NASA’s airborne survey of coral reefs

Coral reefs are home to a quarter of all ocean fish species

Updated - February 01, 2016 03:52 pm IST

Published - January 31, 2016 09:00 am IST

The Great Barrier Reef will be one of the first to be surveyed by CORAL.

The Great Barrier Reef will be one of the first to be surveyed by CORAL.

If 33-50 per cent of the world’s coral reefs have already been degraded or lost due to climate change and human impacts, most of the functioning reef ecosystems may well disappear by mid-century, say reef scientists.

As a first step to estimate the extent of damage to coral reefs, NASA has embarked on an air-borne three-year field experiment called The COral Reef Airborne Laboratory (CORAL), which aims to survey the conditions of the major reefs of the world through remote-sensing.

Dr. Eric Hochberg’s team will survey the condition of entire reef systems in Hawaii, Palau, the Mariana Islands and Australia. The regions were chosen because they represent a wide range of reef types (fringing, barrier, atoll, oceanic and continental) and a wide range of environmental conditions (from pristine to heavily impacted).

CORAL will involve the aerial deployment of a spectrometer called PRISM (Portable Remote Imaging Spectrometer) developed and managed at NASA's Jet Propulsion Laboratory in Pasadena, California, which will detect the spectral signature of the various components of a reef such as coral, algae, sand etc. which will enable assessment of the condition of the reef.

For example, as coral is degraded, it is replaced by algae and hence the ratio of algae to coral is an indicator of reef condition. PRISM records the spectrum (all the different colours) of incoming light from the ocean below, across the ultraviolet, through the visible region and up to the near infrared. The CORAL data processing takes into account the complex interactions of sunlight with the atmosphere, ocean, and reef.

The signatures are used for identifying reef areas that are coral, algae, etc. CORAL also uses those signatures to model photosynthesis.

The PRISM data are validated by in-water measurements. There are three fundamental types of data to be gathered by PRISM: optical, reef benthic cover (area of the ocean-bottom covered by the reef), and reef primary productivity.

“For the optics, we use high-tech instruments to measure (a) the light leaving the water, (b) how light is absorbed and scattered within the water, and (c) how much light reflects from different reef components (coral, algae, etc.). For the reef cover, we use underwater photographs, which are analysed back in the lab. The primary productivity determinations are complicated, but they rely on measuring changes in oxygen in the water,” noted Dr. Hochberg, Principal Investigator of CORAL, in an email to this Correspondent. Dr. Hochberg is scientist at the Bermuda Institute of Ocean Sciences, St. George’s.

The in-water validation of optical properties of light passing through the water, seafloor optical properties and reef community composition will be done. The latter two validations will be done by scuba divers.

Measuring the oxygen concentration is very important as productivity is indicated by the change in oxygen over time for a given area of the reef. A more productive reef releases more oxygen.

During the 3-year period only 3 to 4 per cent of the world’s reefs will have been covered by CORAL. “CORAL will focus on the data collected during the investigation. Hopefully, future investigations can increase the coverage,” noted Dr. Hochberg. “The project has begun, but data collection has not. We are still in the planning and preparation stage,” he added.

Coral reefs are home to a quarter of all ocean fish species. They protect shorelines from storms and provide food for millions of people, yet very little of the world's reef area has been studied scientifically. Virtually all measurements have been made by expensive, labour-intensive diving expeditions. Many reefs have never been surveyed, and those reefs that have been studied were measured only at a few dive sites.

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