CoAuthors

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

Satellite Laser Ranging (SLR) data, made available by the International Laser Ranging Service (ILRS), is essential to validate and quantify the orbit precision of the altimeter satellites. It is the only independent and unambiguous validation method that can provide the absolute radial orbit accuracy by means of high elevation passes. However, the accuracy of the data, even of some of the core stations, is irregular. Biases and drifts are observed in the ranging data. The SLR data are considered unbiased in the altimeter satellites’ orbit validation process (i.e., range or time bias are not estimated). As a consequence, unknown or not communicated errors in the ranging data (note: the ILRS provides incomplete station error information) directly affect the validation results.
SLR station biases from 2001 to 2015 were re-estimated in precise orbit determinations on the geodetic satellites LAGEOS-1/2 (at 5900 km altitude) and Starlette/Stella (at about 850 km), using the ITRF2014 station coordinates in this reprocessing (instead of ITRF2008 in 2015). All advertized station corrections by the ILRS were applied in this computation. The remaining estimated biases of single satellites as well as per pair (LAGEOS1&2; Stella and Starlette) are compared with orbit validation results of the same stations on Jason-1/2 and Cryosat-2 orbits. The estimated biases of one or the other pair of geodetic satellites are then applied and the Jason-1/2 and Cryosat-2 orbit validation statistics recomputed.