Combined microwave and optical atmospheric remote sensing techniques: a review

Remote sensing of atmospheric parameters with space-based passive microwave and optical sensors matured from research experiments in the 1960s and 1970s to operational systems in the 1970s and 1980s. Atmospheric temperature and humidity profiles can be retrieved using the infrared carbon dioxide resonances, the microwave oxygen resonances, and the water vapor resonances in both spectral bands. Superior retrievals can be obtained by combining these sensors, 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 modern infrared sensors, together with their reduced sensitivity to surface effects. Microwave and infrared soundings from satellites have been combined since their operational introduction in the 1970s, and progress continues to be made. These evolving techniques are reviewed