SECT. 5] 



INTERNAL WAVES 



741 



Fig. 12. Diagram of rays in the sound medium, which has an internal wave on the thermo- 

 cline. 



Sound was emitted from a directional source through an angle of ± 8°. The 

 level dropped from 60 dB (an arbitrary reference level was used) at one foot 

 from the source along a horizontal ray (^ = 0) to one -tenth of full strength 

 along ^±8°. 



All acoustic ray paths passing through the layers were refracted, depending 

 upon their angle of approach and the velocity discontinuity of each interface. 

 For this problem the rays were traveling in a plane parallel with the direction 

 of propagation of the internal waves. Total reflection was assumed at the sea 



SOUND INTENSITY FIELD (dB) 



0. 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 



DISTANCE (FT) 

 I I >I5 r -1 10*15 1 



D5-»I0 E 



10»-5 r.'.'.M O* -7.5 



Fig. 13. Sound level in the medium with an internal wave on the thermocline. The dB 

 reference level is that corresponding to a sound level of 60 dB at 1 ft from the direc- 

 tional source (X = 0, Z—10) along the horizontal. The field is contoured at intervals 

 of 2.5 dB. 



