Land use and land cover are critical elements of ESE and the U.S. Global Change Research Program because they focus attention on the rates and directions of global and regional landscape changes that occur on an interannual or decadal basis, that is, time periods that exceed intervals of catastrophic change due to flooding, fire, hurricanes, or tornadoes. The general premise is that human socioeconomic or political endeavors are manifested in the landscape as spectral and morphological changes. Some of these changes are so subtle that it takes years to measure them from satellite altitudes, and then only through indicators of change. For example, for changes associated with expanding urban populations and the consequent conversion of land uses from rural to urban types, one of the indicators typically is “miles of road per square mile.” This is one quantitative measure of expanding access to hinterlands undergoing economic change. This same indicator is used for forest management to indicate the intensity of deforestation.
In the lexicon of radar, land use and land cover are typically referred to in contexts such as “resource monitoring and management” (Winokur, 1996) and “ecology” (Evans et al., 1995), perhaps because the terms “land use” and “land cover” imply merely a backdrop of baseline attributes to be altered by human activities and natural processes. With a few major exceptions, applications of airborne radar, SAR, and interferometric SAR for imaging land use and land cover have been reported in terms of vegetation mapping, agricultural monitoring, soil-moisture mapping, and flood mapping, rather than in terms of land use or land cover. At the 1996 Workshop on Applications of Future U.S. Spaceborne Imaging Radar Missions (Bard and Leon, 1996), none of the agreed-on “key applications ” related directly to land use or land cover per se; rather, they focused on such topics as mineral exploration, military surveillance, topographic mapping, and hydrologic phenomena. Nevertheless, with a small SAR in orbit, users should have access to data sets that would further validate SAR's contribution to observation of long-term landscape changes.
Among several major exceptions in land use and land cover monitoring was Project RADAM in Brazil. This and later surveys in developing countries (especially in the humid tropics where aerial photography and optical satellite imagery are difficult to obtain on demand) used radar images to produce land use maps, including those for urban areas. This application has received little attention in the current literature. However, recent publications suggest important applications for settlement monitoring (Henderson, 1995; Henderson and Xia, 1997; Xia and Henderson, 1997). Since settlement expansion typically modifies the vegetation environment, this has important implications for monitoring and predicting changes in global biomass and carbon dioxide (CO2).