Featured Application: The proposed Sentinel-2 multispectral signature can potentially be used as a screening tool for the operational monitoring of Planktothrix rubescens-dominated blooms in lakes and reservoirs. Automated flagging of the characteristic blue-to-green spectral pattern could support targeted field sampling and laboratory analyses, providing a cost-effective complementary layer for early-warning workflows for the management of drinking water and recreational water, pending validation across broader datasets and lake types. Cyanobacterial harmful algal blooms threaten freshwater quality, ecosystem stability, and public health, creating a need for spatially extensive monitoring tools that complement in situ observations. This study evaluates whether Sentinel-2 multispectral imagery can be used to identify a recurrent spectral pattern associated with Planktothrix rubescens blooms in two volcanic lakes in Central Italy (Albano and Vico). Sentinel-2 Level-1C data were processed with C2RCC to retrieve water-leaving reflectance and compared with microscopy-based observations across 13 acquisition dates (eight bloom and five no-bloom events). At the event level, bloom and no-bloom conditions were spectrally distinguishable. Six of eight bloom spectra showed a green-band peak at 560 nm and a pronounced increase from blue (443–490 nm) to green wavelengths. The B3/B1 ratio was 3.04 under bloom conditions versus 1.12 under no-bloom conditions, while B3/B2 was 1.77 versus 0.76 (both p < 0.05). Within bloom events, the blue-to-green ratio was not significantly correlated with cell density, indicating that the pattern is more suitable for bloom detection than abundance estimation. The recurrent pattern was formalized as a simple Type A criterion and further assessed using cosine similarity. These results support Sentinel-2 as a proof-of-concept screening tool for P. rubescens-dominated blooms, pending broader validation. © 2026 by the authors.
Multispectral Detection of Planktothrix rubescens Blooms in Volcanic Lakes Using Sentinel-2: Proof of Concept of a Newly Characterized Spectral Signature
Ciccarelli C.;Ajaoud M.;Casazza M.;Lega M.
2026-01-01
Abstract
Featured Application: The proposed Sentinel-2 multispectral signature can potentially be used as a screening tool for the operational monitoring of Planktothrix rubescens-dominated blooms in lakes and reservoirs. Automated flagging of the characteristic blue-to-green spectral pattern could support targeted field sampling and laboratory analyses, providing a cost-effective complementary layer for early-warning workflows for the management of drinking water and recreational water, pending validation across broader datasets and lake types. Cyanobacterial harmful algal blooms threaten freshwater quality, ecosystem stability, and public health, creating a need for spatially extensive monitoring tools that complement in situ observations. This study evaluates whether Sentinel-2 multispectral imagery can be used to identify a recurrent spectral pattern associated with Planktothrix rubescens blooms in two volcanic lakes in Central Italy (Albano and Vico). Sentinel-2 Level-1C data were processed with C2RCC to retrieve water-leaving reflectance and compared with microscopy-based observations across 13 acquisition dates (eight bloom and five no-bloom events). At the event level, bloom and no-bloom conditions were spectrally distinguishable. Six of eight bloom spectra showed a green-band peak at 560 nm and a pronounced increase from blue (443–490 nm) to green wavelengths. The B3/B1 ratio was 3.04 under bloom conditions versus 1.12 under no-bloom conditions, while B3/B2 was 1.77 versus 0.76 (both p < 0.05). Within bloom events, the blue-to-green ratio was not significantly correlated with cell density, indicating that the pattern is more suitable for bloom detection than abundance estimation. The recurrent pattern was formalized as a simple Type A criterion and further assessed using cosine similarity. These results support Sentinel-2 as a proof-of-concept screening tool for P. rubescens-dominated blooms, pending broader validation. © 2026 by the authors.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
