Solar Spectra

The MODTRAN extraterrestrial spectra are high-resolution, with approximately 50,000 data points at 1 wavenumber (1 cm^-1) resolution.

The MODTRAN ETR spectra are grouped in a tab delimited text file. The file includes Chance+Kurucz (MChKur), Cebula+Kurucz (MCebKur), New Kurucz (MNewKur), Thullier+Kurucz (MThKur), Old Kurucz (MOldKur) and the Wherli 1985 (MWherli_WMO) spectra, based on combinations of data from the references. These spectra contain 49,951 wavelengths, except for the MOldKur.dat, which contains 49,934 wavelengths. The original spectral step size (resolution) is normally 1 cm^-1 for these files.

These spectra have been converted to wavelength (nm), irradiance (W m^-2 nm^-1) units from the units of wavenumber (cm^-1) versus irradiance (W cm^-2 cm^-1) used in MODTRAN.

The MODTRAN data are available in a compressed file.

The MODTRAN extraterrestrial spectra were resampled for use with the SMARTS spectral code to 0.5 nm resolution between 280 nm and 400 nm, 1.0 nm resolution from 400 nm to 1700 nm, and 5 nm resolution between 1700 nm and 4000 nm, with a transition wavelength at 1702 nm. The resampling computed the equivalent average energy in the SMARTS2 band from the higher resolution MODTRAN data within the SMARTS2 band by integration over the bandwidth divided by the bandwidth.

Dr. C. Gueymard resampled all the MODTRAN spectra to produce irradiance (W m^-2 nm^-1) data at 2002 discrete wavelengths. These provide user choices for extraterrestrial to use in the SMARTS spectral modeling code. These files are available as SWherli, SChKur, SCebKur, SNewKur, SThKur, and SOldKur. Gueymard also assembled a "synthetic" spectrum of his own based on measurements and papers for use with SMARTS. This additional file is SGuey.

The files used in the SMARTS model are in wavelength units of Angstroms (Å), which have been converted to nanometers for these files to provide consistent units. The irradiance units are W m^-2 nm^-1

The SMARTS files are available as a text file or in a compressed format.

Dr. C. Gueymard produced an excellent survey article, submitted to the journal Solar Energy, covering the history and development of most of these extraterrestrial spectra. He assembled a new extraterrestrial spectrum from more recent sources. The spectrum covers the spectral region from 0.5 nm to 280 nm in 1-nm steps, 280 to 400 nm in 0.5-nm steps, from 400 nm to 1705 nm in 1-nm steps, 5 nm steps from 1705 nm to 4000 nm, and variable steps beyond 4000 nm.

See C. Gueymard, "The Sun's Total and Spectral Irradiance for Solar Energy Applications and Solar Radiation Models." Solar Energy, Vol 76 #4 (April 2004) Pages 423–453.

The New Synthetic Gueymard Spectrum, down to 0.5 nm, is available in a text file or in a compressed format.

Dr. M.P. Thekaekara was instrumental in publishing some of the earliest air mass zero spectra. The 1973 spectrum was the basis for ASTM E490 from 1974 to 2000. For comparative purposes, we provide the Thekaekara spectrum as published in Table 4.5, Page 114 of "The Extraterrestrial Solar Spectrum," A.J Drummond and M.P. Thekaekara, Eds. Institute of Environmental Sciences, Mount Prospect Illinois, 1973.

The historical 1973 Thekaekara Spectrum is available as a text file or in a compressed format.