Sentinel-2 enabled E. coli and Enterococcus faecal bacteria surveillance in coastal-recreational waters

Abstract Monitoring faecal indicator bacteria (FIB) such as Escherichia coli (E. coli) and Enterococcus in water bodies is critical for public health and environmental safety. While satellite data is widely used for water quality monitoring, its use to specifically map and monitor FIB represents a novel and valuable application. This study leverages Sentinel-2 satellite data to develop empirical statistical models to identify, map and monitor E. coli and Enterococcus across 13 beaches in Calvià, Mallorca, Spain. Through the integration of spectral features such as the Shortwave Infrared (SWIR1)/Coastal-Aerosol Ratio (Band11/Band1), SWIR1/SWIR2 Ratio (Band11/Band12), and the Normalized Difference SWIR1-Coastal Index (B11-B1/B11+B1), the models effectively identified and distinguished these bacteria from other key water quality indicators, including chlorophyll-a, turbidity, suspended matter, and coloured dissolved organic matter. The models achieved R2 values of 0.79 for E. coli and 0.74 for Enterococcus, with p-values of 5.37e-13 and 1.17e-11, respectively, demonstrating high accuracy and specificity. This study offers a new tool for monitoring faecal contamination, thus highlighting the potential of satellite technology to enhance environmental monitoring and ensure the safety of recreational waters.