Abstract
This study presents a first assessment of the Top-Of-Atmosphere (TOA) radiances measured in the visible and near-infrared (VNIR) wavelengths from PRISMA (PRecursore IperSpettrale della Missione Applicativa), the new hyperspectral satellite sensor of the Italian Space Agency in orbit since March 2019. In particular, the radiometrically calibrated PRISMA Level 1 TOA radiances were compared to the TOA radiances simulated with a radiative transfer code, starting from in situ measurements of water reflectance. In situ data were obtained from a set of fixed position autonomous radiometers covering a wide range of water types, encompassing coastal and inland waters. A total of nine match-ups between PRISMA and in situ measurements distributed from July 2019 to June 2020 were analysed. Recognising the role of Sentinel-2 for inland and coastal waters applications, the TOA radiances measured from concurrent Sentinel-2 observations were added to the comparison. The results overall demonstrated that PRISMA VNIR sensor is providing TOA radiances with the same magnitude and shape of those in situ simulated (spectral angle difference, SA, between 0.80 and 3.39; root mean square difference, RMSD, between 0.98 and 4.76 [mW m−2 sr−1 nm−1]), with slightly larger differences at shorter wavelengths. The PRISMA TOA radiances were also found very similar to Sentinel-2 data (RMSD < 3.78 [mW m−2 sr−1 nm−1]), and encourage a synergic use of both sensors for aquatic applications. Further analyses with a higher number of match-ups between PRISMA, in situ and Sentinel-2 data are however recommended to fully characterize the on-orbit calibration of PRISMA for its exploitation in aquatic ecosystem mapping.
Highlights
Hyperspectral remote sensing techniques for inland and coastal water monitoring have been developed for more than three decades (e.g., [1,2])
The best matches between PRecursore IperSpettrale della Missione Applicativa (PRISMA), 6SV simulations and Sentinel-2/MSI are obtained in Zeebrugge and Casablanca test sites, which represent two rather different conditions in terms of signal: higher signal for Zeebrugge site and lower signal for Casablanca site
14 July 2019, Sentinel-2/MSI data was higher than both PRISMA and 6SV simulations; this was due to presence of Sun glint in the MSI image acquired the day before
Summary
Hyperspectral remote sensing techniques for inland and coastal water monitoring have been developed for more than three decades (e.g., [1,2]). Other studies [7,8,9,10] have outlined the need for having a spatial resolution of the order of decametres ( typical of terrestrial missions like Landsat and Sentinel-2) to capture the fine spatial features typical of inland and coastal waters. From 2001 to 2017, it was used in a variety of studies dealing with inland and coastal waters mapping [11,12,13,14,15]. Since 2001, the Compact High-Resolution Imaging Spectrometer (CHRIS) on ESA’s Proba-1 microsatellite [16]
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