USING SENTINEL-2 MSI DATA TO MONITOR THE PHYSICAL ENVIRONMENT OF CORAL REEFS IN THE U.S. VIRGIN ISLANDS

Coral reef systems are extremely intricate and sensitive to changes in their surrounding physical environment such as temperature, radiation and water quality. In the U.S. Virgin Islands (USVI), coral reefs are experiencing environmental stress due to a decline in water quality leading to coral degradation. It is therefore critical to implement effective monitoring methods for assessing water quality parameters (WQPs) in reef environments. Satellite remote sensing observations enhance our understanding of dynamic WQPs such as chlorophyll_a by providing high spatial and temporal resolution data in near-real time. In this study, the Case-2 Regional Coast Colour (C2RCC) algorithm was applied to Sentinel-2 Multispectral Image (MSI) data to derive atmospherically corrected remotely sensed chlorophyll_a Level-1 products. Band ratio and C2RCC based chlorophyll_a products were evaluated against in-situ data collected during 2016-2018. Results indicate that blue-green based band ratio algorithms perform better (R² = 0.54, RMSE = 0.08), compared to C2RCC products (R² = 0.40, RMSE = 0.10) in retrieving chlorophyll_a in the USVI. Uncertainties due to path radiance and benthic returns from the USVI’s shallow and optically complex waters limited efficiencies of RS models.