Information on the spectral characteristics of the earth surface at global scale is needed in a wide range of applications dealing with the disposition of radiant energy in the atmosphere and at the surface. In the past, such information has been synthesized from ground measurements, model outputs, and limited satellite observations. In this paper an attempt is being made to use a comprehensive data set of satellite observations at high spatial resolution in two channels of the AVHRR, to update existing spectral reflectance reference models and make them compatible with recent land classifications.

Specifically, use was made of the NOAA National Environmental Satellite Data and Information Service Global Vegetation Index (GVI) monthly mean global data set for (1985-1987,1989-1991) and the ASTER Spectral Library data, to update spectral reference reflectance models initially proposed by Briegleb et al. (1985) for the spectral intervals of 0.2-0.5, 0.5-0.7, 0.7-1.3, 1.3-4 microns. The GVI data provide clear sky AVHRR channel 1 and channel 2 reflectances at the Top of the Atmosphere at 0.144-degree latitude-longitude grids. The TOA reflectance data were corrected for atmospheric influences using the SBDART radiative transfer model to compute spherical and planar reflectances and transmittances for climatological atmospheric conditions of water vapor, ozone and solar zenith angle, and the data are referenced to a solar zenith angle of 60 degrees. Seasonality in the reference model was also introduced as the reflectance models were derived separately for each month, by regressing the corrected, monthly values against the Global Land Cover product as derived at the University of Maryland, Department of Geography, using the NASA/NOAA Pathfinder Land data set at 8 km resolution for 1981-1994. The reference reflectance models proposed in this study should be applicable as input parameters in radiative transfer models, in studies concerned with Earth and atmosphere energy balance, and spectral properties of the surface.