Land Intercalibration and Drift Monitoring of MWR Radiometer on Board SAC-D/Aquarius

The microwave radiometer (MWR) on board the SAC-D/Aquarius mission is a Dicke radiometer operating at 23.8 (H-Pol) and 36.5 GHz (H/V-Pol), which can provide ancillary data for the various retrievals to be performed with Aquarius regarding ocean and land applications. In this study, we report calibration results obtained by a land cross-calibration between Windsat and MWR. Moreover, MWR drifts were monitored using vicarious cold methodology. Results were generated for the 2011-2012 period using version V5.0 S of MWR data. MWR and Windsat cross-calibration was carried out over selected homogeneous targets which include tropical and boreal forests, desert, grassland, and the Sahel. As a result, biases were identified and corrections were proposed. Drifts in MWR observations were identified by implementing the vicarious cold method, which is a statistical approach that estimates the coldest value of the brightness temperature (Tb) (over ocean) histogram. Time series of such cold values are closely related to drifts in the instrument. In general, it was observed that MWR drifts tend to stabilize within 1 K after June 2012, when the software of the on-board computer was updated.