29-15 Assessing Optical Band-Ratio Approaches for Chlorophyll-a Estimation in Vaal Dam, South Africa

Session: Undergraduate Research, Part II (Posters)

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Harmful algal blooms (HABs) pose growing threats to freshwater and marine ecosystems, drinking water supplies, and public health, underscoring the need for reliable and scalable monitoring methods. Optical remote sensing leverages the spectral response of chlorophyll-a to estimate algal biomass and has been widely applied in aquatic environments. This study evaluates the performance of quantitative band-ratio based chlorophyll-a algorithms for water quality assessment in the Vaal Dam reservoir in South Africa. A suite of established band-ratio based algorithms were applied to remotely sensed reflectance data and evaluated against in situ chlorophyll-a measurements. Algorithm performance was assessed qualitatively to evaluate relative predictive capability and robustness across a range of water conditions. The results indicate that algorithms employing blue and blue-green spectral bands, particularly those centered near 413, 443, and 490 nm, provided more reliable chlorophyll-a estimates. Notably, algorithms originally developed for the HICO and GOCI sensors showed the strongest agreement with observed chlorophyll patterns, despite being applied in a sensor-independent context. The results suggest that optical water quality approaches based on carefully selected spectral bands can effectively support HAB monitoring efforts in large inland reservoirs. This work reinforces the value of remote sensing applications for freshwater and highlights their potential role in early warning and long-term monitoring strategies for HAB-prone regions. 

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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