Sonic Depth Finder

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sonic depth finder

[′sän·ik ′depth ‚fīn·dər]
A sonar-type instrument used to measure ocean depth and to locate underwater objects; a sound pulse is transmitted vertically downward by a piezoelectric or magnetostriction transducer mounted on the hull of the ship; the time required for the pulse to return after reflection is measured electronically. Also known as echo sounder.

Sonic Depth Finder


(also echo sounder), a navigation instrument for the automatic measurement of the depth of a body of water by means of hydroacoustic echoes.

A transducer, which is usually mounted on the bottom of a ship, periodically receives electric impulses from an oscillator. The transducer converts the electric impulses into sound pulses that propagate vertically downward within a limited solid angle. A sound pulse reflected from the bottom is received by the transducer and is converted into an electric impulse. After being amplified, the electric impulse is fed to a depth indicator. The depth indicator records the time interval (in seconds) from the moment the sound pulse is sent from the ship to the moment the echo returns from the bottom and converts the recorded time interval into visual readings or a record depth h = Cτ/2, where τ is the time interval, c = 1,500 m/sec is the speed of sound, and h is recorded in meters. The pulse length ranges from 0.05 to 20 milliseconds; the basic frequency employed, from 10 to 200 kilohertz. Short pulse lengths and high frequencies are used in measurements of shallow depths, while long pulse lengths and low frequencies are used to measure great depths.

The transducer may be of the magnetostrictive or piezoelectric type. The depth indicator may be a flashing display with a rotating neon glow lamp that flashes at the moment an echo is received. Dial-type, cathode-ray, and digital displays are also used, as are graphic recorders, which record the measured depth on a moving paper tape either electrothermally or electrochemically.

Sonic depth finders are manufactured for various depth intervals in the range from 0.1 to 12,000 m. They operate at ship speeds of up to 30 knots (55 km/hr) or even higher. The error of such instruments ranges from 1 percent to hundredths of a percent.

Sonic depth finders are also used to search for schools of fish and for submarines, to investigate scattering layers, to determine the type of ground beneath a body of water and the stratification of bottom deposits, and to make other hydroacoustic measurements. (SeeHYDROACOUSTICS.)


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Tolmachev, D., and I. Fedorov. “Navigatsionnye ekholoty.” Tekhnika i vooruzhenie, 1977, no. 1.