Water Quality Retrieval from PRISMA Hyperspectral Images: First Experience in a Turbid Lake and Comparison with Sentinel-2  
[PERSON]  
1 Center for Information and Communication Technology, Fondazione Bruno Kessler, Via Sommarive, 18 1-38123 Trento, Italy; [EMAIL_ADDRESS]  
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[PERSON]  
1 Center for Information and Communication Technology, Fondazione Bruno Kessler, Via Sommarive, 18 1-38123 Trento, Italy; [EMAIL_ADDRESS]  
2  
[PERSON]  
2 Correspondence: [EMAIL_ADDRESS]; Tel. : +39-0461-314392  
this kind of information contributes to a better understanding of processes such as eutrophication and harmful algal blooms, carbon cycle, as well as climate change impacts [6; 7; 8]. Among water quality parameters, the concentration of chlorophyll-a (Chl-a), which is in turn an indicator of the phytoplankton abundance, can be considered a key parameter for assessment of the primary production, the trophic status, and the quality of water [9]. Harmful algal blooms (HABs) can endanger aquatic and human health. The monitoring of HABs requires timely and spatially distributed information about Chl-a concentration [10; 11]. Total suspended matter (TSM) is a measure of organic and mineral solids suspended in the water column [12]. A high concentration of TSM can significantly reduce the light availability for primary production and thus lead to degradation of aquatic habitat, and limit fisheries and drinking water resources [13]. Colored dissolved organic matter (CDOM) is another key water quality indicator that is closely linked to the carbon content. Spatiotemporal monitoring of CDOM can contribute to studies of carbon cycle, aquatic ecology, climate change, and water treatment projects [14; 15; 16]. Remotely sensed data have long been leveraged in quantification and mapping of optically active constituents such as Chl-a, TSM, and CDOM. Information on bathymetry and benthic habitats such as submerged aquatic vegetation can be also derived from water-leaving spectral data [17; 18; 19]. This is only feasible in optically shallow waters where the optical condition (e.g., turbidity and water depth) allows for a back and forth traveling of the light through the entire water column [19; 20; 21; 22]. The multispectral sensors onboard satellite platforms are the main source of optical images for the estimation of biophysical parameters of inland/coastal waters [6]. In this context, ocean color sensors such as the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) and MEdium Resolution Imagining Spectrometer (MERIS) have long been used for estimation of a variety of biophysical parameters in open oceans and coastal environments [6]. The recent twin Ocean and Land Color Instruments (OLCI) onboard Sentinel-3A and Sentinel-3B are follow-ups for the MERIS mission but with significant improvements of six additional bands [23]. However, the spatial resolution of ocean color sensors (300-1000 m) suits only the studying of large water bodies. Studies on smaller water bodies such as lakes benefited from the heritage Landsat mission (30 m), and the Operational Land Imager (OLI) aboard Landsat-8 has received more interest as it provides an enhanced radiometric resolution (12 bit). The improved dynamic range of Landsat-8 OLI provides sensitivity to the variations of water-leaving radiance and thus the in-water constituents [24]. Along with OLI, the twin MultiSpectral Instruments (MSI) onboard Sentinel-2A and Sentinel-2B are currently in the main spotlight of the remote sensing community for analyzing inland/coastal waters at a relatively high spatial resolution (10-30 m). A temporal resolution of about 2-3 days can be achieved by the MSI sensors and this further improves in conjunction with OLI observations (revisits every 16 days). More recently, a revolutionary satellite constellation called PlanetScope consisting of a large number (+130) of CubeSats provides very high-resolution imagery (3 m) on a daily basis [25].