Radiometric saturation of Landsat-7 ETM+ data over the Negev Desert (Israel): Problems and solutions

Unsuccessful efforts to interpret and analyze several sets of images acquired over Israel by Landsat-7 during the first 2 years of its operation (August 1999-August 2001) provided the motivation to examine the hypothesis that image data produced over the desert regions along the climatic transition zone of Israel were subject to radiometric saturation. The objectives of the current study are to characterize the saturation phenomenon, by inspecting different images of Landsat-7, and to suggest a statistic method for solution in the spectral domain. Entropy analysis was also performed on these images in order to compare the information content of the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) sensor with that of the Landsat-5 Thematic Mapper (TM) over the desert environment before and after saturation correlation. The study reveals that radiometric saturation affected several ETM+ bands (especially band 3). Consequently, in terms of entropy, less information can be extracted from the saturated bands relative to equivalent bands of Landsat-5 TM. A statistical solution, based on multivariate correlation analysis among all spectral bands, is proposed to overcome the saturation problem. Satisfactory results were achieved by applying the statistical methods on several samples of saturated scenes. An operational revision in the spectral radiance range and the gain setting, applied to Landsat-7 ETM+ that is affected from July 1, 2000, has improved the saturation phenomenon over the region. The current proposed method can be applied for other climatic regions, such as scenes partially covered by snow, and other multi and hyper spectral sensors.