HERSEY: INTRODUCTION TO LOW-FREQUENCY PROPAGATION AND NOISE WORKSHOP 



we should examine how the resulting understanding of ocean acoustics 

 can be applied in the framework of the broad purposes stated above. 

 In 6.3, we determine as precisely as deemed necessary the significance 

 of ocean acoustics in supplying a particular fleet service, analysis 

 tool, or support for the development of a specific new sonar system. 

 Again, all of these are a proper concern in this workshop. 



In making our assessment of present understanding of low-frequency 

 acoustics, significant confusion may result from the unevenness of our 

 understanding. Acoustical theory has long been able to mod^l complex 

 processes for some simple configurations of the sound medium, and 

 the question has been raised repeatedly whether much, if anything, 

 remains to be done in basic acoustics. Nevertheless, the ocean, its 

 surface, and its floor are so complex that these models are of limited 

 practical use. The last 5 to 8 years have seen an intense effort in 

 the U. S., mainly in 6.2 and 6.3 programs to develop models that would 

 deal in practical and useful detail with the major complexities of 

 the ocean and predict transmitted sound levels and noise. We have 

 depended altogether on modern digital computing techniques and on 

 comparisons with measurements. These modern methods are only now 

 beginning to teach us when and where sweeping simplifications of the 

 shape of the boundaries and the acoustical properties of the ocean 

 are both useful and adequate. We shall be looking at some of these 

 results. How should these computational methods be developed in the 

 future? 



We have done surprisingly few strict comparisons of acoustic 

 measurements with model analysis based on simultaneously measured 

 acoustic data and oceanic properties. The necessary impact of the 

 few comparisons available has not had time to be fully felt and 

 digested. Even so, important lessons are emerging. Nevertheless, 

 we still don't now know how detailed a program of measurements is 

 required. I hope that the workshop can help us chart a good course 

 to answer the nagging question of: How much is enough? 



