Simrad 38-9 - REV B Installation Manual download pdf (Page 14)

System description

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).

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Simrad 38-9 - REV B Installation Manual Page 14