period. When interferometric radar data are collected at multiple points in time, differential interferometric analysis can be used to measure centimeter-scale changes in topography over broad areas, such as those resulting from seismic activity along faults, ground subsidence due to groundwater or oil extraction, and changes in glaciers and ice sheets (Kwok and Fahnestock, 1996; Bürgmann et al., 2000). Although interferometric radar provides coarser resolution than lidar systems, its global coverage from satellite platforms is currently more temporally and spatially extensive, and it shows exceptional promise for many applications in the physical sciences.
There are several areas in watershed science that could benefit from remote sensing applications. The U.S. Geological Survey operates a dense network of stream gauges in the United States, yet there is a paucity of gauges globally and thus large parts of the world lack adequate data on streamflow. With the application of SAR (synthetic aperture radar) and MODIS (Moderate Resolution Imaging Spectroradiometer)—two satellites gathering remote sensing data—it is becoming increasingly possible to measure streamflow (Smith, 1997; Brakenridge et al., 1998, 2007) and sediment load (Gomez et al., 1995) from satellites. Other promising approaches include mapping of stream-channel habitat using hyperspectral imagery (Marcus et al., 2003; Marcus and Fonstad, 2008) and integrating meteorological data and watershed response (Smith et al., 2007). Although launched for mapping gravity anomalies and crustal characteristics, one of the important extensions from the GRACE (Gravity Recovery and Climate Experiment ) satellite has been the documentation of groundwater levels from space (Strassberg, et al. 2009). Destined to be launched in 2013 (NRC, 2007a), the SWOT (Surface Water Ocean Topography) satellite mission offers enormous potential to monitor global-scale hydrological changes and map surface-water elevations. These rapid and remote techniques have great potential for the geographical study of fluvial systems. The utilization and incorporation of remote sensing into a range of investigations of hydrological and ecological phenomena offer researchers opportunities for collaborative and interdisciplinary studies (Walsh et al., 2003) that can lead to more spatially explicit, and therefore more useful, models of biophysical processes.
As the foregoing examples make clear, spatial analysis, field-based research, geographical visualization, and fine-grained contextual studies are critical to assessing the magnitude and types of global biophysical adjustments that are presently occurring. The approaches and techniques of the geographical sciences can help identify and quantify the biophysical changes unfolding on Earth’s surface, and they can offer insights into the processes shaping those changes at different scales. Geographical science approaches and techniques thus have an important role to play in advancing scientific understanding of biophysical changes and facilitating the efforts of resource managers and policy makers to confront Earth’s changing environment.