Modeling the Adjacency Effects at AERONET-OC Sites

A methodology is presented to quantify the adjacency effects induced in satellite ocean color radiometric data by the presence of land in coastal regions. Specifically, the adjacency radiance, defined as the difference in top-of-atmosphere (TOA) signal when accounting for and when neglecting nearby mainland, is parameterized to decouple the dependence on the optical properties of land and water from those of atmosphere and sea surface, and from measurement geometry. The methodology is applied for a set of realistic satellite observation conditions, along a transect in the Northern Adriatic Sea crossing the Acqua Alta Oceanographic Tower (AAOT, 45.31N, 12.51E) ocean color validation site. The newly developed Novel Adjacency pertUrbation Simulator for CoastAl Areas (NAUSICAA) 3D backward MonteCarlo code and the well established highly accurate plane-parallel FEM radiative transfer code, are used to simulate signal contributions at TOA. Results at relevant ocean color center-wavelengths for the AAOT site indicate average adjacency radiance contributions at TOA lower than +/- 0.5% in the visible spectral region, while reaching about 2% at 765 and 865 nm. Summer cases exhibit values above the average, while the opposite is observed for winter cases. As expected, the largest adjacency contributions occur for slanted satellite observations from over the land.