NASA Researchers Use Imaging Radar to Detect Coastal Pollution
A NASA-funded study of marine pollution in Southern California
concluded space-based synthetic aperture radar can be a vital
observational tool for assessing and monitoring ocean hazards in
urbanized coastal regions.
Image above: European Remote Sensing 1 satellite radar image depicting natural oil seeps in the Santa Barbara Channel off Coal Oil Point, California, Jan. 13, 1996. Image credit: ESA.
"Clean beaches and coastal waters are integral to Southern
California's economy and lifestyle," said Dr. Paul DiGiacomo, an
oceanographer at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
He is lead author of the study recently published in the Marine
Pollution Bulletin. "Using Southern California as a model system,
we've shown existing high-resolution space-based radar systems can
be used to effectively detect and assess marine pollution hazards.
This is an invaluable tool for water quality managers to better
protect public health and coastal resources," he said.
DiGiacomo and colleagues from JPL; the University of California,
Santa Barbara; and the University of Southern California, Los
Angeles, examined satellite radar imagery of the coastal waters of
Southern California. The area is adjacent to 20 million people,
nearly 25 percent of the U.S. coastal population. The imaging radar
data from the European Space Agency's European Remote Sensing
Satellites 1 and 2 and Canada's Radarsat were complemented by shore-
based surface current radar data and other field measurements.
Image leftt: European Remote Sensing 1 satellite radar image of stormwater runoff plumes from the Los Angeles and San Gabriel Rivers into the Los Angeles and Long Beach Harbors, Dec. 28, 1992. Image credit: ESA.
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"The key to evaluating and managing pollution hazards in urban
coastal regions is accurate, timely data," DiGiacomo said. "Since
such hazards are usually localized, dynamic and episodic, they're
hard to assess using oceanographic field sampling. Space-based
imaging radar works day and night, regardless of clouds, detecting
pollution deposits on the sea surface. Combined with field surveys
and other observations including shore-based radar data, it greatly
improves our ability to detect and monitor such hazards," he said.
The study described three major pollutant sources for Southern
California: storm water runoff, wastewater discharge and natural
"During late fall to early spring, storms contribute more than 95
percent of the region's annual runoff volume and pollutant load,"
said JPL co-author Ben Holt. "Californians are accustomed to
warnings to stay out of the ocean during and after storms. Even
small storms can impact water quality. Radar data can be especially
useful for monitoring this episodic seasonal runoff," he said.
DiGiacomo noted a regional Southern California marine water quality
monitoring survey is under way involving JPL and more than 60 other
organizations, including the Southern California Coastal Water
Research Project. Its goal is to characterize the distribution and
ecological effects of storm water runoff in the region. Space radar
and other satellite sensor data are being combined, including NASA's
Moderate Resolution Imaging Spectroradiometers. The sensors provide
frequent observations, subject to clouds, of ocean color that can be
used to detect regional storm water runoff and complement the finer
resolution but less frequent radar imagery.
The second largest source of the area's pollution is wastewater
discharge. Publicly owned treatment works discharge daily more than
one billion gallons of treated wastewater into Southern California's
coastal waters. Even though it is discharged deep offshore,
submerged plumes occasionally reach the surface and can contaminate
Natural hydrocarbon seeps are another local pollution hazard.
Underwater seeps in the Santa Barbara Channel and Santa Monica Bay
have deposited tar over area beaches. Space imaging radar can track
seepage on the ocean surface, as well as human-caused oil spills,
which are often affected by ocean circulation patterns that make
other tracking techniques difficult.
Further research is necessary to determine the composition of
pollution hazards detected by radar. "From imaging radar, we know
where the runoff is, but not necessarily which parts of it are
harmful," Holt said. "If connections can be established, imaging
radar may be able to help predict the most harmful parts of the
While the researchers said environmental conditions such as wind and
waves can limit the ability of space radar to detect ocean
pollution, they stressed the only major limitation of the technique
is infrequent coverage. "Toward the goal of a comprehensive coastal
ocean observing system, development of future radar missions with
more frequent coverage is a high priority," DiGiacomo said.
JPL is managed for NASA by the California Institute of Technology in
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Jet Propulsion Laboratory, Pasadena, Calif.
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