Influence of the Suspended Particulate Matter on the Satellite Radiance in the Sunglint Observation Geometry in Coastal Waters

Abstract

The analysis of satellite ocean color data that are acquired over coastal waters is highly relevant to gain understanding of the functioning of these complex ecosystems. In particular, the estimation of the suspended particulate matter (SPM) concentrations is of great interest for monitoring the coastal dynamics. However, a high number of pixels of satellite images could be affected by the surface-reflected solar radiation, so-called the sunglint. These pixels are either removed from the data processing, which results in a loss of information about the ocean optical properties, or they are subject to the application of glint correction techniques that may contribute to increase the uncertainties in the SPM retrieval. The objective of this study is to demonstrate the high potential of exploiting satellite observations acquired in the sunglint viewing geometry for determining the water leaving radiance for SPM dominated coastal waters. For that purpose, the contribution of the water leaving radiance Lw to the satellite signal LTOA is quantified for the sunglint observation geometry using forward radiative transfer modelling. Some input parameters of the model were defined using in-situ bio-optical measurements performed in various coastal waters to make the simulations consistent with real-world observations. The results showed that the sunglint radiance is not sufficiently strong to mask the influence of the oceanic radiance at the satellite level, which oceanic radiance remains significant (e.g., 40% at 560 nm for a SPM concentration value of 9 g m−3). The influence of the sunglint radiance is even weaker for highly turbid waters and/or for strong wind conditions. In addition, the maximum radiance simulated in the sunglint region for highly turbid waters remains lower than the saturation radiances specified for the current ocean color sensors. The retrieval of Lw and SPM should thus be feasible from radiances measured in the sunglint pattern by satellite sensors, thus increasing the number of exploitable pixels within a satellite image. The results obtained here could be used as a basis for the development of inverse ocean color algorithms that would interestingly use the radiance measured in sunglint observation geometry as it has been done for other topics than the field of ocean color research.

Seamless Mosaic Using Removal Sunglint to Support a Large-Scale Mapping Acceleration

“…The result of the mosaic without removing the sunglint will show that the land is darker on the data that contains the sunglint, this is because the water surface that contains the sunglint is very bright, which when the mosaic is done, the color balancing process will be carried out so that the land is sacrificed so that it appears darker. Unlike the case with the deglint process which is mostly done in research on objects under the surface of the water, where underwater objects that will indeed be preserved and sacrificed are land objects as in many studies that have been done (Bernardo et al, 2018;Chami et al, 2020;Martin et al, 2016;Muslim et al, 2019;Traganos et al, 2018). The result of the mosaic by removing the sunglint will produce a seamless mosaic, this is because the water surface that contains the sunglint is removed so that when the mosaic is done, the color balancing process can be done well.…”

Simulation of Parallel Polarization Radiance for Retrieving Chlorophyll a Concentrations in Open Oceans Based on Spaceborne Polarization Crossfire Strategy

“…For the observation geometry of the sunglint, the value of η is minimal due to the pronounced influence of sunglint. The roughness of the sea surface induced by the wind enables the observation of the sunlight reflection effect within a range of ±20 • from the specular direction (θ v = +30 • ) [9]. However, the value of η ppr is much higher compared to that of η in this particular geometry.…”

“…The atmospheric contributions include absorption and scattering of aerosols and molecules. The sea surface contributions include sunglint radiance and skylight radiance, both of which are specularly reflected by wave facets [9]. The traditional atmospheric correction method employs the black pixel assumption at infrared (IR) wavelengths to obtain the aerosol contributions, which has been applied to open ocean waters [10].…”