A Radiative Transfer Model To Analyze Radiometer Data In The Atmospheric Window.

• Main Author: Duffy, Keith J.
• Other Authors: AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
• Format: Text
• Language: English
• Published: 1996
• Subjects: Atmospheric Physics; *RADIATIVE TRANSFER; *ATMOSPHERE MODELS; OPTICAL RADAR; POLARIZATION; COMPUTATIONS; ACCURACY; THESES; BACKSCATTERING; TRANSMITTANCE; PROFILES; RADIANCE; TROPICAL REGIONS; RADIOMETERS; RADIOMETRY; ABSORPTION COEFFICIENTS; ARCTIC REGIONS; CIRRUS CLOUDS; TEMPERATE REGIONS; DIVERSITY RECEPTION; CKD(CORRELATED K DISTRIBUTION); Arctic; Subarctic
• Online Access: http://www.dtic.mil/docs/citations/ADA308943; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA308943

A radiation model was developed to calculate radiance in a plane parallel, vertically nonhomogeneous, nonscattering atmosphere. The radiance model was developed to analyze data collected by a vertically pointed radiometer with a receiver bandwidth of 9.5-11.5 micrometers. These radiometer readings are used in conjunction with backscatter readings from a vertically aligned polarization diversity lidar system to compute various cirrus cloud properties such as infrared (IR) emittance. The model used the correlated k-distribution method (CKD) to calculate absorption coefficient functions and account for the nonhomogeneity of the atmosphere. Transmittance and radiance results from this CKD model were compared with results from FASCODE3, a popular and highly accurate line-by-line (LBL) radiation model. Several different atmospheric profiles, ranging from subarctic to tropical, were compared to determine the accuracy and efficiency of the CKD model with respect to the LBL model. At the highest resolutions, the CKD model was 15-100 times faster than the LBL model. Despite the increased efficiency, the CKD model transmittance errors from the earth surface to 30 km were less than 0.4% with respect to the LBL model in temperate and arctic profiles. Errors were less than 2% in the tropical profile. The CKD model downwelling radiance errors from the surface to 30 km were less than 2% with respect to the LBL model for tropical and temperate profiles. In arctic conditions, radiance errors were as high as 8.5% below 2 km, but tapered off to 3% at cirrus cloud levels. In temperate atmospheres, the CKD model could be run as much as 300 times faster, while still calculating radiance values to within 0.6% of the LBL model.