The aim of the 4 SWOTALIS  cruises was to observe dynamic "fine-scale" ocean structures (of the order of 1-100 kms) in the seamounts region south of New Caledonia, a hot spot of biodiversity. The SWOTALIS cruises were planned to coincide with the calibration/validation period of the French-American altimetry satellite SWOT (launched December 16, 2022), dedicated to the observation of these fine oceanic scales.

In the seamounts region south of New Caledonia, ocean hydrodynamics is complex. When tidal currents encounter these topographical obstacles, they generate what are known as "internal tides", which induce mixing on the slopes and impact benthic and pelagic ecosystems. Small eddies (~1-50 km) and filaments also influence the connectivity of fauna between seamounts and structure ecosystems, from plankton to top predators. All these "fine-scale" oceanic processes are very poorly understood, yet they are an essential part of ocean dynamics. The SWOT satellite has been designed to provide sea surface height measurements with a spatial resolution an order of magnitude better than existing altimetry data, and its data should transform our understanding of these processes.

To ease interpretation of the SWOT satellite data, a calibration/validation period, the "Fast Sampling Phase", took place between April and June 2023. During this 3-month period, SWOT flew on an orbit that provided better temporal resolution (passing over certain swaths every day), at the expense of spatial coverage. Several in-situ sea campaigns were organized under the satellite swaths during this period, in various contrasting regions of the Ocean. These campaigns, which include SWOTALIS, are part of an international consortium, "Adopt-a-Crossover". The motivation is the observability of fine-scale processes through the sea level measured by the SWOT satellite mission. The SWOTALIS campaigns took place just before and during this "Fast Sampling Phase", under a one-day SWOT swath.

More specifically, the SWOTALIS objectives were:

• to better understand the processes of internal tide generation, and the interactions between internal tide propagation and oceanic eddies
• to better understand the dissipation processes of these internal waves and their impact on surface properties (temperature, currents) and ecosystem structuration.
• to better understand the sea level signature of these internal waves and other fine-scale dynamic structures, and their observability by the SWOT satellite.