Synergies between Sentinel-3A altimetry and in-situ multi-platform observation in the Western Mediterranean

The new Sentinel-3A satellite launched February 16, 2016 - as part of the EU Copernicus programme - is in commissioning phase and will reach the operational status in a few months. A scientific collaboration between IMEDEA (CSIC-UIB), CLS and SOCIB has already started to compare the along track altimeter products and multi-platform in-situ observations. Taking advantage of SOCIB/IMEDEA multi-platform approach (see references below), a glider mission was undertaken contemporaneous with and along the same track as the overpass of the Sentinel 3 satellite in the Southern Mallorca region. In addition a one-day ship mission on May 30, synchronous with the overpass of the satellite, captured two transects of moving vessel ADCP with the R/V SOCIB. 

The mission is part of a study conducted in the frame of the Copernicus Marine Environment Monitoring Service (CMEMS) Sea Level Thematic Assembly Center. This study focuses on mesoscale variability and comparison of the new along-track (L3) and gridded interpolated maps (L4) altimetry products provided among others by the Sentinel-3A altimetry mission in the western Mediterranean Sea by using the in-situ data provided by SOCIB (Argo, ADCP, gliders, drifters, HF radar, tide gauges). The analyses are conducted among others through the comparison of Absolute Dynamic Topography (ADT) obtained from the altimetry measurements and Dynamic Heights (DH) derived from temperature and salinity profiles measured by Argo floats and gliders along the trajectories followed by the satellites. 

 

The u (a) and v (b) components of velocity during the return transect from the end-point to the start-point. (c) shows the distance travelled between the mid-point of each ensemble bin, which gives an indication of how constant the ship speed was.
 

Therefore, new in-situ data collected along the Sentinel-3A tracks in the western Mediterranean are needed. The high resolution of glider data will also allow to investigate smaller spatial scales. Knowledge about mesoscale structure like eddies is still incomplete because of their intrinsic time scales and of the difficulties in sampling. Recently, the merging of glider measurements and new generation remotely sensed data, offered the opportunity to investigate some of the characteristics of eddies, such as radius, track and rotational speed. Nevertheless, the lack of high resolution in- situ data, through eddies and along their edges, still remains a main concern. A specific objective is also to study the ocean velocity structure from three platform perspectives, validate the satellite data, and in particular the potential of the Synthetic Aperture Radar Mode (SARM) instrumentation, and ultimately lead to a more complete understanding of physical ocean processes and biogeochemical impacts. This experiment also contributes to the preparatory cal/val activities of the forthcoming wide-swath satellite altimeter (SWOT) that will provide daily high resolution sea surface height measurements during the fast phase after launch around the Balearic Islands.

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