Microwave CLO sounder

摘要

Describes the design of a satellite borne microwave radiometer operating at the frequency of 204.352 GHz for sounding the abundance of stratospheric chlorine oxide (CLO). The CLO sounder is assumed to be at an altitude of 600 km and observes the atmosphere at tangential range of 2780 km at 20 km altitude. The altitude range from 15 km to 45 km is observed in eleven tracks with center-center spacing of 2.73 km and widths of 3.1 km. An innovative antenna design uses a 1.7 m diameter offset feed zone plate reflector and an assembly of feed horns to provide eleven simultaneous beams in the elevation plane with beam-beam angular separations of 0.056 degree and beamwidths of 0.064 degree. Secondary and a tertiary reflectors direct the beams onto an array of feed horns. The secondary reflector provides compensation for aberrations due to the off-axis geometry. The tertiary reflector switches the observed source among soundings and cold sky and hot load calibrations. A low risk radiometer design uses direct down conversion by two stage mixing to convert the 204.352 GHz signal to a 510 MHz band centered at 600 MHz. The 600 MHz IF signal is input to a filter bank which produces outputs in 15 channels with bandwidths from 2 to 128 MHz. With two second integration, the radiometer sensitivity is 0.35 K with 2 MHz bandwidth and 0.04 K with 128 MHz bandwidth. Calibration is provided by periodic hot load and cold sky views.