Measuring the spectral signatures of coral reefs

The measurement of the spectral signatures of coral reefs in sea water is described. The spectral signatures of different species of coral have been measured using a spectroradiometer at off Kuroshima Island, Okinawa, Japan. The spectral difference between different species has been studied. As well as the field experiments, laboratory experiments for measuring the spectral signatures of 16 different species of coral reefs were carried out with the same spectroradiometer. The spectral reflectance of the each coral reef showed an significant result that a narrow absorption band exist in the spectral region between 660 and 680 nm, and very strong spectral reflectance from about 700 nm towards the longer wavelength range. On the other hand, absorption and high reflectance region were not observed from the bottom sands or bare rocks underwater. These experiments suggested that there is a significant spectral difference between coral reefs and bottom sands or bare rocks and so the best spectral range for separating the coral reefs from other underwater objects in the ocean would be between 700 and 800 nm