Sd. Richards et al., THE EFFECT OF SUSPENDED PARTICULATE MATTER ON SOUND-ATTENUATION IN SEAWATER, The Journal of the Acoustical Society of America, 100(3), 1996, pp. 1447-1450
Many shallow-water acoustic applications (e.g., naval mine-hunting son
ars, acoustic Doppler current profilers) involve devices operating in
the frequency range 50-300 kHz over path lengths up to several hundred
meters. At these ranges and frequencies the thermoviscous absorption
of sound energy in the boundary layers of suspended particles leads to
a significant acoustic attenuation. Although the viscous absorption m
echanism is well known, little appears to have been done to quantify i
ts effects over the longer path lengths now of operational interest. A
dditionally, scattering effects, although dominant at much higher freq
uencies, contribute to the total acoustic energy loss. Preliminary cal
culations of the acoustic attenuation due to scattering and viscous ab
sorption by suspended particulates are presented here for particle con
centrations typically encountered and at sonar frequencies of interest
. This attenuation is compared with calculations of the attenuation du
e to seawater alone and found to be a significant contribution to the
total attenuation, possibly giving an additional attenuation of 3 dB o
ver a total path length of 100 m at 100 kHz for a particle concentrati
on of 0.2 kg m(-3). Concentrations of this order or even greater are c
ommon in coastal and estuarine waters. The effect of distributions of
particle sizes on the acoustic attenuation are also investigated. Plan
s for future work are briefly described. (C) 1996 Acoustical Society o
f America.