Algorithm for automatic atmospheric corrections to visible and near-IR satellite imagery

Abstract

Abstract An algorithm is developed for automatic atmospheric correction of satellite imagery of the Earth's surface. The algorithm is based solely on the satellite image being corrected and on climatology of the area. It is applicable to low resolution (1 km field of view) and high resolution (10-80m field of view) imagery of land areas for the solar spectrum. The algorithm requires that some pixels in the image will correspond to dense dark vegetation as the surface cover. Once the presence of such pixels is established, the algorithm automatically chooses these pixels, derives the atmospheric optical thickness (a measure of the amount of haze) and corrects the image. The algorithm is sensitive to the assumed reflectance of the dense dark vegetation. As a result, the accuracy of the corrected surface reflectance (p) is expected to be δp-±0.01. It is not very sensitive to the assumed aerosol characteristics, the accuracy of satellite calibration or the knowledge of the exact fraction of the image covered by the dense dark vegetation. The correction algorithm was applied to clear and hazy Landsat Multispectral Scanner images of the same area in the Washington D.C. and the Chesapeake Bay region. The aerosol optical thickness (ta) derived from the imagery shows a good agreement with simultaneous sunphotometer measurements from the ground within δTa=±0.20 in band 1 (0.5.0.6) and δta=±0.05 in band 2 (0.6-0.7μm). The images in the hazy and clear days were corrected and compared. The comparison shows, for example, that the vegetation index was corrected from 0-39 in the clear day and 0-21 in the hazy day to 0-57± 0.01 in these two days. The algorithm, in its present form, can be applied to satellite imagery that includes at least two channels in the visible part of the spectrum, preferably blue and red. Application to the Advanced Very High Resolution Radiometer type of sensor (with one broad channel in the visible part of the spectrum) would need some modifications.