Impact of Multiple Scattering on Simulated Infrared Cloud Scene Images
Jerry Tessendorf and David Wasson
Characterization and Propagation of Sources and Backgrounds, SPIE Proceedings, vol 2223, 462-473, (1994)
The three-dimensional volumetric character of clouds is a critically important factor in determining cloud structure as seen in infrared imagery. Using a longwave cloud scene simulator which images a three-dimensional cloud volume, the 3D structure has been shown to be particularly important when viewing at low grazing angles. In order to conduct analyses of cloud scene structure in MW and visible bands as well, the longwave simulator has been significantly upgraded to perform imaging of clouds with multiple scattering included. The multiple scattering algorithm is based on a WKB approximation method for the exact radiative transfer problem, and comprehends the spatial variations in optical properties within the cloud volume. As a first analysis, we have generated a cloud scene which is backlit by the sun, and systematically assess the contributions of the thermal, solar, and multiple scattering mechanisms within the imagery. As might be expected, multiple scattering has its greatest impact at the cloud edges in the MW band, where the "silver lining" is formed. In the MW band, scattering can also play a role at cloud edges and create additional clutter by scattering earthshine into the field of view of the low grazing angle camera. In principle, this simulator is capable of operating throughout the visible and infrared bands, for realistically size clouds.