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Marine Geophysical Researches

, Volume 26, Issue 2–4, pp 157–169 | Cite as

Design of a 3D Chirp Sub-bottom Imaging System

  • Jonathan M. Bull
  • Martin Gutowski
  • Justin K. Dix
  • Timothy J. Henstock
  • Peter Hogarth
  • Timothy G. Leighton
  • Paul R. White
Article

Abstract

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.

Keywords

3D Chirp 3D seismic chirp high-resolution seismics seismic sources 

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Copyright information

© Springer 2005

Authors and Affiliations

  • Jonathan M. Bull
    • 1
  • Martin Gutowski
    • 1
  • Justin K. Dix
    • 1
  • Timothy J. Henstock
    • 1
  • Peter Hogarth
    • 2
  • Timothy G. Leighton
    • 3
  • Paul R. White
    • 3
  1. 1.School of Ocean and Earth SciencesNational Oceanography Centre SouthamptonSouthamptonUK
  2. 2.GeoAcoustics Ltd.Great YarmouthUK
  3. 3.Institute of Sound and Vibration ResearchSouthampton UniversityHighfield, SouthamptonUK

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