Capability of the Sentinel 2 mission for tropical coral reef mapping and coral bleaching detection

The Sentinel 2 mission offers continuity of service for the moderate resolution multispectral SPOT XS and Landsat Thematic Mapper series sensors, but also offers several design improvements that may lead to enhanced capability in coral reef mapping applications. In this study modeling and simulated image analyses were conducted to evaluate the relative capability of the Sentinel 2 instrument design compared to SPOT-4 and Landsat ETM+, for mapping bathymetry and benthic composition, and for coral bleaching detection. The analyses involved propagating noise and environmental uncertainties through a radiative transfer model inversion to quantify uncertainty in retrievable parameters from each sensor. The experiment structure included factors for sensor-environmental noise, band choice, and complexity of benthic reflectance model. Results indicate that while variables related to reef ‘health’ such as coral mortality and algal cover cannot be mapped accurately by this class of instrument; Sentinel 2 does have improved ability for discrimination of reef benthic composition over SPOT-4 and Landsat ETM+. The key enabling design factors are the narrowness of bands, increased spatial resolution and additional band at 443 nm; instrument noise was a less significant factor. Rapid revisit times, global coverage, and freely available data suggest the potential for time series analyses. Sentinel 2 may also be capable of bleaching detection by change analysis given effective methods for precise cross-image image radiometric and spatial alignment.