Page 441 echo sounding '513 



But in recent years supersonic frequencies have been increasingly employed in echo- 

 sounding equipment, both for navigation and surveying purposes. This has been made 

 possible by the theoretical study and practical application of magnetostriction and 

 piezoelectric phenomena. 



Important advances have been made in graphic recording, in early use in Europe, 

 as a method of registering echo soundings. This method of registering soundings has 

 only recently been adopted for extensive use in the United States. 



Besides its value in hydrographic surveying and navigation, echo sounding has been 

 used for such varied purposes as the measurement of tides at sea, the measurement of 

 silt deposits on the sea bottom, and the collection of valuable data for geologic and ero- 

 sion studies. 



513. History of Echo Sounding in the Coast and Geodetic Survey 



5131. Sonic Depth Finder 



The first echo-sounding instrument used by the Coast and Geodetic Survey was 

 installed on the ship Guide in 1923 and was first used to take deep oceanic soundings 

 during a voyage from Norfolk, Virginia, to San Diego, California. This apparatus was 

 known as the Sonic Depth Finder, developed by Dr. Hayes of the United States Navy. 

 The following year a similar instrument was installed on the ship Pioneer. In operation, 

 the Sonic Depth Finder transmitted a sound in the water at the precise instant the 

 echo from a previously transmitted signal was heard. The operator used a set of 

 headphones, through which he could hear the transmitted signal through one ear and 

 the echo through the other. By a variable-speed mechanism the operator could vary 

 the interval between transmitted sound signals, until the transmitted sound and an 

 echo were heard simultaneously. The position of the dial on the variable-control 

 mechanism served to indicate the depth. Although the Sonic Depth Finder was far 

 superior to earlier sounding instruments it had numerous shortcomings as a hydro- 

 graphic survey instrument. Among these may be mentioned the inaccuracy of 

 soundings obtained in depths of less than a hundred fathoms even when a special shoal- 

 water device was used; the likelihood of inherent erroneous soundings due to the 

 principles of the instrument; and the personal error, because the accuracy of depth 

 measurements depended on the skill of the operator. 



5132. 312 Fathometer 



In 1925 the first Fathometer (pronounced Fath' (5-me'ter), a commercial instrument 

 designed and built by the Submarine Signal Company, was installed on the ship 

 Lydonia. This instrument, known as the 312 Fathometer, was later installed on all 

 the ships of the Coast and Geodetic Survey and entirely replaced the Sonic Depth 

 Finder. Most of the objectionable features of the Sonic Depth Finder were eliminated 

 from the 312 Fathometer; comparatively shoal soundings could be obtained, the sound- 

 ings could be read visually from a depth scale, little experience was needed to operate 

 the instrument, and all soundings could be taken from the vessel while underway. 

 Deep-water soundings were obtained on the 312 Fathometer by noting the position on 

 a circular depth scale of a continuously rotating white light, at the time the arrival of 

 the echo was heard in the operator's headphone. This method was known as the 

 white-light method but was later replaced by a red-light method similar to that used 

 to obtain soundings in shoal to moderate depths. The red-light method utilizes a 



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