ourselves to one kind of concept. 



The picture that emerges for our current sonar 

 systems [Fig. I7] is the importance of the sound velocity 

 structure (including microstructure) , the sea surface, 

 and the deep scattering layer. Next in importance — and 

 in first place if you are a shallow-water person — is 

 the sea bottom. For future systems LFig. I8] the sea 

 surface becomes prominent, with sound velocity structure 

 and the DSL still ranking. Once again the sea bottom 

 assumes a greater role in shallow water. 



These results are not surprising, but they are not 

 obvious either. One tends to think of the sea surface 

 as something rather awkward and distasteful, but the sum 

 of these two pictures (present and future) reveals that 

 an increased knowledge of the surface characteristics 

 should be one of our major research projects. 



In the context of the importance of sound velocity 

 structure, it is felt that a major problem aside from 

 the microstructure is the spatial variability : what are 

 the space scales over which an on-the-spot profile can 

 be considered representative? During MILOC 68 we took 

 many temperature-depth-salinity"- profiles with our quick- 

 response electronic profiler and were overwhelmed with 

 the time and space variations observed. 



The medium we are studying and the reasons for doing 

 it are complex. MILOC surveys and the program of the 

 SACLANTCEN Oceanography Group are an attempt to match 

 priorities to projects and thereby more effectively 

 study the environment. 



Parenthetically, it is interesting to explain why 

 we refer to a "TDS" system instead of the more 

 common "STD" terminology: for the non-English 

 speaking tongue, TDS is easier to say. In fact, 

 it is easier to say for the English-speaking person 

 also, once you get started on it. 



70 



