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Imagerie sismique et océanographique des masses d'eau sur le plateau continental breton

Abstract : This work is a preliminary study for the development of a new tool, marine seismic reflection, for the observation of the seasonal thermocline of the Iroise Sea. It is the first application of this technique to the observation of shallow oceanographic structures (z < 50 m). In order to define general requirements for the design of a seismic acquisition system suited to the imaging of such targets, the theory of the seismic measurement was first investigated. Four multi-channel seismic reflection profiles from the GO, Carambar and Sigolo cruises were then reprocessed and analyzed in order to assess the potential of conventional seismic systems. They were found ill suited to the imaging of shallow oceanographic structures, because of a high antenna filter induced by large offsets and seismic trace lengths, and sources that do not reconcile with the high level of emission and fine vertical resolution. New oceanographic data acquired in the Iroise Sea during the Fromvar 2010 cruise allowed simulation of the seismic acquisition, and the definition of optimal acquisition parameters for the imaging of the seasonal thermocline. Sea trials of this specifically designed system were performed during the ASPEX survey, conducted in early summer 2012. The seismic device featured: four seismic streamers, each consisting of 6 traces of 1.80 m.; a 1000 J SIG Sparker source, providing a 400 Hz signal with a level of emission of 210 dB re 1 μPa @1m. This survey captured the 15 m thick, 30 m deep seasonal thermocline in unprecedented detail, showing images of vertical displacements of horizontal wavelength of a several hundreds m to a few km , most probably induced by internal waves.
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Submitted on : Wednesday, March 20, 2019 - 9:17:10 AM
Last modification on : Wednesday, September 16, 2020 - 9:57:16 AM
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  • HAL Id : tel-02073588, version 1



Helen Piété. Imagerie sismique et océanographique des masses d'eau sur le plateau continental breton. Sciences de la Terre. Université de Bretagne occidentale - Brest, 2012. Français. ⟨NNT : 2012BRES0078⟩. ⟨tel-02073588⟩



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