General presentation :
Sub-bottom profilers (SBP) are acoustic devices commonly used to explore the first sediment layers below the seafloor over a thickness that reaches tens of meters. For the SBP installed on IFREMER vessels, the frequency range of the transmitted signals lies between 1.8 and 5.3 kHz. The transmitted signals are linear frequency modulated signals. The signal length can be adjusted between 10 ms and 100 ms. The received signal consists in successive echoes generated on the sedimentary layers.
Within the frequency band used, the received energy mainly comes from coherent reflection formed by acoustic impedance discontinuities. Backscattering from the seafloor and from the underlying interfaces is only a weak contributor to the total energy received.
Data from sub-bottom profilers can be used to perform qualitative studies of the geological structures and the sedimentary processes. Data can also be used to estimate geoacoustic parameters (reflection coefficient, absorption…) in order to better characterize the geological environment.
Ifremer sub-bottom profilers
Sub-bottom profilers are installed on the following IFREMER vessels and underwater vehicles :
In 2006-2007, Ifremer has developed a new acquisition system for the sub-bottom profilers (SBP). With a new acquisition software, called SUBOP (SUb-BOttom Profiler), it is possible to generate the transmitted signal and to acquire the received signals, to interface other onboard sensors (navigation, bathymetry, motion sensors) and to record the data in the standard SEGY format.
SBP data exemple
The following SBP profile has been recorded on the RV Le Suroît during the CALIMERO campaign in April 2005 (profile length ~5 km, vertical axis: two-way propagation time in ms). On this profile, the penetration depth reaches about 160 ms (two-way propagation time; that corresponds to about 120 m) and the vertical resolution is about 0.4 ms (that corresponds to about 30 cm).