The three-year, US$15-million Coral Reef Airborne Laboratory (CORAL) project will be the biggest and most detailed study yet of entire reefs, rather than just the small patches that scuba divers can reach. CORAL is part of a growing push to map reefs faster, and in more detail, than ever before. Marine scientists are putting new instruments onto planes, satellites and even drones to gain a broader perspective on how well corals are doing – or not.
(The health of coral reefs is normally assessed by scuba surveys and other close-up views. Image Credit:David Doubilet/National Geographic Creative)
After its surveys in Hawaii, Australia’s Great Barrier Reef, the Mariana Islands and Palau (see ‘Under the sea’), CORAL will have mapped about 3–4% of the world’s reef area, hundreds of times more than previous scuba surveys. Remote sensing of coral reefs is hard because the oceans reflect so much less light than the land, says Heidi Dierssen, a marine ecologist at the University of Connecticut-Avery Point in Groton, who is part of the CORAL team. And scientists have to do elaborate calculations to correct for the distortion of light on its journey through the atmosphere and through water — a bright, deep ocean bottom and a dark, shallow bottom can both look the same to a remote-sensing camera.
The latest Copernicus Sentinel-2A satellite has the capability to look into the water column, to monitor coral health and see whether reefs are undergoing change. Initial results show that the Sentinel satellite can detect the effects from 780km up.
“With Sentinel-2A, we can see 10-15m into the water, which you just couldn’t see if you were using the green band, for example”, explains Dr Benjamin Koetz from the European Space Agency. (Image credit: Copernicus Sentinel data (2016)/ESA). Scientists are working on techniques that would allow them to routinely monitor the health of corals worldwide from orbit.