Multibeam Sonar or Swath Echosounders

A multibeam sonar is an echo sounder which transmits a wide acoustic pulse which extends to either side of the ship, in a manner similar to a sidescan sonar. The receive transducer array resolves the returning signal into numerous beams, recording two-way travel time, and angle of arrival for each beam. In this way, accurate depth soundings (or bathymetry) are achieved for the entire swath. The accuracy of a multibeam sonar is critically dependant on corrections applied for vessel motion (e.g. pitch, roll, yaw, heave), and spatial location, which is achieved by a highly accurate global positioning system (GPS). Consequently, multibeam sonars require real time integration with a number of other specialist sensor systems. Various multibeam sonars are appropriate for use in a range of water depths and environments. High resolution systems (over 400 kHz) can achieve < 1 cm vertical resolution, have over 200 very narrow beams (around 0.5?) and swath widths of approximately 3 – 4x water depth in shallow water (~50 m). Conversely, low-frequency systems are available that can be used in great depths (e.g. several km), however these have lower resolution and much larger beam ‘footprints’. Multibeam sonar systems can also provide ‘backscatter’ information (e.g. reflected sound intensity) in a manner similar to a sidescan sonar, which is useful for determining seabed character.