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.
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.
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,
team was joined by personnel from the Kuwait Institute for Scientific Research
(KISR), Kuwait City.
weeks, the team flew a helicopter equipped with the radar on 12 low-altitude
passes (1,000 feet) over two well-known freshwater aquifers, probing the desert
subsurface down to the water table at depths ranging from 66 feet to 213 feet.
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.
demonstration is a critical first step that will hopefully lead to large-scale
mapping of aquifers, not only improving our ability to quantify ground water
processes, but also helping water managers drill more accurately," says
Muhammad Al-Rashed, director of KISR's Division of Water Resources.
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.
created high-resolution cross sections of the subsurface, showing variations in
the fresh ground water table in the two aquifers studied. The radar results
were validated with ground measurements performed by KISR.
research will help scientists better understand Earth's fossil aquifer systems,
the approximate number, occurrence and distribution of which remain largely
unknown," says Heggy. "Much of the evidence for climate change in
Earth's deserts lies beneath the surface, and is reflected in its ground water.
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."
that 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 all are signs that suggest climate change, and human
activities also are affecting these arid and semi-arid zones.
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. 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.
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
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," says 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.
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.
is managed for NASA by the California Institute of Technology in Pasadena.
NASA Mars Research Helps Find Buried Water on Earth
September 21, 2011