The side view sonar acoustically scans the surface of the seabed. It consists of the sonar fish, the pull cable, the sonar recorder, and the recording unit. The sonar fish is a streamlined body of about 1.5 m in length, which contains a radiation-measuring unit and a recording unit. It is towed through the water behind the ship on the towing cable (transmission cable).
In contrast to ship-based sonar, the sonar fish “floats” at an almost constant height over the sea floor, which ensures a constant scanning range. The sonar fish belongs to the so-called two-beam systems. It emits an acoustic signal to each side, which spreads out in the water column in the form of a sound beam pointing downwards. The much weaker return signals are recorded by the recording unit in the sonar fish and forwarded to the recording unit on the ship using the transmission cable.
There, a computer uses these signals to calculate the areal gray value distribution as a function of the signal strength of the sea floor, as can be seen in the examples shown here. Today, multi-frequency devices are mostly used, e.g. with a 100 kHz signal for wider areas with coarser resolution and with a lower 500 kHz signal for narrower areas with a higher resolution.