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Researchers map freshwater aquifers buried in deserts

US: A NASA-led team used radar sounding technology to create high-resolution maps of freshwater aquifers buried deep beneath Earth desert. The technology was originally developed to explore the subsurface of Mars and this is the first use of airborne sounding radar for aquifer mapping on the Earth.

The radar sounding prototype shares similar characteristics with two instruments flying on Mars- orbiting spacecraft: Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), on the European Space Agency’s Mars Express, and Shallow Radar (SHARAD), on NASA’s Mars Reconnaissance Orbiter.

This technology is helping scientists in locating and mapping Earth’s desert aquifers, understanding current and past hydrological conditions in Earth’s deserts and assessing how climate change is impacting them. Deserts cover roughly 20 percent of Earth’s land surface, including highly populated regions in the Arabian Peninsula, North Africa, west and central Asia and the southwestern United States.

An international team led by research scientist Essam Heggy of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., recently travelled to northern Kuwait to map the depth and extent of aquifers in arid environments using an airborne sounding radar prototype. The 40-megahertz, low-frequency sounding radar was provided by the California Institute of Technology in Pasadena; and the Institut de Physique du Globe de Paris, France. Heggy’s team was joined by personnel from the Kuwait Institute for Scientific Research (KISR), Kuwait City.

The researchers successfully demonstrated that the radar could locate subsurface aquifers, probe variations in the depth of the water table, and identify locations where water flowed into and out of the aquifers. “This demonstration is a critical first step that will hopefully lead to large-scale mapping of aquifers, not only improving our ability to quantify groundwater processes, but also helping water managers drill more accurately,” said Muhammad Al-Rashed, director of KISR’s Division of Water Resources.

The radar is sensitive to changes in electrical characteristics of subsurface rock, sediments and water- saturated soils. Water-saturated zones are highly reflective and mirror the low-frequency radar signal. The returned radar echoes explored the thick mixture of gravel, sand and silt that covers most of Kuwait’s northern desert and lies above its water table.

The team created high-resolution cross sections of the subsurface, showing variations in the fresh groundwater table in the two aquifers studied. The radar results were validated with ground measurements performed by KISR.

“Much of the evidence for climate change in Earth’s deserts lies beneath the surface and is reflected in its groundwater. By mapping desert aquifers with this technology, we can detect layers deposited by ancient geological processes and trace back paleoclimatic conditions that existed thousands of years ago, when many of today’s deserts were wet.”

“Results of this study pave the way for potential airborne mapping of aquifers in hyper-arid regions such as the Sahara and Arabian Peninsula, and can be applied to design concepts for a possible future satellite mission to map Earth’s desert aquifers,” said Craig Dobson, programme officer for Geodetic Imaging and Airborne Instrument Technology Transition programs at NASA Headquarters, Washington.

Source: Terra Daily