Simrad ES80 Reference Manual page 434

Simrad ES80 Reference Manual
Minimum Depth
The bottom detector starts the search for the bottom echo at this depth. The
detector will fail in shallow water if you select a too large depth value, and the tail
of the transmitting pulse may cause problems if a too small value is set.
Note
If you set maximum depth to a value identical or smaller than the minimum value,
the bottom detection algorithm will be disabled. The ES80 will not detect the
bottom at all, and the displayed depth will be 0.00 m.
Bottom Backstep
This parameter allows you to manually modify where on the bottom pulse the
depth shall be detected. The setting does not have an effect on the ability to detect
and track the bottom.
A The peak of the bottom pulse
B Default bottom backstep level
C Approximate bottom backstep level for
flatfish detection
D Approximate bottom backstep level for
seagrass detection
The bottom pulse basically identifies the bottom
depth just prior to the peak of the pulse (A).
However, this may not be the true bottom. For example, if the bottom pulse is
generated by a rock bottom under a thick layer of mud, the actual depth is slightly
shallower. For this reason, the ES80 is by default set up to give you a depth reading
a few milliseconds before the peak of the pulse. This is done by setting the bottom
backstep level to a default value of -50 dB (B).
The actual bottom will never appear at the peak of the bottom pulse (A), it will
always be slightly before the peak. By changing the
you can detect the bottom earlier. This feature can for example be used when you
fish for flatfish, or when you are harvesting seagrass.
Example
If you fish for sole, flounder or similar species, you can use the
Backstep
bottom backstep value (make it more positive) so that the bottom is
detected slightly deeper than the correct depth. The ES80 will then
"push through" the fish better, and the flatfish will be shown as they
are located "above" the bottom.
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parameter to enhance the detection of the fish. Increase the
parameter
Bottom Backstep
Bottom
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