The coast of French Guiana is characterised by the northwestward migration of large mud banks alongshore and by high concentrations of suspended particulate matter (SPM) resulting from the strong influence of the Amazon River outflow. Surface OLI SPM concentration, linked to the footprint of the subtidal part of mud banks due to resuspension and migration processes, was used to develop a method to estimate the location of this footprint. A comparison of the results from this method with those obtained by locating the limit of the wave damping, which characterises muddy coasts, revealed good performance of the method based on recurring SPM values. The migration rates of the mud banks in French Guiana were calculated according to the delimitation of their subtidal parts, and showed slightly higher values (2.31 km/year) than suggested by earlier studies. In comparison with other methods, the migration rate estimated using the method proposed within the framework of this study takes into account the variability of the shape of the subtidal part for the first time. It was also shown that the mud banks existing on the coastal area of French Guiana present two different shapes. Our results clearly demonstrate the advantage of ocean colour data to describe mud banks according to their subtidal part, delimited using the assessment of SPM temporal variability.

The optimal exploitation of the oceanic information provided by recent high spatial resolution sensors such as Landsat 8-OLI is strongly conditioned by the quality of the water reflectance signal retrieval. One main issue stands in the ability to correct water pixels for the contamination of the sun glint, which might induce a seasonal or permanent loss of data according to the latitude. The SWIR information now provided for the most recent high spatial resolution sensors was used for evaluating the sun glint level and correcting the radiative signal for its effect. This has been performed transposing historical empirical formalisms based on the NIR signal. An automated SWIR-based sun glint correction procedure was then developed using a 4-year OLI archive gathered over very turbid waters of French Guiana (227 scenes). This procedure allows the practical limitations associated with past similar empirical methods (sensitivity to water turbidity and manual image per image correction) to be overcome. While a satisfactory preservation of the information over sun glint free pixels was observed, comparison exercises based on in situ R_rs data gathered in sun glint affected areas emphasize the relevance of the proposed methodology (correction by a factor of 14 of the averaged bias in the R_rs values after removing sun glint effects). Current limitations in the applicability of this SWIR-based empirical automated method are mainly associated with the presence of high cloud coverage, thin clouds in the OLI scene or highly spatially variable marine or atmospheric signal (around 47%, 42% and 11%, respectively, of the total of 12% of failure over French Guiana OLI archive). The potential large applicability of the procedure developed in this work was eventually demonstrated over contrasted coastal environments.