A sonar device for obtaining an acoustic image of the seafloor. It is equipped with two transmitting antennas that send out acoustic pulses (or sound waves). The receiving antennas then analyse the echo reflected by the seafloor. Differences in the amplitude of the measured signals provide information about the nature of the seabed. In underwater archaeology, it is used mainly in the context of geophysical surveys. Towed over the seabed by a ship, it can detect wrecks, archaeological sites and objects lying on the seafloor or protruding from the sediment.