Alexandre Couhert (CNES, France); John Moyard (CNES, France)

The analysis of the SLR residuals is an important external validation for the precise orbits. For altimetry satellites the high elevation residuals are used to analyse the radial quality of the orbits.

However, due to the actual performances to verify (better than 1 cm rms in the radial direction), it is now necessary to improve the SLR measurements knowledge : the observed measurement noise can be as good as 2 mm rms, and the limitation is the value of the systematic biases. These biases can be directly observed on many stations.

The current practice is to choose a reduced set of stations (core network) assumed with negligible biases to check the radial performance. The number of used stations can be reduced to 5 stations only.

The objective of this study is to enlarge the core network by estimating the biases for different satellites (Jason 3, Sentinel 3a, Cryosat, Saral), and try to remove the possible geographically correlated errors that can be present in the orbits. This has been checked on sentinel 3a and b, and it was possible to extend the core network from 6 to 12 stations without degrading the initial observations. This will be extended on the other orbits, using a set of common biases for the added stations.