Retrieval of Turbidity of the Upper Lake, a Ramsar site, Bhopal, India using in-situ observation and Landsat-8 OLI satellite data

Abstract

Turbidity, an optical measure of water clarity influenced by suspended sediments and organic matter, is a critical indicator of freshwater quality. Satellite remote sensing offers a practical means to monitor turbidity over space and time by capturing water-leaving reflectance across spectral bands. This study explores the spatiotemporal retrieval of turbidity in the Upper Lake, Bhopal, which is an important urban freshwater body and Ramsar site in India, using Landsat-8 Surface Reflectance (SR) data from 2013 to 2022. Field-based in-situ turbidity data, collected during pre-monsoon and post-monsoon seasons of 2022, were used to calibrate and validate several empirical models based on different band combinations. The best empirical models used the band ratio of the blue and red bands (Band 2 and Band 4), yielding high agreement with field data (R² = 0.89). Temporal turbidity trends revealed a seasonal pattern, with higher turbidity observed in the post-monsoon season due to catchment runoff and anthropogenic activities. The study confirms that Landsat-8 SR, supported by field measurements, is a reliable tool for long-term turbidity monitoring in inland lakes.