Evaluation and refinement of chlorophyll-a algorithms for high-biomass blooms in San Francisco Bay (USA)

Remote Sensing
By: , and 



A massive bloom of the raphidophyte Heterosigma akashiwo occurred in summer 2022 in San Francisco Bay, causing widespread ecological impacts including events of low dissolved oxygen and mass fish kills. The rapidly evolving bloom required equally rapid management response, leading to the use of near-real-time image analysis of chlorophyll from the Ocean and Land Colour Instrument (OLCI) aboard Sentinel-3. Standard algorithms failed to adequately capture the bloom, signifying a need to refine a two-band algorithm developed for coastal and inland waters that relates the red-edge part of the remote sensing reflectance spectrum to chlorophyll. While the bloom was the initial motivation for optimizing this algorithm, an extensive dataset of in-water validation measurements from both bloom and non-bloom periods was used to evaluate performance over a range of concentrations and community composition. The modified red-edge algorithm with a simplified atmospheric correction scheme outperformed existing standard products across diverse conditions, and given the modest computational requirements, was found suitable for operational use and near-real-time product generation. The final version of the algorithm successfully minimizes error for non-bloom periods when chlorophyll a is typically <30 mg m−3, while also capturing bloom periods of >100 mg m−3 chlorophyll a.

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Publication type Article
Publication Subtype Journal Article
Title Evaluation and refinement of chlorophyll-a algorithms for high-biomass blooms in San Francisco Bay (USA)
Series title Remote Sensing
DOI 10.3390/rs16061103
Volume 16
Issue 6
Year Published 2024
Language English
Publisher MDPI
Contributing office(s) California Water Science Center
Description 1103, 15 p.
Country United States
State California
Other Geospatial San Francisco Bay
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