SWOT CTOH Ocean & Coastal Studies

Principle Investigator: Florence Birol (LEGOS - University Toulouse III​)

Co-Investigator(s): Fabien Blarel, Mathilde Cancet, Fabien Leger, Rosemary Morrow, Fernando Niño, Louise Rousselet, Lena Tolu

Collaborator(s): Francesco d’Ovidio, Oscar Vergara, Robin Chevrier

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This proposal covers the planned activities at the SNO CTOH - a French national observation service dedicated to satellite altimetry - for ocean and coastal studies with SWOT data. Our work plan is for 2024-2028, a critical period for SWOT covering the post-launch validation, and the scientific analysis of both 1-day and 21-day orbit phases. CTOH’s R&D work is based on a multi-thematic approach to develop new regional applications at fine scales, including over the open ocean and marginal seas. A major objective is to better understand the smaller-scale dynamical signals and errors over the different surfaces and how they vary in space and time, from conventional and SAR mode 1-D nadir altimeters, compared to SWOT's new wide-swath 2-D data. In addition to new research opportunities, SWOT’s 2D coverage allows us to better understand the local small-scale evolution and the effect of the 1-D sampling on long-term climate time series.

THEME 1 - COASTAL OCEAN DYNAMICS

Understanding, monitoring and predicting the sea level changes affecting the coastal ocean areas at global scale are critical issues. Yet conventional altimetry encounters many problems in coastal environments resulting in a rapid degradation of the data accuracy in the near-shore region (i.e. 30-50 km from the coast). Since the 2010s, improved coastal processing and products (eg XTRACK) /ALES product from AVISO+ & ESA) now provide 1-D sea level observations up to a few kilometres from the coast. However, interpretation of these smaller-scale, rapidly varying nearshore coastal ocean dynamics remains a challenge in 1-D. Our objective is to analyze new 2D SWOT measurements of SSH, tide and wave data to gain new knowledge on the 1-D altimetric sampling of these processes, to obtain an improved long time series suitable for coastal studies in the 0–10 km band. We will use new coastal multi-mission altimetry datasets available (from LRM, SAR and SWOT missions), different in-situ observing systems (mainly tide gauges, coastal observation networks or sea campaigns) and high resolution modelling (eg., Symphonie). Updated coastal X-track products will be explored on the global coastal scale, with a focus on the north-western Mediterranean Sea, or on other coastal domains depending on available observing systems.

THEME 2 - FINE-SCALE OCEAN DYNAMICS: PAIRING SWOT WITH IN SITU OBSERVATIONS

Understanding ocean fine scale processes (<100 km) is crucial for quantifying horizontal and vertical fluxes of energy and matter in the ocean, for understanding marine ecosystem functioning, and for estimating the local effects of climate change. SWOT 2D observations allow us to improve fine-scale dynamical observations, but to be fully understood and exploited, they should be paired with in situ information. In this work, we’ll focus: (i) on the post-cruise exploitation of multisite “Adopt-A-Crossover” in-situ datasets collected during the SWOT validation phase in 2023-2024. We will concentrate on the validation of SWOT SSH in terms of geostrophic or ageostrophic circulation; and the link between SWOT SSH and ocean 3D dynamics. A second objective is to develop a new CTOH operational service centred on the use of SWOT and other fine scale satellite data to assist in the planning (near-real time) and exploitation (delayed time) of ocean in-situ field campaigns.