System description
5
857-160970 / Rev.H
Propagation losses due to absorption are much higher in sea
water than in fresh water. Absorption also increases with
frequency. At 38 kHz the absorption is 0.5 dB/km in fresh water
and 10 dB/km in sea water. At 200 kHz the absorption is 10
dB/km in fresh water and 50 dB/km in salt water. The echo
sounder must know which water type is present in order to
compensate for these losses correctly.
(The dB (decibel) unit has long traditions in underwater
acoustics and other fields in physics. It is a logarithmic measure
for the ratio between two quantities).
Related topics
→ Environment, page 89
→ Echogram, page 85
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