Orbit determination for radar altimetry satellites
Satellite radar altimetry is one of the primary tools to study sea level changes. It allows measuring sea level heights and variations globally at various time scales. Precise orbits of altimetry satellites are a prerequisite for the analysis of altimetry measurements. The list of the major altimetry missions includes past missions GEOSAT (1985-1990), ERS-1 (1991-1996), TOPEX/Poseidon (1992-2005), and GFO (1998-2008), and the current missions ERS-2 (since 1995), Jason-1 (since 2001), ENVISAT (since 2002), Jason-2 (since 2008), and Cryosat-2 (since 2010).
Orbits of altimetry satellites were computed at different institutes using different models in different referent reference frames in the past. To achieve consistency over longer time periods and reduce systematic effects caused by using different, for different satellites, models and reference frames, the unification of orbit quality is very important. One of the major efforts in altimetry satellite orbit reprocessing made recently was 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 time spans given performed at German Research Centre for Geosciences (GFZ) within the project “Sea Level Variations – Prospects from the Past to the Present” (SEAVAR) 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 models and standards available, such as EIGEN-GRACE04S geopotential, FES2004 ocean tide and other models as well as improved, denser, satellite dependent parameterization. GEOSAT orbit was derived using Doppler and single crossover data. ERS-1 and ERS-2 orbits are based on the use of Satellite Laser Ranging (SLR) and single crossover data. TOPEX/Poseidon orbit is 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. The orbit files are available via anonymous ftp.
To have further progress in the altimetry satellite precise orbit determination Section 1.2 studies the use of new static and time varying geopotential and other correction models, improved modeling of non-gravitational forces acting on the altimetry satellites, and new Terrestrial Reference Frame realizations, such as, ITRF2008.
Contact: Dr. Sergei Rudenko