Clark and Yarnall 



We will speculate that these events are atmospheric in origin, but 

 hasten to add that no direct correlation with environmental parameters 

 are available at this time. Figure 27 presents a high-pass filtered 

 spectrum of the H43 data with a filter cut-off in the period range of 

 24 days. This may be compared with Figure 20, the same data with 

 cut-off at about 36 hours. 



A brief comment is in order concerning the major down trend 

 of the H43 phase, A net change of nearly 250 cycles was registered 

 from October 6 to January 30. A large scale temperature decrease, 

 seasonal or longer, is perhaps indicated for the waters of the Florida 

 Straits. As a practical matter, however, there is little point in 

 pursuing this line of thought in the absence of corroboration from 

 direct environmental measurements. It is quite clear that the data 

 from the 100 meter thermistor string is of very limited value in 

 interpreting the H43 hydrophone data. It is also clear that a need 

 exists for a similar installation in the deeper water of the Straits 

 which will serve to "calibrate" the H43 path in the same manner that 

 the 100 m thermistor string has helped to clarify the meaning of the 

 phase data at H3 . 



CONCLUSIONS AND RECOMMENDATIONS 



A spatially averaged, spectral measure of time varying 

 processes in the ocean may be obtained from a coherently detected 

 acoustic signal. The use of fixed source and receiver installations 

 and experimental facilities capable of long continuous operation are 

 required to take full advantage of the measurement technique. 



In the Straits of Florida studies, measures have been 

 obtained for events on the scale of surface waves at the high frequen- 

 cy end to slow changes in the medium which may be seasonal or longer. 

 The measure provided for the short period phenomena (surface waves and 

 short period internal waves), may be limited in space; but, on the 

 scale of events that are tidal or longer, involving processes which 

 are spatially coherent over the propagation path, a synoptic measure 

 is likely provided. Quantitative determinations of spatially averaged 

 properties of the medium (e.g., temperature and current components 

 parallel to the acoustic path) are crude but should improve with fur- 

 ther research. The most serious deficiency of the Straits of Florida 

 studies is the lack of fixed, continuous environmental measurements 

 in the central (Florida Current) regions of the Straits. Satisfactory 

 deep water measurements from one or more fixed instrument strings 

 would affect a substantial increase in our ability to "read" the 

 information provided by the acoustic signal. Such measurements are 

 a necessary "calibration" of the synoptic acoustic environmental 

 probe. 



The limited space scale of the Straits of Florida measure- 

 ments would perhaps place this experiment in the category of a pilot 

 study. It is of interest to speculate about the possibility of 



332 



