Sound Ranging at the U. S. Coast and Geodetic Survey

Abstract

At this Bureau sound ranging is utilized in both the vertical and horizontal directions. The former, or echo method of depth measurement, was started in 1923 with the Sonic Depth Finder, which uses a method of regulating the rate of sending signals until the outgoing signal is binaurally heard to coincide with the incoming echo. From the rate of sending the depth is calculated. This method was displaced by the Fathometer when it was placed on the market in 1925. The Fathometer is direct reading by visual indications, the time elapsed between the outgoing signal and received echo being measured by the angle through which a neon tube has rotated during the interval. Fathometers are now used on practically all Coast Survey Ships. The success of sound ranging in the vertical direction suggested its use in the horizontal direction and the method was developed early in 1924 with the cooperation of the Bureau of Standards. By this method a chronograph on the surveying ship records the explosion of a small bomb of TNT, the sound of which goes to two or more hydrophone stations and automatically causes the emission of radio signals which are recorded on the same chronograph. Such methods are now extensively used by Coast Survey Ships to locate their position in areas beyond the sight of land.