Sentinel-2 and Planet-Scope as reliable tools for water quality monitoring of small reservoirs

In an era marked by increasingly frequent extreme weather events, small inland reservoirs are emerging as crucial yet often overlooked water resources. This study investigates the potential of remote sensing techniques to efficiently monitor the water quality of those reservoirs and improve their management. Although many works in literature have tried to derive water quality parameters from different satellite platforms, micro satellites constellations like PlanetScope have never been investigated: they can be a promising tool for investigation of SRs thanks to their high spatial and temporal resolution. Focusing on Spina Reservoir, a small lake in the province of Perugia where a water quality survey has been conducted, the research combines on-site biochemical analyses with satellite imagery from Sentinel-2, well known and explored free Platform, and PlanetScope. The performances of images corrected with the default atmospheric correction and with a specific pre-processor (ACOLITE) for inland and coastal water are discussed. Water Quality Semi-empirical algorithms (indices) based on one or more spectral bands at different wavelengths are used to build correlation curves respect to in-situ measurements (e.g Chlorophyll-a, turbidity, Cyanobacteria), enabling the evaluation and comparison of the performance. PlanetScope images displayed higher reliability with respect to Sentinel-2 data and correction with ACOLITE lead to more accurate interpolations, except for chlorophyll-a, even if satellite images with lower spatial resolution (Sentinel-2) can also provide a well-distributed dataset. The findings underscore the significant potential of PlanetScope microsatellite constellation for real-time, cost-effective water quality assessment that could be easily applied on a larger scale, as regional assessment.