An alternative method of orbit improvement for a Doppler‐tracked satellite: A step toward Earth gravity model refinement

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Abstract
An alternative method of orbit and gravity field improvement for Doppler‐tracked satellites is presented here, in view of the prospect of future geodetic and altimetric missions (Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS)/SPOT 2, the Ocean Topography Experiment (TOPEX)/Poseidon, ERS 1). Owing to a refined analysis of the Doppler residuals generated by a classical orbit computation, it is successively possible (1) to improve the computed spacecraft orbit with interesting by‐products such as improved tracking station coordinates and Doppler reference frequencies, (2) to recover the disturbing forces due to a mismodeling of the geopptential model (i.e., regional gravity anomalies above the stations, in line‐of‐sight direction, and at satellite altitude), and (3) to globally refine the mismodeled gravity field from a dense set of this regional information. The paper deals with the first two steps with emphasis on step 1. The more classical geodetic problem of step 3 will be the subject of a future paper. Simulation results for Seasat and DORIS are presented and discussed: With a simulated random noise of 0.3 cm/s, orbit error is recovered with an accuracy of a few decimeters. With a noise level of 0.3 mm/s, orbit and force errors are recovered with an rms accuracy better than 0.2m and 0.2 mGal at 800 km altitude. This is very encouraging for future Doppler positioning systems like DORIS.