Consideration of permanent tidal deformation in the orbit determination and data analysis for the Topex/Poseidon mission

The effects of the permanent tidal effects of the Sun and Moon with specific applications to satellite altimeter data reduction are reviewed in the context of a consistent definition of geoid undulations. Three situations are applicable not only for altimeter reduction and geoid definition, but also for the second degree zonal harmonic of the geopotential and the equatorial radius. A recommendation is made that sea surface heights and geoid undulations placed on the Topex/Poseidon geophysical data record should be referred to the mean Earth case (i.e., with the permanent effects of the Sun and Moon included). Numerical constants for a number of parameters, including a flattening and geoid geopotential, are included

DORIS/SLR POD modeling improvements for Jason-1 and Jason-2

International audienceThe long-term stability and the precision of the satellite orbit is a critical component of the Jason-1 and Jason-2 (OSTM) Missions, providing the reference frame for ocean mapping using altimeter data. DORIS tracking in combination with SLR has provided orbits, which are both highly accurate and consistent across missions using the latest and most accurate POD models. These models include GRACE-derived static and time varying gravity fields and a refined Terrestrial Reference Frame based on SLR and DORIS data yielding a uniform station complement. Additional improvements have been achieved based on advances in modeling the satellite surface forces and the tropospheric path delay for DORIS measurements. This paper presents these model improvements for Jason-1 and Jason-2, including a description of DORIS sensitivity to error in tropospheric path delay. We show that the detailed University College London (UCL) radiation pressure model for Jason-1, which includes self-shadowing and thermal re-radiation, is superior to the use of a macromodel for radiation pressure surface force modeling. Improvements in SLR residuals are seen over all Beta-prime angles for both Jason-1 and Jason-2 using the UCL model, with the greatest improvement found over regimes of low Beta-prime where orbit Earth shadowing is maximum. The overall radial orbit improvement for Jason-1 using the UCL model is 3 mm RMS, as corroborated by the improvement in the independent altimeter crossover data. Special attention is paid to Jason-2 POD to assess improvements gained with the latest advances in DORIS receiver technology. Tests using SLR and altimeter crossover residuals suggest the Jason-2 reduced-dynamic DORIS-only, SLR/DORIS, and GPS orbits have all achieved 1-cm radial accuracy. Tests using independent SLR data acquired at high elevation show an average fit value of 1.02 cm for the DORIS-only and 0.94 cm for the GPS reduced-dynamic orbits. Orbit differences suggest that the largest remaining errors in the Jason-2 dynamic orbit solutions are due to radiation pressure mis-modeling and variations in the geopotential not captured in the GRACE-derived annual terms