Uncertainties in the retrieval of the remote sensing reflectance, Rrs, from Ocean Color (OC) satellite sensors have a strong impact on the performance of algorithms for the estimation of chlorophyll-a, mineral concentrations, and inherent optical properties (IOPs). The uncertainties are highest in the blue bands. The total radiance measured at the top of the atmosphere captures the instantaneous state of the atmosphere-ocean system: the in-water conditions, sky and Sun glint reflected from the wind-roughened ocean surface, as well as light scattered from molecules and aerosols in the atmosphere. Each of these components has associated uncertainties, and when combined with the additional uncertainties from the instrument noise and the atmospheric correction process, they contribute to the total uncertainty budget for the retrieved Rrs. We analyzed the contribution of each component uncertainties to the total Rrs uncertainties in SNPP-VIIRS level 2 products, taking advantage of the spectral differences between the components. We examined multiple scenes in the open ocean and coastal waters at spatial resolutions ranging from 2250 to 5250 m by comparing the retrieved Rrs to in situ measurements made at several AERONET-OC sites and at the MOBY site. It was shown that uncertainties associated with the molecular (Rayleigh) scattering play the most significant role, while the contributions of other components are usually smaller. Uncertainties in Rayleigh scattering are primarily attributed to the variability of Rayleigh optical thickness (ROT) with a standard deviation of approximately 1.5% of ROT, which can largely explain the frequency of negative Rrs retrievals as observed using the current standard atmospheric correction process employed by NASA. Variability of the sky light reflected from the ocean surface in some conditions also contributed to uncertainties in the blue; water variability proportional to Rrs had a very pronounced peak in the green at coastal sites.

Uncertainties in remote sensing reflectance Rrs for the Ocean Color sensors strongly affect the quality of the retrieval of concentrations of chlorophyll-a and water properties. By comparison of data from SNPP VIIRS and several AERONET-OC stations and MOBY, it was recently shown that the main uncertainties come from the Rayleigh-type spectral component (Gilerson et al., 2022), which was associated with small variability in the Rayleigh optical thickness in the atmosphere and/or its calculation. In addition, water variability spectra proportional to Rrs were found to play a significant role in coastal waters, while other components including radiances from aerosols and glint were small. This work expands on the previous study, following a similar procedure and applying the same model for the characterization of uncertainties to the Sentinel-3A and B OLCI sensors. It is shown that the primary sources of uncertainties are the same as for VIIRS, i.e., dominated by the Rayleigh-type component, with the total uncertainties for OLCI sensors typically higher in coastal areas than for VIIRS.

The Stokes vector components and the degree of linear polarization of light reflected from the air-water interface contain information about the roughness of the ocean surface, which is correlated with the wave slope statistics and may be used to retrieve it using the Polarization Slope Sensing (PSS) method (Zappa et al., 2008). This statistic is a part of the radiative transfer simulations in the atmospheric correction of the ocean color satellites and other applications. A modification of the method, which minimizes the impact of upwelling light on polarimetric measurements of the reflected light was applied by using Teledyne DALSA camera equipped with a Sony sensor, where each of 1232x1028 pixels had four subpixels with 0-, 90-, 45-and 135-degrees orientation of polarization. In addition, a filter wheel with several color filters was installed in front of the camera, allowing to measure wave slope characteristics at several spectral bands. Shipborne measurements during VIIRS Cal/Val cruises in the Gulf of Mexico and in Hawaii and from a helicopter at several heights during the CCNY cruise in the Chesapeake Bay showed the advantage of the proposed modified polarimetric slope sensing technique. Measured variances of the wave slopes were mostly in the range predicted by Cox-Munk relationships with corresponding standard deviations.