NAVWEPS REPORT 7 6^0 



The data are continuously transmitted as frequency-modulated signals 

 over the supporting cable, and the three measured parameters can be 

 displayed and recorded for detailed examination. The recorded frequency- 

 modulated data can be readily assessed by machine data reduction 

 techniques. 



Velocity of Soimd . The velocity-of -sound meter is used to examine 

 the variations in sound velocity as a function of depth in the ocean, 

 and it provides data of greater accuracy than the bathythermograph. The 

 bathythermograph has been of unquestioned value in providing information 

 on the thermal structure of the ocean, in studying underwater sound trans- 

 mission, and in making sonar predictions. However, the bathythermograph 

 does not yield sound-velocity values directly nor does it provide imme- 

 diate data readout. 



The hydrographic method of sound-velocity determination is also an 

 indirect method requiring measurement in situ of temperature, pressure, 

 and salinity. It does not provide either continuous or immediate 

 readings of the velocity of sound. 



From 1950 to 195^ and under the Office of Naval Research sponsorship, 

 five experimental undervmter velocity-of- sound meters were developed by 

 Springer, Cook, the University of Michigan, and the National Bureau of 

 Standards. Two of these meters employed phase -measuring techniques, 

 two employed the pulse -feedback principle, and one was a re sonant -cavity 

 type. Between 195^ and 1956, all five meters were reviewed by the U. S. 

 Navy Underwater Sound Laboratory and the meters with the pulse-feedback 

 principle were considered to be the best for measuring the velocity of 

 sound in the ocean (Ref. 3)' 



In 1957 Greenspan and Tschiegg of the National Bureau of Standards 

 reported on a "sing-around" velocity measuring technique that seemed 

 most promising for use as a continuous reading instrument for all depths 

 in the ocean (Ref. l). Consequently, it was decided that this circuitry 

 should be incorporated in a NOTS field instrvunent that would also measure 

 pressure and temperature. 



Temperature . Most observations of sea-water temperature at depths 

 greater than 3OO meters have been made with reversing thermometers. 

 Reversing thermometers, first used in 187^, have been improved until 

 well-made instruments are now accurate to within 0.01°C. The Hydro- 

 graphic Office indicates that the accuracy of the reversing thermometers 

 in the field appears to be +0.02°C (Ref. k). 



The recently developed thermistor-controlled Wien-bridge oscillator 

 at NOTS has produced a temperature accuracy of 0.02°C, and it was 

 selected for use in the SVTP instrument (Ref. 2). 



