| The GEOSAT exact repeat orbit will be used by the Navy's GEOSAT Follow-On (GFO) satellite to be launched in 1997. GFO is a Navy mission which will provide altimetry data. GFO's follow on, GFO-2, will also perform very accurate oceanographic altimetry from space. Ideally, the location of the satellite which makes the measurements should be known to centimeter level accuracy.;Each of the satellite missions mentioned will have Global Positioning System (GPS) receivers on board in order to track the satellites. The purpose of the dissertation is to predict how accurately the orbits for the GFO satellites may be determined. A study of radial orbit accuracy for a satellite in the GEOSAT and the TOPEX/Poseidon orbits has been completed with the Jet Propulsion Laboratory's (JPL's) GIPSY-OASIS II software. A previous study by Gold, et al., 1995, has shown that radial orbit accuracy in the GEOSAT orbit will be approximately 5.5 cm for GFO (five GPS satellite receiver) and 4.3 cm for EOS ALT-R (ten GPS satellite receiver). This thesis further investigates orbit error for the GFO satellites (Irish, 1996). In the preliminary study, the JGM-2 gravity field was used in the simulations. Here, the JGM-3 gravity field will be included in the simulations in order to determine the effect using the newer field will have on the radial orbit error. Analysis has been completed for both GEOSAT and T/P orbits. The results show that using the JGM-2 field and 13 stations, the RMS error is as low as 3.0 cm for the GEOSAT orbit and 1.6 cm for the T/P orbit. Using the newer JGM-3 field, these results are improved to 1.5 cm for the GEOSAT orbit and 1.1 cm for the T/P orbit. At the end of the analysis period, a new geopotential model, EGM96, was made available, and was used to obtain orbit accuracy results. Those results are preliminary, and because a clone is not yet available, the results do not truly reflect the increased accuracy of the new field. The preliminary orbit accuracy results obtained using EGM96 for the GEOSAT orbit are as low as 1.9 cm and are as low as 2.2 cm RMS for the T/P orbit. |
