Low-Cost System to Support and Expand Cyanobacterial Harmful Algal Bloom Monitoring with New-Generation Ocean Color Satellites

Cyanobacterial harmful algal blooms (CyanoHABs) pose global risks to public health, ecosystems, and economies. Despite advancements in satellite remote sensing, monitoring gaps persist, particularly in smaller, remote, and resource-limited regions, where CyanoHABs often remain undetected. Satellite-based methods, though effective for large-scale monitoring, suffer from a low spatial resolution, cloud cover, and reliance on in situ validation data. Traditional in situ monitoring equipment, including high-precision spectroradiometers, is costly and logistically challenging, further exacerbating global monitoring inequities. Cyanosense 2.0 (CS2.0) is a low-cost system for real-time in situ CyanoHAB detection and satellite validation designed to address these monitoring voids. CS2.0 integrates two hyperspectral Hamamatsu spectrometers and a microcontroller system, recording Remote Sensing Reflectance (R_rs) with high agreement to industry-grade instruments (<i>R</i> ² = 0.86, Normalized Root Mean Squared Error (NRMSE) = 9.82%), at a fraction of the cost (∼$1300). During field validation in multiple CyanoHAB-prone U.S. lakes, CS2.0 showed a strong performance when tested for widely used satellite-based CyanoHAB models and indices (<i>R</i> ² = 0.74-0.83; NRMSE = 13%-18%). The system's weatherproof design supports long-term autonomous deployments, making it functional in remote environments. As a scalable and accessible solution, CS2.0 holds the potential to democratize CyanoHAB monitoring and improve global water quality assessments, especially in under-represented regions.