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The Advanced Microwave Sounding Unit (AMSU), launched on May 13 1998, is a twenty-channel passive microwaveradiometer designed to provide information on atmospheric temperature and humidity structure in clear and cloudy con-ditions, complementing existing infra-red radiometers which provide information only in clear areas. AMSU has somechannels similar to those flown on existing missions and others which are new. Observed radiances from the Special Sen-sor Microwave Imager (SSM/I) and the Microwave Sounding Unit (MSU) are compared with radiances calculated fromnumerical weather prediction (NWP) model profiles, and the differences discussed. A processing method for ATOVSradiances is described, and differences from previous techniques are highlighted. An initial evaluation of AMSU data isgiven. Finally the impact of passive microwave observations on the skill of numerical weather forecasts is discussed.Key-words: Numerical weather prediction, ATOVS, AMSU, MSU, SSMII, preprocessing, idvar, radiance, assimilation |
