Investigations On The Envisat Ra2 Tropspheric Correction
Blarel, Fabien; Legresy, Benoît

The Centre for the Topography of Oceans and the Hydrosphere (CTOH), the Altimeter Data Service of the LEGOS laboratory pursue an effort to validate and improve ENVISAT RA2 altimetry. We investigated the stability and reliability of different corrections for the altimetric measurements. With the previous processing, the ICE Validation chain of the CTOH detected some problems with the dry tropospheric correction over the Cryosphere. Here we present validation of the latest re-processing (v2.1) of ENVISAT data. We observe the limitation of this re-processed dry tropospheric correction, especially the jump observed at cycle 44 over Antarctica which causes significant local trend, suspect changes in the variability of this correction over time. We investigated a solution and suggest an alternative algorithm to re-compute this correction over all the earth with the ERA ECMWF pressure fields and by using directly the altimetric range measurement rather than any digital elevation model (DEM). We present the results of this investigation, the statistics of previous and new corrections and in the context of different surfaces. The improvement is significant, and we discuss the aspects and impacts of this improvement, in terms of meteo-fields, procedure, and location.