The below table and charts illustrate how frequency, water temperature, and salinity affect
absorption
Seawater Absorption Values: Salinity = 35ppt, pH=8
3
dB/km
Freshwater Absorption Values: Salinity = 0.5ppt, pH=7
dB/km
Table 12: Absorption Values for Seawater and Freshwater at 400 kHz and 200 kHz
3
Equation used for computation is from: Ainslie M.A., McColm J.G., “A simplified formula for viscous and
chemical absorption in sea water”, Journal of the Acoustic Society of America, 103(3), 1671-1672 as employed
on the NPL website, op cit.
Page 146 of 210
Version 5.0 Rev r002
Date 05-08-2014
Part No. 96000001