United States of America As Represented by the Secretary of the Air Force

Leonard W Abreu

Gail P Anderson

James H Chetwynd

Francis X Kneizys

Eric P Shettle

David C Robertson

Larry Bernstein

William O Gallery

Lex Berk

John E Selby

Shepard A Clough

MODTRAN is a moderate resolution model and computer code used to predict atmospheric transmittance and background radiance in the microwave, infrared, visible and near ultraviolet spectral regions (0 to 50,000 cm.sup.-1 or 0.2 m to infinity). The code maintains complete compatibility with LOWTRAN 7, specifically, MODTRAN retains all of the capabilities of the LOWTRAN 7 model. Both codes contain the same six built-in model atmospheres; spherical refractive geometry, aerosol models, clouds (water and ice), rain attenuation and options to calculate single scattered solar/lunar radiance, solar/lunar irradiance and multiply scattered thermal and solar radiance. The MODTRAN code improves LOWTRAN'S spectral resolution from 20 to 2 cm.sup.-1 full width/half maximum (fwhm) with an option to vary the resolution between 2 and 50 cm.sup.-1 (fwhm). The band model parameters were formulated from the HITRAN line atlas for twelve atmospheric gases: H.sub.2 O, CO.sub.2, O.sub.3, N.sub.2 O, CO, CH.sub.4, O.sub.2, NO, SO.sub.2, NO.sub.2, NH.sub.3, and HNO.sub.3. These parameters were calculated for 1 cm.sup.-1 bins from 0-17900 cm.sup.-1 at 5 temperatures from 200 to 300 degrees K, all stored on an external data file which is accessed by the program.

System for modelling moderate resolution atmospheric propagation

LOWTRAN 7 is a low-resolution propagation model and computer code for predicting atmospheric transmittance and background radiance from 0 to 50,000 cm.sup.- at a resolution of 20 cm.sup.-. The code is based on the LOWTRAN 6 (1983) model with a number of improvements. Multiple scattered radiation has been added to the model as well as new molecular band model parameters and new ozone and molecular oxygen absorption parameters for the UV. Other modifications include a wind-dependent desert model, new cirrus cloud models, and new cloud and rain models. The code also includes new representative (geographical and seasonal) atmospheric models and updated aerosol models with options to replace them with user-derived values. An improved extra-terrestrial solar source function is also included. Six modes of program execution are allowed with the new model and computer code for a given slant path geometry.

System for modelling low resolution atmospheric propagation

Growing community of inventors

Chelmsford, MA, United States of America

Leonard W Abreu