Intra-day analysis of water quality parameters in a highly dynamic shallow lake from multiple satellite sensors

Graphical abstract workflow diagram. Left: Satellite map of Lake Trasimeno with the WISPstation location. Center: List of 14 multi- and hyperspectral sensors. Right: Data processing steps from Level-2 images to BOMBER outputs, showing intra-day maps of SPM and CHL variations. Lake Trasimeno (Italy) is a shallow, highly dynamic lake that exhibits intra-day variability in optically active parameters such as suspended particulate matter (SPM) and chlorophyll-a (CHL), posing challenges for monitoring through traditional field-based techniques or a single satellite sensor. This study investigates the spatio-temporal dynamics in SPM and CHL using a synergistic approach that combines in situ data from an above-water fixed spectroradiometer (WISPstation) with multisensor satellite imagery collected between 2019 and 2024. Remote Sensing Reflectances derived from 14 satellites showed good agreement with in situ data, enabling the application of a bio-optical model, in three configurations based on the lake's trophic conditions, to retrieve SPM and CHL concentrations with high accuracy. Statistical analysis identified wind speed and air temperature as the primary drivers of SPM and CHL variability, respectively. Daily mapping highlighted the lake's high dynamism, while intra-day analysis revealed limited SPM changes influenced by local perturbations, whereas CHL exhibited a progressive increase throughout the day consistent with circadian algal growth patterns. These results demonstrate the capability of a multisensor satellite approach to capture rapid intra-day variations, suggesting promising applications for continuous, large-scale monitoring of other lake ecosystems.