The Ushant front forms on the continental shelf to the west of Brittany in the Iroise Sea each summer. This tidal warm front separates stratified water (warm at surface) to the West, from homogeneous waters mixed by the tide (cool at surface) to the East. Understanding the dynamics of this structure is of interest both in terms of biology (e.g. occurrences of phytoplankton blooms) and physical oceanography (mesoscale structures and fine structures linked to the internal tide and mixing processes). In situ measurement techniques for physical parameters of water (XBT, CTD, gliders) offer only limited horizontal resolution, which limits our ability to apprehend the details of oceanographic structures. Imaging of the water column using seismic reflection is a fairly new technique which can be used to image the thermohaline structure at a horizontal scale of about ten metres, which is two to three times better than the so-called classic oceanographic methods. The objective of this cruise is to obtain imaging of the water column structure in the Iroise Sea using combined and simultaneous seismic and oceanographic acquisitions. The project follows on from a series of oceanographic cruises called FromVar (2006-2010) conducted by the LPO at Ifremer, which aimed to advance our knowledge about the Ushant Front's physical structure, dynamics, variability and associated phenomena. In addition, it is part of a PhD study underway (to be defended in late 2012) financed by the Brittany regional council and fits into the current drive for new seismic oceanographic studies with a network of partners over Europe. This cruise is related to a PhD grant from the Brittany regional council (ISOMER) and to the LabexMer project.