Reinquin Franck (CNES, France); Alexandre Couhert (CNES, France)

Satellite Laser Ranging (SLR) data, made available by the International Laser Ranging Service (ILRS), is used to validate and quantify precise orbits of the altimeter satellites. It is essentially the only independent and unambiguous validation method that can provide the absolute radial orbit accuracy. However, the accuracy of the data, even of the core stations, is fluctuating. Unknown errors in the ranging data (the ILRS provides incomplete station error information), which are used in the validation process without bias estimation, directly affect validation results.
The geodetic satellites LAGEOS-1/2 (at 5900 km altitude) and Starlette/Stella (at about 850 km) are used to estimate SLR station biases from 2001 to 2014. All advertized station corrections by the ILRS are applied in this computation. The estimated biases are compared with validation results of the same stations on Jason-1/2 and Cryosat-2 orbits. Finally, a more realistic external validation of the Jason-1/2 and Cryosat-2 orbits is obtained by taking the station biases into account.