INFLUENCE AND MODELING OF VIEW ANGLES AND MICRORELIEF ON SURFACE-TEMPERATURE MEASUREMENTS OF BARE AGRICULTURAL SOILS

The exploitation of remote sensing instruments with large fields of vi ew necessarily implies the analysis of instruments acquired over a wid e variety of viewing geometries. The purpose of this study is to under line the effects of view angles and microrelief on the directional sur face temperature measurements of cultivated bare soils. A campaign of measurements was carried out at Poznan (Poland) in April 1995. The dir ectional temperatures were measured on a furrowed sandy soil. The meas urements were acquired at ground level with a radiothermometer in the 8-14 mu m band. The radiothermometer was fixed on a special goniometri c support 2.1 m above the soil surface and was directed at the soil wi th view zenith angles varying from -60 degrees to +60 degrees by steps of 10 degrees. The data were collected for solar zenith angles rangin g from 40.2 degrees to 62.3 degrees. In the experiment, for a given su n position, the difference between oblique and nadir measurements coul d reach 6 degrees C. A model aimed at explaining the variations of the surface temperature measurements of furrowed soil in relation to its viewing conditions is presented. This model requires the precise soil microrelief geometry configuration, the illumination and viewing condi tions of the surface and the radiative temperatures of the shaded and sunlit soil facets. The results show a good correlation between the pr edicted and the measured data. This type of modelling can be used to c orrect radiative temperature measurements of soils from view angles an d soil microrelief geometry effects. (C) 1998 Elsevier Science B.V. Al l rights reserved.