Citation
Abstract
Techniques for determination of very precise orbits for satellites of the Global Positioning System (GPS) are currently being studied and demonstrated. These techniques can be used to make cm-accurate measurements of station locations relative to the geocenter, monitor earth orientation over timescales of hours, and provide tropospheric and clock delay calibrations during observations made with deep space radio antennas at sites where the GPS receivers have been collocated, For high-earth orbiters, meter-level knowledge of position will be available from GPS, while at low altitudes, sub-decimeter accuracy will be possible. Estimation of satellite orbits and other parameters such as ground station positions is carried out with a multi-satellite batch sequential pseudo-epoch state process noise filter. Both square-root information filtering (SRIF) and UD-factorized covariance filtering formulations are implemented in the software. A Bierman-modified Rauch-Tung-Striebal (BRTS) smoother runs in conjunction with the SRIF and UD filters tu compute smoothed estimates and covariances. The filtering algorithms have been arranged to take advantage of sparse matrices and other characteristics of the GPS measurement scenarios. The filrer includes unique error evaluation capabilities to assess effects from mismodeling. Process noise plays a key role in the orbit determination for stochastic behavior of transmitter/receiver clocks, atmosphere-induced delay fluctuations, and unmodeled satellite accelerations. The efficiency and accuracy of the SRIF and UD filter formulations are compared for GPS processing under a variety of conditions. With data from recent GPS experiments using the seven satellites currently in orbit, continental ground baselines have been measured with GPS and with VLBI which agree to within 2.5 cm over distances of 2000 km, corresponding to a relative baseline accuracy of better than 1.5 parts in 108.
Details
- Volume
- 42-97
- Published
- May 15, 1989
- Pages
- 1–20
- File Size
- 1.2 MB