MODTRAN : A moderate resolution model for LOWTRAN7

Abstract

The LOWTRAN computer codes, with LOWTRAN 7 being the most current version, are widely used to calculate atmospheric transmittance and/or radiance in the infrared, visible and near ultraviolet spectral regions; LOWTRAN 7 has been extended to include the microwave spectral region. The code is easily used, runs quickly and provides the user with a wide variety of atmospheric models and options. Its spectral resolution is 20 1/cm Full Width/Half Maximum (FWHM) with calculations being done in 5 1/cm increments. This report describes work done to increase LOWTRAN's spectral resolution from 20 to 2 1/cm (FWHM). Specifically, the technical objectives for this program were: 1) to develop algorithms providing 2 1/cm resolution (FWHM); 2) to model molecular absorption of atmospheric molecules as a function of temperature and pressure; 3) to calculate band model parameters for twelve LOWTRAN molecular species; and 4) to integrate the LOWTRAN 7 capabilities into the new algorithms, maintaining compatibility with the multiple scattering option. MODTRAN, the final product of this effort, is a moderate resolution LOWTRAN code. Molecular absorption is calculated in 1 1/cm spectral bins, while the other parts of the calculation remain unchanged. The molecular species affected are: water vapor, carbon dioxide, ozone, nitrous oxide, carbon monoxide, methane, oxygen, nitric oxide, sulfur dioxide, nitrogen dioxide, ammonia and nitric acid.