Optical data collected with airborne drone platform, and processed with MapEO Water software v1 at VITO into chlorophyll-a concentrations. Chlorophyll-a is a green pigment found in plants. It absorbs sunlight and converts it into sugar during photosynthesis. Chlorophyll-a concentrations are an indicator of phytoplankton abundance and biomass in inland, coastal, and estuarine waters. CHL is expressed in μg L-1 or mg m-3.