High-Resolution Surface Currents From Satellite Observations in the North-Western Mediterranean Sea: Eddies Along The Iberian Coast

Abstract

The Catalan Coast in the NW Mediterranean Sea has been used as a test area for a remotely-sensed moni-toring system of surface currents. This area is characterized by small Rossby radius (~15 km), weak tidal currents and occasional strong winds making easier to separate the different contributions to the velocity field and to obtain independent estimates of it . The area in front of the Ebro Delta is covered by a HF radar. In addition, the abundant availability of cloud-free images allows testing indirect approaches to derive sur-face currents based on infrared measurements of Sea Surface Temperature (SST). Furthermore, the Casa-blanca oil platform, which has been previously used to test new remote sensing concepts, will be equipped with an ADCP for the direct measurement of ocean currents.

Within this area, we are currently testing a pre-operational system for monitoring high-resolution surface currents in collaboration with the Spanish Search and Rescue Service (SASEMAR). This system is based on the derivation of surface currents applying the Surface Quasi-Geostrophic (SQG) approximation to SST from AVHRR measurements . The system will soon incorporate additional SST data from Sentinel-3 meas-urements and merge them with Sea Surface Height (SSH) observations from the same platform. This ob-servational system is complemented by the release of drifting buoys by SASEMAR and oceanographic cruises.

The results show that our pre-operational system is able to reconstruct the velocity field associated to coastal eddies with diameters of ~10 km, but also unveil the different limitations of our approach. One of such limitations is the lack of Sea Surface Salinity (SSS) measurements. Indeed, in spite that SST and SSS gradients tend to be aligned, their sign may be inhomogeneous. To overcome this limitation we plan to exploit the synergy between SST, SSH and the new generation of SMOS-derived SSS maps in the Medi-terranean Sea, provided by the Barcelona Expert Centre in Remote Sensing (bec.icm.csic.es)