Breakthrough provides picture of underground water

Superman isn’t the only one who can see through solid surfaces. In a development that could revolutionize the management of precious groundwater around the world, Stanford researchers have pioneered the use of satellites to accurately measure levels of water stored hundreds of feet below ground. Their findings were published recently in Water Resources Research.

Groundwater provides 25 to 40 percent of all drinking water worldwide, and is the primary source of freshwater in many arid countries, according to the National Groundwater Association. About 60 percent of all withdrawn groundwater goes to crop irrigation. In the United States, the number is closer to 70 percent. In much of the world, however, underground reservoirs or aquifers are poorly managed and rapidly depleted due to a lack of water-level data. Developing useful groundwater models, availability predictions and water budgets is very challenging.

Study co-author Rosemary Knight, a professor of geophysics and senior fellow, by courtesy, at the Stanford Woods Institute for the Environment, compared groundwater use to a mismanaged bank account: “It’s like me saying I’m going to retire and live off my savings without knowing how much is in the account.”

Lead author Jessica Reeves, a postdoctoral scholar in geophysics, extended Knight’s analogy to the connection among farmers who depend on the same groundwater source. “Imagine your account was connected to someone else’s account, and they were withdrawing from it without your knowing.”

Until now, the only way a water manager could 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, Reeves, Knight, Stanford Woods Institute-affiliated geophysics and electrical engineering Professor Howard Zebker, Stanford civil and environmental engineering Professor Peter Kitanidis and Willem SchreĆ¼der of Principia Mathematica Inc. looked to the sky.

The basic concept: 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.

With funding from NASA, 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,” Reeves said.

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.

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,” Knight said. With Zebker, postdoctoral fellow Jingyi Chen and colleagues at the University of South Carolina, Knight recently submitted a grant proposal for this concept to NASA.

Taking the ‘pulse’ of volcanoes using satellite images

This image shows averaged 2006-2009 ground velocity map of the west Sunda volcanic region from the Japanese Space Agency's ALOS satellite. Positive velocity (red colors) represents movement towards the satellite (e.g. uplift) and negative velocity (blue colors) movement away from the satellite (e.g. subsidence). Locations of volcanoes are marked by black triangles, historically active volcanoes by red triangles. Insets show six inflating volcanoes. -  Estelle Chaussard, University of Miami
This image shows averaged 2006-2009 ground velocity map of the west Sunda volcanic region from the Japanese Space Agency’s ALOS satellite. Positive velocity (red colors) represents movement towards the satellite (e.g. uplift) and negative velocity (blue colors) movement away from the satellite (e.g. subsidence). Locations of volcanoes are marked by black triangles, historically active volcanoes by red triangles. Insets show six inflating volcanoes. – Estelle Chaussard, University of Miami

A new study by scientists at the University of Miami (UM) Rosenstiel School of Marine & Atmospheric Science uses Interferometric Synthetic Aperture Radar (InSAR) data to investigate deformation prior to the eruption of active volcanoes in Indonesia’s west Sunda arc. Led by geophysicist Estelle Chaussard and UM Professor Falk Amelung, the study uncovered evidence that several volcanoes did in fact ‘inflate’ prior to eruptions due to the rise of magma. The fact that such deformation could be detected by satellite is a major step forward in volcanology; it is the first unambiguous evidence that remotely detected ground deformation could help to forecast eruptions at volcanoes.

“Surveying entire volcanic regions using satellite data is of primary importance to the detection of ground deformation prior to the onset of eruptions. If volcanic inflation is observed, it can help us to predict where the next eruption may occur. Moreover, in regions like Indonesia, where volcanoes are prevalent and pose a threat to millions of people, and where ground-based monitoring is sparse, remote sensing via satellite could become a major forecasting tool,” said Chaussard.

Analyzing more than 800 InSAR images from the Japanese Space Exploration Agency’s ALOS satellite, the team surveyed 79 volcanoes in Indonesia between 2006 and 2009. They detected deformation at six volcanic centers, three of which erupted after the observation period, confirming that inflation is a common precursor of volcanic eruptions at west Sunda volcanoes.

“The notion of detecting deformation prior to a volcanic eruption has been around for a while,” said Amelung, who has been studying active volcanoes for 15 years. “Because this region is so volcanically active, our use of InSAR has been very successful. We now have a tool that can tell us where eruptions are more likely to occur.”

The team will now study other parts of Indonesia and then in the Philippines, also prone to volcanic activity. They will use data from the Japanese Space Agency’s ALOS-2 which will be launched next year.

“The monitoring of changes to the Earth’s surface helps us to better predict the onset of volcanic activity, which can have devastating impacts on human life,” said Amelung. “Like with earthquakes and tsunamis, however, we cannot predict activity with certainty, but we hope that new tools like satellite remote sensing will help us to gather critical information in near real-time so we can anticipate the risk of eruptions and deploy resources in a timely manner.”

This study also reveals that there are regional trends in depths of magma storage. Indonesian volcanoes have magma reservoirs at shallow depths probably due to the tectonic setting of the region, which account for the way the region is deforming. If a volcanic chamber is located close to the surface it is usually associated with a higher risk for significant eruption, thus these observations play a major role in volcanic hazard assessment.