One of the major efforts in altimetry satellite orbit reprocessing made in 2005-2008 was the determination of precise orbits of four altimetry satellites, namely, GEOSAT (1985-1989), ERS-1 (1991-1996), TOPEX/Poseidon (1992-2005) and ERS-2 (1995-2006) at the given time spans  performed at the German Research Centre for Geosciences (GFZ) within the SEAVAR project using “Earth Parameter and Orbit System – Orbit Computation” (EPOS-OC) software and the Altimeter Database and processing System (ADS) developed at GFZ. The orbits were computed in the same (ITRF2000) reference frame for all satellites using common, most precise, at that time, models and standards available, such as EIGEN-GRACE04S geopotential, FES2004 ocean tide and other models as well as improved, denser, satellite dependent parameterization. GEOSAT orbits were derived using Doppler and single crossover data. ERS-1 and ERS-2 orbits were based on the use of Satellite Laser Ranging (SLR) and single crossover data, while TOPEX/Poseidon orbits were computed using SLR and Doppler Orbitography Integrated by Satellite (DORIS) observations. These orbits called “SEAVAR orbits” show improved quality, as compared to earlier GFZ and other orbits. Thus, use of improved standards and denser parameterization of atmosphere drag coefficients and empirical accelerations, especially in the period of high solar activity, resulted in improved (reduced) values of RMS crossover differences for GFZ EIGEN-GRACE04S orbits of GEOSAT, as compared to NASA JGM-3 orbits of this satellite (see Figure).

The orbit files are available via anonymous ftp at

ftp://ftp.gfz-potsdam.de/home/kg/orbit/SEAVAR/.

The description of these orbits is given in the following paper.

Rudenko, S., Schoene T., Gendt, G., Zhang F., and Thaller D., 2007. Precise orbits of altimetry satellites and analysis of GPS data at tide gauges for sea level research. Observations of the System Earth from Space: status seminar, 22 - 23 November 2007, Bavarian Academy of Sciences and Humanities, Munich; Programme & Abstracts, Koordinierungsbuero GEOTECHNOLOGIEN, 41-46.