Ch. 20] SUPERSONIC SOUNDING EQUIPMENT 353 



nomically, on large projects or reservoirs, future soundings will be made 

 by supersonic equipment. 



Supersonic Sounding Equipment 



Although fathometers using the general principle of supersonic sound- 

 ing have been in use for more than 25 years, this type of equipment 

 was improved and developed during World War II so that it is now 

 the most practical and economical means of making soundings in reser- 

 voirs or other bodies of water. This equipment determines water 

 depths by utilizing supersonic-sound-pressure waves and precision tim- 

 ing. There are two principal units and essential accessories. One unit 

 is a projector, the function of which is to transmit sound-pressure 

 waves to the reservoir bottom and to receive the reflected waves. The 

 second unit is a recorder electrically connected with the projector 

 which, by electronic and mechanical means, gives a permanent and 

 continuous record on a calibrated chart of the depths of water through 

 which the sound waves are sent. A 12-volt storage battery powers the 

 equipment. Total power consumption approximates 120 watts. (See 

 Fig. 2.) 



With this equipment, rapid, automatic determination of depths of 

 water and observations of the configuration of the bottom of the reser- 

 voir are obtained. In operation, the power switch is turned on, send- 

 ing electrical impulses at a frequency in the supersonic range to the 

 transmitting projector, where each impulse is converted to a sound- 

 pressure wave. This wave is projected downward through the water 

 to the bed of the reservoir, whence it is reflected upward to the re- 

 ceiving projector. The reflected sound-pressure wave is converted in 

 the receiving projector to an electrical impulse which, in turn, records 

 on the chart. The wave is very accurately timed in units of depth for 

 the round trip. The elapsed time interval is converted into feet or 

 fathoms on the basis of the velocity of sound in water for direct re- 

 cording of depths of water on the chart. The chart speed is 1 inch per 

 minute. For the type of equipment being used in the Tennessee Valley, 

 depths of water are recorded in feet up to 200 feet and beyond that 

 depth in fathoms up to 200 by a change in scale of the equipment. 

 Soundings in feet are recorded at the rate of 200 per minute and in 

 fathoms at the rate of 33% per minute. Soundings are recorded on 

 rectilinear or curvilinear charts, depending on the design of the equip- 

 ment. Both types of charts have their advantages. 



On reservoir investigations, the echo-sounding equipment is operated 



