Challenges for chlorophyll-a remote sensing in a highly variable turbidity estuary, an implementation with sentinel-2
Fernanda Maciel, Signe Haakonsson, Lucía Ponce de León, Sylvia Bonilla, Francisco Pedocchi
Abstract
Coastal waters have high ecological and economic relevance and are globally threatened by intense human activities leading to eutrophication. The decameter resolution of Sentinel-2 Multispectral Instrument (S2-MSI) provides an advantage to detect spatially heterogeneous phenomena that are limited in extent, such as harmful cyanobacterial blooms (cyanoHABs). Chlorophyll-a is typically used in remote sensing of blooms; however, it remains to be evaluated in several coastal regions of the world. The Río de la Plata estuary (South America) provides a key case study due to its highly variable concentrations of suspended sediments, and the increasing frequency of cyanoHABs. Here, we evaluate the potential and limitations of S2-MSI indices to retrieve chlorophyll-a in these optically complex waters, obtaining regional algorithms and comparing them to previously available ones. We propose an approach to follow the evolution of chlorophyll-a thresholds (10 and 24 <i>μ</i>g/L) that can contribute to monitoring programs and early warning strategies of cyanoHABs.