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MOX: A parallel Monte Carlo radiative transfer code for Ocean Colour simulations

MOX is a high-performance Monte Carlo (MC) radiative transfer code for large-scale Ocean Colour (OC) simulations. The scope of the MOX development is to enable theoretical quality assessment of OC radiometric data products derived from in-situ optical profiles performed using in-water and above-water radiometer systems in optically complex coastal waters. Accurate in-situ OC data products are of critical importance for validation of remote sensing OC observations and calibration of satellite sensors in current space missions including MERIS on-board of ESA’s ENVISAT platform, as well as MODIS and SeaWIFS on-board of NASA’s Aqua and OrbView-2 satellites, respectively. MOX simulates in-water and above-water light fields at high spatial resolution in an extended domain by tracing a number of photons and tracking their trajectories. Simulated light fields are then used for “virtual” optical profiling to quantify uncertainties on in-situ radiometric measurements due to environmental perturbations (e.g., light focusing and defocusing effects and sun/sky glint effects, both caused by sea-surface waves) and measurement protocols (e.g., tilt and deployment speed of in-water sensors, sampling frequency, and integration time). Although the MC approach is highly flexible and versatile, a major drawback of MC simulations is the amount of computation time required for reducing intrinsic statistical noise below a level that permits thorough quantification of the uncertainty budgets. Therefore, high-performance computing (HPC) solutions have been adopted to permit large-scale MOX simulations in an acceptable amount of time. The MOX code development has incorporated a high level of expertise in different research fields, i.e., HPC, statistical modeling, and in-situ marine radiometry. MOX is indeed a fruitful result of extensive joint work by Davide D’Alimonte from CENTRIA and José Cardoso e Cunha and Tamito Kajiyama from CITI, in close collaboration with Dr. Giuseppe Zibordi (Joint Research Centre of the European Commission, Italy) from the applied optics perspective. This joint effort at the institutional level represents a significant part of the originality of this work.