Satellites Help Pinpoint Threats to World’s Coral Reefs

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SAN FRANCISCO — New space-based instrument and analysis techniques are helping U.S. National Oceanic and Atmospheric Administration (NOAA) scientists identify and pinpoint threats to coral reefs. Those threats, including pollution, warming water temperatures and ocean acidification, are becoming so severe, however, that some scientists worry corals are in danger of disappearing completely.

“We are obtaining information that is helping us understand what the changes in the coral reefs are likely to be,” said C. Mark Eakin, coordinator of NOAA’s Coral Reef Watch, an organization that relies on remote sensing and local sensors to monitor, model and publish data on the condition of coral reefs. “The big concern is that we develop that understanding while we still have corals to observe.”

Coral Reef Watch began developing satellite-based monitoring tools in the late 1990s. For more than a decade, the organization has been relying on those tools to alert the public when ocean temperatures rise so high that corals are in danger of losing the symbiotic algae that live in their tissue, producing energy through photosynthesis and giving them their distinct colors. When corals are under stress, they expel the algae and become pale or white. This type of event, known as coral bleaching, makes the corals vulnerable to disease and can lead to death of all or part of a coral colony.

In recent years, coral bleaching has occurred with increasing frequency due, at least in part, to warming ocean temperatures. “We are seeing not only warmer temperatures, but longer warm periods in the tropical waters around coral reefs,” Eakin said. “It’s leading to more frequent and more severe bleaching events.”

Nearly 20 percent of the Earth’s coral reefs already have been lost and another 35 percent “are seriously threatened with loss” by the middle of the century, according to “Status of Coral Reefs of the World: 2008,” the most recent analysis by the International Coral Reef Initiative, a United Nations environmental program.

NOAA’s Coral Reef Watch monitors global sea surface temperatures with data obtained from the Advanced Very High Resolution Radiometer onboard NOAA-19, one of the agency’s two polar orbiting environmental satellites, and also on MetOp-A, the polar-orbiting satellite operated by the European Organization for the Exploitation of Meteorological Satellites, or Eumetsat.

To provide more detailed data on sea surface temperatures, Coral Reef Watch is beginning to blend data from those polar-orbiting spacecraft with information gathered by sensors flying on satellites in geosynchronous orbit operated by NOAA, Eumetsat and Japan’s Meteorological Agency, Eakin said. Geostationary satellites offer far more data for specific regions. In contrast to the polar-orbiting spacecraft, which provide data for each location only three or four times per day, geostationary satellites gather sea surface temperature readings every 15 minutes for some locations and every one to three hours for others. “That gives you a great advantage because there is a lot more data,” Eakin said.

Those additional data, coupled with new analysis techniques and faster computers, are allowing Coral Reef Watch to begin moving from its current data products, which map regions with 50-kilometer pixels, to new maps with pixel sizes of 4 to 11 kilometers.

“This is not something that will happen a long time in the future,” Eakin said. “This is imminent.”

Further improvements in data quantity and quality are expected to come from the Visible Infrared Imager Radiometer Suite (VIIRS), an instrument built by Raytheon Space and Airborne Systems of El Segundo, Calif., and scheduled for launch in October on the National Polar-orbiting Operational Environment Satellite Systems Preparatory Project. VIIRS also is slated to fly on NOAA’s Joint Polar Satellite System (JPSS). The first JPSS spacecraft was slated for launch in 2014, but that program has been delayed 12 to 14 months due to a lack of funding in the 2011 budget, NOAA officials said Feb. 14 during a briefing on the agency’s 2012 budget request.

VIIRS is designed to measure sea surface temperature at resolutions of between one-half and 1 kilometer, Eakin said. In addition, the new satellites designed to carry VIIRS will feature sophisticated on-board electronics capable of storing the entire VIIRS dataset and transferring it to ground stations.

“In the future, we are going to be looking at higher-resolution imagery from observational platforms,” Eakin said. “Once we have that, we can start working on developing higher resolution products.”

Future data products also are likely to combine various types of space-based data that provide clues to the health of coral reefs. In addition to gauging the impact of sea surface temperature, coral reef scientists are studying the impact of varying amounts of sunlight on coral reefs. NOAA’s Center for Satellite Applications and Research is developing new ways to measure solar irradiance over oceans as well as over lands, Eakin said.

“That is very important because it’s both the temperature and the light that are important to the corals and are producing coral bleaching,” Eakin said.