Sounding

Sounding, determination of the depth of a body of water. The simplest method of sounding, which has been used since very early times and is still employed for measuring comparatively shallow depths, is the use of the sounding line or lead, consisting of a long rope or cord with a lead weight on the end. The cord is marked at appropriate intervals so that when it is dropped into the water, the operator, the so-called leadsman, can determine the depth as soon as the lead strikes the bottom. Adaptations of the lead include some elaborate sounding devices in which the depth is determined by pressure-recording devices.

The most modern form of sounding machine is the echo sounder. In this device a sound-generating mechanism set up in the bottom of a ship produces a series of sounds that are reflected or echoed from the water bottom. Sound travels about 1,463 m (4,800 ft) per sec in water, and by measuring the time taken for the sound waves to travel from the ship to the bottom of the water and back, it is possible to calculate the depth of the water. Most echo sounders measure the time interval by means of electronic circuits and produce a continuous record of the depth of water beneath the vessel in the form of a chart or graph. Such sounders were highly developed in World War II and have since been used extensively not only for measuring the depth of the water but also for locating submerged ships and large schools of fish. The use of such sounders is valuable to navigation, particularly in shoal or coastal waters.

See Navigation.