Remote Sensing Technology Images Groundwater Stores

Researchers at the University of California, San Diego (UC San Diego) are deploying remote sensing technology called InSAR to gain insights into sustainable groundwater in the San Joaquin Valley. The satellite-based InSAR (for “interferometric synthetic aperture radar”) creates high-resolution maps of land surface motion in space and time, including subsidence measurements (measurement of sinking). InSAR and the fine-scale resolution images it delivers are useful in evaluating subsidence patterns and habits according to crop type.

Subsidence can occur when large quantities of groundwater are removed from underground stores. It influences the ability to monitor and manage groundwater in agricultural regions, like the San Joaquin Valley, which is a challenge due to a lack of reliable methods for data acquisition.

InSAR interpretations vary across locations, a response to displacement, which, in this context, is defined as a response to a change in the location of groundwater storage. Geology, soil, and vegetation, independently and in combination, affect where groundwater is stored and in what amounts.

Though the researchers must combine InSAR with other sources of geophysical data to achieve location-specific information, it is advantageous to gauging climate with satellite measurements that have the same interpretation in any location.

Other land surface data sets include land cover, surface water supply network location, and evapotranspiration (a measure of plant water demand).

New work from UC San Diego could be revolutionary for managing groundwater use in agricultural regions around the world, as groundwater monitoring and management have been notoriously difficult to carry out due to lack of reliable data. Courtesy of 'adamkaz.'

Uses of InSAR to directly monitor groundwater use are in early stages of development. California in 2014 passed legislation mandating a gradual, locally led shift toward the sustainable use of groundwater, the resource on which 85% of the state’s population and much of its agriculture industry rely. InSAR data is poised to contribute to the state’s efforts to monitor and manage groundwater in response to climate change.

In a study deploying the technology, the UC San Diego team found that between 2015 and 2017, subsidence occurred at much higher rates in irrigated cultivated land compared to undeveloped land, as well as in dry surface water-limited years relative to wet years. In the San Joaquin Valley in wet years, farmers may receive up to 100% of their surface water allocations. In dry years, they may receive none.

The study also took into account the specific water consumption of different types of crops: fruit and nut crops such as almonds and grapes, field crops such as soy, pasture crops such as alfalfa, and truck crops such as tomatoes.

The UC San Diego-led research was funded by the National Science Foundation’s Innovations at the Nexus of Food, Energy, and Water Systems program; the NASA Earth and Space Science Fellowship; NASA’s support for the NASA-ISRO SAR (NISAR) mission science team; and the School of Global Policy and Strategy’s Big Pixel initiative.

The study was published in Environmental Research Letters (www.doi.org/10.1088/1748-9326/abb55c).