Cloud cover in Landsat observations of the Brazilian Amazon

High spatial resolution Landsat imagery is employed in efforts to understan d the impact of human activities on ecological, biogeochemical and atmosphe ric processes in the Amazon basin. The utility of Landsat multi-spectral da ta depends both on the degree to which surface properties can be estimated from the radiometric measurements and on the ability to observe the surface through the atmosphere. Clouds are a major obstacle to optical remote sens ing of humid tropical regions, therefore cloud cover probability analysis i s a fundamental prerequisite to land-cover change and Earth system process studies in these regions. This paper reports the results of a spatially exp licit analysis of cloud cover in the Landsat archive of Brazilian Amazonia from 1984 to 1997. Monthly observations of any part of the basin are highly improbable using Landsat-like optical imagers. Annual observations are pos sible for most of the basin, but are improbable in northern parts of the re gion. These results quantify the limitations imposed by cloud cover to curr ent Amazon land-cover change assessments using Landsat data. They emphasize the need for improved radar and alternative optical data fusion techniques to provide time-series analyses of biogeophysical properties for regional modelling efforts.