c. Frequency variation (vibrating wire) 



The vibrating wire transducer is a device that can be used 

 to measure depth and currently is being tested at the Hydrographic 

 Office. The vibrating element is simply a very fine tungsten wire 

 which is stretched in a magnetic field. The wire vibrates at some 

 precise frequency which is determined by the length and tension of 

 the wire. Pressure changes, by varying the tension in the wire, 

 change the vibration frequency of the wire. Snodgrass ancTCawley 

 state an accuracy for this device of better than ±0.25 percent, as does 

 the manufacturer. A vibrating wire transducer was incorporated into 

 the Hydrographic Office Electronic BT, and this equipment was tested 

 in 1959 in the field. The results were sufficiently successful to warrant 

 the incorporation of this transducer into certain shallow- water field 

 equipment and the further investigation of it for use with deepwater 

 equipment. 



3. Sonar pinger system 



H. E. Edgerton recently (June I960) described the construction 

 and application of a sonar pinger system for use in determining, with 

 a precision of about one meter, the distance of equipment above the 

 ocean floor. Two types of systems have been used successfully: one 

 for depths to 6,500 feet and the other for depths to 37,500 feet. The 

 system has been particularly successful in positioning underwater 

 cameras at a given distance off the bottom. However, it also can be 

 applied to Nansen bottle casts, bottom coring operations, etc. 



A transducer, located with the subsurface equipment, emits short 

 bursts of high frequency energy (12 kilocycles) at one- second inter- 

 vals. The transmitted pulse travels directly to the surface and also 

 is reflected from the bottom. The converted time difference between 

 the direct signal and the reflected signal gives the distance from the 

 transducer to the bottom. Any sonar receiver or cathode-ray tube 

 display can be used to pick up and display the pulses. An echo sounding 

 recorder is preferred as it gives a graphic picture of the location of 

 the transducer with respect to the bottom and enables maintenance of 

 a constant distance off the bottom. 



The conversion of pulse travel time to distance involves the velocity 

 of sound in sea water . Edgertonuses 5,000 feet per second as an approx- 

 imate value. Use of such a value introduces some error into the use of 

 this device as a depth indicator. Nevertheless, the sonar pinger system 

 seems to show considerable merit for use with oceanographic equip- 

 ment. 



V-6 



