THE PROBLEM 



Develop equipment for measuring the sound attenuation 

 at low frequencies in small samples of sea water. The 

 attending disturbance of the sample from its natural state 

 should be kept as low as possible. 



Correlate the results with other oceanographic variables 

 and explain the correlations obtained. 



RESULTS 



1. Equipment which utilizes cavity resonators with acous- 

 tically soft side walls was developed. The effects of wall 

 contamination on the measurements are therefore kept to 

 a minimum. The attenuation can be measured at discrete 

 frequencies between 5 and 8 kc/s, provided it falls in the 

 range from 10 to 2 00 db/kyd. 



2. Natural sea water with suspended particulate matter 

 and high oxygen content showed attenuations in the whole 

 range the equipment was capable of measuring (10-2 00 

 db/kyd). Sea water free of particulate matter never 

 showed any measurable attenuation. The attenuation of 

 clean sea water is about 0. 5 db/kyd at 5000 c/s, and this 

 is below the lower limit set by the equipment. It is 

 suggested that the excess attenuation may be explained by 

 the presence of a large number of very fine bubbles or 

 bubble nuclei. 



RECOMMENDATIONS 



1. Include an investigation of small bubbles and nuclei in 

 future work. Give special attention to plankton, since air 

 spaces inside a living cell will have an especially marked 

 effect due to the surrounding organic matter. Use cavity 



MBL/WHOI 



D 0301 DOMOSbO 1 



