Estimation of Sub-pixel Impervious Surfaces Using Landsat and Aster Imagery for Assessing Urban Growth

Urban development has expanded rapidly in the Las Vegas, Nevada metropolitan area over the last fifty years. Associated with this growth trend has been the transformation of the landscape from natural cover types to increasingly impervious urban land. To map urban extent and its change over time, an innovative approach is employed that determines sub-pixel impervious surfaces from highresolution digital orthophoto quarter quadrangles (DOQQs) and satellite remotely sensed data. Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper plus (ETM+) data were used as primary imagery sources to estimate urban imperviousness variation from 1984 to 2002 in Las Vegas. Data collected from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) system were also used to map imperviousness in Las Vegas. The 4 spectral bands of visible and near-infrared (VNIR) and 6 spectral bands of short-wave infrared (SWIR) carried by ASTER provided additional information that improved the accuracy of a regression model in distinguishing impervious surfaces from sandy soil and surficial lithologic material. Results were compared with ground measurements for selected sample sites in Las Vegas. The spatial and temporal characteristics of imperviousness in Las Vegas were analyzed to obtain urban development intensities and trends. Results indicate that sub-pixel imperviousness serves as a good indicator of urban composition and development intensity, and provides an efficient means for documenting these changes.