Abstract
Reef-building corals are threatened by global climate change and other problems, and thus the monitoring of regional coral distributions is becoming increasingly important. We developed a glass-bottom-boat-based coral observation system that uses lidar (light detection and ranging) techniques for large-area coral monitoring. The lidar system consisting of an ultraviolet (UV) pulsed laser with a wavelength of 355 nm and a gated ICCD camera has been designed and tested. Most reef-building corals have fluorescent proteins that emit blue-green fluorescence on UV excitation. Seabed images were recorded by emitting UV pulsed laser and receiving fluorescence by the gated ICCD camera synchronized with the laser. Because the exposure time is very short, the sunlight background effect for the lidar image is suppressed, and this makes it possible to detect weak UV excited fluorescence even in the daytime. Live corals can be distinguished from dead coral skeletons based on the fluorescence images by verifying the coral image pattern and fluorescence intensity. We evaluated the system in a testing basin to 30-m depth, and we used the system to observe corals using a glass-bottom boat at Taketomi Island, Okinawa, Japan. Information about the live coral distribution along the boat track was obtained successfully around the island at depths from 2 to 12 m.
