Algae numbers increase as living corals die, so measuring the two across wide areas should give a good indicator of reef health. At the same time, the team will be taking in-water measurements to double-check PRISM's measurements, and also evaluating the surroundings -- physical, chemical and human factors -- to see how these affect individual reefs.

"Estimates of global reef status are synthesized from local surveys with disparate aims, methods and quality," Michelle Gierach, the CORAL project scientist at NASA's Jet Propulsion Laboratory said. "With CORAL, we will provide not only the most extensive picture to date of the condition of a large portion of the world's coral reefs, but a uniform dataset, as well."

CORAL is a three-year project, but the resulting data will still only capture three to four percent of the world's total reefs. It's a drop in the ocean, although scientists say the final figures will be enough to make predictions on reef degradation "based on numbers, rather than just ideas."