Prelaunch Calibration of Microwave Humidity Sounder on China´s FY-3A Meteorological Satellite

China´s Feng Yun-3A (FY-3A) meteorological satellite is a second-generation polar-orbiting meteorological satellite launched in May 2008. The Microwave Humidity Sounder (MWHS) is the main payload, designed for atmospheric humidity sounding. Before the launch of MWHS, a series of experiments was conducted in a thermal/vacuum (T/V) chamber. This letter describes the MWHS T/V calibration, in which the flight model currently operating on FY-3A was tested. The calibration procedure and data-processing methods are presented. Calibration results, such as radiometric resolution, receiver nonlinearity, and calibration bias, were obtained. The results meet the specifications on bias and sensitivity of MWHS. Since the instrument temperatures will be approximately 10°C-20°C on orbit, the calibration errors of MWHS over the range of 100-300 K would be less than 0.3 K using the nonlinearity coefficients derived in the T/V test.