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18 November 1977 Application Of An Efficient Method For Calculating Transmittance Profiles
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A rapid and accurate approximation to the Lorentz line shape has been developed which significantly reduces the time of line-by-line atmospheric transmittance calculations. Computer arithmetic operations are minimized through the separation of quantities which depend on frequency and those which depend on atmospheric variables. The approximation and the standard methods of calculation were applied to the determination of absorption coefficients at five NIMBUS-6 HIRS center filter frequencies in the 4.3 μm spectral region for a 33 level vertical atmospheric path. Water vapor, carbon dioxide, nitrous oxide, and carbon monoxide were considered, involving an average of 1000 spectral lines per absorber. The approximation method was, in all cases considered, an average of nine times faster than the standard method. Absorption coefficients computed by the approximation method provided transmittance values which agreed with those computed using the standard method to four decimal places regardless of absorber type channel or atmospheric level. For atmospheric transmittance calculations over a band, time savings have been predicted by analyzingithe required number of arithmetic operations involved. For 1000 spectral lines over a band of 25 cm-1 and a step increment of 0.02 cm-1 , a reduction in computation time by a factor of at least 4.5 is anticipated.
© (1977) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Richard B. Gomez, Michael T. Potter, and Joseph H. Pierluissi "Application Of An Efficient Method For Calculating Transmittance Profiles", Proc. SPIE 0125, Advances in Laser Technology for the Atmospheric Sciences, (18 November 1977);


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