340 



SUMMARY 



studies are needed to fill in the gaps in our knowledge 

 of the reverberation levels to be expected under vari- 

 ous conditions. In general, measurements of volume 

 reverberation will cast the most light on the funda- 

 mental properties of the ocean. Experiments of the 

 following sort are indicated : 



1. Measurements of reverberation over a very 

 wide range of frequencies, from sonic frequencies up 

 to several hundred kilocycles. 



2. Measurements of the dependence of volume re- 

 verberation on transducer directivity, which would 

 help evaluate the importance of multiple scattering. 



3. Careful correlation of measured volume rever- 

 beration levels with simultaneous measurements of 

 temperature microstructure. 



4. Careful correlation of measured reverberation 

 levels with observed transmitted sound levels, espe- 

 cially with such features as sound penetration into 

 predicted shadow zones. 



5. Reverberation measurements with deep pro- 

 jectors to demonstrate any fundamental differences 

 between the upper and lower layers of the ocean. 



6. A thorough investigation of the deep scattering 

 layers, including the use of underwater photography. 



7. Measurements of reverberation in large fresh- 

 water lakes. 



8. More complete studies of the dependence of re- 



verberation on ping length, especially with very short 

 pings. 



9. Investigation of various probability and correla- 

 tion coefficients of the sort discussed in Chapter 16. 



10. Measurements of the dependence of surface 

 and bottom scattering coefficients on the grazing 

 angle of the incident sound. 



11. Correlation of measured surface reverberation 

 levels with simultaneous measurements of optical 

 transparency and of entrapped air or other ma- 

 terial. 



Theoretical investigations of various questions are 

 also required, so that the results of these experiments 

 may be correctly interpreted. Most of these theo- 

 retical investigations will be of importance in the 

 subject of transmission as well as reverberation. 

 Typical subjects for theoretical research would be the 

 reflection of sound from a rough surface, and scat- 

 tering of sound by thermal microstructure. 



A final subject of great importance, which requires 

 both theoretical and experimental research, is the 

 development of instrumental means for recording and 

 computing various time averages which are of interest 

 in reverberation studies. Such instrumental pro- 

 cedures would greatly reduce both the time and ex- 

 pense involved in the suggested experiments listed 

 above. 



