Johnson’s Reef
on the northwest shore of St. John Island in the U.S. Virgin Islands
forms colorful peaks in this Light Detection and Ranging (LiDAR) image
recorded by NASA’s Experimental Advanced Airborne Research Lidar (EAARL)
in June 2003. The coral reef is part of the Virgin Islands National
Park. Reef managers could use such a complete picture of the shape of
the reef as a standard when tracking reef health, growth or damage. This
EAARL image provides a much-needed overview. Each grid in the image
covers 100 square meters of the reef. The red peaks are sections of the
reef just one meter below the surface of the water. The dark blue
troughs are 10 meters below the surface.
With much of
the reef just below the surface of the water, using a boat to map the
reef was impossible. Remote sensing from the air was a necessity. LiDAR
works just like radar, but bounces a laser off objects to ascertain
their distance instead of radio waves. After being flown over the reef
in a small airplane, EAARL returned a topographic map that is accurate
to within 10 vertical centimeters and 40 horizontal centimeters.
Johnson’s Reef is part of an ongoing study conducted by John Brock of
the U.S. Geological Survey (USGS) and Wayne Wright of NASA’s Wallops
Flight Facility to determine how LiDAR can be used to measure the growth
and health of coral reefs. Brock will explore the reef to match more of
its physical traits to the LiDAR data. Once the scientists better
understand exactly what the LiDAR data tell them about the physical
characteristics of the reef, they can use LiDAR images for noninvasive
insight to the growth and health of coral reefs over time.
Image courtesy: John Brock, USGS, and Wayne Wright, NASA’s Wallops
Flight Facility
