Upon casual examination, it appears possible that the only 

 modification required to the ordinary XBT would be addition of one semi- 

 conductor and one extra electrode, in addition to the one already used on 

 the XBT, since no accurate measurement is being attempted. Since there 

 would be no requirement for batteries or extra cable conductors, the hydro- 

 dynamics and operational requirements would not be altered. 



Availability of such an XCT would allow more judicious use of the 

 XSV suggested in the previous section and would considerable raise the 

 permissable cost of the XSV since it would then only be used when its 

 particular capabilities were necessary. Thus it appears possible that a 

 family of expendable devices may be found to be a more practical solution 

 than any one type of expendable device, regardless of how inexpensive it may 

 be possible to make it. 



The XBT can be modified (Reference 31) to measure the sound 

 velocity profile (SVP) in the ocean directly by installing a hydrophone tuned 

 to the corner frequency of the ships pinger in the f reef ailing probe unit. 

 The p.r.f. of the pinger would be varied on a sing around basis by signals 

 from the XBT. The direct measurement of SVP circumvents the necessity of 

 approximating salinity effects in using the temperature profile for range 

 prediction and would be useful for tactical ASW purposes. The modified 

 XBT unit could simultaniously provide temperature profile data for synoptic 

 prediction purposes. A preliminary error analysis indicated that a sound 

 velocity profile could be produced with a precision which is roughly com- 

 parable with the ±0.15°C temperature capability of the XBT. 



This XSV would be the only mobile velocimeter system to measure 

 true group velocity a low frequencies, because its long acoustical path 



49 



Arthur 2D.lLittlc.Knr. 



