NEWS
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American Geophysical Union University of New Hampshire Joint Release |
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11 April 2006
AGU Release No. 06-12 For Immediate Release UNH Contact: David Sims +1 (603) 862-5369 David.Sims@unh.edu
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AGU Contact: Harvey Leifert
+1 (202) 777-7507 hleifert@agu.org |
Tracking Ocean Slicks Using Improved Satellite Measurements
WASHINGTON – Researchers in France and the United States have developed an improved technique to hone satellite radar images in areas where calm or covered seas currently prevent accurate recordings. The new method can provide more accurate ocean surface readings and improve estimates of El Niño and La Niña events, also providing better observation and tracking of oil spills and other films on the ocean surface. The results were published 11 April in Journal of Geophysical Research-Oceans, a publication of the American Geophysical Union.
The satellite altimetry method now used to measure height in ocean waves generally cannot provide data when calm, or “slick,” sea surface conditions from oil spills, phytoplankton blooms, or lack of winds hampers the satellite observations. The existing altimetry system essentially does not recognize the miniscule ocean waves or characteristics in a nearly stationary ocean. Approximately six percent of all altimetry readings are affected by such data blackouts and discarded in models that would otherwise use the information.
The new system is similar to rainfall analysis methods and artificially increases the number of altimetry signals sent to the ocean during calm conditions. The research team was headed by Jean Tournadre of the French Research Institute for Exploitation of the Sea in Plouzané, France.
“Every year, our altimeters make something like 10 million ocean measurements, so being able to recover at least a portion of that [lost data] gives us better information on sea surface height,” said Douglas C. Vandemark, now a research professor at the University of New Hampshire’s Institute for the Study of Earth, Oceans, and Space and one of the study’s authors. “The percentage is much higher for calmer equatorial regions such as the Pacific, which tells us about the bulge of water that controls El Niño.”
Picture the Pacific Ocean as a big bathtub, he suggests. A bulge in the western end—created by warm water and winds—can set off an El Niño event by creating a wave that propagates very quickly along the equator from Asia towards the Americas, eventually inducing large water temperature changes along the coasts of South and North America. When the bulge makes its inevitable and slower return back, that’s a La Niña event.
The improvement comes from a modeling technique developed by scientists that should enhance and expand the number of altimeter measurements that NASA can collect—using the Jason-1 satellite—from the equatorial Pacific Ocean where El Niño events originate. Jason-1, launched in 2001, is a joint mission of NASA and the Centre National d’Etudes Spatiales (CNES, the French government space agency).
Altimetry works by sending 1,800 separate radar pulses per second down towards Earth from a height of some 800 kilometers [500 miles] and recording how long their echoes take to bounce back. The technique can measure sea height down to one centimeter [0.4 inch], notes lead author Tournadre.
The new research with what Vandemark calls “the problematic subset of echoes from very smooth ocean areas” suggests that altimeters may now be able to estimate the spatial extent of these smooth areas. He notes that having more accurate equatorial Pacific Ocean measurements “provides agencies like NASA and NOAA [the National Oceanic and Atmospheric Administration] more measurements for El Niño prediction and tracking.”
The research was sponsored by CNES, the European Space Agency (ESA), and NASA.
Journalists (only) may obtain a pdf copy of this paper upon request to Jonathan Lifland: jlifland@agu.org. Please provide your name, name of publication, phone, and email address. The paper and this press release are not under embargo.
Title: “A satellite altimeter model for ocean slick detection”
Authors:
Citation:
Tournadre, J., B. Chapron, N. Reul, and D. C. Vandemark (2006),
A satellite altimeter model for ocean slick detection,
J. Geophys. Res., 111, C04004, doi:10.1029/2005JC003109.
Contact information for authors:
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