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 Τ and effective radius R eff 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 Τ and R eff was evaluated. With relative differences of up to 70%, the influence of particle habit on Τ is larger than on R eff (up to 20% differences). Retrieved r values agreed with values derived from concurrent lidar measurements within the measurement uncertainties. © 2009 by the American Geophysical Union.