Method to Apply Homogeneous-Path Transmittance Models to Inhomogeneous Atmospheres

Michael P. Weinreb National Environmental Satellite Service, NOAA, Washington, D. C. 20233

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Arthur C. Neuendorffer National Environmental Satellite Service, NOAA, Washington, D. C. 20233

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Abstract

An accurate approximation to calculate atmospheric profiles of transmittance in instrumental spectral intervals is presented. The approximation assumes a known transmittance model; i.e., that the transmittance in the spectral interval of the instrument is known as a function of quantity of absorber, temperature, and total pressure in homogeneous paths. An inhomogeneous atmosphere is treated as a sequence of homogeneous layers. One applies the model by successively rescaling the quantity of absorber. The method is exact for monochromatic radiation. It avoids the computation of mean line strengths, and it is computationally fast. As an example, transmittance profiles are computed for two spectral intervals in which water vapor is the chief absorber. The results are in excellent agreement with the “exact” point-by-point calculation.

Abstract

An accurate approximation to calculate atmospheric profiles of transmittance in instrumental spectral intervals is presented. The approximation assumes a known transmittance model; i.e., that the transmittance in the spectral interval of the instrument is known as a function of quantity of absorber, temperature, and total pressure in homogeneous paths. An inhomogeneous atmosphere is treated as a sequence of homogeneous layers. One applies the model by successively rescaling the quantity of absorber. The method is exact for monochromatic radiation. It avoids the computation of mean line strengths, and it is computationally fast. As an example, transmittance profiles are computed for two spectral intervals in which water vapor is the chief absorber. The results are in excellent agreement with the “exact” point-by-point calculation.

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