SARAL/ALTIKA wet tropospheric correction: retrieval stategies and performances

Bruno PICARD (CLS, France)

CoAuthors

Marie-Laure Fréry (CLS, France); Estelle Obligis (CLS, France); Laurence Eymard (IPSL, France); Nathalie Steunou (CNES, FRANCE); Nicolas Picot (CNES, France)

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Instrument Processing: Corrections

Presentation type: Type Poster

The AltiKa/SARAL mission is a complement of the Jason altimeter series. A two-channels (23.8 and 37 GHz) microwave radiometer (MWR) is combined to the altimeter in order to correct the altimeter range for the excess path delay (dh) resulting from the presence of water vapour in the troposphere.

The in-flight calibration of AltiKa MWR exhibits very good metrics compared to other radiometers but the classical "mixed" empirical approach successfully used for Envisat shows non-optimal performances for the dh retrieval.

Results from the "mixed" approach are compared to a purely statistical relationship established between measured TBs and sigma0 on one hand and modeled dh on the other hand.

For both approaches, a sensitivity study is conducted for AltiKa, Jason-2 and Envisat radiometers comparing the gain in variance of sea surface height at crossovers using only 23.8 GHz TB, both 23.8 GHz and cloud liquid water content channel, with or without sigma0.

In conclusion, the non optimal performances of the "mixed" approach are due to the differences between simulated and measured Ka backscattering coefficient (sigma0). Adding SST to a statistical approach with the three classical inputs proved to have performances close to what is initially expected with the "mixed" approach for a two-channel microwave radiometer.
 
Bruno PICARD
CLS
France
bpicard@cls.fr