30 



40 



50 60 70 



TEMPERATURE IN DEGREES F 



Figure 2. Typical temperature-depth curve. 



80 



90 



tening at long ranges the ocean is rarely if ever deep. 

 Supersonic listening gear, on the other hand, is 

 usually sharply directional in the vertical plane and 

 will discriminate against bottom-reflected sound from 

 ships in the same way that it will discriminate against 

 bottom-reflected echoes. Thus water which is deep 



for supersonic echo ranging will also be deep for 

 supersonic listening, even though supersonic listening 

 ranges may exceed sonic ranges. 



Evidently, at supersonic frequencies most of the 

 ocean is effectively deep for practical purposes. Even 

 at low sonic frequencies, transmission in water deeper 



