In the framework of the 4DMED-sea project and its extension, an international workshop entitled “Grounding Lagrangian particles in satellite-derived oceanic flow fields” was held from Oct. 30 to Nov. 6, 2024 at the Science Hub of the European Space Agency in ESRIN (ESA Centre for Earth Observation, Frascati, Italy). Leaded by AMU and CSIC, it gathered 12 established experts (from France, Spain, Italy, Netherlands, USA) and 6 early-career researchers to exchange ideas (Oct. 30, 31), to brainstorm collectively and co-write a scientific article (Nov. 4, 5, 6). Beyond the training component, it aims to recall the background and describe the problem to anticipate possible solutions.
Over the past decades, Lagrangian modelling has proven its efficiency for fundamental research on transport, mixing and dispersion processes in the ocean. It has been recently used for more applied research (connectivity of Marine Protected Areas network, Fishery management, etc…) and is now being considered for various societal applications (Search & Rescue operations, tracking plastics, oil spills and other anthropogenic contamination events, assessing water quality for dredging operations in seaport, underwater cabling, offshore wind farms, etc…).
However, the modelled results are dependent on the numerical scheme employed and, most importantly, on the quality of the input flow fields. And contrarily to operational modelled and reanalyses datasets, satellite-derived velocity products are unique because they are the sole source of gridded ocean currents originating only from Earth Observations and covering simultaneously the coastal and open ocean at global scale. In 4DMED-sea, such flow fields have been generated for the first time at high-resolution and within the interior ocean, opening new research and applied opportunities. Yet, factors contributing to inaccuracies near the shores and the bottom topography (closed boundary conditions) are not fully understood nor taken into account. This is especially the case in the coastal ocean where the grounding of numerical particles is prominent, which biases subsequent analyses.
After reviewing the most common impacts (e.g. spurious trajectories, artificial gain/loss of particles, impossibility to distinguish true from fake grounding events) and their causes (intricate coastline, convoluted bathymetry and unresolved coastal multiscale dynamics), the group recapped the main potential solutions (e.g. correcting the flow field itself, correcting nearshore trajectories or parameterizing grounding) in order to anticipate uncertainties, harmonize good-practices and guide future efforts by the larger community (academic and non-academic).
Léo Berline, Chaimaa Rwawi and Vincent Rossi (organizer) from MIO participated in this event, gave various oral presentations and took actively part in the scientific debate. A peer-reviewed collaborative paper on the topic will be published in 2025…
Stay tuned !
Contact : Dr. Vincent Rossi
