Advanced radiative transfer models for the simulation of in situ and satellite ocean color data (ARTEMIS-OC) : the finite element method (FEM) numerical code

The present Report, first of a series, builds on JRC long-standing experience in developing and applying highly accurate radiative transfer models (RTMs) to simulate in situ and satellite data of the aquatic environment. In-house modelling capabilities of the signal at in situ and satellite OC sensors, included in the Advanced Radiative Transfer Models for In situ and Satellite Ocean Color data (ARTEMIS-OC) software suite, comprise: i) the Finite Element Method code (FEM); ii) the SkyFEM code; iii) the FEMrad-OC code; iv) the AquaFEM code; v) the Novel Adjacency Perturbation Simulator for Coastal Areas (NAUSICAA) code. FEM is a highly accurate deterministic numerical scheme for the propagation of unpolarized solar radiation in a horizontally invariant atmosphere-water system, as the open-ocean. NAUSICAA is a stochastic 3D MonteCarlo code for the propagation of unpolarized solar radiation in an atmosphere bounded by an inhomogeneous surface, as in coastal or inland water regions. SkyFEM, FEMrad-OC and AquaFEM are FEM targeted configurations coupled with ad-hoc modelling of atmosphere and water. All algorithms account for multiple scattering and allow varying illumination and observation geometries. The present Report illustrates the FEM code and summarizes a number of applications to investigate and reduce uncertainties in OC products. The final objective of this series of Reports is to consolidate the description of ARTEMIS-OC simulation tools in support of the Copernicus Programme.