About Tilt; Noise And Reverberation - Simrad SX90 - REFERENCE MANUAL REV D Reference Manual

Figure 36 Tilt

Noise and reverberation

307670/D

About tilt

The sonar beam can be tilted vertically in steps of 1 degree, and
the chosen tilt is shown on the sonar picture. At 0 degrees tilt
you will transmit the sonar beam in parallel with the sea surface,
while 90 degrees tilt will direct it straight down.
The challenge will always be to find a tilt that prevents the fish
echoes to be buried in reverberation and bottom echoes.
If you use a steep tilt (A) the fish will easily be disguised by
the bottom echoes, but a strong RCG setting will help. As the
distance from the bottom to the fish increases, the fish will
be easier to see when the RCG removes the bottom echoes.
However, this assumes that the fish echoes are considerably
stronger than the bottom echoes.
If you use a very small tilt (C) you will not be bothered by bottom
echoes. If the sea surface is gusty, you will however easily see
echoes from the waves. These echoes will normally be rather
weak, and will hardly move in relation to your vessel.
By means of a medium tilt angle (B) you will most likely be able
to pick up scattered fish or schools if these are located at some
distance above the bottom. The upper school in the illustration
will appear on the sonar picture before the bottom echo, while the
lower school will easily be disguised by the bottom echoes. Once
again you can activate the RCG function to improve the reading.
Every time you use the sonar the quality of your search
operations will depend on numerous error sources caused by the
natural environment and physical properties of your vessel. We
distinguish between the two terms noise and reverberation.
• Noise is generated by the vessel: engine, propellers, winches,
refrigerating plants etc.
• Reverberation is caused by natural conditions in the sea:
temperature, salinity, sea state and bottom conditions.
Basic theory
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