This data set contains monthly mean values of diffuse irradiance fraction [f(Ediff), or ratio of diffuse-to-total irradiance] at ground level for a 30-degree solar zenith angle and in seven spectral bands (MODIS bands 1-7) as well broadband visible (400-700 nm), near-infrared (700-3000 nm) and shortwave (400-3000 nm). Values are provided for eight SAFARI 2000 core sites, including Ghanzi/Okwa River Crossing, Maun (Main and Floodplain Towers), Pandamatenga, and Tshane, Botswana; Skukuza, South Africa; Etosha National Park, Namibia; and Mongu, Zambia. The fractions were estimated with the 6S radiative transfer model, given the mean aerosol optical depth (AOT) values from AERONET sunphotometer measurements. Where sunphotometers were not deployed at a SAFARI 2000 core site, the nearest neighbor sunphotometer data were used. A rough estimate of the likely spatial extrapolation error is provided. These data can be used to estimate typical surface albedo (blue sky conditions) from the theoretical black-sky and white-sky albedo values provided in the MODIS albedo product (MOD43), as well as in other applications.
Data for all eight sites are contained in one ASCII file, in csv format. The data file provides the ratio of diffuse (atmospherically-scattered) irradiance to total irradiance, both at ground level, for the eight sites in southern Africa. Mean values are provided for each of 12 months in 10 spectral bands between 0.4 and 4.0 microns, computed for a 30-degree solar zenith angle. The native resolution of the AERONET sunphotometer data varies, but is typically less than 1 hour. Information about the site location, IGBP land classification, and nearest AERONET sunphotometer site is also provided.
Cite this data set as follows:
Privette, J. L. 2005. SAFARI 2000 AERONET-derived Diffuse Spectral Irradiance for Eight Core Sites. Data set. Available on-line [http://daac.ornl.gov/] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/791.
Privette, J. L., M. Mukelabai, Z. Hao, and C. B. Schaaf. 2004. Validation of the MODIS albedo product in African savannas and woodlands. IEEE Geosciences and Remote Sensing, submitted.
Holben, B. N. and T. F. Eck. 2004. SAFARI 2000 AERONET Ground-based Aerosol Data, Dry Season 2000. Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.
Holben, B. N., D. Tanre, A. Smirnov, T. F. Eck, I. Slutsker, N. Abuhassan, W. W. Newcomb, J. S. Schafer, B. Chatenet, F. Lavenu, Y. J. Kaufman, J. V. Castle, A. Setzer, B. Markham, D. Clark, R. Frouin, R. Halthore, A. Karneli, N. T. O'Neill, C. Pietras, R. T. Pinker, K. Voss, and G. Zibordi. 2001. An emerging ground-based aerosol climatology: aerosol optical depth from AERONET. J. Geophys. Res. 106(D11): 12067-12097.
The data for all eight sites are contained in one ASCII file (diffuse_irradiance.csv), with the sites in alphabetical sequence. The data file provides the ratio of diffuse (atmospherically-scattered) irradiance to total irradiance, both at ground level, for the eight sites in southern Africa. Mean values are provided for each of 12 months in 10 spectral bands between 0.4 and 4.0 microns. There is also a file showing the original layout of the data set (diffuse_irradiance.pdf).
In the single data file, the data are organized in eight ASCII matrices, corresponding to eight unique sites, of diffuse irradiance fraction for 10 bands (rows) and 12 months (columns). Each site's data matrix contains the site's country (e.g., Botswana), the site's name (e.g., Ghanzi/Okwa River Crossing), the IGBP land classification of the site (e.g., open shrublands), the site's geographic coordinates (in degrees and decimal minutes), the nearest neighbor AERONET sunphotometer site's name and geographic coordinates (e.g., AERONET SITE: Etosha_Pan(7), Latitude: -19.1750, Longitude: 15.9144), and the distance between the SAFARI 2000 Core Site and AERONET sunphotometer site (e.g., Distance: 701.52 km).
Sample Data Record:
|Country||Site Name||IGBP Class||Lat.||Lon.||Closest AERONET Site||Other Close Site|| |
Okwa River Crossing
|Open shrub-lands||22° 24' 33" S||21° 42' 47" E||Etosha_ |
Pan(7), Latitude: -19.1750, Longitude: 15.9144, Distance: 701.52 km
|1 other site was within 10 degrees (883) of closest AERONET site; Epsilon between the two sites: 0.01359|| |
Notes: The data are monthly mean values of diffuse irradiance fraction [f(Ediff), or ratio of diffuse-to-total irradiance] at ground level. The other monthly mean values follow in subsequent columns and the other nine bands follow in subsequent rows. IGBP = International Geosphere Biosphere Programme.
Additional information about the spatial coverage, theory of measurements, data processing, data application and derivation, and data quality is found in the companion file: http://daac.ornl.gov/daacdata/safari2k/atmospheric/diffuse_irradiance/comp/diffuse_irradiance_readme.pdf.