EQUIPMENT AT MOUNTAIN LAKES 



115 



Figure 49. Application of high-frequency s\stem in testing scale model submarine in outdoor test area. 



urements of the reflection coefficient of such models 

 will give a value for the reflection coefficient of the 

 actual target. As the dimensions of the target and 

 the wave length of the sound in actual operations are 

 both reduced in the same ratio, all the reflection and 

 diffraction of sound from the scale model and from 

 the actual craft will occur in exactly the same 

 manner. 



Figure 49 shows a scale model of a submarine with 

 all linear dimensions reduced 60 to 1. Measurements 

 of the reflection coefficient carried out at 1565 kc 

 give the results which would be obtained for similar 

 measurements on the actual object at 26 kc and dis- 

 tances 60 times those used for the model. Sound re- 

 flected from the model is measured by an adjacent 

 hydrophone shielded from the direct radiation of the 

 projector. As the model is placed at several distances 

 from the projector and rotated around various axes 



of symmetry, measurements of the reflection coeffi- 

 cient are obtained as functions of the range and the 

 aspect of the model relative to the projector. 



6.2.4 



Low-Frequency Pressure System 



The low-frequency pressure system at the Moun- 

 tain Lakes laboratory covers 2 to 100 c and was 

 evolved as a result of the increasing need for an ac- 

 curate method of hydrophone calibration at these 

 frequencies under controlled conditions of tempera- 

 ture and pressure. The system was designed and con- 

 structed by the Bell Telephone Laboratories, Inc., 

 under NDRC contract. 40 



Uses and Limitations 



The testing technique with this apparatus is inde- 

 pendent of auxiliary hydrophone standards. The 



