Polarimetric Technique for Satellite Remote Sensing of Superthin Clouds

Superthin clouds with optical depths smaller than ~ 0.3 exist globally and can seriously affect the remote sensing of aerosols, surface temperature, and atmospheric composition. Failing to detect these clouds, the sea-surface temperature retrieved from NASA's Atmospheric Infrared Sounder (AIRS) satellite data is ~ 5–10 K lower than true values at tropical and midlatitude regions, where these clouds frequently exist. Unfortunately, superthin clouds generally cannot be detected by passive satellite instruments that use only total intensity for measurements. Long-term global surveys of superthin clouds using space-borne lidars are limited by the large operational cost and narrow field of view of these active instruments. This chapter reviews the algorithm for remote sensing of superthin clouds based on our previous study results ( Sun et al., 2014 , Sun et al., 2015 ), which show that superthin clouds can be well detected by a polarimetric imager facing toward the backscattering direction of sunlight, exploiting a distinct, characterizing feature of the angle of linear polarization of the backscattered solar radiation (NASA Technology GSC-17392-1). If implemented for satellite remote sensing of the Earth-atmosphere system, this technology will greatly improve the detection of superthin clouds and tremendously impact the remote sensing of clouds, aerosols, surface temperature, atmospheric composition gases, and thus significantly improving data for climate modeling.