 ohms nominal resistance when operated with its rated supply voltage. The transmitter must... capability of the transmitter, measurements of primary supply voltage and transmitter output power must be... voltage measured at the power input terminals to the transmitter terminated in a matching artificial load...

GPS horizontal deformation model in the southern region of the Iberian Peninsula and northern Africa (SPINA)

International Nuclear Information System (INIS)

Rosado Moscoso, B.; Fernández-Ros, A.; Jiménez Jiménez, A.; Berrocoso Domínguez, M.

2017-01-01

Global Navigation Satellite System (GNSS), and in particular Global Positioning System (GPS) technology provides a powerful tool for studying geodynamic processes. As a consequence of GPS studies, it is now possible to analyze the interaction between tectonic plates in order to evaluate and establish the characteristics of their boundaries. In this study, our main interest is to focus on the time series analysis obtained from observations of GNSS-GPS satellites. Each GPS observation session provides topocentric geodetic coordinates (east, north, elevation) of the permanent stations that constitute the geodetic network established for this purpose. This paper shows a detailed topocentric coordinate time-series study for sites belonging to what we call the SPINA network, which stands for south of the Iberian Peninsula, north of Africa region. The series under study are processed by techniques of relative positioning with respect to the IGS (International GNSS Service) reference station located in Villafranca. These times series have been analyzed using filter processes, harmonic adjustments and wavelets. A surface velocity field is derived from the time series of daily solutions for each station, whose observations span 8 years or longer. This allows us to obtain a horizontal displacement model to show the regional geodynamic main characteristics. [es

Implementation and Performance of a GPS/INS Tightly Coupled Assisted PLL Architecture Using MEMS Inertial Sensors

Directory of Open Access Journals (Sweden)

Youssef Tawk

2014-02-01

Full Text Available The use of global navigation satellite system receivers for navigation still presents many challenges in urban canyon and indoor environments, where satellite availability is typically reduced and received signals are attenuated. To improve the navigation performance in such environments, several enhancement methods can be implemented. For instance, external aid provided through coupling with other sensors has proven to contribute substantially to enhancing navigation performance and robustness. Within this context, coupling a very simple GPS receiver with an Inertial Navigation System (INS based on low-cost micro-electro-mechanical systems (MEMS inertial sensors is considered in this paper. In particular, we propose a GPS/INS Tightly Coupled Assisted PLL (TCAPLL architecture, and present most of the associated challenges that need to be addressed when dealing with very-low-performance MEMS inertial sensors. In addition, we propose a data monitoring system in charge of checking the quality of the measurement flow in the architecture. The implementation of the TCAPLL is discussed in detail, and its performance under different scenarios is assessed. Finally, the architecture is evaluated through a test campaign using a vehicle that is driven in urban environments, with the purpose of highlighting the pros and cons of combining MEMS inertial sensors with GPS over GPS alone.

Implementation and Performance of a GPS/INS Tightly Coupled Assisted PLL Architecture Using MEMS Inertial Sensors

Science.gov (United States)

Tawk, Youssef; Tomé, Phillip; Botteron, Cyril; Stebler, Yannick; Farine, Pierre-André

2014-01-01

The use of global navigation satellite system receivers for navigation still presents many challenges in urban canyon and indoor environments, where satellite availability is typically reduced and received signals are attenuated. To improve the navigation performance in such environments, several enhancement methods can be implemented. For instance, external aid provided through coupling with other sensors has proven to contribute substantially to enhancing navigation performance and robustness. Within this context, coupling a very simple GPS receiver with an Inertial Navigation System (INS) based on low-cost micro-electro-mechanical systems (MEMS) inertial sensors is considered in this paper. In particular, we propose a GPS/INS Tightly Coupled Assisted PLL (TCAPLL) architecture, and present most of the associated challenges that need to be addressed when dealing with very-low-performance MEMS inertial sensors. In addition, we propose a data monitoring system in charge of checking the quality of the measurement flow in the architecture. The implementation of the TCAPLL is discussed in detail, and its performance under different scenarios is assessed. Finally, the architecture is evaluated through a test campaign using a vehicle that is driven in urban environments, with the purpose of highlighting the pros and cons of combining MEMS inertial sensors with GPS over GPS alone. PMID:24569773

GPS surveying method applied to terminal area navigation flight experiments

Energy Technology Data Exchange (ETDEWEB)

Murata, M; Shingu, H; Satsushima, K; Tsuji, T; Ishikawa, K; Miyazawa, Y; Uchida, T [National Aerospace Laboratory, Tokyo (Japan)

1993-03-01

With an objective of evaluating accuracy of new landing and navigation systems such as microwave landing guidance system and global positioning satellite (GPS) system, flight experiments are being carried out using experimental aircraft. This aircraft mounts a GPS and evaluates its accuracy by comparing the standard orbits spotted by a Kalman filter from the laser tracing data on the aircraft with the navigation results. The GPS outputs position and speed information from an earth-centered-earth-fixed system called the World Geodetic System, 1984 (WGS84). However, in order to compare the navigation results with output from a reference orbit sensor or other navigation sensor, it is necessary to structure a high-precision reference coordinates system based on the WGS84. A method that applies the GPS phase interference measurement for this problem was proposed, and used actually in analyzing a flight experiment data. As referred to a case of the method having been applied to evaluating an independent navigation accuracy, the method was verified sufficiently effective and reliable not only in navigation method analysis, but also in the aspect of navigational operations. 12 refs., 10 figs., 5 tabs.

Utilization of GPS Tropospheric Delays for Climate Research

International Nuclear Information System (INIS)

Suparta, Wayan

2017-01-01

The tropospheric delay is one of the main error sources in Global Positioning Systems (GPS) and its impact plays a crucial role in near real-time weather forecasting. Accessibility and accurate estimation of this parameter are essential for weather and climate research. Advances in GPS application has allowed the measurements of zenith tropospheric delay (ZTD) in all weather conditions and on a global scale with fine temporal and spatial resolution. In addition to the rapid advancement of GPS technology and informatics and the development of research in the field of Earth and Planetary Sciences, the GPS data has been available free of charge. Now only required sophisticated processing techniques but user friendly. On the other hand, the ZTD parameter obtained from the models or measurements needs to be converted into precipitable water vapor (PWV) to make it more useful as a component of weather forecasting and analysis atmospheric hazards such as tropical storms, flash floods, landslide, pollution, and earthquake as well as for climate change studies. This paper addresses the determination of ZTD as a signal error or delay source during the propagation from the satellite to a receiver on the ground and is a key driving force behind the atmospheric events. Some results in terms of ZTD and PWV will be highlighted in this paper. (paper)

Improve wildlife species tracking—Implementing an enhanced global positioning system data management system for California condors

Science.gov (United States)

Waltermire, Robert G.; Emmerich, Christopher U.; Mendenhall, Laura C.; Bohrer, Gil; Weinzierl, Rolf P.; McGann, Andrew J.; Lineback, Pat K.; Kern, Tim J.; Douglas, David C.

2016-05-03

U.S. Fish and Wildlife Service (USFWS) staff in the Pacific Southwest Region and at the Hopper Mountain National Wildlife Refuge Complex requested technical assistance to improve their global positioning system (GPS) data acquisition, management, and archive in support of the California Condor Recovery Program. The USFWS deployed and maintained GPS units on individual Gymnogyps californianus (California condor) in support of long-term research and daily operational monitoring and management of California condors. The U.S. Geological Survey (USGS) obtained funding through the Science Support Program to provide coordination among project participants, provide GPS Global System for Mobile Communication (GSM) transmitters for testing, and compare GSM/GPS with existing Argos satellite GPS technology. The USFWS staff worked with private companies to design, develop, and fit condors with GSM/GPS transmitters. The Movebank organization, an online database of animal tracking data, coordinated with each of these companies to automatically stream their GPS data into Movebank servers and coordinated with USFWS to improve Movebank software for managing transmitter data, including proofing/error checking of incoming GPS data. The USGS arranged to pull raw GPS data from Movebank into the USGS California Condor Management and Analysis Portal (CCMAP) (https://my.usgs.gov/ccmap) for production and dissemination of a daily map of condor movements including various automated alerts. Further, the USGS developed an automatic archiving system for pulling raw and proofed Movebank data into USGS ScienceBase to comply with the Federal Information Security Management Act of 2002. This improved data management system requires minimal manual intervention resulting in more efficient data flow from GPS data capture to archive status. As a result of the project’s success, Pinnacles National Park and the Ventana Wildlife Society California condor programs became partners and adopted the same

Precise orbit determination and point positioning using GPS, Glonass, Galileo and BeiDou

Directory of Open Access Journals (Sweden)

Tegedor J.

2014-04-01

Full Text Available State of the art Precise Point Positioning (PPP is currently based on dual-frequency processing of GPS and Glonass navigation systems. The International GNSS Service (IGS is routinely providing the most accurate orbit and clock products for these constellations, allowing point positioning at centimeter-level accuracy. At the same time, the GNSS landscape is evolving rapidly, with the deployment of new constellations, such as Galileo and BeiDou. The BeiDou constellation currently consists of 14 operational satellites, and the 4 Galileo In-Orbit Validation (IOV satellites are transmitting initial Galileo signals. This paper focuses on the integration of Galileo and BeiDou in PPP, together with GPS and Glonass. Satellite orbits and clocks for all constellations are generated using a network adjustment with observation data collected by the IGS Multi-GNSS Experiment (MGEX, as well as from Fugro proprietary reference station network. The orbit processing strategy is described, and orbit accuracy for Galileo and BeiDou is assessed via orbit overlaps, for different arc lengths. Kinematic post-processed multi-GNSS positioning results are presented. The benefits of multiconstellation PPP are discussed in terms of enhanced availability and positioning accuracy.

A Forward GPS Multipath Simulator Based on the Vegetation Radiative Transfer Equation Model.

Science.gov (United States)

Wu, Xuerui; Jin, Shuanggen; Xia, Junming

2017-06-05

Global Navigation Satellite Systems (GNSS) have been widely used in navigation, positioning and timing. Nowadays, the multipath errors may be re-utilized for the remote sensing of geophysical parameters (soil moisture, vegetation and snow depth), i.e., GPS-Multipath Reflectometry (GPS-MR). However, bistatic scattering properties and the relation between GPS observables and geophysical parameters are not clear, e.g., vegetation. In this paper, a new element on bistatic scattering properties of vegetation is incorporated into the traditional GPS-MR model. This new element is the first-order radiative transfer equation model. The new forward GPS multipath simulator is able to explicitly link the vegetation parameters with GPS multipath observables (signal-to-noise-ratio (SNR), code pseudorange and carrier phase observables). The trunk layer and its corresponding scattering mechanisms are ignored since GPS-MR is not suitable for high forest monitoring due to the coherence of direct and reflected signals. Based on this new model, the developed simulator can present how the GPS signals (L1 and L2 carrier frequencies, C/A, P(Y) and L2C modulations) are transmitted (scattered and absorbed) through vegetation medium and received by GPS receivers. Simulation results show that the wheat will decrease the amplitudes of GPS multipath observables (SNR, phase and code), if we increase the vegetation moisture contents or the scatters sizes (stem or leaf). Although the Specular-Ground component dominates the total specular scattering, vegetation covered ground soil moisture has almost no effects on the final multipath signatures. Our simulated results are consistent with previous results for environmental parameter detections by GPS-MR.

Development of position measuring technology by GPS; GPS ni yoru sokui gijutsu no kaihatsu

Energy Technology Data Exchange (ETDEWEB)

Ishizaki, T [Ministry of Transportation, Tokyo (Japan)

1994-07-25

With regard to the GPS (global positioning system) which uses the satellites launched and administered by the U.S.A. and has been utilized worldwide for ships, automobiles and geodetic surveys in recent years, Ministry of Transport started investigation and research on the application of its position measuring system from FY 1989. In this fiscal year, a study on position measuring methods and selection of the position measuring system to be developed were made, in FY 1991, the real-time functioning and track display were developed, in FY 1992, the initialization aboard the ship, the measure to prevent cycle slip, and the radio data communication technology were developed, and in FY 1993, a long term demonstration experiment presuming its practical use was conducted attaining the expected purpose. In this article, the developed real-time kinematic position measuring system is introduced. Regarding the position measuring methods by the GPS, there are the one point position measuring method and the relative position measuring method. Regarding this newly developed position measuring device, its application to work ships and structures can be considered in various ways. 4 figs.

Precise Positioning of BDS, BDS/GPS: Implications for Tsunami Early Warning in South China Sea

Directory of Open Access Journals (Sweden)

Kejie Chen

2015-11-01

Full Text Available Global Positioning System (GPS has been proved to be a powerful tool for measuring co-seismic ground displacements with an application to seismic source inversion. Whereas most of the tsunamis are triggered by large earthquakes, GPS can contribute to the tsunami early warning system (TEWS by helping to obtain tsunami source parameters in near real-time. Toward the end of 2012, the second phase of the BeiDou Navigation Satellite System (BDS constellation was accomplished, and BDS has been providing regional positioning service since then. Numerical results indicate that precision of BDS nowadays is equivalent to that of the GPS. Compared with a single Global Satellite Navigation System (GNSS, combined BDS/GPS real-time processing can improve accuracy and especially reliability of retrieved co-seismic displacements. In the present study, we investigate the potential of BDS to serve for the early warning system of tsunamis in the South China Sea region. To facilitate early warnings of tsunamis and forecasting capabilities in this region, we propose to distribute an array of BDS-stations along the Luzon Island (Philippines. By simulating an earthquake with Mw = 8 at the Manila trench as an example, we demonstrate that such an array will be able to detect earthquake parameters in real time with a high degree of accuracy and, hence, contribute to the fast and reliable tsunami early warning system in this region.

Cryospheric monitoring with new low power RTK dGPS systems

Science.gov (United States)

Martinez, K.; Hart, J. K.; Bragg, G. M.; Curry, J. S.

2017-12-01

Differential GPS is often used to measure the movement of glaciers. It requires data to be recorded at a fixed base station as well as the moving rover unit, followed by post-processing in order to compute the rover's positions. The typical dGPS units used consume considerable power and the recording times are often around one hour per reading. While this provides very precise (typically millimetre) precision it comes at a cost of power used and the data is rather large to send offsite regularly. Real-time kinematic modes of dGPS are typically used for rapid mapping and autonomous vehicles. New devices are lower cost and smaller size. They also provide a fix within a few minutes, which can be transmitted home. We describe the design, deployment and preliminary results of two tracking systems to monitor ice movement. The first used a normal GPS and Iridium satellite messaging to track the movement of a Greenland iceberg which calved from the Nattivit Apusiiat glacier (south west Greenland). This system followed the iceberg as it flowed 660 km south along the coast of Greenland. The second system was installed in Iceland to track the movement of glaciers using 2 different dGPS systems. A low power ARM Cortex M4-based controller ran Python code to schedule dGPS activity periodically and gather fixes. An Iridium short messaging unit (Rockblock) was used to transmit RTK location fixes. The aim was to experiment with the use of RTK dGPS as an alternative to recordings to measure how the glaciers responded to small scale changes in temperature and precipitation throughout the year.

Target Localization by Resolving the Time Synchronization Problem in Bistatic Radar Systems Using Space Fast-Time Adaptive Processor

Directory of Open Access Journals (Sweden)

D. Madurasinghe

2009-01-01

Full Text Available The proposed technique allows the radar receiver to accurately estimate the range of a large number of targets using a transmitter of opportunity as long as the location of the transmitter is known. The technique does not depend on the use of communication satellites or GPS systems, instead it relies on the availability of the direct transmit copy of the signal from the transmitter and the reflected paths off the various targets. An array-based space-fast time adaptive processor is implemented in order to estimate the path difference between the direct signal and the delayed signal, which bounces off the target. This procedure allows us to estimate the target distance as well as bearing.

75 FR 14658 - Invitation for Public Comment on Mitigation Options for Global Positioning System Satellite...

Science.gov (United States)

2010-03-26

... Public Comment on Mitigation Options for Global Positioning System Satellite Vehicle Number 49 AGENCY... options prior to changing the health status of Global Positioning System (GPS) satellite IIR-20M (satellite vehicle number 49--SVN 49) from unhealthy to healthy. The potential mitigations are each designed...

Assessment of NOAA NUCAPS upper air temperature profiles using COSMIC GPS radio occultation and ARM radiosondes

Science.gov (United States)

Feltz, M. L.; Borg, L.; Knuteson, R. O.; Tobin, D.; Revercomb, H.; Gambacorta, A.

2017-09-01

The U.S. National Oceanic and Atmospheric Administration (NOAA) recently began operational processing to derive vertical temperature profiles from two new sensors, Cross-Track Infrared Sounder and Advanced Technology Microwave Sounder, which were developed for the next generation of U.S. weather satellites. The NOAA-Unique Combined Atmospheric Processing System (NUCAPS) has been developed by NOAA to routinely process data from future Joint Polar Satellite System operational satellites and the preparatory Suomi-NPP satellite. This paper assesses the NUCAPS vertical temperature profile product from the upper troposphere into the middle stratosphere using radiosonde and GPS radio occultation (RO) data. Radiosonde data from the Department of Energy Atmospheric Radiation Measurement (ARM) program are=] compared to both the NUCAPS and GPS RO temperature products to evaluate bias and RMS errors. At all three fixed ARM sites for time periods investigated the NUCAPS temperature in the 100-40 hPa range is found to have an average bias to the radiosondes of less than 0.45 K and an RMS error of less than 1 K when temperature averaging kernels are applied. At a 95% confidence level, the radiosondes and RO were found to agree within 0.4 K at the North Slope of Alaska site and within 0.83 K at Southern Great Plains and Tropical Western Pacific. The GPS RO-derived dry temperatures, obtained from the University Corporation for Atmospheric Research Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission, are used as a common reference for the intercomparison of NUCAPS temperature products to similar products produced by NASA from Atmospheric Infrared Sounder (AIRS) and by European Organisation for the Exploitation of Meteorological Satellites from MetOp-B Infrared Atmospheric Sounding Interferometer (IASI). For seasonal and zonal scales, the NUCAPS agreement with AIRS and IASI is less than 0.5 K after application of averaging kernels.

Performance analysis of a GPS Interferometric attitude determination system for a gravity gradient stabilized spacecraft. M.S. Thesis

Science.gov (United States)

Stoll, John C.

1995-01-01

The performance of an unaided attitude determination system based on GPS interferometry is examined using linear covariance analysis. The modelled system includes four GPS antennae onboard a gravity gradient stabilized spacecraft, specifically the Air Force's RADCAL satellite. The principal error sources are identified and modelled. The optimal system's sensitivities to these error sources are examined through an error budget and by varying system parameters. The effects of two satellite selection algorithms, Geometric and Attitude Dilution of Precision (GDOP and ADOP, respectively) are examined. The attitude performance of two optimal-suboptimal filters is also presented. Based on this analysis, the limiting factors in attitude accuracy are the knowledge of the relative antenna locations, the electrical path lengths from the antennae to the receiver, and the multipath environment. The performance of the system is found to be fairly insensitive to torque errors, orbital inclination, and the two satellite geometry figures-of-merit tested.

Comparison of GLONASS and GPS time transfers between two west European time laboratories and VNIIFTRI

Science.gov (United States)

Daly, P.; Koshelyaevsky, N. B.; Lewandowski, Wlodzimierz; Petit, Gerard; Thomas, Claudine

1992-01-01

The University of Leeds built a Global Positioning System/Global Orbiting Navigation Satellite System (GPS/GLONASS) receiver about five years ago and since then has provided continuous information about GLONASS time and its comparison with GPS time. For the last two years, VNIIFTRI (All Union Institute for Physical, Technical and Radiotechnical Measurements) and some other Soviet time laboratories have used Soviet built GLONASS navigation receivers for time comparisons. Since June 1991, VNIIFTIR has been operating a GPS time receiver on loan from the BIPM (Bureau International des Poids et Mesures). This offered, for the first time, an opportunity for direct comparison of time transfers using GPS and GLONASS. This experiment shows that even with relatively imprecise data recording and processing, in terms of time metrology, GLONASS can provide continental time transfer at a level of several tens of nanoseconds.

Tracking wildlife by satellite: Current systems and performance

Science.gov (United States)

Harris, Richard B.; Fancy, Steven G.; Douglas, David C.; Garner, Gerald W.; Amstrup, Steven C.; McCabe, Thomas R.; Pank, Larry F.

1990-01-01

Since 1984, the U.S. Fish and Wildlife Service has used the Argos Data Collection and Location System (DCLS) and Tiros-N series satellites to monitor movements and activities of 10 species of large mammals in Alaska and the Rocky Mountain region. Reliability of the entire system was generally high. Data were received from instrumented caribou (Rangifer tarandus) during 91% of 318 possible transmitter-months. Transmitters failed prematurely on 5 of 45 caribou, 2 of 6 muskoxen (Ovibos moschatus), and 1 of 2 gray wolves (Canis lupus). Failure rates were considerably higher for polar (Ursus maritimus) and brown (U. arctos) bears than for caribou (Rangifer tarandus). Efficiency of gathering both locational and sensor data was related to both latitude and topography.Mean error of locations was estimated to be 954 m (median = 543 m) for transmitters on captive animals; 90% of locations were indices of animal activity were developed and evaluated. For several species, the long-term index was correlated with movement patterns and the short-term index was calibrated to specific activity categories (e.g., lying, feeding, walking).Data processing and sampling considerations were evaluated. Algorithms for choosing the most reliable among a series of reported locations were investigated. Applications of satellite telemetry data and problems with lack of independence among locations are discussed.

Relativistic Time Transfer for Inter-satellite Links

Energy Technology Data Exchange (ETDEWEB)

Xie, Yi, E-mail: yixie@nju.edu.cn [Department of Astronomy, School of Astronomy and Space Sciences, Nanjing University, Nanjing (China); Shanghai Key Laboratory of Space Navigation and Position Techniques, Shanghai (China); Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education, Nanjing (China)

2016-04-26

Inter-Satellite links (ISLs) will be an important technique for a global navigation satellite system (GNSS) in the future. Based on the principles of general relativity, the time transfer in an ISL is modeled and the algorithm for onboard computation is described. It is found, in general, satellites with circular orbits and identical semi-major axes can benefit inter-satellite time transfer by canceling out terms associated with the transformations between the proper times and the Geocentric Coordinate Time. For a GPS-like GNSS, the Shapiro delay is as large as 0.1 ns when the ISL passes at the limb of the Earth. However, in more realistic cases, this value will decrease to about 50 ps.

Integrated navigation of aerial robot for GPS and GPS-denied environment

International Nuclear Information System (INIS)

Suzuki, Satoshi; Min, Hongkyu; Nonami, Kenzo; Wada, Tetsuya

2016-01-01

In this study, novel robust navigation system for aerial robot in GPS and GPS- denied environments is proposed. Generally, the aerial robot uses position and velocity information from Global Positioning System (GPS) for guidance and control. However, GPS could not be used in several environments, for example, GPS has huge error near buildings and trees, indoor, and so on. In such GPS-denied environment, Laser Detection and Ranging (LIDER) sensor based navigation system have generally been used. However, LIDER sensor also has an weakness, and it could not be used in the open outdoor environment where GPS could be used. Therefore, it is desired to develop the integrated navigation system which is seamlessly applied to GPS and GPS-denied environments. In this paper, the integrated navigation system for aerial robot using GPS and LIDER is developed. The navigation system is designed based on Extended Kalman Filter, and the effectiveness of the developed system is verified by numerical simulation and experiment. (paper)

Real-time clock and orbit calculation of the GPS satellite constellation based on observation data of RTIGS-station network

International Nuclear Information System (INIS)

Thaler, G.

2011-01-01

Due to the development of faster communication networks and improving computer technology beside postprocessing techniques real-time applications and services are more and more created and used in the eld of precise positioning and navigation using global navigation satellite systems (GNSS) like GPS. Data formats like RTCM (NTRIP) or RTIGS serve in this manner as basic tool to transmit real-time GNSS observation data to a eld of users. To handle this trend to real-time, the International GNSS Service (IGS) or more precisely the Real-Time Working Group (RTWG) of the IGS started to establish a global GNSS station network several years ago. These reference stations (RTIGS stations) transmit their observation data in real-time via the open internet to registerd users to support the development of potential new real-time products and services. One example for such a new real-time application based on the observations of the RTIGS network is the software RTIGU-Control developed within this PHD thesis. RTIGU-Control fulls 2 main tasks. The rst task is the monitoring (integrity) of the predicted IGS orbit and clock products (IGU products) using real-time observations from the station network. The second task deals with calculating more precise satellite and station clock corrections compared to the predicted values of the IGU solutions based on the already very precise IGU orbit solutions. In a rst step RTIGU-Control calculates based on the IGU orbit predictions together with code-smoothed station observations precise values for the satellite and station clock corrections.The code-smoothed observations are additionally corrected for several corrections eecting the GNSS observations (for example the delay of the signal propagation time due to the atmosphere, relativistic eects, etc.). The second calculation step deals with monitoring the IGU predicted orbits using the calculated clock solution in the calculation step before and again the corrected real-time observations

Advanced mobile satellite communications system using Ka and MM-wave bands in Japan's R and D satellite project

Science.gov (United States)

Isobe, Shunkichi; Ohmori, Shingo; Hamamoto, Naokazu; Yamamoto, Minoru

1991-01-01

Communications Research Laboratory (CRL) studied an advanced mobile satellite communications system using Ka and millimeter-wave bands in the R&D Satellite project. The project started in 1990 and the satellite will be launched in 1997. On-board multi-beam interconnecting is one of basic functions to realize one-hop connection among Very Small Aperture Terminals (VSATs), mobile, and hand-held terminals in future mobile satellite communications system. An Intermediate Frequency (IF) filter bank and regenerative transponder are suitable for this function. The transponder configuration of an advanced mobile communications mission of the R&D Satellite for experiment is shown. High power transmitters of Ka and millimeter-wave bands, a 3x3 IF filter band and Single Channel Per Carrier/Time Division Multiplexing (SCPC/TDM) regenerative MODEMS, which will be boarded on the R&D Satellite, are being developed for the purpose of studying the feasibility of advanced mobile communications system.

Perancangan Dan Realisasi Sistem Transmisi Data GPS Menggunakan Teknologi SMS (Short Messaging Service Sebagai Aplikasi Sistem Personal Tracking

Directory of Open Access Journals (Sweden)

DECY NATALIANA

2017-06-01

Full Text Available Abstrak Berprinsip pada pengembangan teknologi dan aplikasi dari sistem penjejakan posisi (tracking, maka dibuatlah sistem personal tracking dengan mentransmisikan data GPS (Global Positioning System dengan menggunakan teknologi SMS (Short Messaging Service pada jaringan GSM (Global System for Mobile Communications sebagai media transmisinya.  Dengan sistem GPS akan diperoleh data garis lintang, serta garis bujur dari GPS receiver.  Data tersebut akan diteruskan oleh mikrokontroler untuk dikirim ke ponsel pengamat melalui komunikasi SMS.  Hasil pengujian menunjukkan bahwa device personal tracking berhasil mengirimkan data berupa IMEI, Tanggal satelit, waktu satelit, koordinat longitude, koordinat latitude, dan jumlah satelit yang berhasil ditangkap oleh device ke ponsel pengamat.  Dari data koordinat tersebut pengamat dapat memantau posisi device personal tracking berada dengan bantuan aplikasi pendukung yaitu Google Maps. Kata kunci: GPS, Personal Tracking, SMS, Google Maps.   Abstract Base on technology and application development of tracking, personal tracking system was made by transmiting GPS (Global Positioning System data using SMS (Short Messaging Service technology with GSM (Global System for Mobile Communications network as transmitter media.  BY GPS system, we can get datas such as latitude and longitude of GPS receiver.  Those datas will be processed by microcontroller to be sent from GSM/GPRS module to user cellular phone through SMS communication.  The test result showed that the device can be sending datas such as IMEI, UTC date, UTC time, longitude coordinate, latitude coordinate, and number sattelite which detected by device to user’s phonecell.  From those coordinate, user can be monitoring the device’s position with the Google Maps application. Keywords: GPS, Personal Tracking, SMS, Google Maps.

77 FR 42419 - Airworthiness Directives; Honeywell International, Inc. Global Navigation Satellite Sensor Units

Science.gov (United States)

2012-07-19

... Airworthiness Directives; Honeywell International, Inc. Global Navigation Satellite Sensor Units AGENCY: Federal.... Model KGS200 Mercury\\2\\ wide area augmentation system (WAAS) global navigation satellite sensor units... similar Honeywell global positioning system (GPS) sensor and the same software as the Model KGS200 Mercury...

GPS Composite Clock Analysis

OpenAIRE

Wright, James R.

2008-01-01

The GPS composite clock defines GPS time, the timescale used today in GPS operations. GPS time is illuminated by examination of its role in the complete estimation and control problem relative to UTC/TAI. The phase of each GPS clock is unobservable from GPS pseudorange measurements, and the mean phase of the GPS clock ensemble (GPS time) is unobservable. A new and useful observability definition is presented, together with new observability theorems, to demonstrate explicitly that GPS time is...

Controlador para un Reloj GPS de Referencia en el Protocolo NTP

Science.gov (United States)

Hauscarriaga, F.; Bareilles, F. A.

The synchronization between computers in a local network plays a very important role on enviroments similar to IAR. Calculations for exact time are needed before, during and after an observation. For this purpose the IAR's GNU/Linux Software Development Team implemented a driver inside NTP protocol (an internet standard for time synchronization of computers) for a GPS receiver acquired a few years ago by IAR, which did not have support in such protocol. Today our Institute has a stable and reliable time base synchronized to atomic clocks on board GPS Satellites according to computers's synchronization standard, offering precise time services to all scientific community and particularly to the University of La Plata. FULL TEXT IN SPANISH

Fast-Acquisition/Weak-Signal-Tracking GPS Receiver for HEO

Science.gov (United States)

Wintemitz, Luke; Boegner, Greg; Sirotzky, Steve

2004-01-01

A report discusses the technical background and design of the Navigator Global Positioning System (GPS) receiver -- . a radiation-hardened receiver intended for use aboard spacecraft. Navigator is capable of weak signal acquisition and tracking as well as much faster acquisition of strong or weak signals with no a priori knowledge or external aiding. Weak-signal acquisition and tracking enables GPS use in high Earth orbits (HEO), and fast acquisition allows for the receiver to remain without power until needed in any orbit. Signal acquisition and signal tracking are, respectively, the processes of finding and demodulating a signal. Acquisition is the more computationally difficult process. Previous GPS receivers employ the method of sequentially searching the two-dimensional signal parameter space (code phase and Doppler). Navigator exploits properties of the Fourier transform in a massively parallel search for the GPS signal. This method results in far faster acquisition times [in the lab, 12 GPS satellites have been acquired with no a priori knowledge in a Low-Earth-Orbit (LEO) scenario in less than one second]. Modeling has shown that Navigator will be capable of acquiring signals down to 25 dB-Hz, appropriate for HEO missions. Navigator is built using the radiation-hardened ColdFire microprocessor and housing the most computationally intense functions in dedicated field-programmable gate arrays. The high performance of the algorithm and of the receiver as a whole are made possible by optimizing computational efficiency and carefully weighing tradeoffs among the sampling rate, data format, and data-path bit width.

Android App Based Vehicle Tracking Using GPS And GSM

Directory of Open Access Journals (Sweden)

Jessica Saini

2017-09-01

Full Text Available Global Positioning System GPS is used in numerous applications in todays world. A real time vehicle tracking system using the GPS technology is proposed in this paper. The project Android App based Vehicle Tracking Using GSM AND GPRS mainly focuses in tracking the location of the vehicle on which the device has been installed. It will then send the data in the form of latitude and longitude coordinates through SMS on the users mobile where the coordinates will be plotted in the Android app automatically. Initially the GPS installed in the device takes input from the satellite and stores it in the microcontrollers buffer. In order to track the vehicle the mobile user has to call on the SIM number that is registered in the GSM module of the device. Once the call is received the device authenticates the calling number. If authenticated the location of the vehicle is sent to the registered mobile number in the form of SMS. After sending the message the GSM is deactivated and the GPS is activated again. The coordinates of the location received in the SMS can be viewed on the android app. The hardware part described in the paper comprises of GPRS GSM module LCD to view the coordinates ATMega Microcontroller MAX 232 Arduino RS232 and relay.

An Analysis of Stand-alone GPS Quality and Simulated GNSS Quality for Road Pricing

DEFF Research Database (Denmark)

Zabic, Martina; Nielsen, Otto Anker

2006-01-01

Use of GPS for road pricing has often been suggested as the way of creating more efficient charging strategies than existing systems based on cordon lines or time use. In Denmark, Copenhagen participated with the AKTA project in the PRoGRESS programme, sponsored by the EU. The major part...... of the AKTA project was to equip 500 cars with GPS receivers. The paper presents the methods and results from a study of GPS quality in relation to road pricing in a dense urban area. The collected data from 500 cars over a two-year period in the Copenhagen region was analyzed in order to determine whether...... the stand alone GPS quality and reliability is adequate for implementation of an operational road pricing system in Copenhagen. The results from the analysis show that the satellite availability in Copenhagen is not sufficient to form the basis for a reliable operational road pricing system. The narrow...

Design of complete software GPS signal simulator with low complexity and precise multipath channel model

Directory of Open Access Journals (Sweden)

G. Arul Elango

2016-09-01

Full Text Available The need for GPS data simulators have become important due to the tremendous growth in the design of versatile GPS receivers. Commercial hardware and software based GPS simulators are expensive and time consuming. In this work, a low cost simple novel GPS L1 signal simulator is designed for testing and evaluating the performance of software GPS receiver in a laboratory environment. A typical real time paradigm, similar to actual satellite derived GPS signal is created on a computer generated scenario. In this paper, a GPS software simulator is proposed that may offer a lot of analysis and testing flexibility to the researchers and developers as it is totally software based primarily running on a laptop/personal computer without the requirement of any hardware. The proposed GPS simulator allows provision for re-configurability and test repeatability and is developed in VC++ platform to minimize the simulation time. It also incorporates Rayleigh multipath channel fading model under non-line of sight (NLOS conditions. In this work, to efficiently design the simulator, several Rayleigh fading models viz. Inverse Discrete Fourier Transform (IDFT, Filtering White Gaussian Noise (FWFN and modified Sum of Sinusoidal (SOS simulators are tested and compared in terms of accuracy of its first and second order statistical metrics, execution time and the later one is found to be as the best appropriate Rayleigh multipath model suitable for incorporating with GPS simulator. The fading model written in ‘MATLAB’ engine has been linked with software GPS simulator module enable to test GPS receiver’s functionality in different fading environments.

Combined spacecraft orbit and attitude control through extended Kalman filtering of magnetometer, gyro, and GPS measurements

Directory of Open Access Journals (Sweden)

Tamer Mekky Ahmed Habib

2014-06-01

Full Text Available The main goal of this research is to establish spacecraft orbit and attitude control algorithms based on extended Kalman filter which provides estimates of spacecraft orbital and attitude states. The control and estimation algorithms must be capable of dealing with the spacecraft conditions during the detumbling and attitude acquisition modes of operation. These conditions are characterized by nonlinearities represented by large initial attitude angles, large initial angular velocities, large initial attitude estimation error, and large initial position estimation error. All of the developed estimation and control algorithms are suitable for application to the next Egyptian scientific satellite, EGYPTSAT-2. The parameters of the case-study spacecraft are similar but not identical to the former Egyptian satellite EGYPTSAT-1. This is done because the parameters of EGYPTSAT-2 satellite have not been consolidated yet. The sensors utilized are gyro, magnetometer, and GPS. Gyro and magnetometer are utilized to provide measurements for the estimates of spacecraft attitude state vector where as magnetometer and GPS are utilized to provide measurements for the estimates of spacecraft orbital state vector.

GPS tomography tests for DInSAR applications on Mt. Etna

Directory of Open Access Journals (Sweden)

Massimo Aranzulla

2015-07-01

Full Text Available Tropospheric artifacts of SAR images in a volcanic area like Mt. Etna cause ambiguity in the interpretation of deformations with such technique. It would be useful to measure the delay caused by tropospheric anomalies in synthetic aperture radar (SAR satellite signals (phase of the back-scattered radar wave that could be interpreted as deformation. From the delay estimated through the GPS data processing, the tropospheric tomography of electromagnetic waves refractivity, has been performed using the SIMULps12 software. The aim of this study was to perform software synthetic tests by using SIMULps12 applied to atmospheric tomography and to verify the influence of the different GPS geodetic network configurations on obtaining a reliable tomography. Three different anomalies of increasing complexity have been investigated in order to understand the representative parameters of a correct tomography, the best spatial resolution and the portions of space in which the tomography is reliable. The tests also focused on fixing/establishing the a-priori atmospheric model and the critical values of the main parameters involved in the tomographic inversion. To this end, we made a random choice of two days, necessary to define the tomographic problem. Three different network configurations with 15, 30 and 90 GPS receivers were studied. The results indicate that the well-resolved area of tomographic images increases with the number of GPS receivers not linearly, and that the actual GPS network of 42 receivers is capable of revealing/detecting the atmospheric anomalies.

Performance Evaluation of Block Acquisition and Tracking Algorithms Using an Open Source GPS Receiver Platform

Science.gov (United States)

Ramachandran, Ganesh K.; Akopian, David; Heckler, Gregory W.; Winternitz, Luke B.

2011-01-01

Location technologies have many applications in wireless communications, military and space missions, etc. US Global Positioning System (GPS) and other existing and emerging Global Navigation Satellite Systems (GNSS) are expected to provide accurate location information to enable such applications. While GNSS systems perform very well in strong signal conditions, their operation in many urban, indoor, and space applications is not robust or even impossible due to weak signals and strong distortions. The search for less costly, faster and more sensitive receivers is still in progress. As the research community addresses more and more complicated phenomena there exists a demand on flexible multimode reference receivers, associated SDKs, and development platforms which may accelerate and facilitate the research. One of such concepts is the software GPS/GNSS receiver (GPS SDR) which permits a facilitated access to algorithmic libraries and a possibility to integrate more advanced algorithms without hardware and essential software updates. The GNU-SDR and GPS-SDR open source receiver platforms are such popular examples. This paper evaluates the performance of recently proposed block-corelator techniques for acquisition and tracking of GPS signals using open source GPS-SDR platform.

A GPS Sensing Strategy for Accurate and Energy-Efficient Outdoor-to-Indoor Handover in Seamless Localization Systems

Directory of Open Access Journals (Sweden)

Yungeun Kim

2012-01-01

Full Text Available Indoor localization systems typically locate users on their own local coordinates, while outdoor localization systems use global coordinates. To achieve seamless localization from outdoors to indoors, a handover technique that accurately provides a starting position to the indoor localization system is needed. However, existing schemes assume that a starting position is known a priori or uses a naïve approach to consider the last location obtained from GPS as the handover point. In this paper, we propose an accurate handover scheme that monitors the signal-to-noise ratio (SNR of the effective GPS satellites that are selected according to their altitude. We also propose an energy-efficient handover mechanism that reduces the GPS sampling interval gradually. Accuracy and energy efficiency are experimentally validated with the GPS logs obtained in real life.

Autonomous Navigation of the SSTI/Lewis Spacecraft Using the Global Positioning System (GPS)

Science.gov (United States)

Hart, R. C.; Long, A. C.; Lee, T.

1997-01-01

The National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD) is pursuing the application of Global Positioning System (GPS) technology to improve the accuracy and economy of spacecraft navigation. High-accuracy autonomous navigation algorithms are being flight qualified in conjunction with GSFC's GPS Attitude Determination Flyer (GADFLY) experiment on the Small Satellite Technology Initiative (SSTI) Lewis spacecraft, which is scheduled for launch in 1997. Preflight performance assessments indicate that these algorithms can provide a real-time total position accuracy of better than 10 meters (1 sigma) and velocity accuracy of better than 0.01 meter per second (1 sigma), with selective availability at typical levels. This accuracy is projected to improve to the 2-meter level if corrections to be provided by the GPS Wide Area Augmentation System (WAAS) are included.

An Intercomparison of GPS RO Retrievals with Colocated Analysis and In Situ Observations within Tropical Cyclones

Directory of Open Access Journals (Sweden)

Henry R. Winterbottom

2010-01-01

Full Text Available Observations from four Global Position System (GPS Radio Occultation (RO missions: Global Positioning System/Meteorology, CHAallenging Minisatellite Payload, Satellite de Aplicaciones Cientificas-C, and Constellation Observing System for Meteorology, Ionosphere and Climate and Taiwan's FORMOsa SATellite Mission #3 (COSMIC/FORMOSAT-3 are collected within a 600 km radius and ±180 minute temporal window of all observed tropical cyclones (TCs from 1995 to 2006 that were recorded in the global hurricane best-track reanalysis data set (Jarvinen et al. (1984; Davis et al. (1984. A composite analysis of tropical cyclone radial mean temperature and water vapor profiles is carried out using the GPS RO retrievals which are colocated with global analysis profiles and available in situ radiosonde observations. The differences between the respective observations and analysis profiles are quantified and the preliminary results show that the observations collected within TCs correspond favorably with both the analysis and radiosonde profiles which are colocated. It is concluded that GPS RO observations will contribute significantly to the understanding and modeling of TC structures, especially those related to vertical variability of the atmospheric state within TCs.

Orbit and clock determination of BDS regional navigation satellite system based on IGS M-GEX and WHU BETS tracking network

Science.gov (United States)

GENG, T.; Zhao, Q.; Shi, C.; Shum, C.; Guo, J.; Su, X.

2013-12-01

BeiDou Navigation Satellite System (BDS) began to provide the regional open service on December 27th 2012 and will provide the global open service by the end of 2020. Compared to GPS, the space segment of BDS Regional System consists of 5 Geostationary Earth Orbit satellites (GEO), 5 Inclined Geosynchronous Orbit satellites (IGSO) and 4 Medium Earth orbit (MEO) satellites. Since 2011, IGS Multiple-GNSS Experiment (M-GEX) focuses on tracking the newly available GNSS signals. This includes all signals from the modernized satellites of the GPS and GLONASS systems, as well as signals of the BDS, Galileo and QZSS systems. Up to now, BDS satellites are tracked by around 25 stations with a variety of different antennas and receivers from different GNSS manufacture communities in M-GEX network. Meanwhile, there are 17 stations with Unicore Communications Incorporation's GPS/BDS receivers in BeiDou Experimental Tracking Stations (BETS) network by Wuhan University. In addition, 5 BDS satellites have been tracking by the International Laser Ranging Service (ILRS). BDS performance is expected to be further studied by the GNSS communities. Following an introduction of the BDS system and above different tracking network, this paper discusses the achieved BDS characterization and performance assessment. Firstly, the BDS signal and measurement quality are analyzed with different antennas and receivers in detail compared to GPS. This includes depth of coverage for satellite observation, carrier-to-noise-density ratios, code noise and multipath, carrier phase errors. Secondly, BDS Precise Orbit Determination (POD) is processed. Different arc lengths and sets of orbit parameters are tested using Position And Navigation Data Analysis software (PANDA) which is developed at the Wuhan University. GEO, IGSO and MEO satellites orbit quality will be assessed using overlap comparison, 2-day orbit fit and external validations with Satellite Laser Range (SLR). Then BDS satellites are equipped

Combined GPS/GLONASS Precise Point Positioning with Fixed GPS Ambiguities

Science.gov (United States)

Pan, Lin; Cai, Changsheng; Santerre, Rock; Zhu, Jianjun

2014-01-01

Precise point positioning (PPP) technology is mostly implemented with an ambiguity-float solution. Its performance may be further improved by performing ambiguity-fixed resolution. Currently, the PPP integer ambiguity resolutions (IARs) are mainly based on GPS-only measurements. The integration of GPS and GLONASS can speed up the convergence and increase the accuracy of float ambiguity estimates, which contributes to enhancing the success rate and reliability of fixing ambiguities. This paper presents an approach of combined GPS/GLONASS PPP with fixed GPS ambiguities (GGPPP-FGA) in which GPS ambiguities are fixed into integers, while all GLONASS ambiguities are kept as float values. An improved minimum constellation method (MCM) is proposed to enhance the efficiency of GPS ambiguity fixing. Datasets from 20 globally distributed stations on two consecutive days are employed to investigate the performance of the GGPPP-FGA, including the positioning accuracy, convergence time and the time to first fix (TTFF). All datasets are processed for a time span of three hours in three scenarios, i.e., the GPS ambiguity-float solution, the GPS ambiguity-fixed resolution and the GGPPP-FGA resolution. The results indicate that the performance of the GPS ambiguity-fixed resolutions is significantly better than that of the GPS ambiguity-float solutions. In addition, the GGPPP-FGA improves the positioning accuracy by 38%, 25% and 44% and reduces the convergence time by 36%, 36% and 29% in the east, north and up coordinate components over the GPS-only ambiguity-fixed resolutions, respectively. Moreover, the TTFF is reduced by 27% after adding GLONASS observations. Wilcoxon rank sum tests and chi-square two-sample tests are made to examine the significance of the improvement on the positioning accuracy, convergence time and TTFF. PMID:25237901

Combined GPS/GLONASS Precise Point Positioning with Fixed GPS Ambiguities

Directory of Open Access Journals (Sweden)

Lin Pan

2014-09-01

Full Text Available Precise point positioning (PPP technology is mostly implemented with an ambiguity-float solution. Its performance may be further improved by performing ambiguity-fixed resolution. Currently, the PPP integer ambiguity resolutions (IARs are mainly based on GPS-only measurements. The integration of GPS and GLONASS can speed up the convergence and increase the accuracy of float ambiguity estimates, which contributes to enhancing the success rate and reliability of fixing ambiguities. This paper presents an approach of combined GPS/GLONASS PPP with fixed GPS ambiguities (GGPPP-FGA in which GPS ambiguities are fixed into integers, while all GLONASS ambiguities are kept as float values. An improved minimum constellation method (MCM is proposed to enhance the efficiency of GPS ambiguity fixing. Datasets from 20 globally distributed stations on two consecutive days are employed to investigate the performance of the GGPPP-FGA, including the positioning accuracy, convergence time and the time to first fix (TTFF. All datasets are processed for a time span of three hours in three scenarios, i.e., the GPS ambiguity-float solution, the GPS ambiguity-fixed resolution and the GGPPP-FGA resolution. The results indicate that the performance of the GPS ambiguity-fixed resolutions is significantly better than that of the GPS ambiguity-float solutions. In addition, the GGPPP-FGA improves the positioning accuracy by 38%, 25% and 44% and reduces the convergence time by 36%, 36% and 29% in the east, north and up coordinate components over the GPS-only ambiguity-fixed resolutions, respectively. Moreover, the TTFF is reduced by 27% after adding GLONASS observations. Wilcoxon rank sum tests and chi-square two-sample tests are made to examine the significance of the improvement on the positioning accuracy, convergence time and TTFF.

47 CFR 80.215 - Transmitter power.

Science.gov (United States)

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Transmitter power. 80.215 Section 80.215... MARITIME SERVICES General Technical Standards § 80.215 Transmitter power. (a) Transmitter power shown on the radio station authorization is the maximum power the licensee is authorized to use. Power is...

47 CFR 101.513 - Transmitter power.

Science.gov (United States)

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Transmitter power. 101.513 Section 101.513... SERVICES 24 GHz Service and Digital Electronic Message Service § 101.513 Transmitter power. The transmitter power will be governed by § 101.113. Further, each application must contain an analysis demonstrating...

Technological utilization of space with special regard to navigation satellite systems

Science.gov (United States)

Stiller, A. H.

With financial support from the German Minister of Research and Technology (BMFT) two German companies have developed two GPS-C/A-Code-receivers for different applications with low weight and small volume. The measured results of positions in connection with the ABS of a car (Anti lock braking system) and in Diff.-GPS-mode are very satisfying and in the range of 15 and/or 3 meters. Both receivers worked quite well and both companies have demonstrated their capability to meet our high exspectations. Unfortunately the GPS-satellite to be launched are behind schedule, therefore the two German companies cannot sell their products and if the GPS-system will be completed in the year 1991 other technologies with smaller and cheaper receivers will be on the market.

47 CFR 101.807 - Transmitter power.

Science.gov (United States)

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Transmitter power. 101.807 Section 101.807... SERVICES Local Television Transmission Service § 101.807 Transmitter power. Stations in this service will not be authorized to use transmitters having a rated power output in excess of the limits set forth in...

Results from Navigator GPS Flight Testing for the Magnetospheric MultiScale Mission

Science.gov (United States)

Lulich, Tyler D.; Bamford, William A.; Wintermitz, Luke M. B.; Price, Samuel R.

2012-01-01

The recent delivery of the first Goddard Space Flight Center (GSFC) Navigator Global Positioning System (GPS) receivers to the Magnetospheric MultiScale (MMS) mission spacecraft is a high water mark crowning a decade of research and development in high-altitude space-based GPS. Preceding MMS delivery, the engineering team had developed receivers to support multiple missions and mission studies, such as Low Earth Orbit (LEO) navigation for the Global Precipitation Mission (GPM), above the constellation navigation for the Geostationary Operational Environmental Satellite (GOES) proof-of-concept studies, cis-Lunar navigation with rapid re-acquisition during re-entry for the Orion Project and an orbital demonstration on the Space Shuttle during the Hubble Servicing Mission (HSM-4).

GPS Software Packages Deliver Positioning Solutions

Science.gov (United States)

2010-01-01

"To determine a spacecraft s position, the Jet Propulsion Laboratory (JPL) developed an innovative software program called the GPS (global positioning system)-Inferred Positioning System and Orbit Analysis Simulation Software, abbreviated as GIPSY-OASIS, and also developed Real-Time GIPSY (RTG) for certain time-critical applications. First featured in Spinoff 1999, JPL has released hundreds of licenses for GIPSY and RTG, including to Longmont, Colorado-based DigitalGlobe. Using the technology, DigitalGlobe produces satellite imagery with highly precise latitude and longitude coordinates and then supplies it for uses within defense and intelligence, civil agencies, mapping and analysis, environmental monitoring, oil and gas exploration, infrastructure management, Internet portals, and navigation technology."

Nuclear-Powered GPS Spacecraft Design Study

Energy Technology Data Exchange (ETDEWEB)

Raab, Bernard

1977-05-01

This is the final report of a study to investigate the potential benefits of a nuclear (radioisotope) - powered satellite for advanced phases of the Global Positioning System (GPS) program. The critical parameters were: power to user; mean mission duration; orbital predictability; thermal control of on-board frequency standards; and vulnerability. The reference design approach is described, and input data are given for two power systems that are under development: an organic Rankine system and a Brayton cycle system. Reference design details are provided and structural design and analysis are discussed, as well as thermal design and analysis. A higher altitude version is also considered.

Dynamic and reduced-dynamic precise orbit determination of satellites in low earth orbits

International Nuclear Information System (INIS)

Swatschina, P.

2009-01-01

The precise positioning of satellites in Low Earth Orbits (LEO) has become a key technology for advanced space missions. Dedicated satellite missions, such as CHAMP, GRACE and GOCE, that aim to map the Earths gravity field and its variation over time with unprecedented accuracy, initiated the demand for highly precise orbit solutions of LEO satellites. Furthermore, a wide range of additional science opportunities opens up with the capability to generate accurate LEO orbits. For all considered satellite missions, the primary measurement system for navigation is a spaceborne GPS receiver. The goal of this thesis is to establish and implement methods for Precise Orbit Determination (POD) of LEO satellites using GPS. Striving for highest precision using yet efficient orbit generation strategies, the attained orbit solutions are aimed to be competitive with the most advanced solutions of other institutions. Dynamic and reduced-dynamic orbit models provide the basic concepts of this work. These orbit models are subsequently adjusted to the highly accurate GPS measurements. The GPS measurements are introduced at the zero difference level in the ionosphere free linear combination. Appropriate procedures for GPS data screening and editing are established to detect erroneous data and to employ measurements of good quality only. For the dynamic orbit model a sophisticated force model, especially designed for LEO satellites, has been developed. In order to overcome the limitations that are induced by the deficiencies of the purely dynamical model, two different types of empirical parameters are introduced into the force model. These reduced-dynamic orbit models allow for the generation of much longer orbital arcs while preserving the spacecraft dynamics to the most possible extent. The two methods for reduced-dynamic orbit modeling are instantaneous velocity changes (pulses) or piecewise constant accelerations. For both techniques highly efficient modeling algorithms are

An estimation of tropospheric corrections using GPS and synoptic data: Improving Urmia Lake water level time series from Jason-2 and SARAL/AltiKa satellite altimetry

Science.gov (United States)

Arabsahebi, Reza; Voosoghi, Behzad; Tourian, Mohammad J.

2018-05-01

Tropospheric correction is one of the most important corrections in satellite altimetry measurements. Tropospheric wet and dry path delays have strong dependence on temperature, pressure and humidity. Tropospheric layer has particularly high variability over coastal regions due to humidity, wind and temperature gradients. Depending on the extent of water body and wind conditions over an inland water, Wet Tropospheric Correction (WTC) is within the ranges from a few centimeters to tens of centimeters. Therefore, an extra care is needed to estimate tropospheric corrections on the altimetric measurements over inland waters. This study assesses the role of tropospheric correction on the altimetric measurements over the Urmia Lake in Iran. For this purpose, four types of tropospheric corrections have been used: (i) microwave radiometer (MWR) observations, (ii) tropospheric corrections computed from meteorological models, (iii) GPS observations and (iv) synoptic station data. They have been applied to Jason-2 track no. 133 and SARAL/AltiKa track no. 741 and 356 corresponding to 117-153 and the 23-34 cycles, respectively. In addition, the corresponding measurements of PISTACH and PEACHI, include new retracking method and an innovative wet tropospheric correction, have also been used. Our results show that GPS observation leads to the most accurate tropospheric correction. The results obtained from the PISTACH and PEACHI projects confirm those obtained with the standard SGDR, i.e., the role of GPS in improving the tropospheric corrections. It is inferred that the MWR data from Jason-2 mission is appropriate for the tropospheric corrections, however the SARAL/AltiKa one is not proper because Jason-2 possesses an enhanced WTC near the coast. Furthermore, virtual stations are defined for assessment of the results in terms of time series of Water Level Height (WLH). The results show that GPS tropospheric corrections lead to the most accurate WLH estimation for the selected

About Non-Line-Of-Sight Satellite Detection and Exclusion in a 3D Map-Aided Localization Algorithm

Directory of Open Access Journals (Sweden)

François Peyret

2013-01-01

Full Text Available Reliable GPS positioning in city environment is a key issue: actually, signals are prone to multipath, with poor satellite geometry in many streets. Using a 3D urban model to forecast satellite visibility in urban contexts in order to improve GPS localization is the main topic of the present article. A virtual image processing that detects and eliminates possible faulty measurements is the core of this method. This image is generated using the position estimated a priori by the navigation process itself, under road constraints. This position is then updated by measurements to line-of-sight satellites only. This closed-loop real-time processing has shown very first promising full-scale test results.

About Non-Line-Of-Sight Satellite Detection and Exclusion in a 3D Map-Aided Localization Algorithm

Science.gov (United States)

Peyraud, Sébastien; Bétaille, David; Renault, Stéphane; Ortiz, Miguel; Mougel, Florian; Meizel, Dominique; Peyret, François

2013-01-01

Reliable GPS positioning in city environment is a key issue actually, signals are prone to multipath, with poor satellite geometry in many streets. Using a 3D urban model to forecast satellite visibility in urban contexts in order to improve GPS localization is the main topic of the present article. A virtual image processing that detects and eliminates possible faulty measurements is the core of this method. This image is generated using the position estimated a priori by the navigation process itself, under road constraints. This position is then updated by measurements to line-of-sight satellites only. This closed-loop real-time processing has shown very first promising full-scale test results. PMID:23344379

Thermospheric neutral densities derived from Swarm accelerometer and GPS data

DEFF Research Database (Denmark)

Doornbos, Eelco; Encarnacao, Joao; van den IJss, Jose

Over the past years, a lot of effort has been put into characterising and correcting the various disturbance signals that were found in the accelerometer data provided by the Swarm satellites. This effort was first and foremost aimed at the Swarm C along-track axis data, which seems to be the least...... affected and most promising data for scientific use. The goal to make the Swarm C accelerometer along-track axis data ready for further processing into level 2 thermosphere density data has now been accomplished, with the help of information on the satellite motion from the GPS tracking as well...... approach, affects the possibility of determining densities from the accelerometer measurements of the Swarm A and B satellites. We also investigate the possibility of determining crosswind speeds from Swarm data.In the meantime, we have investigated the possibility of deriving thermosphere neutral density...

Convergence Time and Positioning Accuracy Comparison between BDS and GPS Precise Point Positioning

Directory of Open Access Journals (Sweden)

ZHANG Xiaohong

2015-03-01

Full Text Available BDS/GPS data from MGEX were processed by TriP 2.0 software developed at Wuhan University. Both static and kinematic float PPP are tested by adopting precise satellite orbits and clocks provided by Research Center of GNSS, Wuhan University. The results show that the convergence time of BDS static PPP is about 80min while kinematic PPP is about 100min. For 3h observations, static positioning accuracy of 5 cm and kinematic positioning accuracy of 8 cm in horizontal, about 12 cm in vertical can be achieved. Similar to GPS PPP, precision in east component is worse than north. At present, BDS PPP needs longer convergence time than GPS PPP to reach an absolute positioning accuracy of cm~dm due to the lack of global tracking stations and the limited accuracy of orbit and clock products.

An orbit determination algorithm for small satellites based on the magnitude of the earth magnetic field

Science.gov (United States)

Zagorski, P.; Gallina, A.; Rachucki, J.; Moczala, B.; Zietek, S.; Uhl, T.

2018-06-01

Autonomous attitude determination systems based on simple measurements of vector quantities such as magnetic field and the Sun direction are commonly used in very small satellites. However, those systems always require knowledge of the satellite position. This information can be either propagated from orbital elements periodically uplinked from the ground station or measured onboard by dedicated global positioning system (GPS) receiver. The former solution sacrifices satellite autonomy while the latter requires additional sensors which may represent a significant part of mass, volume, and power budget in case of pico- or nanosatellites. Hence, it is thought that a system for onboard satellite position determination without resorting to GPS receivers would be useful. In this paper, a novel algorithm for determining the satellite orbit semimajor-axis is presented. The methods exploit only the magnitude of the Earth magnetic field recorded onboard by magnetometers. This represents the first step toward an extended algorithm that can determine all orbital elements of the satellite. The method is validated by numerical analysis and real magnetic field measurements.

Development of Real-Time Precise Positioning Algorithm Using GPS L1 Carrier Phase Data

Directory of Open Access Journals (Sweden)

Jeong-Ho Joh

2002-12-01

Full Text Available We have developed Real-time Phase DAta Processor(RPDAP for GPS L1 carrier. And also, we tested the RPDAP's positioning accuracy compared with results of real time kinematic(RTK positioning. While quality of the conventional L1 RTK positioning highly depend on receiving condition, the RPDAP can gives more stable positioning result because of different set of common GPS satellites, which searched by elevation mask angle and signal strength. In this paper, we demonstrated characteristics of the RPDAP compared with the L1 RTK technique. And we discussed several improvement ways to apply the RPDAP to precise real-time positioning using low-cost GPS receiver. With correcting the discussed weak points in near future, the RPDAP will be used in the field of precise real-time application, such as precise car navigation and precise personal location services.

Laser transmitter system

International Nuclear Information System (INIS)

Dye, R.A.

1975-01-01

A laser transmitter system is disclosed which utilizes mechanical energy for generating an output pulse. The laser system includes a current developing device such as a piezoelectric crystal which charges a storage device such as a capacitor in response to a mechanical input signal. The capacitor is coupled to a switching device, such as a silicon controlled rectifier (SCR). The switching device is coupled to a laser transmitter such as a GaAs laser diode, which provides an output signal in response to the capacitor being discharged

The ionospheric eclipse factor method (IEFM) and its application to determining the ionospheric delay for GPS

DEFF Research Database (Denmark)

Yuan, Y.; Tscherning, C.C.; Knudsen, Per

2006-01-01

A new method for modeling the ionospheric delay using global positioning system (GPS) data is proposed, called the ionospheric eclipse factor method (IEFM). It is based on establishing a concept referred to as the ionospheric eclipse factor (IEF) lambda of the ionospheric pierce point (IPP....... The IEFM-based ionospheric delay estimates are validated by combining an absolute positioning mode with several ionospheric delay correction models or algorithms, using GPS data at an international Global Navigation Satellite System (GNSS) service (IGS) station (WTZR). Our results indicate that the IEFM...

Error and Performance Analysis of MEMS-based Inertial Sensors with a Low-cost GPS Receiver

Directory of Open Access Journals (Sweden)

Yang Gao

2008-03-01

Full Text Available Global Navigation Satellite Systems (GNSS, such as the Global Positioning System (GPS, have been widely utilized and their applications are becoming popular, not only in military or commercial applications, but also for everyday life. Although GPS measurements are the essential information for currently developed land vehicle navigation systems (LVNS, GPS signals are often unavailable or unreliable due to signal blockages under certain environments such as urban canyons. This situation must be compensated in order to provide continuous navigation solutions. To overcome the problems of unavailability and unreliability using GPS and to be cost and size effective as well, Micro Electro Mechanical Systems (MEMS based inertial sensor technology has been pushing for the development of low-cost integrated navigation systems for land vehicle navigation and guidance applications. This paper will analyze the characterization of MEMS based inertial sensors and the performance of an integrated system prototype of MEMS based inertial sensors, a low-cost GPS receiver and a digital compass. The influence of the stochastic variation of sensors will be assessed and modeled by two different methods, namely Gauss-Markov (GM and AutoRegressive (AR models, with GPS signal blockage of different lengths. Numerical results from kinematic testing have been used to assess the performance of different modeling schemes.

Precise Orbit Solution for Swarm Using Space-Borne GPS Data and Optimized Pseudo-Stochastic Pulses

Directory of Open Access Journals (Sweden)

Bingbing Zhang

2017-03-01

Full Text Available Swarm is a European Space Agency (ESA project that was launched on 22 November 2013, which consists of three Swarm satellites. Swarm precise orbits are essential to the success of the above project. This study investigates how well Swarm zero-differenced (ZD reduced-dynamic orbit solutions can be determined using space-borne GPS data and optimized pseudo-stochastic pulses under high ionospheric activity. We choose Swarm space-borne GPS data from 1–25 October 2014, and Swarm reduced-dynamic orbits are obtained. Orbit quality is assessed by GPS phase observation residuals and compared with Precise Science Orbits (PSOs released by ESA. Results show that pseudo-stochastic pulses with a time interval of 6 min and a priori standard deviation (STD of 10−2 mm/s in radial (R, along-track (T and cross-track (N directions are optimized to Swarm ZD reduced-dynamic precise orbit determination (POD. During high ionospheric activity, the mean Root Mean Square (RMS of Swarm GPS phase residuals is at 9–11 mm, Swarm orbit solutions are also compared with Swarm PSOs released by ESA and the accuracy of Swarm orbits can reach 2–4 cm in R, T and N directions. Independent Satellite Laser Ranging (SLR validation indicates that Swarm reduced-dynamic orbits have an accuracy of 2–4 cm. Swarm-B orbit quality is better than those of Swarm-A and Swarm-C. The Swarm orbits can be applied to the geomagnetic, geoelectric and gravity field recovery.

Monitoraggio remoto delle deformazioni nell’isola di Santorini: una procedura integrata di analisi dati GPS presso la Sezione INGV di Bologna

Directory of Open Access Journals (Sweden)

Arianna Pesci

2012-06-01

Full Text Available Il GPS (Global Positioning System è un noto sistema di posizionamento globale in grado di fornire le coordinate spaziali di unoperatore, se munito di antenna e ricevitore satellitari, in qualunque punto della terra esso si trovi, in qualunque condizionemeteo ed in qualsiasi ora del giorno. Oggi al GPS, che è di proprietà del Dipartimento della Difesa degli Stati Uniti d'America(US DoD, si affiancano il GLONASS (sistema analogo russo e altri sistemi di posizionamento globale basati su tecniche interferometriche spaziali a partire da segnali a microonde, ad esempio i nascenti Galileo (europeo e BeiDou (cinese. Per questo motivo si parla diffusamente di sistemi GNSS cioè Global Navigation Satellite System.   Remote monitoring of deformations in the island of Santorini: an integrated procedure for GPS data analysis at the INGV in Bologna The GPS (Global Positioning System is a well-known global positioning  system  capable  of  providing  the  spatial  coordi-nates of an operator, if equipped with an antenna and a re-ceiver satellite, at any point on the earth , and in any weather conditions and at any time of the day. Today, the GPS, which is owned by the Department of Defense of the United States of America (U.S. DoD, is aided by the GLONASS (the Russian analogue system and other global positioning systems based on interferometry from space microwave signals, for example, the  nascent  Galileo  (European  and  Beidou  (China.  For  this reason we talk at today about GNSS Global Navigation Satel-lite System.

Direct RF modulation transmitter, sampling clock frequency setting method for direct RF modulation transmitter

NARCIS (Netherlands)

Fukuda, Shuichi; Nauta, Bram

2013-01-01

PROBLEM TO BE SOLVED: To provide a direct RF modulation transmitter capable of satisfying a radiation level regulation even without providing a SAW filter. SOLUTION: A direct RF modulation transmitter includes: digital/RF converters 105, 106 to which an I digital baseband signal, a Q digital

Direct RF modulation transmitter, sampling clock frequency setting method for direct RF modulation transmitter

NARCIS (Netherlands)

Fukuda, Shuichi; Nauta, Bram

2014-01-01

PROBLEM TO BE SOLVED: To provide a direct RF modulation transmitter capable of satisfying a radiation level regulation even without providing a SAW filter. SOLUTION: A direct RF modulation transmitter includes: digital/RF converters 105, 106 to which an I digital baseband signal, a Q digital

76 FR 31252 - Fixed and Mobile Services in the Mobile Satellite Service Bands at 1525-1559 MHz and 1626.5-1660...

Science.gov (United States)

2011-05-31

... operations in the L-band on GPS and other Global Navigation Satellite System (GNSS) receivers. 24. The... and NTIA about LightSquared's operations in the MSS L-band, LightSquared is working with the GPS... from its base station operations in the MSS L-band spectrum to GPS receivers in the adjacent 1559-1610...

Multi-Flight-Phase GPS Navigation Filter Applications to Terrestrial Vehicle Navigation and Positioning

Science.gov (United States)

Park, Young W.; Montez, Moises N.

1994-01-01

A candidate onboard space navigation filter demonstrated excellent performance (less than 8 meter level RMS semi-major axis accuracy) in performing orbit determination of a low-Earth orbit Explorer satellite using single-frequency real GPS data. This performance is significantly better than predicted by other simulation studies using dual-frequency GPS data. The study results revealed the significance of two new modeling approaches evaluated in the work. One approach introduces a single-frequency ionospheric correction through pseudo-range and phase range averaging implementation. The other approach demonstrates a precise axis-dependent characterization of dynamic sample space uncertainty to compute a more accurate Kalman filter gain. Additionally, this navigation filter demonstrates a flexibility to accommodate both perturbational dynamic and observational biases required for multi-flight phase and inhomogeneous application environments. This paper reviews the potential application of these methods and the filter structure to terrestrial vehicle and positioning applications. Both the single-frequency ionospheric correction method and the axis-dependent state noise modeling approach offer valuable contributions in cost and accuracy improvements for terrestrial GPS receivers. With a modular design approach to either 'plug-in' or 'unplug' various force models, this multi-flight phase navigation filter design structure also provides a versatile GPS navigation software engine for both atmospheric and exo-atmospheric navigation or positioning use, thereby streamlining the flight phase or application-dependent software requirements. Thus, a standardized GPS navigation software engine that can reduce the development and maintenance cost of commercial GPS receivers is now possible.

Surface deformation analysis over Vrancea seismogenic area through radar and GPS geospatial data

Science.gov (United States)

Zoran, Maria A.; Savastru, Roxana S.; Savastru, Dan M.; Serban, Florin S.; Teleaga, Delia M.; Mateciuc, Doru N.

2017-10-01

Time series analysis of GPS (Global Positioning Systems) and InSAR (Interferometric Synthetic Aperture Radar) data are important tools for Earth's surface deformation assessment, which can result from a wide range of geological phenomena like as earthquakes, landslides or ground water level changes. The aim of this paper was to identify several types of earthquake precursors that might be observed from geospatial data in Vrancea seismogenic region in Romania. Continuous GPS Romanian network stations and few field campaigns data recorded between 2005-2012 years revealed a displacement of about 5 or 6 millimeters per year in horizontal direction relative motion, and a few millimeters per year in vertical direction. In order to assess possible deformations due to earthquakes and respectively for possible slow deformations, have been used also time series Sentinel 1 satellite data available for Vrancea zone during October 2014 till October 2016 to generate two types of interferograms (short-term and medium- term). During investigated period were not recorded medium or strong earthquakes, so interferograms over test area revealed small displacements on vertical direction (subsidence or uplifts) of 5-10 millimeters per year. Based on GPS continuous network data and satellite Sentinel 1 results, different possible tectonic scenarios were developed. The localization of horizontal and vertical motions, fault slip, and surface deformation of the continental blocks provides new information, in support of different geodynamic models for Vrancea tectonic active region in Romania and Europe.

Q-Band (37-41 GHz) Satellite Beacon Architecture for RF Propagation Experiments

Science.gov (United States)

Simmons, Rainee N.; Wintucky, Edwin G.

2012-01-01

In this paper, the design of a beacon transmitter that will be flown as a hosted payload on a geostationary satellite to enable propagation experiments at Q-band (37-41 GHz) frequencies is presented. The beacon uses a phased locked loop stabilized dielectric resonator oscillator and a solid-state power amplifier to achieve the desired output power. The satellite beacon antenna is configured as an offset-fed cut-paraboloidal reflector.

Remote atomic clock synchronization via satellites and optical fibers

OpenAIRE

Piester, D.; Rost, M.; Fujieda, M.; Feldmann, T.; Bauch, A.

2011-01-01

In the global network of institutions engaged with the realization of International Atomic Time (TAI), atomic clocks and time scales are compared by means of the Global Positioning System (GPS) and by employing telecommunication satellites for two-way satellite time and frequency transfer (TWSTFT). The frequencies of the state-of-the-art primary caesium fountain clocks can be compared at the level of 10−15 (relative, 1 day averaging) and time scales can be synchronized...

Analysis of signal acquisition in GPS receiver software

Directory of Open Access Journals (Sweden)

Vlada S. Sokolović

2011-01-01

Full Text Available This paper presents a critical analysis of the flow signal processing carried out in GPS receiver software, which served as a basis for a critical comparison of different signal processing architectures within the GPS receiver. It is possible to achieve Increased flexibility and reduction of GPS device commercial costs, including those of mobile devices, by using radio technology software (SDR, Software Defined Radio. The SDR application can be realized when certain hardware components in a GPS receiver are replaced. Signal processing in the SDR is implemented using a programmable DSP (Digital Signal Processing or FPGA (Field Programmable Gate Array circuit, which allows a simple change of digital signal processing algorithms and a simple change of the receiver parameters. The starting point of the research is the signal generated on the satellite the structure of which is shown in the paper. Based on the GPS signal structure, a receiver is realized with a task to extract an appropriate signal from the spectrum and detect it. Based on collected navigation data, the receiver calculates the position of the end user. The signal coming from the satellite may be at the carrier frequencies of L1 and L2. Since the SPS is used in the civil service, all the tests shown in the work were performed on the L1 signal. The signal coming to the receiver is generated in the spread spectrum technology and is situated below the level of noise. Such signals often interfere with signals from the environment which presents a difficulty for a receiver to perform proper detection and signal processing. Therefore, signal processing technology is continually being improved, aiming at more accurate and faster signal processing. All tests were carried out on a signal acquired from the satellite using the SE4110 input circuit used for filtering, amplification and signal selection. The samples of the received signal were forwarded to a computer for data post processing, i. e

Measurements of Interferometer Parameters at Reception of GLONASS and GPS Signals

Directory of Open Access Journals (Sweden)

Nechaeva M.

2016-10-01

Full Text Available The present paper deals with the calibration method of interferometers with antennas having a small effective area, on the quasinoise signals of GLONASS and GPS navigation satellites. Algorithms for calculation of antenna coordinates and instrumental delay from the analysis of correlation interferometer response to signals of satellites in the near field of the instrument were reviewed. The method was tested in VLBI experiments on interferometers with medium and large baselines that included radio telescopes of NIRFI and VIRAC. The values of the antenna coordinates and instrumental delay with an error within the limits of one discrete were obtained. The sources of measurement errors and ways to improve the accuracy of results were analysed.

Borehole induction coil transmitter

Science.gov (United States)

Holladay, Gale; Wilt, Michael J.

2002-01-01

A borehole induction coil transmitter which is a part of a cross-borehole electromagnetic field system that is used for underground imaging applications. The transmitter consists of four major parts: 1) a wound ferrite or mu-metal core, 2) an array of tuning capacitors, 3) a current driver circuit board, and 4) a flux monitor. The core is wound with several hundred turns of wire and connected in series with the capacitor array, to produce a tuned coil. This tuned coil uses internal circuitry to generate sinusoidal signals that are transmitted through the earth to a receiver coil in another borehole. The transmitter can operate at frequencies from 1-200 kHz and supplies sufficient power to permit the field system to operate in boreholes separated by up to 400 meters.

Identification of AR(I)MA processes for modelling temporal correlations of GPS observations

Science.gov (United States)

Luo, X.; Mayer, M.; Heck, B.

2009-04-01

In many geodetic applications observations of the Global Positioning System (GPS) are routinely processed by means of the least-squares method. However, this algorithm delivers reliable estimates of unknown parameters und realistic accuracy measures only if both the functional and stochastic models are appropriately defined within GPS data processing. One deficiency of the stochastic model used in many GPS software products consists in neglecting temporal correlations of GPS observations. In practice the knowledge of the temporal stochastic behaviour of GPS observations can be improved by analysing time series of residuals resulting from the least-squares evaluation. This paper presents an approach based on the theory of autoregressive (integrated) moving average (AR(I)MA) processes to model temporal correlations of GPS observations using time series of observation residuals. A practicable integration of AR(I)MA models in GPS data processing requires the determination of the order parameters of AR(I)MA processes at first. In case of GPS, the identification of AR(I)MA processes could be affected by various factors impacting GPS positioning results, e.g. baseline length, multipath effects, observation weighting, or weather variations. The influences of these factors on AR(I)MA identification are empirically analysed based on a large amount of representative residual time series resulting from differential GPS post-processing using 1-Hz observation data collected within the permanent SAPOS® (Satellite Positioning Service of the German State Survey) network. Both short and long time series are modelled by means of AR(I)MA processes. The final order parameters are determined based on the whole residual database; the corresponding empirical distribution functions illustrate that multipath and weather variations seem to affect the identification of AR(I)MA processes much more significantly than baseline length and observation weighting. Additionally, the modelling

Assessment of the Contribution of BeiDou GEO, IGSO, and MEO Satellites to PPP in Asia—Pacific Region

Directory of Open Access Journals (Sweden)

Qile Zhao

2015-12-01

Full Text Available In contrast to the US Global Positioning System (GPS, the Russian Global Navigation Satellite System (GLONASS and the European Galileo, the developing Chinese BeiDou satellite navigation system (BDS consists of not only Medium Earth Orbit (MEO, but also Geostationary Orbit (GEO as well as Inclined Geosynchronous Orbit (IGSO satellites. In this study, the Precise Point Positioning (PPP and PPP with Integer Ambiguity Resolution (IAR are obtained. The contributions of these three different types of BDS satellites to PPP in Asia-Pacific region are assessed using data from selected 20 sites over more than four weeks. By using various PPP cases with different satellite combinations, in general, the largest contribution of BDS IGSO among the three kinds of BDS satellites to the reduction of convergence time and the improvement of positioning accuracy, particularly in the east direction, is identified. These PPP cases include static BDS only solutions and static/kinematic ambiguity-float and -fixed PPP with the combination of GPS and BDS. The statistical results demonstrate that the inclusion of BDS GEO and MEO satellites can improve the observation condition and result in better PPP performance as well. When combined with GPS, the contribution of BDS to the reduction of convergence time is, however, not as significant as that of GLONASS. As far as the positioning accuracy is concerned, GLONASS improves the accuracy in vertical component more than BDS does, whereas similar improvement in horizontal component can be achieved by inclusion of BDS IGSO and MEO as GLONASS.

Comparison of Global Distributions of Zonal-Mean Gravity Wave Variance Inferred from Different Satellite Instruments

Science.gov (United States)

Preusse, Peter; Eckermann, Stephen D.; Offermann, Dirk; Jackman, Charles H. (Technical Monitor)

2000-01-01

Gravity wave temperature fluctuations acquired by the CRISTA instrument are compared to previous estimates of zonal-mean gravity wave temperature variance inferred from the LIMS, MLS and GPS/MET satellite instruments during northern winter. Careful attention is paid to the range of vertical wavelengths resolved by each instrument. Good agreement between CRISTA data and previously published results from LIMS, MLS and GPS/MET are found. Key latitudinal features in these variances are consistent with previous findings from ground-based measurements and some simple models. We conclude that all four satellite instruments provide reliable global data on zonal-mean gravity wave temperature fluctuations throughout the middle atmosphere.

Active landslide monitoring using remote sensing data, GPS measurements and cameras on board UAV

Science.gov (United States)

Nikolakopoulos, Konstantinos G.; Kavoura, Katerina; Depountis, Nikolaos; Argyropoulos, Nikolaos; Koukouvelas, Ioannis; Sabatakakis, Nikolaos

2015-10-01

An active landslide can be monitored using many different methods: Classical geotechnical measurements like inclinometer, topographical survey measurements with total stations or GPS and photogrammetric techniques using airphotos or high resolution satellite images. As the cost of the aerial photo campaign and the acquisition of very high resolution satellite data is quite expensive the use of cameras on board UAV could be an identical solution. Small UAVs (Unmanned Aerial Vehicles) have started their development as expensive toys but they currently became a very valuable tool in remote sensing monitoring of small areas. The purpose of this work is to demonstrate a cheap but effective solution for an active landslide monitoring. We present the first experimental results of the synergistic use of UAV, GPS measurements and remote sensing data. A six-rotor aircraft with a total weight of 6 kg carrying two small cameras has been used. Very accurate digital airphotos, high accuracy DSM, DGPS measurements and the data captured from the UAV are combined and the results are presented in the current study.

Planning and Scheduling for Fleets of Earth Observing Satellites

Science.gov (United States)

Frank, Jeremy; Jonsson, Ari; Morris, Robert; Smith, David E.; Norvig, Peter (Technical Monitor)

2001-01-01

We address the problem of scheduling observations for a collection of earth observing satellites. This scheduling task is a difficult optimization problem, potentially involving many satellites, hundreds of requests, constraints on when and how to service each request, and resources such as instruments, recording devices, transmitters, and ground stations. High-fidelity models are required to ensure the validity of schedules; at the same time, the size and complexity of the problem makes it unlikely that systematic optimization search methods will be able to solve them in a reasonable time. This paper presents a constraint-based approach to solving the Earth Observing Satellites (EOS) scheduling problem, and proposes a stochastic heuristic search method for solving it.

Lamp reliability studies for improved satellite rubidium frequency standard

Science.gov (United States)

Frueholz, R. P.; Wun-Fogle, M.; Eckert, H. U.; Volk, C. H.; Jones, P. F.

1982-01-01

In response to the premature failure of Rb lamps used in Rb atomic clocks onboard NAVSTAR GPS satellites experimental and theoretical investigations into their failure mechanism were initiated. The primary goal of these studies is the development of an accelerated life test for future GPS lamps. The primary failure mechanism was identified as consumption of the lamp's Rb charge via direct interaction between Rb and the lamp's glass surface. The most effective parameters to accelerate the interaction between the Rb and the glass are felt to be RF excitation power and lamp temperature. Differential scanning calorimetry is used to monitor the consumption of Rb within a lamp as a function of operation time. This technique yielded base line Rb consumption data for GPS lamps operating under normal conditions.

Validation of MODIS integrated water vapor product against reference GPS data at the Iberian Peninsula

Science.gov (United States)

Vaquero-Martínez, Javier; Antón, Manuel; Ortiz de Galisteo, José Pablo; Cachorro, Victoria E.; Costa, Maria João; Román, Roberto; Bennouna, Yasmine S.

2017-12-01

In this work, the water vapor product from MODIS (MODerate-resolution Imaging Spectroradiometer) instrument, on-board Aqua and Terra satellites, is compared against GPS water vapor data from 21 stations in the Iberian Peninsula as reference. GPS water vapor data is obtained from ground-based receiver stations which measure the delay caused by water vapor in the GPS microwave signals. The study period extends from 2007 until 2012. Regression analysis in every GPS station show that MODIS overestimates low integrated water vapor (IWV) data and tends to underestimate high IWV data. R2 shows a fair agreement, between 0.38 and 0.71. Inter-quartile range (IQR) in every station is around 30-45%. The dependence on several parameters was also analyzed. IWV dependence showed that low IWV are highly overestimated by MODIS, with high IQR (low precision), sharply decreasing as IWV increases. Regarding dependence on solar zenith angle (SZA), performance of MODIS IWV data decreases between 50° and 90°, while night-time MODIS data (infrared) are quite stable. The seasonal cycles of IWV and SZA cause a seasonal dependence on MODIS performance. In summer and winter, MODIS IWV tends to overestimate the reference IWV value, while in spring and autumn the tendency is to underestimate. Low IWV from coastal stations is highly overestimated (∼60%) and quite imprecise (IQR around 60%). On the contrary, high IWV data show very little dependence along seasons. Cloud-fraction (CF) dependence was also studied, showing that clouds display a negligible impact on IWV over/underestimation. However, IQR increases with CF, except in night-time satellite values, which are quite stable.

Estimation of sea level variations with GPS/GLONASS-reflectometry technique

Science.gov (United States)

Padokhin, A. M.; Kurbatov, G. A.; Andreeva, E. S.; Nesterov, I. A.; Nazarenko, M. O.; Berbeneva, N. A.; Karlysheva, A. V.

2017-11-01

In the present paper we study GNSS - reflectometry methods for estimation of sea level variations using a single GNSSreceiver, which are based on the multipath propagation effects caused by the reflection of navigational signals from the sea surface. Such multipath propagation results in the appearance of the interference pattern in the Signal-to-Noise Ratio (SNR) of GNSS signals at small satellite elevation angles, which parameters are determined by the wavelength of the navigational signal and height of the antenna phase center above the reflecting sea surface. In current work we used GPS and GLONASS signals and measurements at two working frequencies of both systems to study sea level variations which almost doubles the amount of observations compared to GPS-only tide gauge. For UNAVCO sc02 station and collocated Friday Harbor NOAA tide gauge we show good agreement between GNSS-reflectometry and traditional mareograph sea level data.

Q-Band (37 to 41 GHz) Satellite Beacon Architecture for RF Propagation Experiments

Science.gov (United States)

Simons, Rainee N.; Wintucky, Edwin G.

2014-01-01

In this paper, the design of a beacon transmitter that will be flown as a hosted payload on a geostationary satellite to enable propagation experiments at Q-band (37 to 41 GHz) frequencies is presented. The beacon uses a phased locked loop stabilized dielectric resonator oscillator and a solid-state power amplifier to achieve the desired output power. The satellite beacon antenna is configured as an offset-fed cutparaboloidal reflector.

Satellite technology and the control of parasitic diseases in Africa ...

African Journals Online (AJOL)

The potential application of these techniques in the surveillance, control and prevention of parasitic diseases in Africa is explored in this write-up. Keywords: surveillance, parasitic diseases, satellite techniques, remote sensing, Geographical Information System (GIS), Global Positioning Sytem (GPS), human and robotic, ...

An airborne meteorological data collection system using satellite relay /ASDAR/

Science.gov (United States)

Bagwell, J. W.; Lindow, B. G.

1978-01-01

The paper describes the aircraft to satellite data relay (ASDAR) project which processes information collected by the navigation and data systems of widebody jet aircraft which cross data-sparse areas of the tropics and southern hemisphere. The ASDAR system consists of a data acquisition and control unit to acquire, store, and format latitude, longitude, altitude, wind speed, wind direction, and outside air temperature data; a transmitter to relay the formatted data via satellite to the ground; and a clock to time the data sampling and transmission periods.

Sensitivity of Depth-Integrated Satellite Lidar to Subaqueous Scattering

Directory of Open Access Journals (Sweden)

Michael F. Jasinski

2011-07-01

Full Text Available A method is presented for estimating subaqueous integrated backscatter using near-nadir viewing satellite lidar. The algorithm takes into account specular reflection of laser light, laser scattering by wind-generated foam as well as sun glint and solar scattering from foam. The formulation is insensitive to the estimate of wind speed but sensitive to the estimate of transmittance used in the atmospheric correction. As a case study, CALIOP data over Tampa Bay were compared to MODIS 645 nm remote sensing reflectance, which previously has been shown to be nearly linearly related to turbidity. The results indicate good correlation on nearly all CALIOP cloud-free dates during the period 2006 through 2007, particularly those with relatively high atmospheric transmittance. The correlation decreases when data are composited over all dates but is still statistically significant, a possible indication of variability in the biogeochemical composition in the water. Overall, the favorable results show promise for the application of satellite lidar integrated backscatter in providing information about subsurface backscatter properties, which can be extracted using appropriate models.

A Performance Improvement Method for Low-Cost Land Vehicle GPS/MEMS-INS Attitude Determination

Directory of Open Access Journals (Sweden)

Li Cong

2015-03-01

Full Text Available Global positioning system (GPS technology is well suited for attitude determination. However, in land vehicle application, low-cost single frequency GPS receivers which have low measurement quality are often used, and external factors such as multipath and low satellite visibility in the densely built-up urban environment further degrade the quality of the GPS measurements. Due to the low-quality receivers used and the challenging urban environment, the success rate of the single epoch ambiguity resolution for dynamic attitude determination is usually quite low. In this paper, a micro-electro-mechanical system (MEMS—inertial navigation system (INS-aided ambiguity resolution method is proposed to improve the GPS attitude determination performance, which is particularly suitable for land vehicle attitude determination. First, the INS calculated baseline vector is augmented with the GPS carrier phase and code measurements. This improves the ambiguity dilution of precision (ADOP, resulting in better quality of the unconstrained float solution. Second, the undesirable float solutions caused by large measurement errors are further filtered and replaced using the INS-aided ambiguity function method (AFM. The fixed solutions are then obtained by the constrained least squares ambiguity decorrelation (CLAMBDA algorithm. Finally, the GPS/MEMS-INS integration is realized by the use of a Kalman filter. Theoretical analysis of the ADOP is given and experimental results demonstrate that our proposed method can significantly improve the quality of the float ambiguity solution, leading to high success rate and better accuracy of attitude determination.

A Performance Improvement Method for Low-Cost Land Vehicle GPS/MEMS-INS Attitude Determination

Science.gov (United States)

Cong, Li; Li, Ercui; Qin, Honglei; Ling, Keck Voon; Xue, Rui

2015-01-01

Global positioning system (GPS) technology is well suited for attitude determination. However, in land vehicle application, low-cost single frequency GPS receivers which have low measurement quality are often used, and external factors such as multipath and low satellite visibility in the densely built-up urban environment further degrade the quality of the GPS measurements. Due to the low-quality receivers used and the challenging urban environment, the success rate of the single epoch ambiguity resolution for dynamic attitude determination is usually quite low. In this paper, a micro-electro-mechanical system (MEMS)—inertial navigation system (INS)-aided ambiguity resolution method is proposed to improve the GPS attitude determination performance, which is particularly suitable for land vehicle attitude determination. First, the INS calculated baseline vector is augmented with the GPS carrier phase and code measurements. This improves the ambiguity dilution of precision (ADOP), resulting in better quality of the unconstrained float solution. Second, the undesirable float solutions caused by large measurement errors are further filtered and replaced using the INS-aided ambiguity function method (AFM). The fixed solutions are then obtained by the constrained least squares ambiguity decorrelation (CLAMBDA) algorithm. Finally, the GPS/MEMS-INS integration is realized by the use of a Kalman filter. Theoretical analysis of the ADOP is given and experimental results demonstrate that our proposed method can significantly improve the quality of the float ambiguity solution, leading to high success rate and better accuracy of attitude determination. PMID:25760057

Evaluation of a regional real-time precise positioning system based on GPS/BeiDou observations in Australia

Science.gov (United States)

Ding, Wenwu; Tan, Bingfeng; Chen, Yongchang; Teferle, Felix Norman; Yuan, Yunbin

2018-02-01

The performance of real-time (RT) precise positioning can be improved by utilizing observations from multiple Global Navigation Satellite Systems (GNSS) instead of one particular system. Since the end of 2012, BeiDou, independently established by China, began to provide operational services for users in the Asia-Pacific regions. In this study, a regional RT precise positioning system is developed to evaluate the performance of GPS/BeiDou observations in Australia in providing high precision positioning services for users. Fixing three hourly updated satellite orbits, RT correction messages are generated and broadcasted by processing RT observation/navigation data streams from the national network of GNSS Continuously Operating Reference Stations in Australia (AUSCORS) at the server side. At the user side, RT PPP is realized by processing RT data streams and the RT correction messages received. RT clock offsets, for which the accuracy reached 0.07 and 0.28 ns for GPS and BeiDou, respectively, can be determined. Based on these corrections, an accuracy of 12.2, 30.0 and 45.6 cm in the North, East and Up directions was achieved for the BeiDou-only solution after 30 min while the GPS-only solution reached 5.1, 15.3 and 15.5 cm for the same components at the same time. A further improvement of 43.7, 36.9 and 45.0 percent in the three directions, respectively, was achieved for the combined GPS/BeiDou solution. After the initialization process, the North, East and Up positioning accuracies were 5.2, 8.1 and 17.8 cm, respectively, for the BeiDou-only solution, while 1.5, 3.0, and 4.7 cm for the GPS-only solution. However, we only noticed a 20.9% improvement in the East direction was obtained for the GPS/BeiDou solution, while no improvements in the other directions were detected. It is expected that such improvements may become bigger with the increasing accuracy of the BeiDou-only solution.

TAGGING, TRACKING AND LOCATING WITHOUT GPS

Energy Technology Data Exchange (ETDEWEB)

Cordaro, J.; Coleman, T.; Shull, D.

2012-07-08

The Savannah River National Laboratory (SRNL) was requested to lead a Law Enforcement Working Group that was formed to collaborate on common operational needs. All agencies represented on the working group ranked their need to tag, track, and locate a witting or unwitting target as their highest priority. Specifically, they were looking for technologies more robust than Global Positioning Satellite (GPS), could communicate back to the owner, and worked where normal cell phone communications did not work or were unreliable. SRNL brought together multiple technologies in a demonstration that was held in in various Alaska venues, including metropolitan, wilderness, and at-sea that met the working group's requirements. Using prototypical technologies from Boeing, On Ramp, and Fortress, SRNL was able to demonstrate the ability to track personnel and material in all scenarios including indoors, in heavily wooden areas, canyons, and in parking garages. In all cases GPS signals were too weak to measure. Bi-directional communication was achieved in areas that Wi-Fi, cell towers, or traditional radios would not perform. The results of the exercise will be presented. These technologies are considered ideal for tracking high value material such has nuclear material with a platform that allows seamless tracking anywhere in the world, indoors or outdoors.

One-Centimeter Orbits in Near-Real Time: The GPS Experience on OSTM/JASON-2

Science.gov (United States)

Haines, Bruce; Armatys, Michael; Bar-Sever, Yoaz; Bertiger, Willy; Desai, Shailen; Dorsey, Angela; Lane, Christopher; Weiss, Jan

2010-01-01

The advances in Precise Orbit Determination (POD) over the past three decades have been driven in large measure by the increasing demands of satellite altimetry missions. Since the launch of Seasat in 1978, both tracking-system technologies and orbit modeling capabilities have evolved considerably. The latest in a series of precise (TOPEX-class) altimeter missions is the Ocean Surface Topography Mission (OSTM, also Jason-2). GPS-based orbit solutions for this mission are accurate to 1-cm (radial RMS) within 3-5 hrs of real time. These GPS-based orbit products provide the basis for a near-real time sea-surface height product that supports increasingly diverse applications of operational oceanography and climate forecasting.

Estudio de las observaciones de tropopausa sobre el cono sur de Sudamérica mediante GPS a bordo de los satélites SAC-C y CHAMP Tropopause observation study over southern South America using GPS data from SAC-C and CHAMP satellites

Directory of Open Access Journals (Sweden)

S. Gabriela Lakkis

2006-12-01

Full Text Available En este trabajo se analiza la validez de la técnica de radio ocultación satelital (GPS llevada a cabo por los satélites SAC-C y CHAMP en tres estaciones chilenas y cuatro argentinas, como referencia del Cono Sur, durante el período 2001-2003. La validez de la técnica se discute por medio de la comparación de los parámetros atmosféricos obtenidos a partir de los satélites con los valores de radiosondeo. Una vez validada la ocultación para las latitudes estudiadas, en función de los datos satelitales se calcula temperatura, presión y altura de la tropopausa, así como valores de presión de vapor de agua y su comportamiento. De los resultados obtenidos del trabajo surge que las ocultaciones arrojan valores que se ajustan muy bien a los tradicionales radiosondeos, especialmente en la zona atmosférica comprendida entre superficie y los 10 kilómetros. De los registros satelitales se estimó que la tropopausa extratropical entre las longitudes 80° S y 60° S presenta valores de temperatura que fluctúan entre los 204 y los 222 K para el Hemisferio Sur hasta el trópico de Capricornio, con una altura mínima de 9 kilómetros y una máxima de 15.3 kilómetros. Para los valores de presión de vapor de agua se observó un comportamiento fuertemente decreciente a medida que se asciende desde la troposfera, hasta llegar a la estabilización en la estratosfera una vez atravesada la tropopausa, donde la variable presenta un cambio en la tasa de variación.Validation of radio occultation technique by Global Positioning System (GPS, carried out on board the SAC-C and CHAMP satellites, is analyzed over three stations of Chile and four for Argentine, as a reference for South America during 2001-2003. The discussion is based on the statistical comparison of the data of GPS with data from nearby radiosonde measurements. Though the occultation concept for obtaining profiles of atmospheric parameters, data derived from GPS, were used to calculate

Review of current GPS methodologies for producing accurate time series and their error sources

Science.gov (United States)

He, Xiaoxing; Montillet, Jean-Philippe; Fernandes, Rui; Bos, Machiel; Yu, Kegen; Hua, Xianghong; Jiang, Weiping

2017-05-01

The Global Positioning System (GPS) is an important tool to observe and model geodynamic processes such as plate tectonics and post-glacial rebound. In the last three decades, GPS has seen tremendous advances in the precision of the measurements, which allow researchers to study geophysical signals through a careful analysis of daily time series of GPS receiver coordinates. However, the GPS observations contain errors and the time series can be described as the sum of a real signal and noise. The signal itself can again be divided into station displacements due to geophysical causes and to disturbing factors. Examples of the latter are errors in the realization and stability of the reference frame and corrections due to ionospheric and tropospheric delays and GPS satellite orbit errors. There is an increasing demand on detecting millimeter to sub-millimeter level ground displacement signals in order to further understand regional scale geodetic phenomena hence requiring further improvements in the sensitivity of the GPS solutions. This paper provides a review spanning over 25 years of advances in processing strategies, error mitigation methods and noise modeling for the processing and analysis of GPS daily position time series. The processing of the observations is described step-by-step and mainly with three different strategies in order to explain the weaknesses and strengths of the existing methodologies. In particular, we focus on the choice of the stochastic model in the GPS time series, which directly affects the estimation of the functional model including, for example, tectonic rates, seasonal signals and co-seismic offsets. Moreover, the geodetic community continues to develop computational methods to fully automatize all phases from analysis of GPS time series. This idea is greatly motivated by the large number of GPS receivers installed around the world for diverse applications ranging from surveying small deformations of civil engineering structures (e

Real-time GPS seismology using a single receiver: method comparison, error analysis and precision validation

Science.gov (United States)

Li, Xingxing

2014-05-01

Earthquake monitoring and early warning system for hazard assessment and mitigation has traditional been based on seismic instruments. However, for large seismic events, it is difficult for traditional seismic instruments to produce accurate and reliable displacements because of the saturation of broadband seismometers and problematic integration of strong-motion data. Compared with the traditional seismic instruments, GPS can measure arbitrarily large dynamic displacements without saturation, making them particularly valuable in case of large earthquakes and tsunamis. GPS relative positioning approach is usually adopted to estimate seismic displacements since centimeter-level accuracy can be achieved in real-time by processing double-differenced carrier-phase observables. However, relative positioning method requires a local reference station, which might itself be displaced during a large seismic event, resulting in misleading GPS analysis results. Meanwhile, the relative/network approach is time-consuming, particularly difficult for the simultaneous and real-time analysis of GPS data from hundreds or thousands of ground stations. In recent years, several single-receiver approaches for real-time GPS seismology, which can overcome the reference station problem of the relative positioning approach, have been successfully developed and applied to GPS seismology. One available method is real-time precise point positioning (PPP) relied on precise satellite orbit and clock products. However, real-time PPP needs a long (re)convergence period, of about thirty minutes, to resolve integer phase ambiguities and achieve centimeter-level accuracy. In comparison with PPP, Colosimo et al. (2011) proposed a variometric approach to determine the change of position between two adjacent epochs, and then displacements are obtained by a single integration of the delta positions. This approach does not suffer from convergence process, but the single integration from delta positions to

Light transmittance under diffuse radiation circumstances

International Nuclear Information System (INIS)

Kieboom, A.M.G. van den; Stoffers, J.A.

1985-01-01

For a grower it is important to know the light transmittance of a greenhouse. With this date (and many others) he is able to make a decision about which greenhouse and covering is the most economical in his situation. It is absolute impossible for a grower to use figures that are functions of: • the orientation of the greenhouse, • the relation between direct and global radiation, • the amount of radiation, etc. • He needs one comparable figure. As a comparable figure for light transmittance of a greenhouse we use the transmittance factor that is estimated with a diffuse radiation source. This figure will be the same as the mean transmittance over one year for that greenhouse, even with extreme direct radiation and independent of the orientation of the greenhouse. (author)

Opportunistic transmitter selection for selfless overlay cognitive radios

KAUST Repository

Shaqfeh, Mohammad; Zafar, Ammar; Alnuweiri, Hussein M.; Alouini, Mohamed-Slim

2013-01-01

We propose an opportunistic strategy to grant channel access to the primary and secondary transmitters in causal selfless overlay cognitive radios over block-fading channels. The secondary transmitter helps the primary transmitter by relaying

Precise Positioning of Uavs - Dealing with Challenging Rtk-Gps Measurement Conditions during Automated Uav Flights

Science.gov (United States)

Zimmermann, F.; Eling, C.; Klingbeil, L.; Kuhlmann, H.

2017-08-01

For some years now, UAVs (unmanned aerial vehicles) are commonly used for different mobile mapping applications, such as in the fields of surveying, mining or archeology. To improve the efficiency of these applications an automation of the flight as well as the processing of the collected data is currently aimed at. One precondition for an automated mapping with UAVs is that the georeferencing is performed directly with cm-accuracies or better. Usually, a cm-accurate direct positioning of UAVs is based on an onboard multi-sensor system, which consists of an RTK-capable (real-time kinematic) GPS (global positioning system) receiver and additional sensors (e.g. inertial sensors). In this case, the absolute positioning accuracy essentially depends on the local GPS measurement conditions. Especially during mobile mapping applications in urban areas, these conditions can be very challenging, due to a satellite shadowing, non-line-of sight receptions, signal diffraction or multipath effects. In this paper, two straightforward and easy to implement strategies will be described and analyzed, which improve the direct positioning accuracies for UAV-based mapping and surveying applications under challenging GPS measurement conditions. Based on a 3D model of the surrounding buildings and vegetation in the area of interest, a GPS geometry map is determined, which can be integrated in the flight planning process, to avoid GPS challenging environments as far as possible. If these challenging environments cannot be avoided, the GPS positioning solution is improved by using obstruction adaptive elevation masks, to mitigate systematic GPS errors in the RTK-GPS positioning. Simulations and results of field tests demonstrate the profit of both strategies.

VLBI Observations of Geostationary Satellites

Science.gov (United States)

Artz, T.; Nothnagel, A.; La Porta, L.

2013-08-01

For a consistent realization of a Global Geodetic Observing System (GGOS), a proper tie between the individual global reference systems used in the analysis of space-geodetic observations is a prerequisite. For instance, the link between the terrestrial, the celestial and the dynamic reference system of artificial Earth orbiters may be realized by Very Long O Baseline Interferometry (VLBI) observations of one or several satellites. In the preparation phase for a dedicated satellite mission, one option to realize this is using a geostationary (GEO) satellite emitting a radio signal in X-Band and/or S-Band and, thus, imitating a quasar. In this way, the GEO satellite can be observed by VLBI together with nearby quasars and the GEO orbit can, thus, be determined in a celestial reference frame. If the GEO satellite is, e.g., also equipped with a GNSS-type transmitter, a further tie between GNSS and VLBI may be realized. In this paper, a concept for the generation of a radio signal is shown. Furthermore, simulation studies for estimating the GEO position are presented with a GEO satellite included in the VLBI schedule. VLBI group delay observations are then simulated for the quasars as well as for the GEO satellite. The analysis of the simulated observations shows that constant orbit changes are adequately absorbed by estimated orbit parameters. Furthermore, the post-fit residuals are comparable to those from real VLBI sessions.

Using GPS and leveling data in local precise geoid determination and case study

Science.gov (United States)

Erol, B.; Çelik, R. N.; Erol, S.

2003-04-01

As an important result of developments in high technology, satellite based positioning system has become to use in geodesy and surveying professions. These developments made the measurement works more accurate, more practical and more economic. Today, one of the most recent used satellite based positioning system is GPS (Global Positioning System) and it serves to a very wide range of geodetic applications from monitoring earth crustal deformations till building the basis for a GIS (Geographical Information Systems). The most efficient way to utilize GPS measurement system for mentioned aims is having a reliable geodetic infrastructure in working area. Geodetic infrastructure is a extraterrestrial and time system and involved 4D geodetic reference networks. The forth element of mentioned geodetic reference system is time because having an accurate and reliable geodetic infrastructure is needed to up-date according to physical realities of the region. By the help of a well designed geodetic infrastructure accurate and reliable coordinates of a point can be generated economically every time in a global and up-to-date system. Geoid is one of the important parts of a geodetic infrastructure. As it is well known, geoid is the equipotential surface of the Earth's gravity field which best fits, in a least squares sense, global mean sea level and it is reference for physical height systems like orthometric and normal heights. In the most of the applications, vertical position of a point is expressed with orthometric or normal height. Orthometric or normal height is a physical concept and gives vertical position of a point uniquely. On the other hand, vertical position of a point is derived in a geometrical system according to GPS measurements. GPS datum is WGS84 and in this system, an ellipsoidal height of a point is calculated according to WGS84 ellipsoid. So, it is an necessity to transform the ellipsoidal heights to orthometric heights and this procedure is managed with

Factors influencing the movements during the breeding season of a female booted eagle (Aquila pennata tagged by satellite in central Catalonia (Spain

Directory of Open Access Journals (Sweden)

Bosch Josep

2016-12-01

Full Text Available Foraging movements during the breeding season are a poorly studied aspect of booted eagle behaviour. We have investigated the relationship between weather and other abiotic factors and foraging behaviour, and also resource use by a female booted eagle, tagged by satellite-GPS transmitter in central Catalonia, during summer 2012 and spring 2013. Generalized Linear Models (GLMs revealed that the distance travelled from the nest was significantly related to temperature, but also to the time of day and the age of chicks. Temperature also had a significant positive influence on flight altitude and the latter on flight speed. The Resource Utilization Function (RUF showed significant resource use in locations close to water (rivers and water bodies and also in agricultural areas, preferably close to urban areas and rivers. On the other hand, unlike in other areas of Spain, the use of the edges between forest and agricultural areas and forest areas themselves showed negative coefficients with values not significant, perhaps related to changes in prey availability in the traditional hunting grounds.

GPS Interference Mitigation Using Derivative-free Kalman Filter-based RNN

Directory of Open Access Journals (Sweden)

W. L. Mao

2016-09-01

Full Text Available The global positioning system (GPS with accurate positioning and timing properties has become integral part of all applications around the world. Radio frequency interference can significantly decrease the performance of GPS receivers or even completely prohibit the acquisition or tracking of satellites. The approaches of system performances that can be further enhanced by preprocessing to reject the jamming signal will be investigated. A recurrent neural network (RNN predictor for the GPS anti-jamming applications will be proposed. The adaptive RNN predictor is utilized to accurately predict the narrowband waveform based on an unscented Kalman filter (UKF-based algorithm. The UKF algorithm as a derivative-free alternative to the extended Kalman filter (EKF in the framework of state-estimation is adopted to achieve better performance in terms of convergence rate and quality of solution. The adaptive RNN filter can be successfully applied for the suppression of interference with a number of different narrowband formats, i.e. continuous wave interference (CWI, multi-tone CWI, swept CWI and pulsed CWI, to emulate realistic circumstances. Simulation results show that the proposed UKF-based scheme can offer the superior performances to suppress the interference over the conventional methods by computing mean squared prediction error (MSPE and signal-to-noise ratio (SNR improvements.

The synchronization method for distributed small satellite SAR

Science.gov (United States)

Xing, Lei; Gong, Xiaochun; Qiu, Wenxun; Sun, Zhaowei

2007-11-01

One of critical requirement for distributed small satellite SAR is the trigger time precision when all satellites turning on radar loads. This trigger operation is controlled by a dedicated communication tool or GPS system. In this paper a hardware platform is proposed which has integrated navigation, attitude control, and data handling system together. Based on it, a probabilistic synchronization method is proposed for SAR time precision requirement with ring architecture. To simplify design of transceiver, half-duplex communication way is used in this method. Research shows that time precision is relevant to relative frequency drift rate, satellite number, retry times, read error and round delay length. Installed with crystal oscillator short-term stability 10 -11 magnitude, this platform can achieve and maintain nanosecond order time error with a typical three satellites formation experiment during whole operating process.

APMP Pilot Study on Transmittance Haze

Science.gov (United States)

Liu, Wen-Chun; Hwang, Jisoo; Koo, Annette; Wu, Houping; Leecharoen, Rojana; Yu, Hsueh-Ling

2018-02-01

Five NMIs within APMP, including CMS/ITRI, MSL, NIM, NIMT and KRISS from TCPR applied to the APMP technical committee initiative project for funding to carry out a pilot comparison of transmittance haze in 2012. The project started in 2014 and the final report was completed at the end of 2016. In this pilot comparison, three different haze standards were adopted, and transmittance haze for each standard was measured according to ASTM D1003 or ISO 14782. This paper presents the first results of an APMP pilot study of transmittance haze and the analysis of the variation among different haze measurement systems which are commonly used. The study shows that the variables such as sphere multiplier, transmittance distribution, fluorescence of samples and optical path of the incident beam cause discrepancies among NMIs and highlight deficiencies in current documentary standards.

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.

J2 : An evaluation of new estimates from GPS, GRACE, and load models compared to SLR

NARCIS (Netherlands)

Lavallée, D.A.; Moore, P.; Clarke, P.J.; Petrie, E.J.; Van Dam, T.; King, M.A.

2010-01-01

Changes in J2, resulting from past and present changes in Earth's climate, are traditionally observed by Satellite Laser ranging (SLR). Assuming an elastic Earth, it is possible to infer changes in J2 from changes in Earth's shape observed by GPS. We compare estimates of non-secular J2 changes from

Radiation hardening of CMOS-based circuitry in SMART transmitters

International Nuclear Information System (INIS)

Loescher, D.H.

1993-02-01

Process control transmitters that incorporate digital signal processing could be used advantageously in nuclear power plants; however, because such transmitters are too sensitive to radiation, they are not used. The Electric Power Research Institute sponsored work at Sandia National Laboratories under EPRI contract RP2614-58 to determine why SMART transmitters fail when exposed to radiation and to design and demonstrate SMART transmitter circuits that could tolerate radiation. The term ''SMART'' denotes transmitters that contain digital logic. Tests showed that transmitter failure was caused by failure of the complementary metal oxide semiconductors (CMOS)-integrated circuits which are used extensively in commercial transmitters. Radiation-hardened replacements were not available for the radiation-sensitive CMOS circuits. A conceptual design showed that a radiation-tolerant transmitter could be constructed. A prototype for an analog-to-digital converter subsection worked satisfactorily after a total dose of 30 megarads(Si). Encouraging results were obtained from preliminary bench-top tests on a dc-to-dc converter for the power supply subsection

Precise orbit determination of Multi-GNSS constellation including GPS GLONASS BDS and GALIEO

Science.gov (United States)

Dai, Xiaolei

2014-05-01

In addition to the existing American global positioning system (GPS) and the Russian global navigation satellite system (GLONASS), the new generation of GNSS is emerging and developing, such as the Chinese BeiDou satellite navigation system (BDS) and the European GALILEO system. Multi-constellation is expected to contribute to more accurate and reliable positioning and navigation service. However, the application of multi-constellation challenges the traditional precise orbit determination (POD) strategy that was designed usually for single constellation. In this contribution, we exploit a more rigorous multi-constellation POD strategy for the ongoing IGS multi-GNSS experiment (MGEX) where the common parameters are identical for each system, and the frequency- and system-specified parameters are employed to account for the inter-frequency and inter-system biases. Since the authorized BDS attitude model is not yet released, different BDS attitude model are implemented and their impact on orbit accuracy are studied. The proposed POD strategy was implemented in the PANDA (Position and Navigation Data Analyst) software and can process observations from GPS, GLONASS, BDS and GALILEO together. The strategy is evaluated with the multi-constellation observations from about 90 MGEX stations and BDS observations from the BeiDou experimental tracking network (BETN) of Wuhan University (WHU). Of all the MGEX stations, 28 stations record BDS observation, and about 80 stations record GALILEO observations. All these data were processed together in our software, resulting in the multi-constellation POD solutions. We assessed the orbit accuracy for GPS and GLONASS by comparing our solutions with the IGS final orbit, and for BDS and GALILEO by overlapping our daily orbit solution. The stability of inter-frequency bias of GLONASS and inter-system biases w.r.t. GPS for GLONASS, BDS and GALILEO were investigated. At last, we carried out precise point positioning (PPP) using the multi

An injectable acoustic transmitter for juvenile salmon

Science.gov (United States)

Deng, Z. D.; Carlson, T. J.; Li, H.; Xiao, J.; Myjak, M. J.; Lu, J.; Martinez, J. J.; Woodley, C. M.; Weiland, M. A.; Eppard, M. B.

2015-01-01

Salmon recovery and the potential detrimental effects of dams on fish have been attracting national attention due to the environmental and economic implications. In recent years acoustic telemetry has been the primary method for studying salmon passage. However, the size of the existing transmitters limits the minimum size of fish that can be studied, introducing a bias to the study results. We developed the first acoustic fish transmitter that can be implanted by injection instead of surgery. The new injectable transmitter lasts four times longer and weighs 30% less than other transmitters. Because the new transmitter costs significantly less to use and may substantially reduce adverse effects of implantation and tag burden, it will allow for study of migration behavior and survival of species and sizes of fish that have never been studied before. The new technology will lead to critical information needed for salmon recovery and the development of fish-friendly hydroelectric systems.

GPS data processing of networks with mixed single- and dual-frequency receivers for deformation monitoring

Science.gov (United States)

Zou, X.; Deng, Z.; Ge, M.; Dick, G.; Jiang, W.; Liu, J.

2010-07-01

In order to obtain crustal deformations of higher spatial resolution, existing GPS networks must be densified. This densification can be carried out using single-frequency receivers at moderate costs. However, ionospheric delay handling is required in the data processing. We adapt the Satellite-specific Epoch-differenced Ionospheric Delay model (SEID) for GPS networks with mixed single- and dual-frequency receivers. The SEID model is modified to utilize the observations from the three nearest dual-frequency reference stations in order to avoid contaminations from more remote stations. As data of only three stations are used, an efficient missing data constructing approach with polynomial fitting is implemented to minimize data losses. Data from large scale reference networks extended with single-frequency receivers can now be processed, based on the adapted SEID model. A new data processing scheme is developed in order to make use of existing GPS data processing software packages without any modifications. This processing scheme is evaluated using a sub-network of the German SAPOS network. The results verify that the new scheme provides an efficient way to densify existing GPS networks with single-frequency receivers.

L’ITSS “Majorana-Giorgi” di Genova in orbita con i sistemi di navigazione via satellite

Directory of Open Access Journals (Sweden)

Primo Bartoli

2015-03-01

GNSS satellites (GPS, GLONASS or Galileo, based on a commercial multi-constellation receiver and on a software program developed in National Instruments LabVIEW, with the dual aim to explore the techniques of satellite navigation and to provide an attractive teaching aid for universities and secondary level technical institutes.

Sources of Error in Satellite Navigation Positioning

Directory of Open Access Journals (Sweden)

Jacek Januszewski

2017-09-01

Full Text Available An uninterrupted information about the user’s position can be obtained generally from satellite navigation system (SNS. At the time of this writing (January 2017 currently two global SNSs, GPS and GLONASS, are fully operational, two next, also global, Galileo and BeiDou are under construction. In each SNS the accuracy of the user’s position is affected by the three main factors: accuracy of each satellite position, accuracy of pseudorange measurement and satellite geometry. The user’s position error is a function of both the pseudorange error called UERE (User Equivalent Range Error and user/satellite geometry expressed by right Dilution Of Precision (DOP coefficient. This error is decomposed into two types of errors: the signal in space ranging error called URE (User Range Error and the user equipment error UEE. The detailed analyses of URE, UEE, UERE and DOP coefficients, and the changes of DOP coefficients in different days are presented in this paper.

NRL transmittance measurements at DIRT-III

Science.gov (United States)

Curcio, J. A.; Haught, K. M.; Woytko, M. A.; Gott, C.

1981-06-01

This is a final report on NRL experiments at the DIRT-III tests at Fort Polk, Louisiana in April - May 1980. Spectral transmission data at 3 wavelengths 0.55 microns, 1.06 microns and 10.4 microns is reported for 27 events in natural soil and various prepared soils. Spectral transmittance of smoke and dust clouds generated by explosive charges was found to be independent of wavelengths in about 50% of the events where useful data was obtained. When the charge was buried in wet natural soil transmittance at 10.4 microns was transmittance at 0.55 microns .

Refraction of Radio Waves on the Radio-Occultation Satellite-to-Satellite Paths as a Characteristic of the Atmospheric State

Science.gov (United States)

Matyugov, S. S.; Yakovlev, O. I.; Pavelyev, A. G.; Pavelyev, A. A.; Anufriev, V. A.

2017-10-01

We present the results of analyzing the radio-wave refractive characteristics measured on the radio-occultation paths between the GPS navigation satellites and the FORMOSAT-3 research satellites in the central region of the European territory of Russia in 2007-2013. The diurnal, seasonal, and annual variations in the refraction angle at altitudes of 2 to 25 km are discussed. It is shown that the refraction angle can be used as an independent characteristic of the atmospheric state and its long-term variation trends. Diurnal and nocturnal variations in the refraction angle in the winter and summer seasons are analyzed. Trends in the atmospheric refraction variations over seven years are discussed.

PRECISE POSITIONING OF UAVS – DEALING WITH CHALLENGING RTK-GPS MEASUREMENT CONDITIONS DURING AUTOMATED UAV FLIGHTS

Directory of Open Access Journals (Sweden)

F. Zimmermann

2017-08-01

Full Text Available For some years now, UAVs (unmanned aerial vehicles are commonly used for different mobile mapping applications, such as in the fields of surveying, mining or archeology. To improve the efficiency of these applications an automation of the flight as well as the processing of the collected data is currently aimed at. One precondition for an automated mapping with UAVs is that the georeferencing is performed directly with cm-accuracies or better. Usually, a cm-accurate direct positioning of UAVs is based on an onboard multi-sensor system, which consists of an RTK-capable (real-time kinematic GPS (global positioning system receiver and additional sensors (e.g. inertial sensors. In this case, the absolute positioning accuracy essentially depends on the local GPS measurement conditions. Especially during mobile mapping applications in urban areas, these conditions can be very challenging, due to a satellite shadowing, non-line-of sight receptions, signal diffraction or multipath effects. In this paper, two straightforward and easy to implement strategies will be described and analyzed, which improve the direct positioning accuracies for UAV-based mapping and surveying applications under challenging GPS measurement conditions. Based on a 3D model of the surrounding buildings and vegetation in the area of interest, a GPS geometry map is determined, which can be integrated in the flight planning process, to avoid GPS challenging environments as far as possible. If these challenging environments cannot be avoided, the GPS positioning solution is improved by using obstruction adaptive elevation masks, to mitigate systematic GPS errors in the RTK-GPS positioning. Simulations and results of field tests demonstrate the profit of both strategies.

Simultaneous spacecraft orbit estimation and control based on GPS measurements via extended Kalman filter

Directory of Open Access Journals (Sweden)

Tamer Mekky Ahmed Habib

2013-06-01

Full Text Available The primary aim of this work is to provide simultaneous spacecraft orbit estimation and control based on the global positioning system (GPS measurements suitable for application to the next coming Egyptian remote sensing satellites. Disturbance resulting from earth’s oblateness till the fourth order (i.e., J4 is considered. In addition, aerodynamic drag and random disturbance effects are taken into consideration.

A small satellite design for deep space network testing and training

Science.gov (United States)

Mcwilliams, Dennis; Slatton, Clint; Norman, Cassidy; Araiza, Joe; Jones, Jason; Tedesco, Mark; Wortman, Michael; Opiela, John; Lett, Pat; Clavenna, Michael

1993-01-01

With the continuing exploration of the Solar System and the reemphasis on Earth focused missions, the need for faster data transmission rates has grown. Ka-band could allow a higher data delivery rate over the current X-band, however the adverse effects of the Earth's atmosphere on Ka are as yet unknown. The Deep Space Network and Jet Propulsion Lab have proposed to launch a small satellite that would simultaneously transmit X and Ka signals to test the viability of switching to Ka-band. The Mockingbird Design Team at the University of Texas at Austin applied small satellite design principles to achieve this objective. The Mockingbird design, named BATSAT, incorporates simple, low-cost systems designed for university production and testing. The BATSAT satellite is a 0.64 m diameter, spherical panel led satellite, mounted with solar cells and omni-directional antennae. The antennae configuration negates the need for active attitude control or spin stabilization. The space-frame truss structure was designed for 11 g launch loads while allowing for easy construction and solar-panel mounting. The communication system transmits at 1 mW by carrying the required Ka and X-band transmitters, as well as an S band transmitter used for DSN training. The power system provides the 8.6 W maximum power requirements via silicon solar arrays and nickel-cadmium batteries. The BATSAT satellite will be lofted into an 1163 km, 70 deg orbit by the Pegasus launch system. This orbit fulfills DSN dish slew rate requirements while keeping the satellite out of the heaviest regions of the Van Allen radiation belts. Each of the three DSN stations capable of receiving Ka-band (Goldstone, Canberra, and Madrid) will have an average of 85 minutes of view-time per day over the satellites ten year design life. Mockingbird Designs hopes that its small satellite design will not only be applicable to this specific mission scenario, but that it could easily be modified for instrument capability for

A small satellite design for deep space network testing and training

Science.gov (United States)

McWilliams, Dennis; Slatton, Clint; Norman, Cassidy; Araiza, Joe; Jones, Jason; Tedesco, Mark; Wortman, Michael; Opiela, John; Lett, Pat; Clavenna, Michael

1993-05-01

With the continuing exploration of the Solar System and the reemphasis on Earth focused missions, the need for faster data transmission rates has grown. Ka-band could allow a higher data delivery rate over the current X-band, however the adverse effects of the Earth's atmosphere on Ka are as yet unknown. The Deep Space Network and Jet Propulsion Lab have proposed to launch a small satellite that would simultaneously transmit X and Ka signals to test the viability of switching to Ka-band. The Mockingbird Design Team at the University of Texas at Austin applied small satellite design principles to achieve this objective. The Mockingbird design, named BATSAT, incorporates simple, low-cost systems designed for university production and testing. The BATSAT satellite is a 0.64 m diameter, spherical panel led satellite, mounted with solar cells and omni-directional antennae. The antennae configuration negates the need for active attitude control or spin stabilization. The space-frame truss structure was designed for 11 g launch loads while allowing for easy construction and solar-panel mounting. The communication system transmits at 1 mW by carrying the required Ka and X-band transmitters, as well as an S band transmitter used for DSN training. The power system provides the 8.6 W maximum power requirements via silicon solar arrays and nickel-cadmium batteries. The BATSAT satellite will be lofted into an 1163 km, 70 deg orbit by the Pegasus launch system. This orbit fulfills DSN dish slew rate requirements while keeping the satellite out of the heaviest regions of the Van Allen radiation belts. Each of the three DSN stations capable of receiving Ka-band (Goldstone, Canberra, and Madrid) will have an average of 85 minutes of view-time per day over the satellites ten year design life. Mockingbird Designs hopes that its small satellite design will not only be applicable to this specific mission scenario, but that it could easily be modified for instrument capability for

47 CFR 90.215 - Transmitter measurements.

Science.gov (United States)

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Transmitter measurements. 90.215 Section 90.215... MOBILE RADIO SERVICES General Technical Standards § 90.215 Transmitter measurements. (a) The licensee of... current station authorization. On authorizations stating only the input power to the final radiofrequency...

GPS operations at Olkiluoto in 2011

International Nuclear Information System (INIS)

Koivula, H.; Kallio, U.; Nyberg, S.; Jokela, J.; Poutanen, M.

2012-06-01

The Finnish Geodetic Institute has studied crustal deformations at Olkiluoto, Kivetty and Romuvaara in co-operation with Posiva Oy since 1995. At Olkiluoto a total of 32 GPS campaigns have been carried out at inner network since 1995 and 17 campaigns at outer network since 2003. Kivetty and Romuvaara were not measured in 2011. In the Olkiluoto inner network 80 percent of the estimated change rates are smaller than 0.10 mm/a. One third of the change rates are statistically significant. They are mainly related to the Olkiluoto permanent station (GPS1) and to the pillars GPS6 and GPS13. The change rates related to GPS6 are not realistic due to the site-specific changes affecting the time series. The maximum change rate (-0.20 mm/a ± 0.05 mm/a) is related to GPS13. The time series of GPS13 is half the length of other pillars and therefore, the change rates are more uncertain. In the Olkiluoto outer network the maximum and statistically significant change rate is between GPS1-GPS11 (0.39 mm/a ± 0.06 mm/a). Pillar GPS12 was not observed this year. The change rates of baselines GPS1-GPS14 and GPS1-GPS15 are first time statistically significant. The change rates indicate a small movement of the GPS1 pillar. The baseline GPS1-GPS11 crosses an old fracture zone locating in the direction of the Eurajoensalmi, which might be a reason for the deformation. On the other hand, the Onkalo excavations in the vicinity of the Olkiluoto permanent station (GPS1) may cause some movement. Electronic distance measurements have been performed at Olkiluoto at the baseline GPS7-GPS8 using the Mekometer since 2002. The measurements have been carried out simultaneously with GPS campaigns. Based on 19 measurements in 10 years, the trends of the two time series seems to be similar. Due to unmodelled or dismodelled geometrical offsets and the scale difference between GPS measurements and EDM there is about 0.3 mm difference between distances GPS7-GPS8 derived from GPS measurements and EDM. It is

GPS operations at Olkiluoto in 2011

Energy Technology Data Exchange (ETDEWEB)

Koivula, H.; Kallio, U.; Nyberg, S.; Jokela, J.; Poutanen, M. [Finnish Geodetic Institute, Masala (Finland)

2012-06-15

The Finnish Geodetic Institute has studied crustal deformations at Olkiluoto, Kivetty and Romuvaara in co-operation with Posiva Oy since 1995. At Olkiluoto a total of 32 GPS campaigns have been carried out at inner network since 1995 and 17 campaigns at outer network since 2003. Kivetty and Romuvaara were not measured in 2011. In the Olkiluoto inner network 80 percent of the estimated change rates are smaller than 0.10 mm/a. One third of the change rates are statistically significant. They are mainly related to the Olkiluoto permanent station (GPS1) and to the pillars GPS6 and GPS13. The change rates related to GPS6 are not realistic due to the site-specific changes affecting the time series. The maximum change rate (-0.20 mm/a {+-} 0.05 mm/a) is related to GPS13. The time series of GPS13 is half the length of other pillars and therefore, the change rates are more uncertain. In the Olkiluoto outer network the maximum and statistically significant change rate is between GPS1-GPS11 (0.39 mm/a {+-} 0.06 mm/a). Pillar GPS12 was not observed this year. The change rates of baselines GPS1-GPS14 and GPS1-GPS15 are first time statistically significant. The change rates indicate a small movement of the GPS1 pillar. The baseline GPS1-GPS11 crosses an old fracture zone locating in the direction of the Eurajoensalmi, which might be a reason for the deformation. On the other hand, the Onkalo excavations in the vicinity of the Olkiluoto permanent station (GPS1) may cause some movement. Electronic distance measurements have been performed at Olkiluoto at the baseline GPS7-GPS8 using the Mekometer since 2002. The measurements have been carried out simultaneously with GPS campaigns. Based on 19 measurements in 10 years, the trends of the two time series seems to be similar. Due to unmodelled or dismodelled geometrical offsets and the scale difference between GPS measurements and EDM there is about 0.3 mm difference between distances GPS7-GPS8 derived from GPS measurements and EDM

Positioning performance improvements with European multiple-frequency satellite navigation - Galileo

Science.gov (United States)

Ji, Shengyue

2008-10-01

The rapid development of Global Positioning System has demonstrated the advantages of satellite based navigation systems. In near future, there will be a number of Global Navigation Satellite System (GNSS) available, i.e. modernized GPS, Galileo, restored GLONASS, BeiDou and many other regional GNSS augmentation systems. Undoubtedly, the new GNSS systems will significantly improve navigation performance over current GPS, with a better satellite coverage and multiple satellite signal bands. In this dissertation, the positioning performance improvement of new GNSS has been investigated based on both theoretical analysis and numerical study. First of all, the navigation performance of new GNSS systems has been analyzed, particularly for urban applications. The study has demonstrated that Receiver Autonomous Integrity Monitoring (RAIM) performance can be significantly improved with multiple satellite constellations, although the position accuracy improvement is limited. Based on a three-dimensional urban building model in Hong Kong streets, it is found that positioning availability is still very low in high-rising urban areas, even with three GNSS systems. On the other hand, the discontinuity of navigation solutions is significantly reduced with the combined constellations. Therefore, it is possible to use cheap DR systems to bridge the gaps of GNSS positioning, with high accuracy. Secondly, the ambiguity resolution performance has been investigated with Galileo multiple frequency band signals. The ambiguity resolution performance of three different algorithms is compared, including CAR, ILS and improved CAR methods (a new method proposed in this study). For short baselines, with four frequency Galileo data, it is highly possible to achieve reliable single epoch ambiguity resolution, when the carrier phase noise level is reasonably low (i.e. less than 6mm). For long baselines (up to 800 km), the integer ambiguity can be determined within 1 min on average. Ambiguity

Multiple Interference Cancellation Performance for GPS Receivers with Dual-Polarized Antenna Arrays

Directory of Open Access Journals (Sweden)

Moeness G. Amin

2008-11-01

Full Text Available This paper examines the interference cancellation performance in global positioning system (GPS receivers equipped with dual-polarized antenna arrays. In dense jamming environment, different types of interferers can be mitigated by the dual-polarized antennas, either acting individually or in conjunction with other receiver antennas. We apply minimum variance distorntionless response (MVDR method to a uniform circular dual-polarized antenna array. The MVDR beamformer is constructed for each satellite. Analysis of the eigenstructures of the covariance matrix and the corresponding weight vector polarization characteristics are provided. Depending on the number of jammers and jammer polarizations, the array chooses to expend its degrees of freedom to counter the jammer polarization or/and use phase coherence to form jammer spatial nulls. Results of interference cancellations demonstrate that applying multiple MVDR beamformers, each for one satellite, has a superior cancellation performance compared to using only one MVDR beamformer for all satellites in the field of view.

47 CFR 101.129 - Transmitter location.

Science.gov (United States)

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Transmitter location. 101.129 Section 101.129... SERVICES Technical Standards § 101.129 Transmitter location. (a) The applicant must determine, prior to... adequate to render the service proposed. In cases of questionable antenna locations, it is desirable to...

Space Solar Power: Satellite Concepts

Science.gov (United States)

Little, Frank E.

1999-01-01

Space Solar Power (SSP) applies broadly to the use of solar power for space related applications. The thrust of the NASA SSP initiative is to develop concepts and demonstrate technology for applying space solar power to NASA missions. Providing power from satellites in space via wireless transmission to a receiving station either on earth, another celestial body or a second satellite is one goal of the SSP initiative. The sandwich design is a satellite design in which the microwave transmitting array is the front face of a thin disk and the back of the disk is populated with solar cells, with the microwave electronics in between. The transmitter remains aimed at the earth in geostationary orbit while a system of mirrors directs sunlight to the photovoltaic cells, regardless of the satellite's orientation to the sun. The primary advantage of the sandwich design is it eliminates the need for a massive and complex electric power management and distribution system for the satellite. However, it requires a complex system for focusing sunlight onto the photovoltaic cells. In addition, positioning the photovoltaic array directly behind the transmitting array power conversion electronics will create a thermal management challenge. This project focused on developing designs and finding emerging technology to meet the challenges of solar tracking, a concentrating mirror system including materials and coatings, improved photovoltaic materials and thermal management.

Opportunistic transmitter selection for selfless overlay cognitive radios

KAUST Repository

Shaqfeh, Mohammad

2013-11-01

We propose an opportunistic strategy to grant channel access to the primary and secondary transmitters in causal selfless overlay cognitive radios over block-fading channels. The secondary transmitter helps the primary transmitter by relaying the primary messages opportunistically, aided by a buffer to store the primary messages temporarily. The optimal channel-aware transmitter- selection strategy is the solution of the maximization of the average secondary rate under the average primary rate requirement and the buffer stability constraints. Numerical results demonstrate the gains of the proposed opportunistic selection strategy. © 2013 IEEE.

High frequency variations of Earth Rotation Parameters from GPS and GLONASS observations.

Science.gov (United States)

Wei, Erhu; Jin, Shuanggen; Wan, Lihua; Liu, Wenjie; Yang, Yali; Hu, Zhenghong

2015-01-28

The Earth's rotation undergoes changes with the influence of geophysical factors, such as Earth's surface fluid mass redistribution of the atmosphere, ocean and hydrology. However, variations of Earth Rotation Parameters (ERP) are still not well understood, particularly the short-period variations (e.g., diurnal and semi-diurnal variations) and their causes. In this paper, the hourly time series of Earth Rotation Parameters are estimated using Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), and combining GPS and GLONASS data collected from nearly 80 sites from 1 November 2012 to 10 April 2014. These new observations with combining different satellite systems can help to decorrelate orbit biases and ERP, which improve estimation of ERP. The high frequency variations of ERP are analyzed using a de-trending method. The maximum of total diurnal and semidiurnal variations are within one milli-arcseconds (mas) in Polar Motion (PM) and 0.5 milli-seconds (ms) in UT1-UTC. The semidiurnal and diurnal variations are mainly related to the ocean tides. Furthermore, the impacts of satellite orbit and time interval used to determinate ERP on the amplitudes of tidal terms are analyzed. We obtain some small terms that are not described in the ocean tide model of the IERS Conventions 2010, which may be caused by the strategies and models we used or the signal noises as well as artifacts. In addition, there are also small differences on the amplitudes between our results and IERS convention. This might be a result of other geophysical excitations, such as the high-frequency variations in atmospheric angular momentum (AAM) and hydrological angular momentum (HAM), which needs more detailed analysis with more geophysical data in the future.

Selection of the signal synchronization method in software GPS receivers

Directory of Open Access Journals (Sweden)

Vlada S. Sokolović

2011-04-01

Full Text Available Introduction This paper presents a critical analysis of the signal processing flow carried out in a software GPS receiver and a critical comparison of different architectures for signal processing within the GPS receiver. A model of software receivers is shown. Based on the displayed model, a receiver has been realized in the MATLAB software package, in which the simulations of signal processing were carried out. The aim of this paper is to demonstrate the advantages and disadvantages of different methods of the synchronization of signals in the receiver, and to propose a solution acceptable for possible implementation. The signal processing flow was observed from the input circuit to the extraction of the bits of the navigation message. The entire signal processing was performed on the L1 signal and the data collected by the input circuit SE4110. A radio signal from the satellite was accepted with the input circuit, filtered and translated into a digital form. The input circuit ends with the hardware of the receiver. A digital signal from the input circuit is brought into the PC Pentium 4 (AMD 3000 + where the receiver is realized in Matlab. Model of software GPS receiver The first level of processing is signal acquisition. Signal acquisition was realized using the cyclic convolution. The acquisition process was carried out by measuring signals from satellites, and these parameters are passed to the next level of processing. The next level was done by monitoring the synchronization signal and extracting the navigation message bits. On the basis of the detection of the navigation message the receiver calculates the position of a satellite and then, based on the position of the satellite, its own position. Tracking of GPS signal synchronization In order to select the most acceptable method of signal synchronization in the receiver, different methods of signal synchronization are compared. The early-late-DLL (Delay Lock Loop, TDL (Tau Dither Loop

Variation of GPS-TEC in a low latitude Indian region during the year 2012 and 2013

Science.gov (United States)

Patel, Nilesh C.; Karia, Sheetal P.; Pathak, Kamlesh N.

2018-05-01

The paper is based on the ionospheric variations in terms of vertical total electron content (VTEC) for the period from January 2012 to December 2013 based on the analysis of dual frequency signals from the Global Positioning System (GPS) satellites recorded at ground stations Surat (21.16°N, 72.78°E Geog.), situated under the northern crest of the equatorial ionization anomaly region (EIA) and other three International GNSS Service (IGS) stations Bangalore (13.02°N, 77.57°E Geog.), Hyderabad (17.25°N, 78.30°E Geog.), and Lucknow (26.91°N, 80.95°E Geog.) in India. We describe the diurnal and seasonal characteristics. It was observed that GPS-TEC reaches its maximum value between 12:00 and 16:00 IST. Further, Seasonal variations of GPS-TEC is categorized into four seasons, i.e., March equinox (February, March, and April), June solstice (May, June, and July), September equinox (August, September, and October) and December solstice (November, December and January). The forenoon rate of production in Lucknow (beyond EIA crest) is faster than Bangalore, Hyderabad and Surat station. It is found that September equinox shows GPS-TEC slightly higher than the March equinox, followed by June solstice and the lowest GPS-TEC are in winter solstice at four stations. The equinoctial asymmetry clearly observed in the current study. Also GPS-TEC shows a semiannual variation.

Satellite communication system for emergency monitoring within the Chernobyl exclusion zone

International Nuclear Information System (INIS)

Franchini, C.; Mensa, M.; Kanevsky, V.A.

1997-01-01

A Satellite Emergency Monitoring system of the Chernobyl Exclusive Zone (SEM CEZ) was designed to provide the Ukraine authorities and the neighbouring countries with updated information when an emergency situation occurs in the Exclusion Zone. This is of particular importance when environment contamination has transboundary effect. SEM system consists of mobile and fixed sensors reporting data via a dedicated satellite communications link. Mobile sensors are fitted with Global Positioning System (GPS) receivers that determine current coordinates of the sensor. Sensors data are transmitted to the Emergency Monitoring Centre equipped with PC and a satellite terminal. Both sensors data and the current position are visualized on digital maps

Digital transmitter for data bus communications system

Science.gov (United States)

Proch, G. E. (Inventor)

1975-01-01

An improved digital transmitter for transmitting serial pulse code modulation (pcm) data at high bit rates over a transmission line is disclosed. When not transmitting, the transmitter features a high output impedance which prevents the transmitter from loading the transmission line. The pcm input is supplied to a logic control circuit which produces two discrete logic level signals which are supplied to an amplifier. The amplifier, which is transformer coupled to the output isolation circuitry, converts the discrete logic level signals to two high current level, ground isolated signals in the secondary windings of the coupling transformer. The latter signals are employed as inputs to the isolation circuitry which includes two series transistor pairs operating into a hybrid transformer functioning to isolate the transmitter circuitry from the transmission line.

Accuracy comparison of Pléiades satellite ortho-images using GPS ...

African Journals Online (AJOL)

resolution satellite ortho-image when different types of ground control are used. This required the execution of two orthorectification tests where only the type of GCPs differed. The results of these tests were interesting since it highlighted the ...

Research-related intercultural higher education in satellite geodesy

Science.gov (United States)

Mayer, M.; Heck, B.; Krueger, C. P.

2009-04-01

In order to improve the education of young researchers (master degree, PhD, PostDocs) a cooperation between the Department of Geomatics (DGEOM), Federal University of Paraná (UFPR), Curitiba (Brazil) and the Geodetic Institute (GIK), University Karlsruhe (TH), Karlsruhe (Germany) was established which now exists since more than five years. The joint venture is actually called "PROBRAL: Precise positioning and height determination by means of GPS: Modeling of errors and transformation into physical heights" and focuses on research and education within the field of satellite geodesy. PROBRAL is funded by the Brazilian academic exchange service CAPES and the German academic exchange service DAAD. The geodetic aim of the research project is to validate and improve the quality of 3d positions derived from observations related to satellite navigation systems like GPS. In order to fulfill this ambitious goal sustainably, research has to be carried out in close cooperation. At the same time, e.g. to guarantee continuous success, a coordinated education has to be ensured. Besides technical education aspects key competences (e.g. language, capacity for teamwork, project management skills) are trained. Within the presentation the lessons which were learned from this project are discussed in detail.

Transmittance measurements at DIRT-II

Science.gov (United States)

Curcio, J. A.; Haught, K. M.; Woytko, M. A.

1980-07-01

This is a report on the NRL experiments at the DIRT-II tests sponsored by the Atmospheric Sciences Laboratory at the White Sands Missile Range in July 1970. The NRL experiment was designed to measure spectral transmittance through smoke and dust clouds generated by detonations of various explosive charges and also by impact of artillery rounds. Spectral transmission data as a function of time for 0.55 micrometers, 1.06 micrometers, and 10.37 micrometers were obtained for 63 events comprised of static detonations and artillery rounds. Transmission data for 1.06 micrometers, in most cases were similar and equal to 0.55 micrometers. In dry soil conditions the 10.37 micrometers channel showed higher transmittance values than the visible channel. There are indications that 10.37 micrometers transmittance in wet soil events is lower than visible presumably because of strong liquid water absorption at the IR wavelength.

Efficacy of using radio transmitters to monitor least tern chicks

Science.gov (United States)

Whittier, Joanna B.; Leslie, David M.

2005-01-01

Little is known about Least Tern (Sterna antillarum) chicks from the time they leave the nest until fledging because they are highly mobile and cryptically colored. We evaluated the efficacy of using radiotelemetry to monitor Interior Least Tern (S. a. athalassos) chicks at Salt Plains National Wildlife Refuge, Oklahoma. In 1999, we attached radio transmitters to 26 Least Tern chicks and tracked them for 2-17 days. No adults abandoned their chicks after transmitters were attached. Transmitters did not appear to alter growth rates of transmittered chicks (P = 0.36) or prevent feather growth, although dermal irritation was observed on one chick. However, without frequent reattachment, transmitters generally did not remain on chicks feather growth and transmitter removal, presumably by adult terns. Although the presence of transmitters did not adversely affect Least Tern chicks, future assessments should investigate nonintrusive methods to improve retention of transmitters on young chicks and reduce the number of times that chicks need to be handled.

TWT transmitter fault prediction based on ANFIS

Science.gov (United States)

Li, Mengyan; Li, Junshan; Li, Shuangshuang; Wang, Wenqing; Li, Fen

2017-11-01

Fault prediction is an important component of health management, and plays an important role in the reliability guarantee of complex electronic equipments. Transmitter is a unit with high failure rate. The cathode performance of TWT is a common fault of transmitter. In this dissertation, a model based on a set of key parameters of TWT is proposed. By choosing proper parameters and applying adaptive neural network training model, this method, combined with analytic hierarchy process (AHP), has a certain reference value for the overall health judgment of TWT transmitters.

TLALOCNet continuous GPS-Met Array in Mexico supporting the 2017 NAM GPS Hydrometeorological Network.

Science.gov (United States)

Cabral-Cano, E.; Salazar-Tlaczani, L.; Adams, D. K.; Vivoni, E. R.; Grutter, M.; Serra, Y. L.; DeMets, C.; Galetzka, J.; Feaux, K.; Mattioli, G. S.; Miller, M. M.

2017-12-01

TLALOCNet is a network of continuous GPS and meteorology stations in Mexico to study atmospheric and solid earth processes. This recently completed network spans most of Mexico with a strong coverage emphasis on southern and western Mexico. This network, funded by NSF, CONACyT and UNAM, recently built 40 cGPS-Met sites to EarthScope Plate Boundary Observatory standards and upgraded 25 additional GPS stations. TLALOCNet provides open and freely available raw GPS data, and high frequency surface meteorology measurements, and time series of daily positions. This is accomplished through the development of the TLALOCNet data center (http://tlalocnet.udg.mx) that serves as a collection and distribution point. This data center is based on UNAVCO's Dataworks-GSAC software and also works as part of UNAVCO's seamless archive for discovery, sharing, and access to GPS data. The TLALOCNet data center also contains contributed data from several regional GPS networks in Mexico for a total of 100+ stations. By using the same protocols and structure as the UNAVCO and other COCONet regional data centers, the scientific community has the capability of accessing data from the largest Mexican GPS network. This archive provides a fully queryable and scriptable GPS and Meteorological data retrieval point. In addition, real-time 1Hz streams from selected TLALOCNet stations are available in BINEX, RTCM 2.3 and RTCM 3.1 formats via the Networked Transport of RTCM via Internet Protocol (NTRIP) for real-time seismic and weather forecasting applications. TLALOCNet served as a GPS-Met backbone for the binational Mexico-US North American Monsoon GPS Hydrometeorological Network 2017 campaign experiment. This innovative experiment attempts to address water vapor source regions and land-surface water vapor flux contributions to precipitation (i.e., moisture recycling) during the 2017 North American Monsoon in Baja California, Sonora, Chihuahua, and Arizona. Models suggest that moisture recycling is

Comparison of Satellite Surveying to Traditional Surveying Methods for the Resources Industry

Science.gov (United States)

Osborne, B. P.; Osborne, V. J.; Kruger, M. L.

Modern ground-based survey methods involve detailed survey, which provides three-space co-ordinates for surveyed points, to a high level of accuracy. The instruments are operated by surveyors, who process the raw results to create survey location maps for the subject of the survey. Such surveys are conducted for a location or region and referenced to the earth global co- ordinate system with global positioning system (GPS) positioning. Due to this referencing the survey is only as accurate as the GPS reference system. Satellite survey remote sensing utilise satellite imagery which have been processed using commercial geographic information system software. Three-space co-ordinate maps are generated, with an accuracy determined by the datum position accuracy and optical resolution of the satellite platform.This paper presents a case study, which compares topographic surveying undertaken by traditional survey methods with satellite surveying, for the same location. The purpose of this study is to assess the viability of satellite remote sensing for surveying in the resources industry. The case study involves a topographic survey of a dune field for a prospective mining project area in Pakistan. This site has been surveyed using modern surveying techniques and the results are compared to a satellite survey performed on the same area.Analysis of the results from traditional survey and from the satellite survey involved a comparison of the derived spatial co- ordinates from each method. In addition, comparisons have been made of costs and turnaround time for both methods.The results of this application of remote sensing is of particular interest for survey in areas with remote and extreme environments, weather extremes, political unrest, poor travel links, which are commonly associated with mining projects. Such areas frequently suffer language barriers, poor onsite technical support and resources.

Global diagnostics of the ionospheric perturbations related to the seismic activity using the VLF radio signals collected on the DEMETER satellite

Directory of Open Access Journals (Sweden)

O. Molchanov

2006-01-01

Full Text Available The analysis of the VLF signals radiated by ground transmitters and received on board of the French DEMETER satellite, reveals a drop of the signals (scattering spot connected with the occurrence of large earthquakes. The extension of the "scattering spots" zone is large enough (1000–5000 km and, probably, it increases with the magnitude of the "relative" earthquake. A possible model to explain the phenomenology, based on the acoustic gravity waves and the ionosphere turbulence, is proposed. The method of diagnostics applied to this study has the advantage to be a global one due to the world wide location of the powerful VLF transmitters and of the satellite reception. However, a specific disadvantage exists because the method requires rather a long time period of analysis due to the large longitudinal displacements among the successive satellite orbits. At the moment, at least, one month seems to be necessary.

GPS: Public Utility or Software Platform

Science.gov (United States)

2016-09-01

train for GPS loss, encourage use of GPS signal integrity monitors , develop in- vehicle GPS backups, and evaluate the range of radio...literature prevent the full quantification of exactly how vulnerable GPS is to service interruption. This thesis used constant comparison analysis to...criticality, resilience, and vulnerability. This methodology overcomes research limitations by using GPS system design, operations, and policies as

Cyber security with radio frequency interferences mitigation study for satellite systems

Science.gov (United States)

Wang, Gang; Wei, Sixiao; Chen, Genshe; Tian, Xin; Shen, Dan; Pham, Khanh; Nguyen, Tien M.; Blasch, Erik

2016-05-01

Satellite systems including the Global Navigation Satellite System (GNSS) and the satellite communications (SATCOM) system provide great convenience and utility to human life including emergency response, wide area efficient communications, and effective transportation. Elements of satellite systems incorporate technologies such as navigation with the global positioning system (GPS), satellite digital video broadcasting, and information transmission with a very small aperture terminal (VSAT), etc. The satellite systems importance is growing in prominence with end users' requirement for globally high data rate transmissions; the cost reduction of launching satellites; development of smaller sized satellites including cubesat, nanosat, picosat, and femtosat; and integrating internet services with satellite networks. However, with the promising benefits, challenges remain to fully develop secure and robust satellite systems with pervasive computing and communications. In this paper, we investigate both cyber security and radio frequency (RF) interferences mitigation for satellite systems, and demonstrate that they are not isolated. The action space for both cyber security and RF interferences are firstly summarized for satellite systems, based on which the mitigation schemes for both cyber security and RF interferences are given. A multi-layered satellite systems structure is provided with cross-layer design considering multi-path routing and channel coding, to provide great security and diversity gains for secure and robust satellite systems.

Error Analysis System for Spacecraft Navigation Using the Global Positioning System (GPS)

Science.gov (United States)

Truong, S. H.; Hart, R. C.; Hartman, K. R.; Tomcsik, T. L.; Searl, J. E.; Bernstein, A.

1997-01-01

The Flight Dynamics Division (FDD) at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) is currently developing improved space-navigation filtering algorithms to use the Global Positioning System (GPS) for autonomous real-time onboard orbit determination. In connection with a GPS technology demonstration on the Small Satellite Technology Initiative (SSTI)/Lewis spacecraft, FDD analysts and programmers have teamed with the GSFC Guidance, Navigation, and Control Branch to develop the GPS Enhanced Orbit Determination Experiment (GEODE) system. The GEODE system consists of a Kalman filter operating as a navigation tool for estimating the position, velocity, and additional states required to accurately navigate the orbiting Lewis spacecraft by using astrodynamic modeling and GPS measurements from the receiver. A parallel effort at the FDD is the development of a GPS Error Analysis System (GEAS) that will be used to analyze and improve navigation filtering algorithms during development phases and during in-flight calibration. For GEAS, the Kalman filter theory is extended to estimate the errors in position, velocity, and other error states of interest. The estimation of errors in physical variables at regular intervals will allow the time, cause, and effect of navigation system weaknesses to be identified. In addition, by modeling a sufficient set of navigation system errors, a system failure that causes an observed error anomaly can be traced and accounted for. The GEAS software is formulated using Object Oriented Design (OOD) techniques implemented in the C++ programming language on a Sun SPARC workstation. The Phase 1 of this effort is the development of a basic system to be used to evaluate navigation algorithms implemented in the GEODE system. This paper presents the GEAS mathematical methodology, systems and operations concepts, and software design and implementation. Results from the use of the basic system to evaluate

GNSS global real-time augmentation positioning: Real-time precise satellite clock estimation, prototype system construction and performance analysis

Science.gov (United States)

Chen, Liang; Zhao, Qile; Hu, Zhigang; Jiang, Xinyuan; Geng, Changjiang; Ge, Maorong; Shi, Chuang

2018-01-01

Lots of ambiguities in un-differenced (UD) model lead to lower calculation efficiency, which isn't appropriate for the high-frequency real-time GNSS clock estimation, like 1 Hz. Mixed differenced model fusing UD pseudo-range and epoch-differenced (ED) phase observations has been introduced into real-time clock estimation. In this contribution, we extend the mixed differenced model for realizing multi-GNSS real-time clock high-frequency updating and a rigorous comparison and analysis on same conditions are performed to achieve the best real-time clock estimation performance taking the efficiency, accuracy, consistency and reliability into consideration. Based on the multi-GNSS real-time data streams provided by multi-GNSS Experiment (MGEX) and Wuhan University, GPS + BeiDou + Galileo global real-time augmentation positioning prototype system is designed and constructed, including real-time precise orbit determination, real-time precise clock estimation, real-time Precise Point Positioning (RT-PPP) and real-time Standard Point Positioning (RT-SPP). The statistical analysis of the 6 h-predicted real-time orbits shows that the root mean square (RMS) in radial direction is about 1-5 cm for GPS, Beidou MEO and Galileo satellites and about 10 cm for Beidou GEO and IGSO satellites. Using the mixed differenced estimation model, the prototype system can realize high-efficient real-time satellite absolute clock estimation with no constant clock-bias and can be used for high-frequency augmentation message updating (such as 1 Hz). The real-time augmentation message signal-in-space ranging error (SISRE), a comprehensive accuracy of orbit and clock and effecting the users' actual positioning performance, is introduced to evaluate and analyze the performance of GPS + BeiDou + Galileo global real-time augmentation positioning system. The statistical analysis of real-time augmentation message SISRE is about 4-7 cm for GPS, whlile 10 cm for Beidou IGSO/MEO, Galileo and about 30 cm

Study of sporadic E layers based on GPS radio occultation measurements and digisonde data over the Brazilian region

Science.gov (United States)

Resende, Laysa C. A.; Arras, Christina; Batista, Inez S.; Denardini, Clezio M.; Bertollotto, Thainá O.; Moro, Juliano

2018-04-01

This work presents new results about sporadic E-layers (Es layers) using GPS (global positioning system) radio occultation (RO) measurements obtained from the FORMOSAT-3/COSMIC satellites and digisonde data. The RO profiles are used to study the Es layer occurrence as well as its intensity of the signal-to-noise ratio (SNR) of the 50 Hz GPS L1 signal. The methodology was applied to identify the Es layer on RO measurements over Cachoeira Paulista, a low-latitude station in the Brazilian region, in which the Es layer development is not driven tidal winds only as it is at middle latitudes. The coincident events were analyzed using the RO technique and ionosonde observations during the year 2014 to 2016. We used the electron density obtained using the blanketing frequency parameter (fbEs) and the Es layer height (h'Es) acquired from the ionograms to validate the satellite measurements. The comparative results show that the Es layer characteristics extracted from the RO measurements are in good agreement with the Es layer parameters from the digisonde.

High Frequency Variations of Earth Rotation Parameters from GPS and GLONASS Observations

Directory of Open Access Journals (Sweden)

Erhu Wei

2015-01-01

Full Text Available The Earth’s rotation undergoes changes with the influence of geophysical factors, such as Earth’s surface fluid mass redistribution of the atmosphere, ocean and hydrology. However, variations of Earth Rotation Parameters (ERP are still not well understood, particularly the short-period variations (e.g., diurnal and semi-diurnal variations and their causes. In this paper, the hourly time series of Earth Rotation Parameters are estimated using Global Positioning System (GPS, Global Navigation Satellite System (GLONASS, and combining GPS and GLONASS data collected from nearly 80 sites from 1 November 2012 to 10 April 2014. These new observations with combining different satellite systems can help to decorrelate orbit biases and ERP, which improve estimation of ERP. The high frequency variations of ERP are analyzed using a de-trending method. The maximum of total diurnal and semidiurnal variations are within one milli-arcseconds (mas in Polar Motion (PM and 0.5 milli-seconds (ms in UT1-UTC. The semidiurnal and diurnal variations are mainly related to the ocean tides. Furthermore, the impacts of satellite orbit and time interval used to determinate ERP on the amplitudes of tidal terms are analyzed. We obtain some small terms that are not described in the ocean tide model of the IERS Conventions 2010, which may be caused by the strategies and models we used or the signal noises as well as artifacts. In addition, there are also small differences on the amplitudes between our results and IERS convention. This might be a result of other geophysical excitations, such as the high-frequency variations in atmospheric angular momentum (AAM and hydrological angular momentum (HAM, which needs more detailed analysis with more geophysical data in the future.

Efficient GPS Position Determination Algorithms

National Research Council Canada - National Science Library

Nguyen, Thao Q

2007-01-01

... differential GPS algorithm for a network of users. The stand-alone user GPS algorithm is a direct, closed-form, and efficient new position determination algorithm that exploits the closed-form solution of the GPS trilateration equations and works...

Crustal Deformation along San Andreas Fault System revealed by GPS and Sentinel-1 InSAR

Science.gov (United States)

Xu, X.; Sandwell, D. T.

2017-12-01

We present a crustal deformation velocity map along the San Andreas Fault System by combining measurements from Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) velocity models (CGM V1). We assembled 5 tracks of descending Sentinel-1 InSAR data spanning 2014.11-2017.02, and produced 545 interferograms, each of which covers roughly 250km x 420km area ( 60 bursts). These interferograms are unwrapped using SNAPHU [Chen & Zebker, 2002], with the 2Npi unwrapping ambiguity corrected with a sparse recovery method. We used coherence-based small baseline subset (SBAS) method [Tong & Schmidt, 2016] together with atmospheric correction by common-point stacking [Tymofyeyeva and Fialko, 2015] to construct deformation time series [Xu et. al., 2017]. Then we project the horizontal GPS model and vertical GPS data into satellite line-of-sight directions separately. We first remove the horizontal GPS model from InSAR measurements and perform elevation-dependent atmospheric phase correction. Then we compute the discrepancy between the remaining InSAR measurements and vertical GPS data. We interpolate this discrepancy and remove it from the residual InSAR measurements. Finally, we restore the horizontal GPS model. Preliminary results show that fault creep over the San Jacinto fault, the Elsinore fault, and the San Andreas creeping section is clearly resolved. During the period of drought, the Central Valley of California was subsiding at a high rate (up to 40 cm/yr), while the city of San Jose is uplifting due to recharge, with a quaternary fault acting as a ground water barrier. These findings will be reported during the meeting.

Design of a search and rescue terminal based on the dual-mode satellite and CDMA network

Science.gov (United States)

Zhao, Junping; Zhang, Xuan; Zheng, Bing; Zhou, Yubin; Song, Hao; Song, Wei; Zhang, Meikui; Liu, Tongze; Zhou, Li

2010-12-01

The current goal is to create a set of portable terminals with GPS/BD2 dual-mode satellite positioning, vital signs monitoring and wireless transmission functions. The terminal depends on an ARM processor to collect and combine data related to vital signs and GPS/BD2 location information, and sends the message to headquarters through the military CDMA network. It integrates multiple functions as a whole. The satellite positioning and wireless transmission capabilities are integrated into the motherboard, and the vital signs sensors used in the form of belts communicate with the board through Bluetooth. It can be adjusted according to the headquarters' instructions. This kind of device is of great practical significance for operations during disaster relief, search and rescue of the wounded in wartime, non-war military operations and other special circumstances.

Geomagnetic Storm Impact On GPS Code Positioning

Science.gov (United States)

Uray, Fırat; Varlık, Abdullah; Kalaycı, İbrahim; Öǧütcü, Sermet

2017-04-01

This paper deals with the geomagnetic storm impact on GPS code processing with using GIPSY/OASIS research software. 12 IGS stations in mid-latitude were chosen to conduct the experiment. These IGS stations were classified as non-cross correlation receiver reporting P1 and P2 (NONCC-P1P2), non-cross correlation receiver reporting C1 and P2 (NONCC-C1P2) and cross-correlation (CC-C1P2) receiver. In order to keep the code processing consistency between the classified receivers, only P2 code observations from the GPS satellites were processed. Four extreme geomagnetic storms October 2003, day of the year (DOY), 29, 30 Halloween Storm, November 2003, DOY 20, November 2004, DOY 08 and four geomagnetic quiet days in 2005 (DOY 92, 98, 99, 100) were chosen for this study. 24-hour rinex data of the IGS stations were processed epoch-by-epoch basis. In this way, receiver clock and Earth Centered Earth Fixed (ECEF) Cartesian Coordinates were solved for a per-epoch basis for each day. IGS combined broadcast ephemeris file (brdc) were used to partly compensate the ionospheric effect on the P2 code observations. There is no tropospheric model was used for the processing. Jet Propulsion Laboratory Application Technology Satellites (JPL ATS) computed coordinates of the stations were taken as true coordinates. The differences of the computed ECEF coordinates and assumed true coordinates were resolved to topocentric coordinates (north, east, up). Root mean square (RMS) errors for each component were calculated for each day. The results show that two-dimensional and vertical accuracy decreases significantly during the geomagnetic storm days comparing with the geomagnetic quiet days. It is observed that vertical accuracy is much more affected than the horizontal accuracy by geomagnetic storm. Up to 50 meters error in vertical component has been observed in geomagnetic storm day. It is also observed that performance of Klobuchar ionospheric correction parameters during geomagnetic storm

A modification to the standard ionospheric correction method used in GPS radio occultation

Directory of Open Access Journals (Sweden)

S. B. Healy

2015-08-01

Full Text Available A modification to the standard bending-angle correction used in GPS radio occultation (GPS-RO is proposed. The modified approach should reduce systematic residual ionospheric errors in GPS radio occultation climatologies. A new second-order term is introduced in order to account for a known source of systematic error, which is generally neglected. The new term has the form κ(a × (αL1(a-αL2(a2, where a is the impact parameter and (αL1, αL2 are the L1 and L2 bending angles, respectively. The variable κ is a weak function of the impact parameter, a, but it does depend on a priori ionospheric information. The theoretical basis of the new term is examined. The sensitivity of κ to the assumed ionospheric parameters is investigated in one-dimensional simulations, and it is shown that κ ≃ 10–20 rad−1. We note that the current implicit assumption is κ=0, and this is probably adequate for numerical weather prediction applications. However, the uncertainty in κ should be included in the uncertainty estimates for the geophysical climatologies produced from GPS-RO measurements. The limitations of the new ionospheric correction when applied to CHAMP (Challenging Minisatellite Payload measurements are noted. These arise because of the assumption that the refractive index is unity at the satellite, made when deriving bending angles from the Doppler shift values.

29 CFR 1921.15 - Transmittal of record.

Science.gov (United States)

2010-07-01

... 29 Labor 7 2010-07-01 2010-07-01 false Transmittal of record. 1921.15 Section 1921.15 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR... WORKERS' COMPENSATION ACT Decision and Order § 1921.15 Transmittal of record. Immediately following the...

Standardization of GPS data processing

International Nuclear Information System (INIS)

Park, Pil Ho

2001-06-01

A nationwide GPS network has been constructed with about 60 permanent GPS stations after late 1990s in Korea. For using the GPS in variety of application area like crustal deformation, positioning, or monitoring upper atmosphere, it is necessary to have ability to process the data precisely. Now Korea Astronomy Observatory has the precise GPS data processing technique in Korea because it is difficult to understand characteristics of the parameters we want to estimate, resolve the integer ambiguity, and analyze many errors. There are three reliable GPS data processing software in the world ; Bernese(University of Berne), GIPSY-OASIS(JPL), GAMIT(MIT). These software allow us to achieve millimeter accuracy in the horizontal position and about 1 cm accuracy vertically even for regional networks with a diameter of several thousand kilometers. But we established the standard of GPS data processing using Bernese as main tool and GIPSY O ASIS as side

GPS Position Time Series @ JPL

Science.gov (United States)

Owen, Susan; Moore, Angelyn; Kedar, Sharon; Liu, Zhen; Webb, Frank; Heflin, Mike; Desai, Shailen

2013-01-01

Different flavors of GPS time series analysis at JPL - Use same GPS Precise Point Positioning Analysis raw time series - Variations in time series analysis/post-processing driven by different users. center dot JPL Global Time Series/Velocities - researchers studying reference frame, combining with VLBI/SLR/DORIS center dot JPL/SOPAC Combined Time Series/Velocities - crustal deformation for tectonic, volcanic, ground water studies center dot ARIA Time Series/Coseismic Data Products - Hazard monitoring and response focused center dot ARIA data system designed to integrate GPS and InSAR - GPS tropospheric delay used for correcting InSAR - Caltech's GIANT time series analysis uses GPS to correct orbital errors in InSAR - Zhen Liu's talking tomorrow on InSAR Time Series analysis

Semantic Enrichment of GPS Trajectories

NARCIS (Netherlands)

de Graaff, V.; van Keulen, Maurice; de By, R.A.

2012-01-01

Semantic annotation of GPS trajectories helps us to recognize the interests of the creator of the GPS trajectories. Automating this trajectory annotation circumvents the requirement of additional user input. To annotate the GPS traces automatically, two types of automated input are required: 1) a

Transition of NOAA's GPS-Met Data Acquisition and Processing System to the Commercial Sector

Science.gov (United States)

Jackson, M. E.; Holub, K.; Callahan, W.; Blatt, S.

2014-12-01

In April of 2014, NOAA/OAR/ESRL Global Systems Division (GSD) and Trimble, in collaboration with Earth Networks, Inc. (ENI) signed a Cooperative Research and Development Agreement (CRADA) to transfer the existing NOAA GPS-Met Data Acquisition and Processing System (GPS-Met DAPS) technology to a commercial Trimble/ENI partnership. NOAA's GPS-Met DAPS is currently operated in a pseudo-operational mode but has proven highly reliable and running at over 95% uptime. The DAPS uses the GAMIT software to ingest dual frequency carrier phase GPS/GNSS observations and ancillary information such as real-time satellite orbits to estimate the zenith-scaled tropospheric (ZTD) signal delays and, where surface MET data are available, retrieve integrated precipitable water vapor (PWV). The NOAA data and products are made available to end users in near real-time. The Trimble/ENI partnership will use the Trimble Pivot™ software with the Atmosphere App to calculate zenith tropospheric (ZTD), tropospheric slant delay, and integrated precipitable water vapor (PWV). Evaluation of the Trimble software is underway starting with a comparison of ZTD and PWV values determined from GPS stations located near NOAA Radiosonde Observation (Upper-Air Observation) launch sites. A success metric was established that requires Trimble's PWV estimates to match ESRL/GSD's to within 1.5 mm 95% of the time, which corresponds to a ZTD uncertainty of less than 10 mm 95% of the time. Initial results indicate that Trimble/ENI data meet and exceed the ZTD metric, but for some stations PWV estimates are out of specification. These discrepancies are primarily due to how offsets between MET and GPS stations are handled and are easily resolved. Additional test networks are proposed that include low terrain/high moisture variability stations, high terrain/low moisture variability stations, as well as high terrain/high moisture variability stations. We will present results from further testing along with a timeline

Effects of radio transmitters on nesting captive mallards

Science.gov (United States)

Houston, Robert A.; Greenwood, Raymond J.

1993-01-01

Radio packages may subtly affect bird behavior and condition, and thus could bias results from studies using this technique. To assess effects on reproduction of mallards (Anas platyrhynchos), we tested 3 types of back-mounted radio packages on captive females. Eight paired females were randomly assigned to each of 4 treatments: 4-g transmitter attached with sutures and glue, 10-g or 18-g transmitter attached with a harness, and no transmitter (control). All mallards were fed ad libitum. No differences were detected among treatments in number of clutches, clutch size, nesting interval, egg mass, or body mass; powers (range = 0.15-0.48) of tests were low. Feather wear and skin irritation around radio packages were minimal. Birds retained sutured transmitters for an average of 43.5 days (range = 3-106 days) and harness transmitters for the duration of the study (106 days). Sutures were not reliable and presently are not recommended as an attachment method. Caution is advised in applying these results to radio-equipped mallards in the wild.

Data transmission through power line of smart transmitter

International Nuclear Information System (INIS)

Kim, Jong Hyun; Kang, Hyun Gook; Seong, Poong Hyun

1996-01-01

In this study, the method to use the phase shift keying (PSK) communication technique in smart transmitter is presented. In nuclear applications, smart transmitters for various parameters are expected to improve the accuracy of measurement and to reduce the load of calibration work. The capability of communication in field level is the most important merit of the smart transmitter. The most popular method is using of digital and analog techniques simultaneously - transmitting measurements from the field at 4-20mA while modulating the current to carry digital information in both directions over the same twisted pairs. Conventional smart transmitters use the frequency shift keying (FSK) method for digital communication. Generally, however, the FSK method has the speed limit at 1200 bps. Amount of information to transmit becomes increasing as the processing technique is improved. The PSK method is noticeable alternative for high speed digital communication, but it has non-zero DC component. In order to use the PSK method in the field transmission with smart transmitter, the method to remove the DC component is studied in this work

GPS water vapour tomography: preliminary results from the ESCOMPTE field experiment

Science.gov (United States)

Champollion, C.; Masson, F.; Bouin, M.-N.; Walpersdorf, A.; Doerflinger, E.; Bock, O.; Van Baelen, J.

2005-03-01

Water vapour plays a major role in atmospheric processes but remains difficult to quantify due to its high variability in time and space and the sparse set of available measurements. The GPS has proved its capacity to measure the integrated water vapour at zenith with the same accuracy as other methods. Recent studies show that it is possible to quantify the integrated water vapour in the line of sight of the GPS satellite. These observations can be used to study the 3D heterogeneity of the troposphere using tomographic techniques. We develop three-dimensional tomographic software to model the three-dimensional distribution of the tropospheric water vapour from GPS data. First, the tomographic software is validated by simulations based on the realistic ESCOMPTE GPS network configuration. Without a priori information, the absolute value of water vapour is less resolved as opposed to relative horizontal variations. During the ESCOMPTE field experiment, a dense network of 17 dual frequency GPS receivers was operated for 2 weeks within a 20×20-km area around Marseille (southern France). The network extends from sea level to the top of the Etoile chain (˜700 m high). Optimal results have been obtained with time windows of 30-min intervals and input data evaluation every 15 min. The optimal grid for the ESCOMTE geometrical configuration has a horizontal step size of 0.05°×0.05° and 500 m vertical step size. Second, we have compared the results of real data inversions with independent observations. Three inversions have been compared to three successive radiosonde launches and shown to be consistent. A good resolution compared to the a priori information is obtained up to heights of 3000 m. A humidity spike at 4000-m altitude remains unresolved. The reason is probably that the signal is spread homogeneously over the whole network and that such a feature is not resolvable by tomographic techniques. The results of our pure GPS inversion show a correlation with

Sensing Human Activity: GPS Tracking

Science.gov (United States)

van der Spek, Stefan; van Schaick, Jeroen; de Bois, Peter; de Haan, Remco

2009-01-01

The enhancement of GPS technology enables the use of GPS devices not only as navigation and orientation tools, but also as instruments used to capture travelled routes: as sensors that measure activity on a city scale or the regional scale. TU Delft developed a process and database architecture for collecting data on pedestrian movement in three European city centres, Norwich, Rouen and Koblenz, and in another experiment for collecting activity data of 13 families in Almere (The Netherlands) for one week. The question posed in this paper is: what is the value of GPS as ‘sensor technology’ measuring activities of people? The conclusion is that GPS offers a widely useable instrument to collect invaluable spatial-temporal data on different scales and in different settings adding new layers of knowledge to urban studies, but the use of GPS-technology and deployment of GPS-devices still offers significant challenges for future research. PMID:22574061

Sensing Human Activity: GPS Tracking

Directory of Open Access Journals (Sweden)

Remco de Haan

2009-04-01

Full Text Available The enhancement of GPS technology enables the use of GPS devices not only as navigation and orientation tools, but also as instruments used to capture travelled routes: as sensors that measure activity on a city scale or the regional scale. TU Delft developed a process and database architecture for collecting data on pedestrian movement in three European city centres, Norwich, Rouen and Koblenz, and in another experiment for collecting activity data of 13 families in Almere (The Netherlands for one week. The question posed in this paper is: what is the value of GPS as ‘sensor technology’ measuring activities of people? The conclusion is that GPS offers a widely useable instrument to collect invaluable spatial-temporal data on different scales and in different settings adding new layers of knowledge to urban studies, but the use of GPS-technology and deployment of GPS-devices still offers significant challenges for future research.

Research for annual travel-route changes of reindeer living around the Arctic Circle using satellite remote sensing

Science.gov (United States)

Suzuki, G.; Sakka, T.; Tashiro, T.; Kawamata, H.; Tatsuzawa, S.; Naruse, N.; Takahashi, Y.

2017-12-01

For a long time, nomads living in the Arctic Circle around Siberia have been making a living by hunting reindeer traditionally. Wild reindeer have a recurrent migration every year, however, the travel-route of reindeer has been changing recently, so the nomads cannot expect the route in their traditional experience. To support them, one of authors (Tatsuzawa) investigated the route by installing GPS transmitter to some reindeer. The reason of the changing route, however, remain unclear. Previous works indicated that the reason of changing the route must be a global warming, forest fires, thunders, and floods, but they only discuss only on the basis of measurements in specific area. The purpose of this study is to research why the arctic reindeer alter the travel route annually through 1) the annual change of vegetation (NDVI: normalized difference vegetation index) in reindeer ground, and through 2) the annual change of soil water content (mNDWI: modified normalized difference water index) which can be reflected precipitation near Lena river. First, we analyzed NDVI using MODIS images that can be observed over a wide area, filmed in July and August; the reindeer started to travel. We have compared the seasonal changes of the NDVI images with the trace obtained by GPS data from 2010 to 2012. Although NDVI images in July showed similar numerical values in every year, the satellite images taken at August 29 is annually different; NDVI values become lower (0.5 or less) when the reindeer travel to the north area in winter. This suggests that reindeer move to secure enough food in the end of summer. In contrast, mNDWI becomes high when the reindeer travel to the north area. The annual changes of the route may be related to the amount of rainfall.

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

Comparison between ASHRAE and ISO thermal transmittance calculation methods

DEFF Research Database (Denmark)

Blanusa, Petar; Goss, William P.; Roth, Hartwig

2007-01-01

is proportional to the glazing/frame sightline distance that is also proportional to the total glazing spacer length. An example calculation of the overall heat transfer and thermal transmittance (U-value or U-factor) using the two methods for a thermally broken, aluminum framed slider window is presented....... The fenestration thermal transmittance calculations analyses presented in this paper show that small differences exist between the calculated thermal transmittance values produced by the ISO and ASHRAE methods. The results also show that the overall thermal transmittance difference between the two methodologies...... decreases as the total window area (glazing plus frame) increases. Thus, the resulting difference in thermal transmittance values for the two methods is negligible for larger windows. This paper also shows algebraically that the differences between the ISO and ASHRAE methods turn out to be due to the way...

GPS Space Service Volume: Ensuring Consistent Utility Across GPS Design Builds for Space Users

Science.gov (United States)

Bauer, Frank H.; Parker, Joel Jefferson Konkl; Valdez, Jennifer Ellen

2015-01-01

GPS availability and signal strength originally specified for users on or near surface of Earth with transmitted power levels specified at edge-of-Earth, 14.3 degrees. Prior to the SSV specification, on-orbit performance of GPS varied from block build to block build (IIA, IIRM, IIF) due to antenna gain and beam width variances. Unstable on-orbit performance results in significant risk to space users. Side-lobe signals, although not specified, were expected to significantly boost GPS signal availability for users above the constellation. During GPS III Phase A, NASA noted significant discrepancies in power levels specified in GPS III specification documents, and measured on-orbit performance. To stabilize the signal for high altitude space users, NASA DoD team in 2003-2005 led the creation of new Space Service Volume (SSV) definition and specifications.

Topside ionospheric vertical electron density profile reconstruction using GPS and ionosonde data: possibilities for South Africa

Directory of Open Access Journals (Sweden)

P. Sibanda

2011-02-01

Full Text Available Successful empirical modeling of the topside ionosphere relies on the availability of good quality measured data. The Alouette, ISIS and Intercosmos-19 satellite missions provided large amounts of topside sounder data, but with limited coverage of relevant geophysical conditions (e.g., geographic location, diurnal, seasonal and solar activity by each individual mission. Recently, methods for inferring the electron density distribution in the topside ionosphere from Global Positioning System (GPS-based total electron content (TEC measurements have been developed. This study is focused on the modeling efforts in South Africa and presents the implementation of a technique for reconstructing the topside ionospheric electron density (Ne using a combination of GPS-TEC and ionosonde measurements and empirically obtained Upper Transition Height (UTH. The technique produces reasonable profiles as determined by the global models already in operation. With the added advantage that the constructed profiles are tied to reliable measured GPS-TEC and the empirically determined upper transition height, the technique offers a higher level of confidence in the resulting Ne profiles.

An ultra-wide bandwidth-based range/GPS tight integration approach for relative positioning in vehicular ad hoc networks

International Nuclear Information System (INIS)

Shen, Feng; Cheong, Joon Wayn; Dempster, Andrew G

2015-01-01

Relative position awareness is a vital premise for the implementation of emerging intelligent transportation systems, such as collision warning. However, commercial global navigation satellite systems (GNSS) receivers do not satisfy the requirements of these applications. Fortunately, cooperative positioning (CP) techniques, through sharing the GNSS measurements between vehicles, can improve the performance of relative positioning in a vehicular ad hoc network (VANET). In this paper, while assuming there are no obstacles between vehicles, a new enhanced tightly coupled CP technique is presented by adding ultra-wide bandwidth (UWB)-based inter-vehicular range measurements. In the proposed CP method, each vehicle fuses the GPS measurements and the inter-vehicular range measurements. Based on analytical and experimental results, in the full GPS coverage environment, the new tight integration CP method outperforms the INS-aided tight CP method, tight CP method, and DGPS by 11%, 15%, and 24%, respectively; in the GPS outage scenario, the performance improvement achieves 60%, 65%, and 73%, respectively. (paper)

The SMS-GPS-Trip-Method

DEFF Research Database (Denmark)

Reinau, Kristian Hegner; Harder, Henrik; Weber, Michael

2015-01-01

This article presents a new method for collecting travel behavior data, based on a combination of GPS tracking and SMS technology, coined the SMS–GPS-Trip method. The state-of-the-art method for collecting data for activity based traffic models is a combination of travel diaries and GPS tracking...

Stability Analysis of Receiver ISB for BDS/GPS

Science.gov (United States)

Zhang, H.; Hao, J. M.; Tian, Y. G.; Yu, H. L.; Zhou, Y. L.

2017-07-01

Stability analysis of receiver ISB (Inter-System Bias) is essential for understanding the feature of ISB as well as the ISB modeling and prediction. In order to analyze the long-term stability of ISB, the data from MGEX (Multi-GNSS Experiment) covering 3 weeks, which are from 2014, 2015 and 2016 respectively, are processed with the precise satellite clock and orbit products provided by Wuhan University and GeoForschungsZentrum (GFZ). Using the ISB calculated by BDS (BeiDou Navigation Satellite System)/GPS (Global Positioning System) combined PPP (Precise Point Positioning), the daily stability and weekly stability of ISB are investigated. The experimental results show that the diurnal variation of ISB is stable, and the average of daily standard deviation is about 0.5 ns. The weekly averages and standard deviations of ISB vary greatly in different years. The weekly averages of ISB are relevant to receiver types. There is a system bias between ISB calculated from the precise products provided by Wuhan University and GFZ. In addition, the system bias of the weekly average ISB of different stations is consistent with each other.

Identification of scintillation signatures on GPS signals originating from plasma structures detected with EISCAT incoherent scatter radar along the same line of sight.

Science.gov (United States)

Forte, Biagio; Coleman, Chris; Skone, Susan; Häggström, Ingemar; Mitchell, Cathryn; Da Dalt, Federico; Panicciari, Tommaso; Kinrade, Joe; Bust, Gary

2017-01-01

Ionospheric scintillation originates from the scattering of electromagnetic waves through spatial gradients in the plasma density distribution, drifting across a given propagation direction. Ionospheric scintillation represents a disruptive manifestation of adverse space weather conditions through degradation of the reliability and continuity of satellite telecommunication and navigation systems and services (e.g., European Geostationary Navigation Overlay Service, EGNOS). The purpose of the experiment presented here was to determine the contribution of auroral ionization structures to GPS scintillation. European Incoherent Scatter (EISCAT) measurements were obtained along the same line of sight of a given GPS satellite observed from Tromso and followed by means of the EISCAT UHF radar to causally identify plasma structures that give rise to scintillation on the co-aligned GPS radio link. Large-scale structures associated with the poleward edge of the ionospheric trough, with auroral arcs in the nightside auroral oval and with particle precipitation at the onset of a substorm were indeed identified as responsible for enhanced phase scintillation at L band. For the first time it was observed that the observed large-scale structures did not cascade into smaller-scale structures, leading to enhanced phase scintillation without amplitude scintillation. More measurements and theory are necessary to understand the mechanism responsible for the inhibition of large-scale to small-scale energy cascade and to reproduce the observations. This aspect is fundamental to model the scattering of radio waves propagating through these ionization structures. New insights from this experiment allow a better characterization of the impact that space weather can have on satellite telecommunications and navigation services.

GPS operations at Olkiluoto in 2009

Energy Technology Data Exchange (ETDEWEB)

Kallio, U.; Nyberg, S.; Koivula, H.; Jokela, J.; Poutanen, M.; Ahola, J. (Finnish Geodetic Institute, Masala (Finland))

2010-06-15

The GPS based deformation studies have been made at the investigation areas of Posiva since 1995, when the network of ten GPS pillars was established at Olkiluoto. One pillar in the investigation area belongs to the Finnish permanent GPS network, FinnRef. 28 GPS measurement campaigns have been carried out at Olkiluoto since 1995. According to the time series of the GPS results 1/3 of the baselines at Olkiluoto have statistically significant change rates. However, the observed movements are smaller than +-0.20 mm/a. There are five pillars, which have statistically significant horizontal velocities at Olkiluoto. These local velocity components are small but taking into account the standard deviations the largest velocity components seems to be reliably determined. At Olkiluoto a baseline for electronic distance measurements (EDM) was built in 2002. The baseline has been measured using EDM instruments in connection to the GPS observations. Changes in he difference between the GPS and EDM results indicate the systematic change in GPS results. No corrections based on only one baseline were not applied to GPS vectors. The GPS network at Olkiluoto was extended in 2003. The new pillars were built close to Kuivalahti village and on a small island of Iso Pyrekari. According to the geological evidence it is expected that a fracture zone is located between the new stations, thus enabling the determination of possible deformations along the fracture zone. The new pillars have been observed since 2003 and now we have computed the first deformation analysis from the six years data. Four new permanent stations will be established in summer 2010 at Olkiluoto. We have automated the processing of the campaign data by using the Bernese processing engine (BPE) together with our own Perl scripts. The local crustal deformations have been studied in GeoSatakunta project, too. This GPS network is located in Cities of Pori and Rauma and their neighbouring municipalities. Two new pillars

GPS operations at Olkiluoto in 2009

International Nuclear Information System (INIS)

Kallio, U.; Nyberg, S.; Koivula, H.; Jokela, J.; Poutanen, M.; Ahola, J.

2010-06-01

The GPS based deformation studies have been made at the investigation areas of Posiva since 1995, when the network of ten GPS pillars was established at Olkiluoto. One pillar in the investigation area belongs to the Finnish permanent GPS network, FinnRef. 28 GPS measurement campaigns have been carried out at Olkiluoto since 1995. According to the time series of the GPS results 1/3 of the baselines at Olkiluoto have statistically significant change rates. However, the observed movements are smaller than ±0.20 mm/a. There are five pillars, which have statistically significant horizontal velocities at Olkiluoto. These local velocity components are small but taking into account the standard deviations the largest velocity components seems to be reliably determined. At Olkiluoto a baseline for electronic distance measurements (EDM) was built in 2002. The baseline has been measured using EDM instruments in connection to the GPS observations. Changes in he difference between the GPS and EDM results indicate the systematic change in GPS results. No corrections based on only one baseline were not applied to GPS vectors. The GPS network at Olkiluoto was extended in 2003. The new pillars were built close to Kuivalahti village and on a small island of Iso Pyrekari. According to the geological evidence it is expected that a fracture zone is located between the new stations, thus enabling the determination of possible deformations along the fracture zone. The new pillars have been observed since 2003 and now we have computed the first deformation analysis from the six years data. Four new permanent stations will be established in summer 2010 at Olkiluoto. We have automated the processing of the campaign data by using the Bernese processing engine (BPE) together with our own Perl scripts. The local crustal deformations have been studied in GeoSatakunta project, too. This GPS network is located in Cities of Pori and Rauma and their neighbouring municipalities. Two new pillars

GPS deformation measurements at Olkiluoto in 2013

International Nuclear Information System (INIS)

Nyberg, S.; Kallio, U.; Koivula, H.

2014-08-01

The Finnish Geodetic Institute has monitored crustal deformations since mid-1990s at Olkiluoto, Kivetty and Romuvaara. The research was focused on the Olkiluoto area in 2001, when Olkiluoto was chosen to the site for the final disposal facility of the spent nuclear fuel. The work and the results of the GPS deformation monitoring at Olkiluoto in 2013 are presented. The measurement consisted of two GPS measurement campaigns, observations at local permanent stations and control markers measurements at four stations. In spring six new stations were set up for permanent tracking. In total 12 permanent stations were operating continuously from April to the end of the year. The residual time series of the stations showed periodic trends up to 3 mm in height and 1 mm in horizontal component relative to the GPS1 station. A few stations were still measured as campaign-based and analysed baseline by baseline. The data from permanent stations (GPS1-GPS9, and GPS13) were included. The analysis of the inner network based on campaign sessions showed very small motions as in previous years: 75 % of change rates are smaller than 0.10 mm/y. Roughly one third of the change rates could be considered statistically significant at 1 % significance level. Statistically significant change rates were estimated for baselines from GPS1 and GPS5. The trends and strains differed at some baselines clearly from the earlier analysis because of different troposphere modelling. The results of the outer network showed the largest difference on the baseline GPS1-GPS11 where the trend decreased from -0.42 mm/y to -0.28 mm/y. The strain pattern of the outer network shows an eastwards motion of GPS1. The estimated strains for the baselines east of GPS1 were -0.03/-0.04 ppm/y. The control marker measurements were carried at the stations GPS1, GPS2, GPS4 and GPS6. A comparison of the results with the previous measurements showed that the distance between control markers at GPS6 continues to increase. Also