Clark and Yarnall 



Subsequent to the January 1965 test an opportunity was 

 found to establish a direct environmental correlation of the acoustic 

 signatures with wave height. The small scale "single reflection" ex- 

 periment of Figure 15 was set up near the site of the Fowey Rocks pro- 

 jector. The inverted fathometer was employed, and a USRL type J9 

 transducer was used as the signal source. A typical sample of the 

 data obtained is shown in Figure 15. In view of the periodicities 

 observed in the visual study of the January 1965 Bimini acoustic data, 

 little commentary is needed on the power spectral density (PSD) analy- 

 ses of this special test. It should be noted, perhaps, that surface 

 wave periods in the range of 3 to 4 seconds can be considered typical 

 for moderate seas in the Straits. 



In the light of previous studies conducted elsewhere, 15,16 

 these results from the Straits of Florida were not at all surprising. 

 This is particularly so in regard to the very competent fixed- system 

 experimental work reported by Scrimger. ■'■^ Scrimger's data also includ- 

 ed signal phase and amplitude and surface wave height. His experiments 

 were performed in significantly shallower water and with smaller wave 

 heights, but were not limited to a single frequency. Unfortunately 

 there has not been an opportunity to make a detailed comparison of the 

 two sets of data. 



Returning briefly to the theme of the acoustic data as a 

 synoptic measure of time varying processes in the environment, the 

 authors are of the opinion that the term " synoptic" should be applied 

 with caution to the surface wave signatures in the Straits of Florida 

 data. The ray configurations illustrated in Figure 7c are obtained 

 from computer calculations which attempted "realistic" approximations 

 of the bottom boundary and of actual sound speed profiles. A conclu- 

 sion of that study was that most surface reflections probably occur 

 at the extreme ends of the propagation path. 



It is possible that only the surface over the shallow water 

 slopes of the propagation path are being effectively "sampled" by the 

 acoustic energy. Comparative studies over ocean paths in which surf- 

 ace channel or RSR modes of propagation predominate would perhaps 

 provide interesting contrasts with the surface data now available. 



SHORT PERIOD INTERNAL WAVE SIGNATURES 



Interpretation of surface wave signatures in the acoustic 

 data has been facilitated by correlation with surface wave measure- 

 ments. No correlation of environmental measurement with acoustic 

 signatures exists for the short period internal waves. The validity 

 of the association of signatures with short period internal waves 

 depends upon two theoretical criteria: 



32Z 



