CONAE Microwave Radiometer (MWR) Counts to Tb Algorithm and On-Orbit Validation

The Aquarius/SAC-D, International Earth Science Satellite Mission, is a collaboration between NASA and the Argentine Space Agency (Comisión Nacional de Actividades Espaciales, CONAE) that was launched on June 10, 2011 to provide scientists with monthly global maps of sea surface salinity (SSS) to understand the Earth’s hydrological cycle and to investigate global climate change. This paper concerns the microwave radiometer (MWR), a CONAE science instrument developed to provide simultaneous and spatially collocated environmental measurements that complement the prime L-band radiometer/scatterometer sensor (Aquarius) for measuring SSS. MWR is a 3-channel (23.8-GHz H-pol and 36.5-GHz V- and H-pol) passive microwave instrument that measures the Earth’s brightness temperature (Tb). This paper describes the MWR counts to Tb algorithm (V6.0) and presents results of the on-orbit Tb validation using intersatellite radiometric calibration with the Naval Research Laboratory’s WindSat (WS) satellite radiometer. In addition, an alternative MWR counts to Tb algorithm (V7.0) is presented that normalizes the MWR Tbs to WS. This latter version (V7.0) has the advantage of removing MWR time-varying radiometric calibration biases between antenna beams and channels as verified by on-orbit comparisons with WS.