Along Track Scanning Radiometer-2 (ATSR-2) measurement made over tropical cirrus clouds are analyzed on the basis of radiative transfer calculations for clouds consisting of hexagonal ice crystals. Single scattering properties are calculated using the geometrical-optics approximation and ray-tracing techniques. The imperfect shape that is usually found in real atmospheric ice crystals in mimicked by applying a random variation in photon paths at air/ice interfaces. Multiple scattering is calculated on the basis of the doubling-adding method. The ATSR-2 measurements are analyzed at a non-absorbing and an absorbing wavelength and for nadir and forward viewing direction. The measurements reveal that for small optical thickness the relationship between the reflectivities at the two wavelengths considered is highly linear, whereas for increasing optical thickness the gradient decreases and eventually vanishes. This characteristic pattern can be well reproduced by the model using a stratiform cloud consisting of imperfect randomly oriented columnar ice crystals of type 'C2'. The variation in crystal size across the optically thick part of the cloud system is modest.

Date Published: 14 December 1998
PDF: 10 pages
Proc. SPIE 3495, Satellite Remote Sensing of Clouds and the Atmosphere III, (14 December 1998); doi: 10.1117/12.332669

Published in SPIE Proceedings Vol. 3495:
Satellite Remote Sensing of Clouds and the Atmosphere III
Jaqueline E. Russell, Editor(s)