Coral reef reflectance for remote sensing applications: a case study from French Polynesia

Coral reef environments are threatened by multiple anthropogenic stressors. To inform more efficient local management strategies that support coral reef resilience, high-resolution spatial data of key environmental parameters is critically needed. High-resolution maps of, for example, coral type distribution, reef structural complexity, bleaching, and water quality would be highly useful in the selection of priority sites for coral reef protection and restoration action. Excitingly, new remote-sensing technologies are increasingly enabling such maps to be produced at low cost and over large spatial scales. Importantly, understanding the optical properties of different species of corals is a key condition for the development of advanced remote-sensing applications: in clear and shallow coral reef environments, benthic reflectance makes a major contribution to the total optical signal retrieved by a remote-sensing instrument. Here, we present initial results from a fieldwork campaign in summer 2022 at Tetiaroa, a low-lying atoll in French Polynesia. Coral reef reflectance was measured at 21 sites using TriOS RAMSES hyperspectral sensors (optical resolution: 3.3 nm). The coral reflectance data indicates differences between coral species and corroborates previous findings in the literature. The next step of this research project is to complement these initial findings with the analysis of the inherent optical properties of water constituents. This will allow for forming a comprehensive understanding of the different factors contributing to the total optical signal detected by remote-sensing instruments. Ultimately, better understanding the optical properties of coral reef environments will enable the production of high-resolution spatial-temporal shallow water products. Future work will build on these results to map and monitor the flows and hotspots of nutrients across the coral reef seascape using multispectral/hyperspectral drone and satellite imagery.