Développements électroacoustiques en sismique marine Très Haute Résolution

High to Very High Resolution marine seismics are of common use to build and refine models of sediment processes and to explore, for instance, relationships between sediment stratigraphy and sea level variations. The frequency range of this technology lays between 200 and 4000 Hz, providing a vertical resolution of metric to sub-metric scale. Marine experiments with seismic source and receivers towed close to the seafloor are set up in order to limit the energy loss related to wave front divergence and unwanted 3D effects or diffraction hyperbolas deteriorating the quality of the resulting seismic image. The technological challenge was thus to provide users with appropriate seismic acquisition system able to deal with high hydrostatic pressure which forbids the use of any conventional surface-towed explosive source. The Janus-Helmholtz acoustic source, initially designed for low frequency active sonar, allows a wide frequency bandwidth and offers a highly repeatable acoustic signal perfectly tailored for accurate soil characterisation. The potential of this acoustic sources may be achieved only if the receiving array is able to take full advantage of the quality of the emitted signal and therefore hydrophones and streamer were designed to meet those requirements.