The sediment echo-sounder
In the sub-bottom profiler configuration, the multibean system on the Marion Dufresne uses a narrow, high-energy beam which yields deep penetration and good horizontal resolution. The system uses a chirp source with a central frequency of 3.5 kHz. The return signal is received on 92 channels and combined to form the beam, reduce the relative level of the secondary side lobes and improve the signal to noise level. Vertical resolution is approximately 0.3 m. 40 m penetration was routinely achieved on most coring sites, and 60-100 m penetration was achieved where sediment thickness and composition permitted.


Onboard electronics controlling the echo sounder.
Sounder display.
Paper output.

3.5 kHz echo sounding is routinely used for monitoring the seafloor and the upper few hundred meters of the sediment cover. It is therefore a crucial tool for detecting potential coring sites during site surveying. The 3.5 kHz echo sounder record reflects the geometry and thickness of the of the upper few hundred meters of sediment, but also provides some information about the sedimentation rate and the composition of the sediment. However, the geological interpretation of echo sounding records is still speculative to a large degree.