... The data sets included various levels of measurement corruption, in-cluding receiver noise, s... more ... The data sets included various levels of measurement corruption, in-cluding receiver noise, selective availability, errors in the GPS broadcast ephemeris and clock information and force model mis-matches in gravity, drag and solar radiation pressure. ...
Your browser or your browser's settings are not supported. To get the best experience possib... more Your browser or your browser's settings are not supported. To get the best experience possible, please download a compatible browser. If you know your browser is up to date, you should check to ensure that javascript is enabled. ... HEAT.PRO computer program ...
Geophysical applications of the Global Positioning System (GPS) require the capability to estimat... more Geophysical applications of the Global Positioning System (GPS) require the capability to estimate and propagate satellite orbits with high precision. An accurate model of all the forces acting on a satellite is an essential part of achieving high orbit accuracy. Methods of analyzing the perturbation due to thermal radiation and determining its effects on the long-term orbital behavior of GPS satellites are presented. The thermal imbalance force, a nongravitational orbit perturbation previously considered negligible, is the focus of this article. The earth's shadowing of a satellite in orbit causes periodic changes in the satellite's thermal environment. Simulations show that neglecting thermal imbalance in the satellite force model gives orbit error larger than ten meters over several days for eclipsing satellites. This orbit mismodeling can limit accuracy in orbit determination and in estimation of baselines used for geophysical applications.
Abstract The TOPEX/POSEIDON oeanographic satellite was launched in August 1992 carrying a high pe... more Abstract The TOPEX/POSEIDON oeanographic satellite was launched in August 1992 carrying a high performance GPS receiver. The purpose of the receiver is to evaluate GPS for precise orbit determination of low orbiting Earth satellites. Using GPS, we have ...
A modular approach to the multisensor-multitarget problem is presented. This approach reduces the... more A modular approach to the multisensor-multitarget problem is presented. This approach reduces the multitarget problem to several single-target problems. An algorithm based on this approach is described. The application of this algorithm to the simulated tracking of several maneuvering targets in an underwater environment and the numerical results obtained in this application are discussed. The validity of using the observation residuals in the data discrimination process and the data-target correlation is demonstrated through application
: The problem of estimating the trajectory of a maneuvering target using passive measurements obt... more : The problem of estimating the trajectory of a maneuvering target using passive measurements obtained from an array of stationary sensors is investigated. The formulation is considered in a two-dimensional rectangular coordinate system. The unknown acceleration components are modelled as Brownian motion processes and consequently the dynamic model is linear. The types of measurements used in the estimation process are the frequency and the bearing angle of some are nonlinear functions of the state vector which consists of a reference frequency and the components of position, velocity and acceleration. Computation algorithms for Extended Kalman Filter and 'batch-sequential' filter are presented. Equations for including the effects of process noise on the batch solution are derived and the computation algorithm is also given. The performance of these filters is compared using noisy measurements simulated for two different scenarios with typical target maneuvers and sensor loc...
The method of modified back differences, a technique that significantly reduces the numerical int... more The method of modified back differences, a technique that significantly reduces the numerical integration errors associated with crossing shadow boundaries using a fixed-mesh multistep integrator without a significant increase in computer run time, is presented. While Hubbard's integral approach can produce significant improvements to the trajectory solution, the interpolation method provides the best overall results. It is demonstrated that iterating on the point mass term correction is also important for achieving the best overall results. It is also shown that the method of modified back differences can be implemented with only a small increase in execution time.
Accelerometers on the CHAMP and GRACE satellites provide high-resolution (seconds) thermospheric ... more Accelerometers on the CHAMP and GRACE satellites provide high-resolution (seconds) thermospheric neutral densities. CHAMP carries the STAR accelerometer and GRACE carries an upgraded SuperSTAR accelerometer. Both instruments are on high-inclination satellites. These data are compared to two types of orbital drag data. One set is from HASDM (High Accuracy Satellite Drag Model). This approach provides spatially and temporally varying density corrections involving tracking of some 100 satellites. A weighted least squares fit to all of the tracking data produces a global density solution with a time resolution of several hours. The second set consists of individual measurements from each of twenty radar-tracked satellites. Densities were derived using newly developed techniques to provide one-day resolution. These data are relatively localized in latitude since all satellites were in highly elliptical orbits. HASDM data are available only during two periods; the first half of 2001 and A...
Shuttle mission STS-69 was launched on September 7, 1995, 10:09 CDT, carrying the Wake Shield Fac... more Shuttle mission STS-69 was launched on September 7, 1995, 10:09 CDT, carrying the Wake Shield Facility (WSF-02). The WSF-02 spacecraft included a set of payloads provided by the Texas Space Grant Consortium, known as TexasSat. One of the TexasSat payloads was a GPS TurboRogue receiver loaned by the University Corporation for Atmospheric Research. On September 11, the WSF-02 was unberthed from the Endeavour payload bay using the remote manipulator system. The GPS receiver was powered on prior to release and the WSF-02 remained in free-flight for three days before being retrieved on September 14. All WSF-02 GPS data, which includes dual frequency pseudorange and carrier phase, were stored in an on-board recorder for post-flight analysis, but "snap- shots" of data were transmitted for 2-3 minutes at intervals of several hours, when permitted by the telemetry band- widdl The GPS experiment goals were: (1) an evaluation of precision orbit determination in a low altitude environ...
The SEASAT altimeter measurements have an accuracy of about 10 cm. In order to make best use of t... more The SEASAT altimeter measurements have an accuracy of about 10 cm. In order to make best use of the altimeter measurements for oceanographic and other applications, the radial component of the satellite orbit must be known with an accuracy of about 10 cm. In the orbit computation, drag and solar radiation pressure are significant perturbations. Uncertainties in the reference which appear in these models along with errors in the atmospheric density model are primary error sources, limiting the orbit determination accuracy. In the case of SEATSAT, the effective areas vary considerably with time. In this research, models which account for the actual area variations are developed. To account for the atmospheric density model errors, a set of empirical density model parameters is defined and estimated in the data analysis process. These models are used to achieve laser range residual of 0.939 meter root mean square for a 16 day SEASAT orbit, a factor of about four improvement, over that ...
International Association of Geodesy Symposia, 1990
Major changes in the Cooperative International GPS Network (CIGNET) tracking hardware took place ... more Major changes in the Cooperative International GPS Network (CIGNET) tracking hardware took place in 1989. Prior to 1989, the CIGNET solely consisted of TI-4100 receivers except for the Mini-Mac receiver at Tsukuba. In January, 1989, the National Geodetic Survey (NGS) installed Mini-Mac 2816AT receivers at Mojave, Westford and Richmond which, with the Tsukuba receiver, brought the network to an almost equal number of TI and Mini-Mac receivers. Simultaneous operations of TI and Mini-Mac receivers were conducted by the NGS at the three U.S. sites for a period of several weeks. Using this simultaneous data set in addition to the other CIGNET data, an investigation has been conducted into the compatibility of the all-TI and the mixed receiver configuration. The preliminary results have verified the existence of a 1 ms time tag discrepancy in the Mini-Mac data reported by others, however, a 2.5 cm unresolved discrepancy was found on the short TI to Mini-Mac baseline at Mojave. When the discrepancy in GPS time was corrected, several meter RMS orbit differences were found; however, the 1400 km test baseline between Onsala and Tromso demonstrated less than two parts in 108 agreement between the two cases. The results also demonstrated the existence of a change in Tromso antenna position from the location previously reported.
ABSTRACT Geophysical applications of the Global Positioning System (GPS) require the capability t... more ABSTRACT Geophysical applications of the Global Positioning System (GPS) require the capability to estimate and propagate satellite orbits with high precision. An accurate model of all the forces acting on a satellite is an essential part of achieving high orbit accuracy. Methods of analyzing the perturbation due to thermal radiation and determining its effects on the long-term orbital behaviour of GPS satellites are presented. The thermal imbalance force, a nongravitational orbit perturbation previously considered negligible, is the focus of this paper. The Earth's shadowing of a satellite in orbit causes periodic changes in the satellite's thermal environment. Simulations show that neglecting thermal imbalance in the satellite force model gives orbit errors larger than 10 m over several days for eclipsing satellites. This orbit mismodeling can limit accuracy in orbit determination and in estimation of baselines used for geophysical applications.
... The data sets included various levels of measurement corruption, in-cluding receiver noise, s... more ... The data sets included various levels of measurement corruption, in-cluding receiver noise, selective availability, errors in the GPS broadcast ephemeris and clock information and force model mis-matches in gravity, drag and solar radiation pressure. ...
Your browser or your browser's settings are not supported. To get the best experience possib... more Your browser or your browser's settings are not supported. To get the best experience possible, please download a compatible browser. If you know your browser is up to date, you should check to ensure that javascript is enabled. ... HEAT.PRO computer program ...
Geophysical applications of the Global Positioning System (GPS) require the capability to estimat... more Geophysical applications of the Global Positioning System (GPS) require the capability to estimate and propagate satellite orbits with high precision. An accurate model of all the forces acting on a satellite is an essential part of achieving high orbit accuracy. Methods of analyzing the perturbation due to thermal radiation and determining its effects on the long-term orbital behavior of GPS satellites are presented. The thermal imbalance force, a nongravitational orbit perturbation previously considered negligible, is the focus of this article. The earth's shadowing of a satellite in orbit causes periodic changes in the satellite's thermal environment. Simulations show that neglecting thermal imbalance in the satellite force model gives orbit error larger than ten meters over several days for eclipsing satellites. This orbit mismodeling can limit accuracy in orbit determination and in estimation of baselines used for geophysical applications.
Abstract The TOPEX/POSEIDON oeanographic satellite was launched in August 1992 carrying a high pe... more Abstract The TOPEX/POSEIDON oeanographic satellite was launched in August 1992 carrying a high performance GPS receiver. The purpose of the receiver is to evaluate GPS for precise orbit determination of low orbiting Earth satellites. Using GPS, we have ...
A modular approach to the multisensor-multitarget problem is presented. This approach reduces the... more A modular approach to the multisensor-multitarget problem is presented. This approach reduces the multitarget problem to several single-target problems. An algorithm based on this approach is described. The application of this algorithm to the simulated tracking of several maneuvering targets in an underwater environment and the numerical results obtained in this application are discussed. The validity of using the observation residuals in the data discrimination process and the data-target correlation is demonstrated through application
: The problem of estimating the trajectory of a maneuvering target using passive measurements obt... more : The problem of estimating the trajectory of a maneuvering target using passive measurements obtained from an array of stationary sensors is investigated. The formulation is considered in a two-dimensional rectangular coordinate system. The unknown acceleration components are modelled as Brownian motion processes and consequently the dynamic model is linear. The types of measurements used in the estimation process are the frequency and the bearing angle of some are nonlinear functions of the state vector which consists of a reference frequency and the components of position, velocity and acceleration. Computation algorithms for Extended Kalman Filter and 'batch-sequential' filter are presented. Equations for including the effects of process noise on the batch solution are derived and the computation algorithm is also given. The performance of these filters is compared using noisy measurements simulated for two different scenarios with typical target maneuvers and sensor loc...
The method of modified back differences, a technique that significantly reduces the numerical int... more The method of modified back differences, a technique that significantly reduces the numerical integration errors associated with crossing shadow boundaries using a fixed-mesh multistep integrator without a significant increase in computer run time, is presented. While Hubbard's integral approach can produce significant improvements to the trajectory solution, the interpolation method provides the best overall results. It is demonstrated that iterating on the point mass term correction is also important for achieving the best overall results. It is also shown that the method of modified back differences can be implemented with only a small increase in execution time.
Accelerometers on the CHAMP and GRACE satellites provide high-resolution (seconds) thermospheric ... more Accelerometers on the CHAMP and GRACE satellites provide high-resolution (seconds) thermospheric neutral densities. CHAMP carries the STAR accelerometer and GRACE carries an upgraded SuperSTAR accelerometer. Both instruments are on high-inclination satellites. These data are compared to two types of orbital drag data. One set is from HASDM (High Accuracy Satellite Drag Model). This approach provides spatially and temporally varying density corrections involving tracking of some 100 satellites. A weighted least squares fit to all of the tracking data produces a global density solution with a time resolution of several hours. The second set consists of individual measurements from each of twenty radar-tracked satellites. Densities were derived using newly developed techniques to provide one-day resolution. These data are relatively localized in latitude since all satellites were in highly elliptical orbits. HASDM data are available only during two periods; the first half of 2001 and A...
Shuttle mission STS-69 was launched on September 7, 1995, 10:09 CDT, carrying the Wake Shield Fac... more Shuttle mission STS-69 was launched on September 7, 1995, 10:09 CDT, carrying the Wake Shield Facility (WSF-02). The WSF-02 spacecraft included a set of payloads provided by the Texas Space Grant Consortium, known as TexasSat. One of the TexasSat payloads was a GPS TurboRogue receiver loaned by the University Corporation for Atmospheric Research. On September 11, the WSF-02 was unberthed from the Endeavour payload bay using the remote manipulator system. The GPS receiver was powered on prior to release and the WSF-02 remained in free-flight for three days before being retrieved on September 14. All WSF-02 GPS data, which includes dual frequency pseudorange and carrier phase, were stored in an on-board recorder for post-flight analysis, but "snap- shots" of data were transmitted for 2-3 minutes at intervals of several hours, when permitted by the telemetry band- widdl The GPS experiment goals were: (1) an evaluation of precision orbit determination in a low altitude environ...
The SEASAT altimeter measurements have an accuracy of about 10 cm. In order to make best use of t... more The SEASAT altimeter measurements have an accuracy of about 10 cm. In order to make best use of the altimeter measurements for oceanographic and other applications, the radial component of the satellite orbit must be known with an accuracy of about 10 cm. In the orbit computation, drag and solar radiation pressure are significant perturbations. Uncertainties in the reference which appear in these models along with errors in the atmospheric density model are primary error sources, limiting the orbit determination accuracy. In the case of SEATSAT, the effective areas vary considerably with time. In this research, models which account for the actual area variations are developed. To account for the atmospheric density model errors, a set of empirical density model parameters is defined and estimated in the data analysis process. These models are used to achieve laser range residual of 0.939 meter root mean square for a 16 day SEASAT orbit, a factor of about four improvement, over that ...
International Association of Geodesy Symposia, 1990
Major changes in the Cooperative International GPS Network (CIGNET) tracking hardware took place ... more Major changes in the Cooperative International GPS Network (CIGNET) tracking hardware took place in 1989. Prior to 1989, the CIGNET solely consisted of TI-4100 receivers except for the Mini-Mac receiver at Tsukuba. In January, 1989, the National Geodetic Survey (NGS) installed Mini-Mac 2816AT receivers at Mojave, Westford and Richmond which, with the Tsukuba receiver, brought the network to an almost equal number of TI and Mini-Mac receivers. Simultaneous operations of TI and Mini-Mac receivers were conducted by the NGS at the three U.S. sites for a period of several weeks. Using this simultaneous data set in addition to the other CIGNET data, an investigation has been conducted into the compatibility of the all-TI and the mixed receiver configuration. The preliminary results have verified the existence of a 1 ms time tag discrepancy in the Mini-Mac data reported by others, however, a 2.5 cm unresolved discrepancy was found on the short TI to Mini-Mac baseline at Mojave. When the discrepancy in GPS time was corrected, several meter RMS orbit differences were found; however, the 1400 km test baseline between Onsala and Tromso demonstrated less than two parts in 108 agreement between the two cases. The results also demonstrated the existence of a change in Tromso antenna position from the location previously reported.
ABSTRACT Geophysical applications of the Global Positioning System (GPS) require the capability t... more ABSTRACT Geophysical applications of the Global Positioning System (GPS) require the capability to estimate and propagate satellite orbits with high precision. An accurate model of all the forces acting on a satellite is an essential part of achieving high orbit accuracy. Methods of analyzing the perturbation due to thermal radiation and determining its effects on the long-term orbital behaviour of GPS satellites are presented. The thermal imbalance force, a nongravitational orbit perturbation previously considered negligible, is the focus of this paper. The Earth's shadowing of a satellite in orbit causes periodic changes in the satellite's thermal environment. Simulations show that neglecting thermal imbalance in the satellite force model gives orbit errors larger than 10 m over several days for eclipsing satellites. This orbit mismodeling can limit accuracy in orbit determination and in estimation of baselines used for geophysical applications.
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Papers by P.A.M. ABUSALI