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Design of a 3D Chirp sub-bottom imaging system

Record type: Article

Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1–24 kHz) to produce decimetre vertical resolution cross-sections of the sub-seabed. Here the design and development of the first true 3D Chirp system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and precise positioning of sources and receivers. Full 3D numerical modelling of the combined source and receiver directivity was completed to determine optimal source and receiver geometries. The design incorporates four source transducers (1.5–13 kHz) that can be arranged into different configurations, including Maltese Cross, a square and two separated pairs. The receive array comprises 240 hydrophones in 60 groups whose group-centres are separated by 25 cm in both horizontal directions, with each hydrophone group containing four individual elements and a pre-amplifier.
After careful consideration, it was concluded that the only way to determine with sufficient accuracy the source–receiver geometry, was to fix the sources and receivers within a rigid array. Positional information for the array is given by a Real Time Kinematic GPS and attitude system incorporating four antennas to give position, heading, pitch and roll. It is shown that this system offers vertical positioning accuracy with a root-mean-square (rms) error less than 2.6 cm, while the horizontal positioning rms error was less than 2.0 cm. The system is configured so that the Chirp source signature can be chosen by software aboard the acquisition vessel.
The complete system is described and initial navigational and seismic data results are presented. These data demonstrate that the approach of using fixed source-receiver geometry combined with RTK navigation can provide complete 3D imaging of the sub-surface.

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Citation

Bull, J.M., Gutowski, M., Dix, J.K., Henstock, T.J., Hogarth, P., Leighton, T.G. and White, P.R. (2005) Design of a 3D Chirp sub-bottom imaging system Marine Geophysical Researches, 26, (2-4), pp. 157-169. (doi:10.1007/s11001-005-3715-8).

More information

Published date: June 2005
Keywords: 3D chirp, 3D seismic, chirp, high-resolution seismics, seismic sources

Identifiers

Local EPrints ID: 24147
URI: http://eprints.soton.ac.uk/id/eprint/24147
ISSN: 0025-3235
PURE UUID: 9a458d93-d61d-462a-a32e-5d6a8f83bb65
ORCID for T.J. Henstock: ORCID iD orcid.org/0000-0002-2132-2514
ORCID for T.G. Leighton: ORCID iD orcid.org/0000-0002-1649-8750
ORCID for P.R. White: ORCID iD orcid.org/0000-0002-4787-8713

Catalogue record

Date deposited: 23 Mar 2006
Last modified: 17 Jul 2017 16:14

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