The SWOT satellite mission (Surface Water and Ocean Topography), launched in December 2022, is measuring sea surface height with a resolution an order of magnitude higher than conventional altimeters, providing an unprecedented view of the variability of the sea surface topography. This document reports the activities carried out at sea during the two campaigns of the FaSt-SWOT project (PID2021-122417NB-I00 funded by MCIN/AEI/10.13039/501100011033/ FEDER,UE). These campaigns had two main objectives: 1) participate to the SWOT satellite cal/val activities by collecting in-situ observations of fine-scale structures in the area covered by the satellite during its initial fast-sampling phase, and 2) improve the characterization and understanding of these structures by combining in-situ multi-platform and satellite data with numerical models and other computational techniques. The FaSt-SWOT experiments were conducted in the Balearic Sea (Western Mediterranean Sea) between 25-28 April and 7-10 May 2023, using R/V SOCIB. The experiments consisted in 2 legs both using multi-scale ship-based instruments (CTD, Moving Vessel Profiler, thermosalinograph, ADCP and GoPro action cameras), autonomous platforms (surface drifters and gliders), and satellite observations (SST, ocean color and altimetry). In addition, 2km-resolution data-assimilative modelling simulations were produced to provide a complementary representation of the fine-scale ocean variability. Finally, machine-learning-based optimization algorithms were also tested to define adaptive sampling strategies during the experiment. The sampling first focused on a small anticyclonic eddy, with a diameter around 20-25km. Several cross-sections of the Moving Vessel Profiler and underwater gliders provided insights into the vertical structure of temperature and salinity fields and the associated signals in chlorophyll and dissolved oxygen. Two gliders were programmed to perform back-and-forth sections during a 3-week time with a 1-day delay between them, allowing to evaluate the temporal variability of the ocean fields at the period of repetitivity of the satellite. The second leg started 9 days after the end of the first one. A 48-hour dense radiator-like pattern was performed by R/V SOCIB, allowing to characterize the evolution of the small eddy observed during the first leg. A total of 45 surface drifters were deployed during the two phases to evaluate in-situ surface currents and their associated convergence and divergence in the vicinity of the eddy. This report presents the details of the sampling strategy and collected measurements, also including data management aspects and description of the supporting numerical simulations and external communication activities associated with these field campaigns.

FaSt-SWOT project; PID2021-122417NB-I00 funded by MCIN/AEI/10.13039/501100011033/ FEDER,UE.

Peer reviewed