Estimating Chlorophyll-a Concentration in Water Bodies of Coimbatore, Tamil Nadu Using Geospatial Techniques

Water quality monitoring based on remote sensing principles are in high demand due to the growing occurrence of algal blooms on water bodies. Remote sensing techniques have been broadly employed to monitor water quality indicators in recent decades. This study focuses on using spectral indices, viz., normalised difference vegetation index (NDVI) and normalised difference chlorophyll index (NDCI), to identify surface water and chlorophyll-a over Coimbatore city in Tamil Nadu. Coimbatore, the second-largest city in the region and one of Tamil Nadu’s most industrialised cities, is referred to as the textile centre of South India which is situated on the banks of the Noyyal River. The city’s water bodies, which are mostly fed by the Noyyal River, serve as system tanks and primary groundwater recharge sites. The analysis was performed on the Google Earth Engine (GEE) platform using Sentinel-2 imagery for a period of 6 years from 2017 to 2022. This study used medium-resolution atmospherically corrected satellite data and a cloud computing platform to detect and analyse water quality. It is inferred that the chlorophyll-a content is in the range of 4.5–11.03 μgL−1 (mesotrophic) and 11.03–30.55 μgL−1 (eutrophic state) and fewer wetlands in super-eutrophic state (30.55–69.05 μg−1). The results of this study suggested that NDCI can be used to effectively monitor chlorophyll-a levels. The findings highlighted the necessity of monitoring the water quality of the water bodies and comprehending the underlying causes, which would assist all stakeholders in developing policies and strategies for the prompt preservation of water quality.