instruments can be high enough to cover all these requirements. Repre- 

 sentative devices, based on the "sing around" circuit, are sold for $1700 

 to $3000, to which one must add about $2000 for readout electronics or 

 about $5000 for printout electronics, in addition to a cable and winch. 



The third group, the expendable velocimeters, Table III-2, (Ref- 

 erence 29, 30, 31) are intended mainly for taking the velocity profile in 

 tactical situations. The instrument must have fine resolution and fast 

 response, while absolute accuracy is of secondary importance. 



As Tables III-l and III-2 show, several instruments for oceano- 

 graphic work are available commercially and at least two manufacturers have 

 designed and demonstrated expendable velocimeters for naval tactical 

 applications (Reference 29, 30), and one system designed along the lines of, 

 and of little more complexity than, the present expendable bathythermograph 

 has been proposed. (Reference 31). 



We do not intend to judge in this report the performance and 

 quality of instruments without having actually performed tests ourselves. 

 We do, however, quote specifications and other information on design that 

 is available from the manufacturers so that we may discuss this material 

 critically. The US Naval Oceanographic Instrumentation Center has a test 

 and evaluation program for velocimeters and the results, issued as "fact- 

 sheets" (Reference 32), were also used in the preparation of this report. 

 In addition, users of velocimeters were interviewed and the large body of 

 literature on the measurement of the speed of sound was studied. A number 

 of basic engineering problems emerged, all apparently recognized by the 

 manufacturers, and in addition we heard opinions about the performance of 

 specific instruments. The section on the comparison of instruments and 



27 



Arthur 21.1Little.3lnr. 



