Impact of the pixel size on the estimation of the marine reflectance

The fundamental parameter in ocean colour is the remote sensing reflectance, Rrs. It is related to the inherent optical properties of the seawater (IOPs) . Rrs is a non-linear function of the backscattering and absorption coefficients of the seawater. This non-linearity has long been investigated from radiative transfer calculations and field measurements (Lee et al., 2012). For validation purposes, where in situ measurements are performed at a much smaller spatial scale than the investigated pixel, and with the future ocean color missions characterized by different spatial resolutions, it is timely to investigate the behavior of this non-linearity with the spatial scale considered. It is necessary to investigate how the definition/estimation of Rrs as a function of IOPs can be applied to a satellite pixel and how the change of resolution can impact the estimation of this parameter (and subsequent biogeochemical parameters) as the products at low resolution are not necessarily arithmetic or geometric means of those at higher resolution, especially in coastal waters. We will present estimation of the Rrs from the IOPs using simulated and satellite images for different mean formula, for different simulated scenes of IOPs and Rrs (bi-modal, gradient for instance) and different size of the pixels (50, 100, 200, 250, 500, 1000 m) will be presented. The theoretical results are compared with the results of Lee et al. (2012) and are applied to high and low resolution MERIS images. This work is useful for the next European ocean color sensor, Ocean and Land Color Imager on-board the Sentinel-3 satellite and for the Sentinel-2 missions.