Kongsberg Simrad SN90 Reference Manual page 644

Simrad SN90 Reference Manual
There are several types of reverberation.
Volume reverberation
The volume reverberation is caused by minute plankton and air-bubbles in the
water. This reverberation has often daily cycles in intensity.
Surface reverberation
The surface reverberation depends on the weather condition and the waves.
Bottom reverberation
The bottom reverberation depends on the roughness and physical properties of
the sea bottom.
Reverberation is often a limiting factor, especially if you are searching for smaller
targets. The echoes from the bottom will always depend on the sea bottom properties.
How uneven the seabed is will affect the echoes. What kind of bottom you have under
your vessel is also significant, as rock, mud or sand will provide different reverberation.
The bottom reverberation usually makes it difficult to investigate targets located close
to the seabed.
Your current tilt setting will also have an effect on the reverberation. The echoes from
the sea surface will vary with the current sea state and your current tilt setting.
The illustration demonstrates how the sea bottom and the sea surface return echoes
back to your sonar system.
In this situation you will be able to identify the upper school of fish, but the lower
A
school will be hidden in the shadow of the seabed rock formation.
In this situation you will see several weak echoes from the waves and from the rock
B
on the bottom, but you will still be able to identify the school of fish.
The reverberation is caused by the transmission pulse itself. It can only be reduced by
shortening the pulse duration or using a smaller beamwidth.
Related topics
Improving the recognition of fish and schools using receiver filters, page 118
Concept descriptions, page 625
Acoustic noise, page 636
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