Similar remarks might be expected to apply to the case of velocity 

 changes caused by internal waves. There has been considerable interest 

 in this subject(e.g. Reference 13). 



The space-time aspects can only be separated by a stationary 

 experiment holding velocimeter arrays at various fixed depths, an expensive 

 experiment. 



2. Interfaces 



Anomalous effects may occur at both the sea water-sea bottom 

 interface, which depends on bottom type; and at the water-air interface, 

 which depends on sea state. 



Sound reflected at anything beyond normal incidence is 

 affected in both cases. 



a. Bottom Interface Sometimes an increase in temperature of 

 deep water close to the ocean floor has been observed. This is attributed 



to the geothermal flux through the floor, a heat flux which amounts to some 



— ft 9 



1 x 10 cals per cm per second for the Atlantic (e.g. Reference 14). 



The depths concerned are approximately 4000 meters (see e.g., Gerard et al. 



Reference 15) . Such an increase in temperature would cause an increase in 



sound velocity. Descents with a deep submersible should indicate any such 



effect. 



Any small changes in velocity at the lower interface would only 



affect grazing angle of the sound travelling in a deep channel. Although 



this would not be a tactical consideration to surface ship sonars, present 



instruments usually have sufficient depth capability to investigate this 



effect where it occurs. 



b. Air-water Interface The behavior of the upper interface is 

 tactically more interesting because sound transmission in the duct can 



15 



3rtliur ZD.IUttfclJnr. 



