Correção atmosférica em imagens Landsat contaminadas por efeito de adjacência.

Abstract

A physical model of atmospheric correction which considers the influence of background contamination on the apparent reflectance of a target, is implemented to evaluate the effects of molecular composition and aerosols in the satellite imagery. The model simulates the signal detected by the sensor as a function of successive orders of interaction of the solar radiation with the earth-atmosphere system. It was applied to the images TM of LANDSAT-5, for the pixels on Sao Goncalo reservoir, which is located in the interior of the State of Paraiba. The effect of the adjacency is computed from the reflectance of the surface background (vegetation + soil) and the functions related to the size of the target. The aerosol's optical parameters (asymmetry factor, single scattering albedo) were obtained from the literature. The optical depth is evaluated through the pyranometer data. Different methods of solution of the Equation of Radiative Transfer (ETR) and, the aerosol's phase functions were utilized to determine the intrinsic reflectance of the atmosphere. The model is discussed by comparison with the reflectance data measured "in situ". From the analyses of the results, the single scattering model used to determine the atmospheric reflectance with the two-term approximation of Henyey-Greenstein for the phase function of the aerosols, were selected. The reflectance values of water evaluated for Sao Goncalo reservoir were satisfactory and they show clearly the background influence. The model was also employed to simulate the planetary reflectance detected from the sensors, considering the different characteristic targets of the region under study. The results show that the atmospheric reflectance is predominant for low reflectance targets and it is true even in the case of lower values of the aerosol's optical depth. Exactly the opposite occurs in the case of the medium reflectance targets where the predominant reflectance is that of the target.