CUMULUS CLOUD-BASE HEIGHT ESTIMATION FROM HIGH SPATIAL-RESOLUTION LANDSAT DATA - A HOUGH TRANSFORM APPROACH

Cloud base height is an essential variable governing surface energy budgets, but it is notoriously difficult to determine using satellite data. This study develops a semiautomated methodology to estimate cumulus cloud base heights using high spatial resolution LANDSAT Multispectral Scanner data. The approach employs a variety of image processing techniques to match cloud edges with their corresponding shadow edges. Cloud base height then is estimated by computing the separation distance between the corresponding Generalized Hough Transform reference points. Sixteen subregions, each 30 km x 30 km in size, are selected for four LANDSAT scenes. Standard deviations of cloud base height within each of the subregions range from about 100 m to 150 m. Differences between cloud base heights computed using the Hough Transform and a manual verification technique are small (on the order of 100 m or less). The cloud base heights also compare favorably with the few surface observations available. On the basis of these results, it is estimated that cloud base height accuracies of 50-70 m may be possible using HIRIS and ASTER instruments in the EOS Global Climate Change program.