MEASUREMENT OF VISCOUS SOUND-ABSORPTION AT 50-150 KHZ IN A MODEL TURBID ENVIRONMENT

The visco-thermal absorption of sound by suspended particulate matter can be reliably measured using a reverberation technique. This absorpt ion may have an adverse effect on the performance of sonars operating at 50-300 kHz in coastal waters where suspensions are often present in significant concentrations. A series of experiments has been performe d to study the viscous absorption by suspensions in the frequency rang e of 50-150 kHz. In the test volumes employed, the effect is small. It is therefore measured by taking the difference in reverberation times of a volume of water with and without particles. This greatly reduces the effect on the measurement of the other sources of absorption. Eve n so, it is necessary to design the experiment to characterize and min imize acoustic losses which occur at the surfaces of the container, th e hydrophones, and their cables, and losses associated with bubbles an d turbulence. These effects are discussed and results for particulate absorption for suspensions of spherical glass beads are presented and compared to theoretical predictions. Measured absorption agrees well w ith that predicted by theory for concentrations above 0.5 kg/m(3) and up to 2.0 kg/m(3). [S0001-4966(98)01610-5]