INTRODUCTION 



In many cases when underwater sound measurements 

 have been needed, it has been the practice to assemble 

 available hydrophones, cables, amplifiers, recorders, volt- 

 meters, etc. , making such provisions for calibration as 

 permitted by the available equipment. This practice was 

 often time-consuming and sometimes resulted in a less 

 than effective system. 



The need for an underwater sound measuring system 

 has long been recognized and several such systems have 

 been designed and built, for example, the "Suitcase" 

 system 1 and the Noise Measuring Set AN/PQM-1A. 2 Such 

 systems have proved to be very useful tools, but for some 

 applications the size, weight, and power requirements have 

 been a problem, and the procedures for accomplishing com- 

 prehensive calibrations have been tedious and time- 

 consuming. 



Included in the objectives for the system described 

 herein was the minimization of size, weight, and power 

 requirements. Other special objectives were: 



1. Frequency range from 10 Hz to 10 kHz. 



2. Minimum self-noise and maximum sensitivity for 

 the measurement of low background noise levels. 



3. Flexibility: capability for use from a rowboat on 

 the one hand, or from a relatively large ocean-going 

 research ship on the other. 



4. "Off-the-shelf" components: catalog items or items 

 of standard manufacture. 



5. Simplicity in both operation and calibration. 



Since system self-noise of an underwater measuring 

 system involves not only the equipment used but also the 

 way in which it is used, the definition of the system must 

 necessarily include a discussion of the techniques and proce- 

 dures of its use. 



Superscript numbers identify references listed at end of report. 



