Microwave radiometer aboard SARAL/ALtiKa : Correction of 37GHz channel

Marie-Laure Frery (CLS, France)

CoAuthors

Bruno Picard (CLS, France); Estelle Obligis (CLS, France); Nathalie Steunou (CNES, France); Christophe Goldstein (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 has been launched on 25th of February, 2013. For the first time, an altimeter in Ka band is used to determine the ocean topography. This Ka band altimeter is combined to a two-channels microwave radiometer (23.8GHz and 37GHz) in order to correct for the excess path delay resulting from the presence of water vapour in the troposphere. The radiometer performs measurements of brightness temperatures in both bands at the location of the altimeter footprint.

After a few months, the hot calibration measurements of the 37GHz channel have been received saturated which had lead to degraded values of the gain for this channel. This had obviously a direct impact on the brightness temperatures of the 37GHz channel. Moreover, it had also impacted the geophysical products retrieved by the inversion algorithms including the wet tropospheric correction used in the estimation of the altimeter path delay. Update of the onboard radiometer database values on October 2013 allowed to retrieve a correct reception of these hot calibration measurements.
We present first an impact assessment of this saturation on the brightness temperatures and on the wet tropospheric correction.
A correction is under development to retrieve the correct dynamic of the gain. This correction is presented and evaluated using data of cycles without saturation. The assessment of the quality of the corrected dataset is performed at L1B level with the brightness temperatures and at L2 level with the wet tropospheric correction.
 
Marie-Laure Frery
CLS
France
mfrery@cls.fr