The Simple Model of the Atmospheric Radiative Transfer of Sunshine (SMARTS), developed by Dr. Christian Gueymard, computes clear sky spectral irradiances (including direct beam, circumsolar, hemispherical diffuse, and total on a tilted or horizontal receiver plane) for specified atmospheric conditions. SMARTS users can specify conditions from any of 10 standard atmospheres or their own data. Users can also specify output for one or many points in time or solar geometries. SMARTS 2.9.2 is the basis for American Society of Testing and Materials (ASTM) reference spectra (ASTM G-173 and ASTM G-177) used for photovoltaic performance testing and materials degradation studies.
The algorithms used by SMARTS were developed to match the output from the MODTRAN complex band models within 2%. The algorithms are implemented in compiled FORTRAN code for Macintosh and PC platforms. Source code is available. The algorithms are used in conjunction with files for atmospheric absorption of atmospheric components and spectral albedo functions. The spectral resolution is 0.5 nm for 280-400 nm, 1 nm for 400-1,750 nm, and 10 nm for 1,750-4,000 nm. For more information about SMARTS development and applications, explore its references list.
To use SMARTS, users construct text files of 20-30 lines of simple text and numbers to specify input conditions and up to 28 spectral output parameters. Users can specify field-of-view angles for direct-beam computations and a separate computation for the circumsolar component. Gaussian or triangular smoothing functions with user-defined bandwidth can also be specified to compare model results with measurements made with the specified passband. Users can specify only ultraviolet (280–400 nm) computations for erythemal dose, UV index, and similar measurements. Photometric (luminous flux) computations, weighted by a selected photopic response curve, can also be specified.
SMARTS' output consists of spreadsheet-compatible American Standard Code for Information Interchange (ASCII) text files with header information and prescribed conditions.