Abstract
The relatively high spatial resolution, short revisit time and red-edge spectral band (705 nm) of the ESA Sentinel-2 Multi Spectral Imager makes this sensor attractive for monitoring water quality of coastal and inland waters. Reliable atmospheric correction is essential to support routine retrieval of optically active substance concentration from water-leaving reflectance. In this study, six publicly available atmospheric correction algorithms (Acolite, C2RCC, iCOR, l2gen, Polymer and Sen2Cor) are evaluated against above-water optical in situ measurements, within a robust methodology, in two optically diverse coastal regions (Baltic Sea, Western Channel) and from 13 inland waterbodies from 5 European countries with a range of optical properties. The total number of match-ups identified for each algorithm ranged from 1059 to 1668 with 521 match-ups common to all algorithms. These in situ and MSI match-ups were used to generate statistics describing the performance of each algorithm for each respective region and a combined dataset. All ACs tested showed high uncertainties, in many cases >100% in the red and >1000% in the near-infra red bands. Polymer and C2RCC achieved the lowest root mean square differences (~0.0016 sr−1) and mean absolute differences (~40–60% in blue/green bands) across the different datasets. Retrieval of blue-green and NIR-red band ratios indicate that further work on AC algorithms is required to reproduce the spectral shape in the red and NIR bands needed to accurately retrieve the chlorophyll-a concentration in turbid waters.
Highlights
The first of a series of Multi-Spectral Imager (MSI) instruments was launched in June 2015 by the European Space Agency (ESA) on board Sentinel-2A
An analysis of the root mean square difference (RMSD) between observations on different detectors and different atmospheric correction (AC) algorithms suggested no evidence that one detector performed worse than others, but a varying presence of banding was visible in all bands after AC by all algorithms
Six atmospheric correction algorithms were tested with Sentinel-2A MSI data
Summary
The first of a series of Multi-Spectral Imager (MSI) instruments was launched in June 2015 by the European Space Agency (ESA) on board Sentinel-2A. Designed as a land monitoring component of the Copernicus programme, MSI records over coastal marine regions and can be considered an asset in water quality monitoring of inshore regions and inland water bodies that are not observable by current ocean colour sensors such as OLCI and MODIS. The MSI optical waveband configuration resembles previous landmonitoring satellites such as NASA/USGS Landsat 7 and 8. These sensors have demonstrated use cases for water remote sensing applications (e.g. Doña et al (2015), Khattab and Merkel (2014), Vanhellemont and Ruddick (2015), Pahlevan et al (2017b), Bresciani et al (2018)). Combining the higher spatial resolution, and additional wavebands, MSI is of considerable value for inland water monitoring
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