Marine observations with a harmonic single-beam echo-sounder

International audienceTo characterise the seabed or water-column targets with acoustics, it is common to use multiple frequencies and therefore several sonar transducers or echo-sounders. The single beam echo-sounder we present here is able, thanks to non-linearity of the sea water, to generate more than three harmonics above its fundamental transmitted frequency, in effect producing four distinct frequencies with a single echo-sounder. In addition, all transmitted signals are perfectly in phase because they are carried by the same pulse, which has obvious benefits for further processing of the echoes. In this presentation, after a short review of the entire system, its application to seabed characterisation using the reflectivity level (acoustic backscattering strength from the seafloor) will be exposed. Further developments of plans to use this echo-sounder for fishery acoustics will then be highlighted, based on datasets acquired in the Bay of Brest (France). (Project funded by ANR and DGA / ANR-14-ASTR-0022-00)