The saturation of LANDSAT MSS detectors over large ice masses

Abstract

LANDSAT provides synoptic imagery for the study of large ice masses in the inaccessible polar regions. Even minor ice surface topographic detail can be identified as differences in relative brightness. However, radiance from such surfaces can be greater than the maximum MSS detector calibration. This results in detector saturation and consequent loss of information. Using MSS digital data from snow surfaces in both polar regions, corrected to radiance values to account for detector calibration changes, a model relating detector saturation in each MSS band to changes in Sun elevation is presented. Band 5 becomes saturated at the lowest Sun angles whereas band 7 remains unsaturated in all imagery examined. Secondary factors affecting detector saturation are atmospheric haze, the magnitude and orientation of surface slopes, variations in detector calibration and the character of the surface. Given a knowledge of the Sun elevation at which each band becomes saturated over large ice masses (of low gradient and snow-covered surface), and information on variations in Sun elevation with latitude and time of year, the spatial and temporal pattern of detector saturation can be predicted. This information is useful in the selection of MSS images for future glaciological studies, and in the scheduling by NASA of the optimum periods to acquire unsaturated MSS data of the polar regions.