Satellite observations of sea surface height (SSH) have enhanced the understanding of the global ocean large and mesoscale circulation over the last few decades. Altimetric gridded products built from satellite measurements provide daily maps of SSH with a mean effective spatial resolution of ~200 km wavelength for the global ocean at mid-latitudes and ~130 km for the Mediterranean Sea.
The launch of the new Surface Water and Ocean Topography (SWOT) satellite mission conducted in December 2022 is considered a major advance in satellite ocean observation as it is expected to provide SSH observations in two dimensions along a wide-swath altimeter track with an effective resolution down to 15-30 km wavelength, one order of magnitude higher than present altimeters. Data acquired by SWOT will be particularly important to improve the understanding of fine-scales in the ocean, that is of those ocean processes that are smaller than the present-day resolution of altimetric observations, i.e., ~1-100 km.
The goal of the paper Recommendations for the design of in situ sampling strategies to reconstruct fine-scale ocean currents in the context of SWOT satellite mission is to optimize the design of in situ experiments aimed to reconstruct fine-scale ocean currents (~20 km), such as those that will be conducted to validate the first available tranche of SWOT data.
A set of Observing System Simulation Experiments were developed to evaluate different sampling strategies and their impact on the reconstruction of fine-scale sea level and surface ocean velocities. The analysis focused (i) within a swath of SWOT on the western Mediterranean Sea and (ii) within a SWOT crossover on the subpolar northwest Atlantic.
The work has 5 main results:
- In both regions of study distinct strategies provide reconstructions similar to the ocean truth, especially those consisting of rosette Conductivity Temperature Depth (CTD) casts down to 1000 m and separated by a range of distances between 5 and 15 km.
- A good compromise considering the advantages of each configuration is the reference design, consisting of CTD casts down to 1000 m and 10 km apart.
- Faster strategies in the Mediterranean comprise: (i) CTD casts down to 500 m and separated by 10 km and (ii) an underway CTD with a horizontal spacing between profiles of 6 km and a vertical extension of 500 m.
- The thermocline and halocline need to be sampled to reconstruct the geostrophic flow at the upper layer.
- Concerning seasonality, the reference configuration is a design that provides reconstructions similar to the ocean truth in both regions for the period evaluated in summer and also in winter in the Mediterranean.
Results from the simulations will be used to inform the FaSt-SWOT campaign.
FOR MORE INFORMATION
Bàrbara Barceló-Llull and Ananda Pascual (2023). Recommendations for the design of in situ sampling strategies to reconstruct fine-scale ocean currents in the context of SWOT satellite mission. Front. Mar. Sci. Sec. Ocean Observation Volume 10. https://doi.org/10.3389/fmars.2023.1082978
Read also: FaSt-SWOT blog: New Jupyther Notebook to design Sampling strategy using a Moving Vessel Profiler (MVP)