Remote Sounding of Cirrus Cloud Optical Depths and Ice Crystal Sizes from AVHRR Data: Verification Using FIRE II IFO Measurements

Abstract

Using the data obtained from the Advanced Very High Resolution Radiometer (AVHRR) 3.7-µm and 10.9-µm channels, a retrieval scheme has been developed to simultaneously infer cirrus cloud optical depth and mean effective ice crystal size based on the theory of radiative transfer and parameterizations. A numerical scheme is further developed to remove the solar component in the 3.7-µm radiance for applications to daytime satellite data. This scheme is based on the correlation between the 3.7-µm (solar) and 0.63-µm reflectances. Validation of the algorithm has been performed by using various datasets that were collected during the FIRE-II IFO (Nov-Dec 1991) at Coffeyville, Kansas. We have focused on the 26 November and 5 December cases. The retrieval analysis over a 0.5°?1.0° area is performed around Coffeyville for each case based on AVHRR-HRPT data. For validation the authors analyze the photomicrograph data collected by the balloonborne replicator, determine the microphysical and optical properties of the sampled cirrus clouds, and derive their position at the satellite overpass based on sounding data. It is demonstrated that the retrieved cirrus cloud temperature, mean effective ice crystal size, and optical depth closely match the observed values. Further, the retrieved cirrus cloud properties are applied to the computation of surface radiative fluxes using a radiative transfer program that involves a consistent representation of cirrus cloud fields. The computed values are compared with the data measured from ground-based radiometers, and it is shown that the computed downward surface IR and solar fluxes are within 5 and 10 W m?2 of the measured values, respectively, near the time of satellite overpass.