Evaluation of Remote Sensing Reflectance Derived From the Sentinel-2 Multispectral Instrument Observations Using POLYMER Atmospheric Correction

With a five-day revisit frequency over coastal regions and a spatial resolution of 10–60 m, the Sentinel-2 multispectral instrument (MSI) has shown its capacity to provide a reasonably accurate remote sensing reflectance ( $R_{\mathrm {rs}}$ ) data product over water when the standard “black pixel” (BP) atmospheric correction algorithm was applied to the top-of-atmospheric (TOA) reflectance data. Alternative atmospheric correction approaches, such as the POLYnomial-based algorithm applied to Medium Resolution Imaging Spectrometer (MERIS) (POLYMER), may show advantages under nonoptimal observation conditions (e.g., in the presence of strong sun glint). Here, POLYMER is implemented to process the data collected by both MSI and the Moderate Resolution Imaging Spectroradiometer (MODIS) with the resulting $R_{\mathrm {rs}}$ evaluated with concurrent and colocated in situ $R_{\mathrm {rs}}$ data collected from the AERONET-OC platforms. The results indicate less uncertainties in the MSI $R_{\mathrm {rs}}$ than those in the MODIS $R_{\mathrm {rs}}$ , and also less uncertainties in the MSI $R_{\mathrm {rs}}$ than those reported earlier. This is possibly attributed to the spatial heterogeneity of coastal waters where MODIS coarse-resolution data may suffer, and to the high-quality AERONET-OC data. In addition, for the evaluation data set, MSI $R_{\mathrm {rs}}$ does not appear to suffer from adjacency effects from the AERONET-OC platform and clouds, leading to more coverage than MODIS in nearshore waters. However, MSI $R_{\mathrm {rs}}$ is noisy in relatively clear waters, possibly due to the noisy TOA reflectance in the atmospheric correction bands over clear waters.