Satellites survey water levels deep underground
Scientists say they can use satellites to accurately measure levels of water stored hundreds of feet below ground.
Until now, the only way to gather data about the state of water tables in a watershed was to drill monitoring wells. The process is time and resource intensive, especially for confined aquifers, which are deep reservoirs separated from the ground surface by multiple layers of impermeable clay.
Even with monitoring wells, good data is not guaranteed. Much of the data available from monitoring wells across the American West is old and of varying quality and scientific usefulness. Compounding the problem, not all well data is openly shared.
To solve these challenges, the researchers looked to the sky.
Satellites that use electromagnetic waves to monitor changes in the elevation of Earth’s surface to within a millimeter could be mined for clues about groundwater. The technology, Interferometric Synthetic Aperture Radar (InSAR), had previously been used primarily to collect data on volcanoes, earthquakes, and landslides.
The researchers used InSAR to make measurements at 15 locations in Colorado’s San Luis Valley, an important agricultural region and flyway for migrating birds. Based on observed changes in Earth’s surface, the scientists compiled water-level measurements for confined aquifers at three of the sampling locations that matched the data from nearby monitoring wells.
“If we can get this working in between wells, we can measure groundwater levels across vast areas without using lots of on-the-ground monitors,” says Jessica Reeves, a postdoctoral scholar in geophysics at Stanford University and lead author of the study.
The breakthrough holds the potential for giving resource managers in Colorado and elsewhere valuable data as they build models to assess scenarios such as the effect on groundwater from population increases and droughts.
Plans for the future
Just as computers and smartphones inevitably get faster, satellite data will only improve. That means more and better data for monitoring and managing groundwater. Eventually, InSAR data could play a vital role in measuring seasonal changes in groundwater supply and help determine levels for sustainable water use.
In the meantime, Knight envisions a Stanford-based, user-friendly online database that consolidates InSAR findings and a range of other current remote sensing data for soil moisture, precipitation, and other components of a water budget.
“Very few, if any, groundwater managers are tapping into any of the data,” says Rosemary Knight, professor of geophysics in the Stanford School of Earth Sciences and coauthor of the study published in Water Resources Research.
Other researchers from Stanford, Principia Mathematica Inc., and the University of South Carolina collaborated on the project, which was funded by Stanford and NASA.
Source: Stanford University