Nav: Home

Stanford researchers calculate groundwater levels from satellite data

June 09, 2016

A new computer algorithm developed at Stanford University is enabling scientists to use satellite data to determine groundwater levels across larger areas than ever before.

The technique, detailed in the June issue of the journal Water Resources Research, could lead to better models of groundwater flow. "It could be especially useful in agricultural regions, where groundwater pumping is common and aquifer depletion is a concern," said study coauthor Rosemary Knight, a professor of geophysics in the Stanford School of Earth, Energy & Environmental Sciences.

Knight and her colleagues recently applied the algorithm to determine groundwater levels across the entire agricultural basin of Colorado's San Luis Valley. As a starting point, the algorithm uses data acquired using a satellite technology called Interferometric Synthetic Aperture Radar, or InSAR, to calculate changing groundwater levels in the San Luis Valley between 1992 and 2000.

InSAR satellites use electromagnetic waves to monitor tiny, centimeter-scale changes in the elevation of Earth's surface. The program was initially developed in the 1980s by NASA to collect data on volcanoes, earthquakes and landslides, but Knight and her colleague Howard Zebker, a professor of geophysics and of electrical engineering at Stanford, have in recent years adapted the technology for groundwater monitoring.

The Stanford scientists, led by former postdoctoral scholar Jessica Reeves, had previously shown that changes in surface elevation could be correlated with fluctuations in groundwater levels. However, they were only able to do so for a relatively small area because they had to manually identify and analyze high-quality pixels in InSAR satellite images not covered by crops or other surface features that could obscure elevation measurements.

The new algorithm, developed by Jingyi "Ann" Chen, a Stanford postdoctoral researcher in Knight's group, automates this previously time-consuming pixel selection process. "What we've demonstrated in this new study is a methodology that allows us to find high-quality InSAR pixels in many more locations throughout the San Luis Valley," said Chen, who is first author of the new study.

Chen's algorithm also goes a step further by filling in, or interpolating, groundwater levels in the spaces between pixels where high-quality InSAR data are not available. Interpolation is a form of averaging, but it requires high-quality InSAR data from places that are located near monitoring wells where groundwater levels are already known in order to calibrate the link between the InSAR data and groundwater levels. In the previous work led by Reeves, only three monitoring wells were "co-located" with high-quality InSAR pixels. Using the new algorithm, that number increased to 16.

As a result, the team was able to calculate surface deformations -- and, by extension, groundwater levels -- for the entire agricultural basin of the San Luis Valley, an area covering about 4,000 square kilometers -- or about five times greater than the area for which groundwater levels were calculated in the prior study. What's more, the team members were able to show how groundwater levels in the basin changed over time from 2007 to 2011 -- the years when InSAR data that could be analyzed by the algorithm were available.

"Jessica showed that there was useful information in the InSAR-derived deformation, and Ann has made the technique for extracting that information reliable and practical," Zebker said.

Having a continuous map of deformation in the San Luis Valley led to the team discovering that there is a delay between the time when groundwater is pumped out of an aquifer and when the ground sinks, or subsides, in response to the water removal. These time lags might be useful indicators of the geological properties of an aquifer, said Knight.

"In a sand aquifer, there is no time lag between when the water is pumped out and the ground surface deforms," Knight said. "However, if clay is present, it will take much longer to deform in response to pumping, so there will be a detectable time lag."

The next step, Zebker said, is to take the information about groundwater levels and aquifer characteristics extracted from InSAR satellites and incorporate it with data from other sources to develop improved models of groundwater flow.

"The goal is to take into account the full water budget," Zebker said. "This means accounting for water recharge such as rainfall and for discharge sources such as evaporation and runoff."
-end-


Stanford's School of Earth, Energy & Environmental Sciences

Related Groundwater Articles:

Majority of groundwater stores resilient to climate change
Fewer of the world's large aquifers are depleting than previously estimated, according to a new study by the University of Sussex and UCL.
Monitoring groundwater changes more precisely
A new method could help to track groundwater changes better than before.
Cause of abnormal groundwater rise after large earthquake
Abnormal rises in groundwater levels after large earthquakes has been observed all over the world, but the cause has remained unknown due to a lack of comparative data before & after earthquakes.
Shrub encroachment on grasslands can increase groundwater recharge
A new study led by Adam Schreiner-McGraw, a postdoctoral hydrology researcher at the University of California, Riverside, modeled shrub encroachment on a sloping landscape and reached a startling conclusion: Shrub encroachment on slopes can increase the amount of water that goes into groundwater storage.
River-groundwater hot spot for arsenic
Naturally occurring groundwater arsenic contamination is a problem of global significance, particularly in South and Southeast Asian aquifers.
Groundwater, a threatened resource requiring sustainable management
The WEARE group at the University of Cordoba analyzed a case of aquifer recovery and concluded that supervision, governance and use of water for high value crops are some of the keys to guaranteeing sustainability of these reserves
Co-occurring contaminants may increase NC groundwater risks
Eighty-four percent of the wells sampled in the Kings Mountain Belt and the Charlotte and Milton Belts of the Piedmont region of North Carolina contained concentrations of vanadium and hexavalent chromium that exceeded health recommendations from the North Carolina Department of Health and Human Services.
Fresh groundwater flow important for coastal ecosystems
Groundwater is the largest source of freshwater, one of the world's most precious natural resources and vital for crops and drinking water.
Natural contaminant threat to drinking water from groundwater
Climate change and urbanisation are set to threaten groundwater drinking water quality, new research from UNSW Sydney shows.
Switching to solar and wind will reduce groundwater use
IIASA researchers explored optimal pathways for managing groundwater and hydropower trade-offs for different water availability conditions as solar and wind energy start to play a more prominent role in the state of California.
More Groundwater News and Groundwater Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Warped Reality
False information on the internet makes it harder and harder to know what's true, and the consequences have been devastating. This hour, TED speakers explore ideas around technology and deception. Guests include law professor Danielle Citron, journalist Andrew Marantz, and computer scientist Joy Buolamwini.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.