The Digital Imaging and Remote Sensing laboratory's Image Generation model, DIRSIG, combines computer aided design (CAD), ray tracing techniques, radiometric principles, and thermodynamic models to create synthetic imagery. The model emphasizes rigorous radiometric solutions that account for spectral reflectance effects, angular emissivities, atmospheric transmission and upwelled and downwelled sky radiance. This paper describes enhancements to the radiometric portion of the code that permits inclusion of variations with azimuth of downwelling sky radiance, solution of the radiometric propagation models using specific radiosonde data including adjustments for the time of day, and the incorporation of background effects from objects adjacent to the target. Simulated scenes are presented that show how these enhancements produce imagery that more closely match observed phenomena. In particular, the importance of properly modeled sky radiance is shown both for low altitude oblique imagery where the sky is directly observed and for near nadir imagery where reflected sky radiance is important.

Date of creation, presentation, or exhibit



Copyright 1993 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

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Document Type

Conference Paper

Department, Program, or Center

Chester F. Carlson Center for Imaging Science (COS)


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