The future of satellite remote sensing in hydrogeology

Excerpt

The past three or four decades have seen a rapid development of remote sensing technology. Earth observation from space has been applied to many topics in the geosciences successfully. Not surprisingly, the first scientists who were attracted to the newly available observations were those that could apply them most immediately. Land cover or land use classifications on the basis of satellite data have long become routine for remote sensing geographers. Geomorphologists are now using satellite-observed structural information and oceanographers can monitor and interpret many ocean parameters from color to wave patterns. Several satellite missions have focused on different parts of the water cycle. Atmospheric water vapor, cloud cover, water levels in large open water bodies, or the extent and topography of the ice sheets are only some of the observations that have been made from satellites. Hydrogeologists have been comparatively slow to embrace satellite sensors as tools in their work. To a large extent this may have been due to the fact that the principle object of interest in hydrogeology remains hidden beneath the Earth’s surface. Most satellite sensors measure emitted or reflected electromagnetic radiation at frequencies that cannot penetrate more than a few centimeters into the Earth. Hence, these satellites can provide no direct measurements of subsurface water. An interesting recent exception is the relatively direct observation of changes in water storage using precise measurements of gravity changes (Tapley et al. 2004). …