Sound echo-sounder

Fig. 13. Structure of the bottom of Long Island Sound revealed by acoustic reflection profiles made with 7-kHz acoustic pulses. (Upper echo is produced by a 2(X)-kHz echo sounder.) (a) Section of end moraine capped by boulders and almost buried by marine mud. (b) Thick deposit of marine mud in central Long Island Sound on top of outwash sand with reflector above thought to be surface of lacustrine deposits, (c) Sand-to-mud transition zone in central Long Island Sound. In all records each division on the vertical scale is 600 mm.

Underwater Sound. Applications for underwater acoustics include devices for underwater communication by acoustic means, remote control devices, underwater navigation and positioning systems, acoustic thermometers to measure ocean temperature, and echo sounders to locate schools of fish or other biota. Low-frequency devices can be used to explore the seabed for seismic research. 

All soundings shall be carried out by means of a recording trace dual frequency echo-sounder with sufficient sensitivity to permit measurement of the bed levels to an accuracy of +/-100 mm. The echo sounding equipment shall be regularly calibrated by means of a sounding plate. 

Depending on the aim of the bathymetric survey, the equipment and line density is chosen. For an overall bathymetric survey that is carried out for example on the North Sea, a line density of one hne every 25 or 50 metres using a single beam echo sounder can be sufficient. On the other hand, in case of monitoring the transport behaviour of so-called sand waves much more detail is needed and hence the use of multibeam echo sounding to obtain a full coverage of the sea bottom is advised. 

The multi beam echo sounder is used in coastal areas where water depths range from about 2 metres below the ship up to about 1000 metres or more. Deep echo sounding with a multi beam system is possible deeper than 1000 metres, but the data coverage will decrease due to the travel time of the acoustic waves. This causes a loss of sea bottom detail (an important aspect of multi beam). For deep echo sounding, a single beam echo sounder is generally preferred because it is easier to use than multi-beam echo sounders. 

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