AN ATMOSPHERIC CORRECTION METHOD FOR THE AUTOMATIC RETRIEVAL OF SURFACE REFLECTANCES FROM TM IMAGES

Most of the atmospheric correction methods proposed in the literature are not easily applicable in real cases. The most sophisticated models frequently require inputs which are not commonly available, whilst tr aditional simple dark object subtraction techniques do not generally g ive real reflectance values. In the present work an atmospheric correc tion method applicable to Landsat-TM data is described, which requires only inputs that are commonly available and the presence in the image d scenes of some dark surfaces in TM bands 1 (blue) and 3 (red). The m ethod consists of an inversion algorithm based on a simplified radiati ve transfer model in which the characteristics of atmospheric aerosols are estimated by the use of the path radiance in two TM bands rather than a priori assumed. On the basis of this information, which is cruc ial for determining the atmospheric properties, the retrieval of real reflectances from TM images is possible. The method can be applied to all TM scenes in which some dark points can be realistically supposed to be present, which is particularly advantageous in retrospective stu dies. Several TM scenes taken from different landscapes and in differe nt seasons were corrected using the model. The reflectance values foun d were tested against ground measurements and compared with data from the literature. The results show a substantial improvement in the accu racy of the reflectance estimates with respect to estimates without at mospheric correction. Given some care in the identification of dark va lues, the relative error in actual reflectance retrieval is always rat her low (congruent-to 10-20 per cent); this error can be considered ac ceptable for most practical applications.