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GLOBAL
CORAL REEF MONITORING NOW FEASIBLE WITH NEW LANDSAT 7 DATA
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The
structure and extent of coral reefs can now, for the first
time, be monitored globally, thanks to new observations from
NASA's Landsat 7 spacecraft. Detailed images of reefs from
nearly 900 locations around the world have been collected
in the first year of the Landsat 7 mission.
"Landsat 7's ability to see land features as small as 100
feet (30 meters) across and to repeatedly observe coral reefs
worldwide makes this archive of images a unique and valuable
scientific resource," said Landsat Project Scientist Darrel
Williams of NASA's Goddard Space Flight Center in Greenbelt,
Md. "No one else has been willing or able to acquire and archive
this type of high-resolution global data for use by the scientific
community."
Scientists at the University of South Florida, in collaboration
with colleagues at the College of Charleston and Dalhousie
University (Halifax, Nova Scotia), have completed initial
tests of Landsat 7's ability to study coral reefs and are
presenting their results at the 9th International Coral Reef
Symposium in Bali this week. Nearly 1500 scientists are expected
to attend the quadrennial meeting.
Landsat 7 measurements of live coral in the Carysfort Reef,
the largest reef in the Florida Keys, matches detailed surveys
taken on the ground, according to a joint study by Frank Muller-Karger,
Serge Andrefouet, and Dave Palandro of the University of South
Florida's College of Marine Science and Phil Dustan of the
College of Charleston. The surface area of live coral in this
reef has declined from more than 50 percent to less than 5
percent since 1975.
"Reefs around the world are in ecological collapse, especially
in the Florida Keys," says Dustan. "We need to use remote
sensing to help fight for their conservation."
Andrefouet has also completed a Landsat 7 inventory of the
extensive coral atolls in French Polynesia in the South Pacific
using 22 separate scenes, each covering about 12,000 square
miles. He was able to identify and map many different types
of reef formations, from entire atolls covering hundreds of
square miles to individual marine habitats. "This study shows
coral reef scientists how to do a large-scale reef inventory
anywhere around the world," says Andrefouet, a remote-sensing
scientist who was raised in French Polynesia.
"With the Landsat 7 data we can rigorously test hypotheses
about how entire reef ecosystems form," says coral reef ecologist
Bruce Hatcher of Dalhousie University. "We no longer are limited
to the observations we can collect by wandering around in
small boats and sampling individual reefs to infer large-scale
processes from a few samples."
Hatcher and doctoral student Abdulla Naseer from the Maldives
Ministry of Fisheries are using Landsat 7 data to understand
how wind, waves, and sea level have shaped the coral-reef
nation of the Maldives, south of India. By combining weather
and tidal records with a catalog of the physical features
of the 2800 reefs derived from Landsat 7 images, the scientists
can identify patterns of reef growth and erosion caused by
monsoons and the ocean's waves and currents. A detailed understanding
of how these climate forces shape coral reefs will enable
scientists to better predict how reefs will respond to future
climate changes.
With the Landsat 7 image archive, physical damage to reefs
can now be monitored in near real-time, says Hatcher. "With
Landsat 7's repeated coverage of coral reefs throughout the
year and its fine-scale imaging capability, we will be able
to see damage to reef structure caused by hurricanes."
Over 5,000 coral reef images have been collected to date by
the Landsat 7 mission. Many reefs have been imaged several
times, providing a glimpse of seasonal changes in reef structure
and biology.
Landsat 7 was launched by NASA in April 1999 and began routine
science observations in June 1999. Images are archived, processed,
and distributed by the U.S. Geological Survey, which also
assumed responsibility for day-to-day operations of Landsat
7 this month.
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