Coral monitoring with fluorescence imaging lidar

It has been pointed out that globally hermatypic corals in coral reefs have been seriously damaged in recent years, and it is predicted that such damages will expand in area in the future. It is important to monitor corals globally, in detail, and over long-term periods, for preservation of the marine environment and biodiversity. The spot-check method, one of the major coral monitoring methods, is operated by snorkelers or divers, and therefore, its operation is limited by the seastate, and its monitoring areas are often for specific observation points. On the other hand, the satellite remote sensing, another major coral monitoring methods, can cover composite coral reef areas, but the image resolution is a few meters, and it is not possible to monitor small size coral colonies and deep sea areas. The boat-based fluorescence imaging lidar system has been developed to complement these coral monitoring methods. This system obtains linear coral observation data along the boat track, and makes it possible to build a cooperative coral monitoring network. Since most hermatypic corals have fluorescent proteins, living tissues can be monitored using the blue-to-green fluorescence from UV excitation. It is possible to observe the UV-excited fluorescence images from live coral even in the daytime, by the UV excited fluorescence imaging lidar. Additionally, laser bathymetry is also possible by time-of-flight measurement. We have succeeded in observing the pseudo-coral fluorescent images and depths down to 30 m depth at the testing basin. Secondly, we have succeeded in observing the live coral fluorescent images and their depths by the lidar system using a glass-bottom-boat at Taketomi island, Okinawa, Japan. The system summary and observed data are reported in this paper.