widely used by fishermen and small boat owners, to much more sophisticated, 

 highly accurate instruments that permanently record depth data and have numer- 

 ous features to enhance flexibility and data quality. Fathometers are used in 

 borrow source exploration to provide accurate data on water depths along the 

 survey tracklines covered during the exploration program. For this purpose, 

 they should be recording- type , high-quality models with sufficient flexibility 

 to meet the anticipated requirements for bathymetric data of the exploration 

 area. 

 Principles of operation 



73. The basic principle of Fathometer operation is suggested by its 

 popular name of "echo sounder." It is common knowledge that if one shouts or 

 makes any loud noise in a hilly area, the sound will be repeated as an echo at 

 the point of origin after the elapse of a short period of time. The delay is 

 due to the fact that the sound must travel at a finite velocity from the 

 source to the object that reflects it and back again. The farther the reflec- 

 tor is from the source, the longer the time lapse. Because the velocity of 

 sound in various mediums such as rocks, sediments, or water is known or can be 

 accurately determined, it is possible to calculate the distance between the 

 sound source and reflector by the following formula: 



D = Y£ CD 



where 



D = distance to reflector 



V = velocity of sound in the medium 



t = two-way travel time 

 Fathometers make use of this principle by generating repetitive acoustic 

 pulses at the water surface and measuring the time necessary for each signal 

 to travel to the bottom and reflect to the surface. This measurement is con- 

 verted to an equivalent depth and recorded on a chart. 

 Available equipment 



74. The basic components of a Fathometer are a transducer that both 

 emits the acoustic pulses and receives the reflected signal, and a transceiver 

 unit that provides power and control to the transducer, processes the return 



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