Sometimes called the "bellwether of the seas," coral reefs can give first indications of marine ecosystem health. "Scientists can use coral health as a sensitive indicator of the health of the marine environment," said Liane Guild, a scientist at NASA Ames Research Center, Moffett Field, Calif.

"We're looking into how you could remotely detect coral reef health using aircraft with visible light sensors," Guild said. "First, we have to look at the coral close up, underwater, to see what spectral reflectance the sensor picks up from diseased, stressed and healthy coral."

One of the first steps her team took to develop aerial coral monitoring was to take undersea light-reflectance readings of elkhorn coral with a handheld spectroradiometer, or light meter.

A team of four scuba divers, from the Universities of Miami, South Florida and Puerto Rico, helped Guild take the first readings at varying depths in summer 2002 near Andros Island, Bahamas, with assistance from the U.S. Navy Atlantic Undersea Test and Evaluation Center. A spectroradiometer measures the amount of ultraviolet, visible and infrared light reflected from an object, and is similar to sensors aboard remote-sensing airplanes and satellites.

"We moved up from the coral, little by little, to the surface to learn how light intensity decreases in the water column, which affects our coral reflected-light readings," Guild said.

"There also will be a layer of atmosphere between the coral, the water and the sensor when it eventually flies aboard an airplane to survey the reefs," she added.

"The effects of the atmosphere on light are pretty well known, but the challenge is to correct for t
'"/>

Contact: John Bluck
jbluck@mail.arc.nasa.gov
650-604-5026
NASA/Goddard Space Flight Center
12-Dec-2003