Unanticipated Uses of the Global Positioning System

Global Positioning System (GPS) instruments are routinely used today to measure crustal deformation signals from tectonic plate motions, faulting, and glacial isostatic adjustment. In parallel with the expansion of GPS networks around the world, several new and unexpected applications of GPS have been developed. For example, GPS instruments are now being used routinely to measure ground motions during large earthquakes. Access to real-time GPS data streams has led to the development of better hazard warnings for tsunamis, flash floods, earthquakes, and volcanic eruptions. Terrestrial water storage changes can be derived from GPS vertical coordinate time series. Finally, GPS signals that reflect on the surfaces below a GPS antenna can be used to measure soil moisture, snow accumulation, vegetation water content, and water levels. In the future, combining GPS with the signals from the Russian, European, and Chinese navigation constellations will significantly enhance these applications. GPS data are now routinely used to study the dynamics of earthquake rupture. GPS instruments are an integral part of warning systems for earthquakes, tsunamis, flash floods, and volcanic eruptions. Reflected GPS signals provide a new source of soil moisture, snow depth, vegetation water content, and tide gauge data. GPS networks can sense changes in soil moisture, groundwater, and snow depth and thus can contribute to water resource assessments.