MODTRAN® Overview

MODTRAN® is an atmospheric radiative transfer model co-developed by the US Air Force Research Laboratory and Spectral Sciences Inc. The atmosphere is modeled as stratified horizontal layers and molecular and particulate constituent profiles may be defined either using built-in models or by user-specified vertical profiles. The spectral range extends from the UV into the far-infrared (0 - 50,000 cm-1), providing resolution as fine as 0.2 cm-1.

MODTRAN®5 is a significant improvement over previous versions. It is highly recommended that you no longer use MODTRAN®4, or earlier versions, for your atmospheric radiative transport calculations. Some of the more significant enhancements include:

  • Reformulating the band model parameters and radiation transport formalism to increase the resolution of MODTRAN® spectral calculations to 0.2 cm-1;
  • Increasing the TOA solar database resolution to 0.1 cm-1;
  • Incorporating code interface changes between MODTRAN® and DISORT to increase its speed and accuracy of multiple scattering calculations;
  • Upgrading MODTRAN® to perform spectral radiance computations for auxiliary molecules (by including their concentrations and spectral parameters) that are not part of the traditional MODTRAN® database; Band models are provided for all HITRAN molecular species;
  • Incorporating effect of a thin layer of water, which can either simply wet the ground or accumulate on it, on radiance computations;
  • Capability to model a boundary layer aerosol whose extinction coefficient obeys the Angstrom law or to modify the extinction of a model aerosol with an Angstrom law perturbation;
  • Capability to determine the spherical albedo and reflectance of the atmosphere and diffuse transmittance from a single MODTRAN® run;
  • Ability to include only the solar contribution to multiple scattering and ignore the thermal component where it is not significant;
  • An option to write spectral output in binary, and a utility to convert the binary output to ASCII;
  • Capability to process several tape5 input files by a single execution of MODTRAN®;
  • Upgraded the MODTRAN®-DISORT interface so that only a single parameter (MXCMU in routine PARAMS.h) needs to be modified to change the maximum number of streams available for DISORT runs.
  • Added dithering of the solar angle in cases where the DISORT particular solution to the solar problem was unstable.

NOTICE (July 2009):

Recent changes, listed below, have been made to the code. Some of these changes are undergoing continued testing under a rigorous Air Force code validation process, with all indications positive. However unanticipated results could affect specific limited cases. All licensed recipients of the code will receive updates to this version, as part of included first year support and maintenance services. To see a complete chronological list of code changes, see the readme.txt file included with the release.

  • Extended the band model file temperature grid, increasing the maximum temperature from 305K to 330K by adding a 7th temperature.
  • New Mod5 binary file output file options for tape 7 & fluxes was modified from initial beta versions.
  • Removed hard stops from the Correlated-k algorithm.
  • Added N2 to the list of molecular profiles that can be scaled.
  • Changed the format of brightness temperature output in *.chn files to eliminate spacing problem.
  • Corrected the path cosine used to define layer solar irradiance.
  • Corrected an error in calculation of Sine Integral used by the sinc, sinc-squared and hamming filter functions.
  • Fixed error at non-zero ground altitudes when vertical aerosol optical depth is input (VIS < 0. on CARD 2).
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