NASA Mars Research Helps Find Buried Water on Earth

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Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

News release: 2011-290 Sept. 14, 2011

NASA Mars Research Helps Find Buried Water on Earth

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-290&cid=release_2011-290

PASADENA, Calif. – A NASA-led team has used radar sounding technology developed to explore
the subsurface of Mars to create high-resolution maps of freshwater aquifers buried deep beneath an
Earth desert, in the first use of airborne sounding radar for aquifer mapping.

The research may help scientists better locate and map Earth's desert aquifers, understand current and
past hydrological conditions in Earth's deserts and assess 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 traveled 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.

For two weeks, the team flew a helicopter equipped with the radar on 12 low-altitude passes (1,000
feet, or 305 meters) over two well-known freshwater aquifers, probing the desert subsurface down to
the water table at depths ranging from 66 to 213 feet (20 to 65 meters). 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.

"This research will help scientists better understand Earth's fossil aquifer systems, the approximate
number, occurrence and distribution of which remain largely unknown," said Heggy. "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."

Heggy said most recent observations, scientific interest and data analyses of global warming have
concentrated on Earth's polar regions and forests, which provide direct measurable evidence of large-
scale environmental changes. Arid and semi-arid environments, which represent a substantial portion
of Earth's surface, have remained poorly studied. Yet water scarcity and salt content, changes in
rainfall, flash floods, high rates of aquifer exploitation and growth of desert regions are all signs that
suggest climate change and human activities are also affecting these arid and semi-arid zones.

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. MARSIS, jointly developed by JPL and the Italian Space Agency, probes
the Martian subsurface sediments and polar ice caps to a maximum depth of about 1.9 miles (3
kilometers). SHARAD, also built by the Italian Space Agency, looks for liquid or frozen water in the
first few hundred feet of Mars' crust and probes Mars' polar caps. Both instruments have found
evidence of ice in the Martian subsurface, but have not yet detected liquid water. The Kuwait results
may lead to revised interpretations of data from these two instruments.

The research follows earlier work by JPL scientists to probe the subsurface of the Sahara desert using
higher-frequency Synthetic Aperture Radar instruments flown onboard three space shuttle missions in
1981, 1984 and 1994. That work located shallow drainage networks and large dry basins, suggesting
the Sahara has had extensive surface water activity in its recent geological past.

Kuwait's well-mapped shallow aquifers and flat surface provided the team with an ideal test location.
Extreme dryness, such as that present in this region of Kuwait, is necessary to allow the radar's
waves to penetrate deep into the surface and reflect on water-saturated layers beneath. Kuwait's flat
topography and low radio noise also reduced clutter and improved the radar signal's return.

"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, program officer for Geodetic
Imaging and Airborne Instrument Technology Transition programs at NASA Headquarters,
Washington. The work is a pathfinder for the Orbiting Arid Subsurface and Ice Sheet Sounder
(OASIS), a NASA spacecraft mission concept designed to map shallow aquifers in Earth's most arid
desert regions and measure ice sheet volume, thickness, basal topography and discharge rates.

The study was co-funded by the California Institute of Technology's Keck Institute for Space Studies
and KISR. The Kuwaiti Police Air Force provided technical support for the flight tests.

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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