Influence of ice crystal shape on retrieval of cirrus optical thickness and effective radius: A case study

Abstract

Airborne measurements of spectral upwelling radiances (350�2200 nm) reflected by cirrus using the Spectral Modular Airborne Radiation measurement sysTem (SMART)-Albedometer were made over land and water surfaces. Based on these data, cloud optical thickness tau and effective radius Reff of the observed cirrus were retrieved. By using different crystal shape assumptions (hexagonal plates, solid and hollow columns, rough aggregates, planar and spatial rosettes, ice spheres, and a mixture of particle habits) in the retrieval, the influence of crystal shape on the retrieved tau and Reff was evaluated. With relative differences of up to 70%, the influence of particle habit on t is larger than on Reff (up to 20% differences). Retrieved tau values agreed with values derived from concurrent lidar measurements within the measurement uncertainties.