Angular variation of the bidirectional reflectance of bare soils in the thermal infrared band

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Abstract
The angular distribution of the bidirectional reflectivity of various bare soils has been investigated both experimentally and theoretically in the thermal infrared band. It shows large variations and great spectral variability with the studied medium through both its surface roughness and nature; nevertheless backscattering is always present. To analyze the experimental data, the two-scale model of J. C. Leader was used and modified to take care of large macroscopic structures of the surface, using an appropriate new shadowing function. This modified model leads to a good fit in most situations, except when higher-order scattering (which has been neglected) is important as for the reststrahlung band of quartz. This model should therefore permit correctly relating the remotely measurable backscattering BDR to the directional emissitivity. Incorporation of the full spectral effects as well as polarization effects, which need further consideration, is in progress.