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Proceedings Paper

Characterizing the effects of natural clouds on scene simulations
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Paper Abstract

In modeling and simulations the importance of the natural environment has always been recognized with regard to its influence on contrast transmission. However, the variability of surface illumination and solar loading due to broken clouds, the resulting impact of dynamic range on recognition, and clouds as backgrounds, along with the traditional influences due to transmission and path radiance, are emerging areas of relevance due to improvements in the modeling of these effects. The Air Force LOWTRAN model has been the traditional choice for multi- waveband analysis of spectral atmospheric effects on systems performance. But this code only has spatially varying effects in the vertical direction. Dynamic range impacts of horizontally variable illumination conditions cannot be addressed. We describe a series of codes designed to allow the linking of predictions of cloud fractions, base heights, layer depths, and layer cloud types with a model to predict the cloud density structure. These results are coupled to a radiative transfer model. We describe the salient features of this physics based model. We then describe the point-to- point calculation method to produce path radiance and transmittance statistics at multi-channel resolution. The weighted spectra are used to describe the effects on a given sensor channel. We further describe the perspective view generation method used to render cloudy scenes from a variety of observer positions. The radiative transfer model is robust in the sense that its results are not limited to low cloud densities. The spectral region covered is the same as that treated by LOWTRAN and LOWTRAN output is used to initialize the upper boundary for incident direct (solar/lunar) and diffuse radiation source and used to determine the background molecular absorption (by modeled layer) of the scattering volume. Typical scattering volumes treated have an 8 km X 8 km footprint and are either 4 km, 8 km, or 16 km high. These volume choices can be used for addition of clouds as scene elements in simulations, usage of the surface illumination information as a positionally varying solar loading or brightness data set, and for path characterization for contrast transmission calculations.

Paper Details

Date Published: 20 June 1997
PDF: 11 pages
Proc. SPIE 3062, Targets and Backgrounds: Characterization and Representation III, (20 June 1997); doi: 10.1117/12.276676
Show Author Affiliations
David H. Tofsted, Army Research Lab. (United States)
Sean G. O'Brien, New Mexico State Univ. (United States)

Published in SPIE Proceedings Vol. 3062:
Targets and Backgrounds: Characterization and Representation III
Wendell R. Watkins; Dieter Clement, Editor(s)

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