An Investigation of Methods for Computing Long Path Atmospheric Transmittance
AEROSPACE CORP EL SEGUNDO CA CHEMISTRY AND PHYSICS LAB
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The reliability of the statistical band model for long path length, low transmittance conditions is investigated by comparing the band model with precise line by line calculations. Two test systems are utilized a system of H2O absorbers and a system of computer generated line parameters. It is found that the statistical band model is fairly reliable for calculating band transmittance in the range bar T 0.1, but for transmittance less than this, it is not reliable and can be in error by several orders of magnitude. An explanation for this behavior is offered. In the second part of this investigation, an new nonstatistical method based on a simple approximation of the k-distribution function is developed. It is compared with precise line by line calculations and is found to be very reliable for all transmittance conditions.