Coral reef mapping from Sentinel-2

Sentinel-2 (S2) offers a great potential coral reef mapping as its spatial resolution up to 10 m is comparable to the patchy distribution typically met in coral environments, and data acquired in 13 spectral bands offer improved spectral diversity for assessing the variety of coral colors. With a revisit time of 10 days, that will be five in 2017 when the second satellite will be in orbit, S2 will enable the observation of ecosystems processes such as coral bleaching, coral mortality or shifts to macroalgal domination. Nevertheless, the acquisition plan needs adjustments to include coral reefs globally in remote oceanic reef environments. The aim of the study is to present a freely available operational processing chain for mapping submersed habitats from space to support coral reef monitoring and research. Implemented algorithms encompass image-based methods (e.g. pseudo-invariant-features) and physic-based approaches, such as optimization techniques for bio-optical models inversion. The algorithm performances are shown for selected test areas (e.g. Lizard Island, Australia and Lampi Island, Myanmar) where reference field data have been collected in coincidence with S2. The preliminary results show the capability of S2 in describing colonization patterns of corals, to detect seagrass and to produce realistic bottom depths. The preliminary results show the capability of S2 to describe colonization patterns of corals, sea grass and marine habitats, and produce validated depths. With respect to this last point, an ongoing aim is to assess the capability for deriving bathymetry with S2 data in the context of the International Hydrographic Organisation standards.