LONG-RANGE SOUND CHANNEL PROPAGATION 



217 



i 



1 RADIO SIGNAL 



2 SHALLOW HYDROPHONE 



3 DEEP HYDROPHONE 



-I_ 



2 3 4 



10 10 10 ID 



FREQUENCY 



INC 



i^^ 'fJ*/ _. „■»**« , ' 



END OF SOUND CHANNEL ARRIVALS 



A SHOT 34, RANGE 50 MILES 



2 S 4 

 10 10 10 10 

 FREQUENCY 



lac 



END OF SOUND CHANNEL ARRIVALS- 

 B SHOT 43, RANGE 300 MILES 



Figure 21. Typical records of explosive sound received at long ranges. Times marked along top of each oscillogram 

 are in seconds. Curves at left give relative amplitude response of each channel to the various frequencies. 



The first series was conducted just outside the Ba- 

 hama Islands and consisted in the recording of im- 

 pulses from shallow explosions on two hydrophones, 

 one at shallow depth and the other at 1,600 ft, at 

 various ranges all less than 30 miles. The second 

 series was made some time later in regions extending 

 northeastward and eastward from the same locality. 

 In addition to the shallow shots, explosions at 4,000 ft, 

 near the axis of the main sound channel, and a hydro- 

 phone near this depth as well as a shallow one were 

 used. The ranges for this series extended out to 900 

 miles. "^ Data pertaining to the conditions of these ex- 

 periments are given in Table 5. The velocity-depth 

 curve for the first series is the one shown previously 

 in Figure 17; that for the second series is very 

 similar, and the curves of Figure 18 can be applied 

 with little error to either series. 



Figure 21 shows some typical records obtained in 

 these experiments along with thumbnail sketches of 

 the frequency response characteristics of the various 

 recording channels used. The following paragraphs 

 point out a number of features of these records which 

 agree with the predictions of ray theory as outlined 

 in Section 9.3.1. 



Table 5. Experimental arrangements used in long- 

 range transmission studies by WHOI. 



■> More recent experiments which have not yet been re- 

 ported in full have yielded detectable signals at a range of 

 2,300 mUes. 



Identification of the paths by which the various 

 pulses arrive is usually difficult because of the large 

 number of arrivals and because the predicted time 

 for any arrival can be appreciably influenced by un- 

 certainties in the depths of som-ce and receiver and 

 by small variations of the velocity-depth curve along 

 the route. However, the general appearance of the 

 records is very much as one would expect from the 

 considerations given in Section 9.3.1. Thus, in 

 Figure 21B the arrivals at the deep hydrophone come 

 in groups of four while for the shallow hydrophone 

 the four pulses show up as two, each of which is pre- 

 sumably double but unresolved because of the short- 



