Evaluation of an ASTER emissivity product with field spectral radiance measurements for natural surfaces

Abstract

ABSTRACTThis article evaluates the accuracy of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) emissivity product AST05 with field spectral radiance measurements using a Model 102F handheld portable Fourier transform infrared spectroradiometer for several natural surfaces. Note that thermal sensors are only able to detect radiance, which is subject to the combined interactions of the atmosphere, land surface temperature and land surface emissivity (LSE). To accurately calculate the LSE, the measured radiance must be decoupled. A scheme is proposed to determine the spectral emissivity of natural surfaces from field radiance measurements using a piecewise linear spectral emissivity method. The method derives reasonable emissivity spectra for natural surfaces: sand, bare soil, alfalfa, and water. The channel emissivities are derived by convolving the spectral emissivity with the spectral response function of the ASTER thermal infrared channels. Comparisons of channel LSEs from field measurements with those from AST05 show that good agreements are obtained for sand and soil, while big differences existed for alfalfa and water, with a maximum bias up to 0.045 in channel 10 for the water surface, which demonstrates that the AST05 product provides accurate LSEs for higher spectral contrast surfaces but inaccurate LSEs for low spectral contrast surfaces.