Presenter: Bror Jönsson (Plymouth Marine Laboratory)

Description:
Global biogeochemical ocean models are invaluable tools to examine how physical, chemical, and biological processes interact in the ocean. Another indispensable resource is ocean-color properties derived from satellite, which provide observations of the surface ocean with unprecedented coverage and resolution. While the potential for using ocean color products to evaluate the skill of biogeochemical models is significant, there are challenges when comparing model output and analogous satellite products (e.g. chlorophyll-a). Most approaches are based on point-by-point comparisons in space and time where spuriously large errors can occur from small spatial and temporal mis-matches, whereas global statistics provide no information on how well a model resolves processes at regional scales.   Here we suggest an alternative methodology for robust comparisons between models and satellite data. The focus is to compare probability density functions of different properties within and between different eco-regions to evaluate how the model resolves physical and biological processes. Differences in distributions of Chl concentration provide information on matches and mismatches between models and observations. In particular, mismatches help isolate regional sources of discrepancy, which can lead to improving both simulations and satellite algorithms. We leverage recent advances where ecosystem models  simulate the spectral properties of phytoplankton and remote-sensing reflectances, bringing model outputs closer to what the satellites observe, once atmospheric correction has been applied. This use of radiative transfer theory in the model help mimic remotely-sensed products facilitate model-data comparisons of optical properties of the ocean. Finally, we use Earth Mover's Distance (EMD) to quantify the differences in probability distributions and show that EMD can be an effective scalar measure for summarizing the full distributional difference between two data sources.