Preliminary analysis of the Aquarius/SAC-D Microwave Radiometer (MWR) antenna temperature: Possible antenna pattern issue

The Microwave Radiometer (MWR) flying on the Aquarius/SAC-D satellite is a Dicke radiometer operating at 23.8 and 36.5 GHz that was developed by the Argentine Space Agency CONAE. This instrument complements Aquarius (NASA's L-band radiometer/scatterometer) by providing simultaneous spatially collocated environmental measurements such as oceanic wind speed for roughness correction and rain rate for flagging corrupted salinity retrievals. This paper describes the initial findings on the MWR antenna beam pattern issue. The antenna pattern issue is best described as unwanted earth radiation entering the side-lobes of the directed beam, possibly of unexpected high gain, of certain MWR feedhorns. A first look at the understanding of this problem is presented.