Keywords : sub-bottom, profiler

Sub-bottom profiler of the AUV

General presentation

IXSEA and Ifremer have launched in 2006 the development of a new deep-sea low-frequency sub-bottom profiler (SBP). For this new SBP, the main required specifications were:

  • Use of low frequency signals to reduce the signal attenuation (the required penetration depth is about 50 m with a vertical resolution of about 25 cm).
  • Working depth: up to 6000 m.
  • Compact and light equipment.

The acoustic emission is based on the use of a Janus-Helmholtz transducer. The frequency band extends from 1800 to 6200 Hz. Power electronics and impedance matching unit have been specifically optimized to deliver a sound level of 190 dB, compatible with a 50 m penetration depth. The vertical resolution is better than 20 cm. The receiver is a three-hydrophone array. Data acquisition is performed with the acquisition system SUBOP.

This SBP can be used with Ifremer AUV AsterX or IdefX. During a deep-sea diving, the AUV configuration is:

  • Altitude: 50 m.
  • Speed: 3-4 knots.
  • Operating depth: up to 3000 m.
  • Survey distance: 50 km typical.

A photograph of the different parts of this SBP, integrated on a temporary structure, is given below (bottom left: reception array; bottom right: emission transducer; under the structure: container with the power electronics and the acquisition system).

The drawing below shows the integration of the SBP in the fore part of the AUV (container, emission transducer TX, reception array RX).

SBP data example

The following SBP profile has been recorded with the SBP of the AUV during the first operational cruise in 2008 (profile length ~1.4 km, vertical axis: two-way propagation time in ms).