Ice cloud modeling upgrade to GRC's Advanced Surveillance Testbed

Anthony L. Daniell; Howard M. Robbins

doi:10.1117/12.217678

1 September 1995 Ice cloud modeling upgrade to GRC's Advanced Surveillance Test-bed

Anthony L. Daniell, Howard M. Robbins

Proceedings Volume 2561, Signal and Data Processing of Small Targets 1995; (1995) https://doi.org/10.1117/12.217678
Event: SPIE's 1995 International Symposium on Optical Science, Engineering, and Instrumentation, 1995, San Diego, CA, United States

Abstract

The development and evaluation of signal and data processing algorithms for IR surveillance systems is critically dependent on realistic simulations of targets and background. The Advanced Surveillance Testbed has been developed by GRC to perform such simulations. It has recently been upgraded to include models for the scattering of sunlight from high-altitude clouds of ice-crystals. The ice cloud models in the Advanced Surveillance Testbed are designed primarily for the SWIR and MWIR bands. The ice clouds are assumed to have nominally flat upper surfaces, and to be composed of hexagonal crystals (plates, columns, or intermediates), with any of several alternative distributions of shapes and sizes. The ice- crystals are assumed to rotate randomly about their hexagonal axes, but the user can choose from several models for the orientation of this axis: random isotropic, random horizonal, or nominally vertical. A single scattering model is used, with the small-angle forward scattering removed by renormalization. The scattering is calculated by geometrical optics, using algorithms based on the papers published by Liou, Takano, Cai, and Coleman. However, the GRC implementation includes some innovations that greatly increase its computational efficiency. In the SWIR band, the refractive index is highly variable. Its imaginary part varies by orders of magnitude, and its real part can be less than unity, causing total external reflections. Therefore, it is necessary to perform the computations for multiple IR wavelengths and combine the results. The calculations include two-way atmospheric transmission for the relevant wavelengths and the assumed cloud altitude. The model and its utility will be discussed.

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Anthony L. Daniell and Howard M. Robbins "Ice cloud modeling upgrade to GRC's Advanced Surveillance Test-bed", Proc. SPIE 2561, Signal and Data Processing of Small Targets 1995, (1 September 1995); https://doi.org/10.1117/12.217678

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KEYWORDS

Crystals

Clouds

Scattering

Short wave infrared radiation

Surveillance

Laser crystals

Systems modeling

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