Abstract: Interaction of tidal flow with a complex topography and bathymetry including headlands, islands, coral reefs and shoals create a rich submesoscale field of tidal jets,
vortices, unsteady wakes, lee eddies and free shear layers, all of which impact both the aggregation and dispersion of coral spawn, cyanobacteria and pollutants. A
unique and detailed view of the submesoscale variability in a part of the Great Barrier Reef lagoon, Australia, that includes a number of small islands has been obtained
by using a “stereo” pair of 2 m-resolution visible-band images that were acquired just 54 seconds apart by satellite WorldView-3. Near-surface current and vorticity were
extracted from those data using a cross-correlation technique and an optical flow method, each yielding a similar result.

The above-mentioned data were used to test the ability of the unstructured-mesh, fi nite-element model SLIM to reproduce the details of the currents in the region. The
model succeeded in simulating the large scale (> 1 km) current patterns, such as the main current and the width and magnitude of the jets developing in the gaps between
the islands. The smaller scales (< 500 m) were resolved by the model, although various discrepancies with the data were observed. However, the magnitude of the
vorticity and many vortices downstream of the islands were correctly reproduced. The smallest scales (< 50 m) were unresolved by both the model and image-derived
velocity fields.

This study showed that high resolution models are able to a signi cant degree to simulate accurately the currents close to a rugged coast. Very high resolution
satellite oceanography stereo images o er a new way to obtain snapshots of currents near a complex topography that has reefs, islands and shoals and should be used to
assess the ability of models to resolve the macroturbulence in coastal flows.

Biography: Philippe is an engineer in applied mathematics. For his master’s thesis, he developed a spatio-temporal model of the spread of rotavirus, an infantile infectious disease.
After completing his master’s degree, Philippe began a PhD in fluid mechanics numerical modelling. His research focuses on the development of SLIM 3D, a 3d dg finite-element model for coastal flows. This model is suitable for complex topography regions, such as the Great Barrier Reef. When the benefits of this model are numerous, such as a better approximation of the coastline, an easy definition of the grid resolution and a high precision where it is needed, difficulties are also present in the mathematical algorithms, which gives many challenges to Philippe’s work.

Philippe is now working with the 2D version of SLIM, assessing it on the modelling of the submesoscale activity in the Great Barrier Reef.