f AIRBORNE ELECTROMAGNETIC SURVEYS FOR GROUNDWATER CHARACTERIZATION

Airborne electromagnetic (AEM) surveys provide densely sampled data over large areas (typically several hundred sq. km) that cannot be covered effectively using ground-based methods. AEM data are inverted to estimate the three-dimensional distribution of electrical resistivity structures from shallow depths to several hundred meters. These models convey unparalleled details that are used to make inferences about hydrogeologic properties and processes at the watershed and local scale. This information is being used in groundwater models that are critical to water management decisions, to better understand geologic frameworks, and to improve climate change models. The U.S. Geological Survey (USGS) has been engaged in the application of AEM to many watershed and local scale groundwater projects within United States. We present the results of several frequency- and time-domain AEM surveys acquired by the USGS that have been used for mapping alluvial valleys, buried glacial aquifers, fault-bounded basins, salinity problems, and understanding permafrost distributions.