ECHO SOUNDER

Wairarapa Times-Age, 12 July 1941, Page 6

ECHO SOUNDER

AN INGENIOUS DEVICE. MEASURES DEPTH OF WATER. Because of great savings in time and labour, sound waves are now being more and more used in measuring depths, replacing the older lead and \vire systems. The time economy effected is shown plainly by the fact that a sounding in 4000 fathoms (24.000 feet.) can be taken by an echo sounder Avith greater accuracy than would result from hours of labour by the old wire methods. Moreover, echo soundings are possible with the vessel in motion, up to speeds of 15 to 20 knots.

The echo-sounding apparatus consists of tAvo microphones, one registering the sending of the sound signal. and the other the arrival of the echo reflected from the ocean floor. A delicate time recorder —providing readings to one-thousandth of a second, measuring the time interval between the sending of the sound and the arrival of the echo —enables the depth to be deduced. The velocity of sound in sea Avater averages 4800 feet per second. As a result shallow water soundings can be found in a fraction of a second, and much greater depths in a small fraction of a minute.

One type of echo sounding apparatus includes a relay by means of Avhich a graduated disk is set to revolving the instant the underwater sound is made. The arrival of the echo stops the rotation of the disk and the angle through which the disk has turned provides a measure of the time it took the sound to travel to the bottom and back. Depths are engraved on the disk so that the figures for the sounding can be read directly by noting the point at Avhich the disk stopped.

Modifications of the echo sounder have been devised for detecting the presence of icebergs, although echoes sent back from the ice have proved quite feeble compared with those obtainable from the bed of the sea. — W. P. Keasbey. in the Christian Science Monitor.