Seismic reflection imaging of shallow oceanographic structures

Type Article
Date 2013-05
Language English
Author(s) Piete Helene1, Marie Louis2, Marsset Bruno3, Thomas Yannick3, Gutscher Marc-Andre1
Affiliation(s) 1 : Univ Brest, Lab Domaines Ocean, IUEM, F-29280 Plouzane, France.
2 : IFREMER, Ctr Brest, Lab Phys Oceans, F-29280 Plouzane, France.
3 : IFREMER, Ctr Brest, F-29280 Plouzane, France.
Source Journal Of Geophysical Research-oceans (0148-0027) (Amer Geophysical Union), 2013-05 , Vol. 118 , N. 5 , P. 2329-2344
DOI 10.1002/jgrc.20156
WOS© Times Cited 9
Keyword(s) seismic oceanography, seismic acquisition system, seasonal thermocline, Iroise Sea, Gulf of Cadiz, Florida Straits
Abstract Multichannel seismic (MCS) reflection profiling can provide high lateral resolution images of deep ocean thermohaline fine structure. However, the shallowest layers of the water column (z < 150 m) have remained unexplored by this technique until recently. In order to explore the feasibility of shallow seismic oceanography (SO), we reprocessed and analyzed four multichannel seismic reflection sections featuring reflectors at depths between 10 and 150 m. The influence of the acquisition parameters was quantified. Seismic data processing dedicated to SO was also investigated. Conventional seismic acquisition systems were found to be ill-suited to the imaging of shallow oceanographic structures, because of a high antenna filter effect induced by large offsets and seismic trace lengths, and sources that typically cannot provide both a high level of emission and fine vertical resolution. We considered a test case, the imagery of the seasonal thermocline on the western Brittany continental shelf. New oceanographic data acquired in this area allowed simulation of the seismic acquisition. Sea trials of a specifically designed system were performed during the ASPEX survey, conducted in early summer 2012. The seismic device featured: (i) four seismic streamers, each consisting of six traces of 1.80 m; (ii) a 1000 J SIG sparker source, providing a 400 Hz signal with a level of emission of 205 dB re 1 μPa @ 1 m. This survey captured the 15 m thick, 30 m deep seasonal thermocline in unprecedented detail, showing images of vertical displacements most probably induced by internal waves
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