A PHYSICAL MODEL FOR INTERPRETING THE LAND SURFACE-TEMPERATURE OBTAINED BY REMOTE SENSORS OVER INCOMPLETE CANOPIES

At the present moment, land surface temperature cannot be obtained in a routine way from satellite data due, in part, to the nonexistence of a complete theoretical model that permits us to know the physical significance of land surface temperature obtained by remote sensors. In this article a relationship between the effective temperature of the radiative system vegetation-ground and the temperatures of each part of the system (top, sunny and shaded wall of vegetation, and sunny and shaded soil) has been derived. It depends on the proportions of each component observed by the sensor, on the ground and vegetation emissivities, and on the crop structure (mean height, width, and spacing). The model was validated in an orange grove at Valencia during October 1990 and a standard error of estimate about 1-degrees-C was obtained. A manual scanning system for measuring the effective temperature and a emissivity box for determining ground and vegetation emissivities were designed. Measurements were made in the 8-14-mu-m waveband. Assuming a priori knowledge of the crop structure and ground and vegetation emissivities, inversion strategies have been suggested for evaluating component temperatures from remote sensing measurements.