POSTER SESSION 4
10:30–12:30, Thursday, September 17
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
ABSTRACT 1246 | POSTER 104
CYANOBACTERIA DISCRIMINATION USING SECOND-DERIVATIVE HYPERSPECTRAL ANALYSIS IN OPTICALLY COMPLEX INLAND WATERS
Phytoplankton forms the foundation of aquatic food webs, and reliable detection of dominant phytoplankton groups is increasingly important for ecosystem monitoring. Combining hyperspectral reflectance measurements with microscopic observations enables evaluation of optical methods for retrieving detailed information on phytoplankton community structure. One promising approach is the analysis of second derivatives of reflectance spectra. Within the ESA AQUATIME project, which aims to advance ecosystem and biodiversity monitoring for inland and coastal waters, this approach was tested in Lake Võrtsjärv (Estonia). Võrtsjärv is a large (270 km²), shallow, and turbid lake, with a maximum depth of 6 m. Optically active substances were measured monthly. Chlorophyll-a ranged 3.4-72.2 mg m–3 (median 40.4 mg m–3), total suspended matter from 1.6 to 52.7 g m-3 (median 16 g m–3), and coloured dissolved organic matter absorption at 442 nm from 1.9 to 8.9 m-1 (median 2.9 m–1). Reflectance spectra were used as input for second-derivative calculations. Measurements were obtained using the HYPSTAR system (https://hypstar.eu/), which provided automated in situ multi-angular reflectance observations from the lake pier since 2023, covering the 380–1020 nm spectral range. Second-derivative analysis revealed a consistent spectral feature near 552 nm associated with cyanobacterial biomass, demonstrating the potential of derivative-based hyperspectral methods for discriminating cyanobacteria in optically complex inland waters. Higher cyanobacterial biomass produced more negative second-derivative values. A sensitivity analysis using four normalisation strategies (no normalisation, 442.5, 620, 665 nm reference wavelengths) confirmed that sign-based classification is robust to normalisation choice, with 665 nm recommended for instrument-independent application.
Kersti Kangro, University of Tartu, [email protected], https://orcid.org/0000-0001-6143-9330
Gladys Villegas, Royal Belgian Institute of Natural Sciences, [email protected]
Ian-Andreas Rahn, Tartu Observatory, University of Tartu, [email protected]
Joel Kuusk, Tartu Observatory, University of Tartu, [email protected]
Dimitry van der Zande, Royal Belgian Institute of Natural Sciences, [email protected]
Krista Alikas, Tartu Observatory, University of Tartu, [email protected]
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
