The authors are Dr. Richard Bird and Dr. Carol Riordan. The Excel@ Spreadsheet implementation was done by Daryl Myers using equations from the technical report . The model computes clear sky spectral direct beam, hemispherical diffuse, and hemispherical total irradiances on a prescribed receiver plane - tilted or horizontal - at a single point in time. For tilted planes, the user specifiy the incidence angle of the direct beam (FORTRAN version) or the tilt and azimuth of the plane (Excel@ version). The wavelength spacing is irregular, covering 122 wavelengths from 305 nm to 4000 nm. Aerosol optical depth, total precipitable water vapor (cm), and equivalent ozone depth (cm) must be specified by the user. No variations in atmospheric constituents or structure are available. There is no separate computation of circumsolar radiation. The direct beam spectral irradiance is assumed to contain the circumsolar radiation within a 5° solid angle. No smoothing functions are provided.
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