Simrad ES70 Operator's Manual page 118

Simrad ES70
On the echogram the white line will then "climb" up the slope. Make sure that you do
not increase the sensitivity too much. This will have an effect on the fish detection
on a flat bottom, and the biomass values will be wrong. Our experience show that an
approximately -75 dB bottom backstep value can be used safely.
By increasing the bottom backstep value (make it more positive) the bottom will be
detected later, and it will appear to be deeper.
Tip
Rule of thumb:
• Reduce the bottom backstep level (make it more negative) to detect the bottom earlier,
and thus increase bottom detection "sensitivity".
• Increase the bottom backstep level (make it more positive) to detect the bottom later,
and thus increase "penetration".
Figure 41 Bottom slopes
will cause the bottom line (E) to be distorted.
Example 14 Using the Bottom Backstep parameter for seagrass detection
If you use an Olex system, you can take advantage of the
parameter to detect seagrass. Decrease the bottom backstep value (make it
more negative) so that the bottom is detected at the top of an area of seagrass.
The Olex will then detect the real bottom, and the result is the height of
the seagrass.
→ How to adjust the bottom detection to find seagrass on page 92
116
Example 13 Bottom slopes
The edge of the beam (A)
hits the bottom first, and starts
to give an echo. The bottom
detector in the ES70 measures
the strongest echo, detects what
it thinks is the bottom, and
starts the white line.
The area above the bottom
detection (B) will be masked
off, and even though it may
contain fish these will not
be visible because the echo
from the bottom is stronger
than those from the fish. The
estimated depth (C) will be
shown.
(CD010217-002)
On the ES70 the phenomenon
Bottom Backstep
343539/B