Echosounders are used for bathymetric surveying. With acoustic signals, they sound out the seafloor below a ship. Based on the time the sound needs to travel from the ship to the seafloor and back, the depth of the seafloor is calculated. Standard echosounders record a single depth value for each measurement. Multibeam swath echsounders, however, almost simultaneously record a line of depth values with each measurement. From the ship, a swath of depth values is recorded across the ships track. In this way a stripe of seafloor is covered during each survey. The width of this stripe depends on the water depth. Under perfect conditions, it can be as wide as six times the water depth. In addition to depth information, multibeam swath echosounder data also contain information on seafloor characteristics. From these data, it is for example possible to determine if mud, sand or rock is exposed at the seafloor. Thus, supplementary to seafloor maps, multibeam swath echsounders also provide valuable information for biological and geological studies.
Polarstern has a hull-mounted STN-Atlas-Hydrographic HYDROSWEEP DS III deep-water multibeam swath echosounder permanently installed. With frequencies between 13.6 and 16.6 kHz it is capable to measure down to 11,000 m water depth. With each measurement, 320 depth values (so-called hard beams) are directly determined. Up to further 920 additional soundings (so-called soft beams) are calculated by the system software.