Plen. 1 COMBINED MICROWAVE AND OPTiCAL ATMOSPHERIC REMOTE SENSING TECHNIQUES: A REVIEW*

Remote sensing of atmospheric parameters with space-based passive microwave and optical sensors matured fntm research experiments in the 1960’s and 1970’s to operational systems in the lW0’s and 1980’s. Atmospheric temperature and humidity pfdes can be retrieved using the infrated carbon dioxide resonances, the microwave oxygen res”, and the water vapor resonances in both spectral bands. Superior retrievals can be obtained by combining these tensors, taking advantage of the superior ability of microwaves to penetrate many cloud types and to respond better to low temperatures and negative lapse rates, while simultaneously taking advantage of the high spatial resolution, channel count, and sensitivity of modem inhared sensors, together with their reduced sensitivity to surface effects. Microwave and infrared soundings from satellites have been combined since their operational introduction in the 197O’s, and progress continues to be made. These evolving techniques are reviewed here. I. PhysicaIIssues The infrared and microwave atmospheric remote sensing bands differ in their spectroscopic characteristics, propagation characteristics through clouds and other aerosols, and surface emission characteristics. Th