Technique for Selecting an Aerosol Model Useful for Infrared Atmospheric Transmittance Calculations

摘要

Vertical profiles of meteorological parameters are used with the LOWTRAN 6 atmospheric transmittance/radiance computer code to model measurements of near horizon infrared radiances. It is shown that calculations with the Navy Maritime Aerosol Model can exactly reproduce the measured horizon pixel radiance using nonunique combinations of air mass factors and surface visibilities. This feature is the result of the visibility scaling factor of the size distribution remaining nearly constant for any appropriate combination of the two factors, and the relative insensitivity of the calculated extinction coefficients for the far infrared wavelengths to the air mass factor term. Using measurements taken on two consecutive days during low wind-speed conditions, it is shown that any appropriate combination of the two factors will allow the calculated and measured radiances at other angles above the horizon to differ less than 2% . These agreements place confidence in using the selected aerosol model in transmittance calculations for the far infrared wavelength bands over other propagation paths. Atmospheric transmittance/infrared radiance; Infrared transmittance; Infrared horizon; Pixel radiance; near-infrared LIDAR system; Atmosphere models; Light transmission. (edc)