Remotely Sensed Hyperspectral Data to Determine Chlorophyll-a in River Water

Regardless of challenges in estimation of chlorophyll-a (Chl-a) by remote sensing, Chl-a assessment by remote sensing offers the potential for significant understanding of algal pollution in ambient waterbodies. In this study, the fluorescence enveloped area (FEA) was estimated from remotely sensed hyperspectral data to determine chlorophyll-a (Chl-a) in river water. The FEA was estimated by integrating the fluorescence height and fluoresce peak positions. The research is built on the work, which requires both lab-scale and field-scale analytical capabilities to determine Chl-a concentrations. Firstly, field water samples were collected from a river, and a portable spectroradiometer was used to generate hyperspectral data of ambient water samples. Secondly, these samples were processed in lab using spectrophotometer to determine actual Chl-a concentrations in water samples. This measurement requires using conventional analytical methods that involves algae cell destruction, and Chl-a extraction using acetone solvent. Finally, relationships between FEA, and actual Chl-a concentrations, and wet biomass were determined to evaluate the capabilities of FEA-based approach to determine the Chl-a concentrations in river water. This approach was applied to Putah Creek for retrieval of Chl-a concentrations from hyperspectral data obtained from water samples collected in July 10 & July 26, 2023. The relationships between actual Chl-a concentrations, and retrieved Chl-a concentrations from hyperspectral showed that the approach used here can be applied to evaluate the algal biomass and Chl-a in river waters, particularly high Chl-a concentrations.