Observations of TOPEX/POSEIDON Orbit Errors Due to Gravitational and Tidal Modeling Errors Using the Global Positioning System

Abstract

Satellite altimetry is faced with the challenge of measuring subtle variations in the dynamic topography of the world’s oceans with cm-level accuracy. The TOPEX/Poseidon (T/P) mission was designed to resolve these signals by measuring the radial component of the orbit with an accuracy of 13 cm, or better, in a root-mean-square (RMS) sense. Owing to major advances in precision orbit determination, the actual level of performance is estimated to be nearly an order of magnitude better than that [e.g., Tapley et al., 1994a]. This is primarily due to improvements in the gravity model for the Earth, including the tide model, and the effectiveness of the 3 precision tracking systems carried on the spacecraft (see next section). This paper summarizes the results obtained from a comparison between two distinct types of T/P orbits: classical dynamic orbits and GPS-based reduced-dynamic orbits. Surface manifestations of the relative spatial and temporal behavior of these orbits are described in terms of their effect on altimetric observations of dynamic topography.