微波湿度计(MWHS)是风云3号卫星的主要有效载荷之一,其频率为150GHz(双极化)和183.31GHz(三通道),采用垂直于飞行方向的交轨扫描方式,科学目标是探测大气湿度的垂直分布.本文简要介绍微波大气湿度探测的基本原理,阐述了微波湿度计的系统构成及工作原理;描述了微波湿度计的性能指标要求.测试结果表明,微波湿度计性能指标满足设计要求.

FY-3meteorological satellite is the2nd generation ofChina spolar-orbitmeteorological satellite, and theMicro-waveHumidity Sounder (MWHS) is one of itsmain payloads. The basic principle of atmospheric humidity sounding by microwave radiometer and the technical specifications ofMWHS onboard FY-3 satellite are briefly introduced in this paper.The block diagram and operatingmodes ofMWHS are presented. MWHS is a dual-frequency, five-channelmillmi eterwave radiometerwhich is a totalpower typemicrowave radiometerbased on a heterodyne receiver, and performs cross-track scan-ning. The frequencies ofMWHS include both the atmospheric transparentwindows of150GHz and water vapour absorption lines around 183.31GHz. The 150GHz radiometer has two polarizations ofV and H, and the 183. 31GHz radiometer has three channels of183.31±1GHz, 183.31±3GHz and 183.31±7GHz, respectively.The swathwidth of about2700km is mi plemented by cross-track scanning of the antenna beams. Final testing verifies that the performance ofMWHS satisfies technical requirements of specifications.MWHS consists of three units: antenna and receiverunit, electronic unitand power supply unit. Antenna and receiver unit collcets emission from the atmosphere.The received signal is focused to the horn-feed and the firstelementof the high frequency front end, and then down-converted by a double side band mixer to Intermediate Frequency; IF signal is been down-converted toLowFrequency(LF) by a detector, and then integrated. The electronic unitdigitizes theLF signa,l con-trols the scanningmechanism andmeasuresphysical temperature ofthe on-board hottarget forcalibration, and communicates with satellite through a 1553B data bus. The power supplyunitperformsDC/DC conversion, distributies the DC lines to the various sub assemblies and switches between the nominal and the redundantunit.Onemotordrives two separated reflectors for the 150GHz and the 183.31GHz channels,the scanning period is2.667s.Main beams of the antenna scan over the observing swath (±53.35°from nadir) in the cross-track direction at a constant periodicity of1.71s. During each period, two-point calibration are performed to calibrate the receiver gain and noise. The calibration is mi plemented by observing an onboard hot target and the background emission of the cold sky.