First evaluation of PRISMA Level-2 data for inland, coastal and marine water applications

PRISMA (PRecursore IperSpettrale della Missione Applicativa) is a pre-operational hyperspectral sensor developed by the Italian Space Agency (ASI). Launched on March 2019, the PRISMA mission is mainly devoted to expert users, as scientific researchers, Earth Observation private companies and institutional organizations, interested in algorithm implementation, products and applications development, as well as environmental mapping and monitoring. In the framework of PRISCAV project (Scientific CAL/VAL of PRISMA mission), funded by ASI and started in 2019, ground based and airborne Fiducial Reference Measurements (FRM) simultaneous to PRISMA overpasses over different targets (agriculture, forest, sea, inland and coastal water, snow) were gathered to assess PRISMA radiometric performance. In this context, an evaluation of remote sensing reflectances (Rrs) derived from PRISMA hyperspectral imager was performed within the visible and infrared range (VNIR) over inland and coastal sites. Sentinel-3 OLCI imagery and above-water in situ reflectance measurements from autonomous hyper- and multispectral radiometer systems were used to evaluate the performance of PRISMA Level-2D (L2D) surface reflectance, a standard product distributed by ASI. PRISMA L2D products were also compared to Rrs data derived from the atmospheric correction tool ACOLITE, adapted for PRISMA processing. In this study, three optically diverse Italian sites, equipped with fixed positioned autonomous multispectral and hyperspectral radiometer systems, were selected for the comparison: Lake Trasimeno, a shallow and turbid lake in central Italy; the Acqua Alta Oceanographic Tower (AAOT), located 8 nautical miles off the lagoon of Venice in the Adriatic Sea and characterized by clear to moderately sediment dominant waters; and the Oceanographic Observatory (OO), mounted at about 3.3 nautical miles southwest of the island of Lampedusa, where oligotrophic water and stable conditions are present. At the time of submission, a total of 26 PRISMA images, 30 OLCI L2-Water Full Resolution (WFR) products, and available synchronous in situ measured reflectances were collected for the match-up analysis. Common statistic metrics were used for the quantitative assessment considering each single site and the combined dataset. The results demonstrated the quite good performance of PRISMA over the range of optical properties that characterize the three investigated waterbodies. Overall, ACOLITE Rrs showed lower uncertainties, better correlation and closer spectral similarity with in situ measurements than PRISMA L2D, especially in the central part of the VNIR, between 450 and 600 nm. Compared with PRISMA L2D, ACOLITE outputs were also more consistent with concurrent OLCI L2-WFR data, resulting in significant improvements against the PRISMA standard products in the blue spectral region. This study, beside to represent a key element of PRISCAV project, will also be relevant for aquatic ecosystem applications with the upcoming spaceborne hyperspectral missions, such as Copernicus Hyperspectral Imaging Mission (CHIME), NASA Surface Biology and Geology (SBG) and Plankton, Aerosol, Cloud, ocean Ecosystem (PACE), DLR Environmental Mapping and Analysis Program (EnMAP), and is involved in the pre-formulation studies of the PRISMA Second Generation (PSG).