Simrad ES80 Reference Manual page 429

•
Bottom
A Bottom echogram is mainly used when you wish to examine the echoes from
fish close to the bottom. Since this echogram is referenced to the bottom, the
sea surface will vary with the actual depth, while the bottom is drawn flat. This
makes it easy to study the echoes from the bottom. You can investigate the
bottom conditions and hardness, and detect fish.
The echogram is only drawn for pings that have a successful bottom detection.
•
Pelagic
A Pelagic echogram is mainly used when you wish to look at the water column
starting from any distance below the sea surface down towards the bottom, but
without seeing the bottom contour. Pelagic echograms are useful when you
work in deeper waters. The reduced range and the fact that you do not need to
wait for the bottom echo means that the ES80's ping rate is increased.
In a Pelagic echogram the calculations disregard any bottom detection. All
calculations are based on the entire echogram shown in the view. If the bottom
echo is present in the echogram, the biomass calculation will be wrong.
•
Trawl
Trawl sensor systems (such as Simrad PI, PX and ITI) communicate headrope
depth, and/or the distance from the headrope to the footrope (trawl opening),
to the ES80 at regular intervals. This information is required for the trawl
echogram to be generated. The Trawl echogram covers the vertical opening of
the trawl with reference to the depth of the headrope. In addition to the trawl
opening, the echogram covers a certain range over and under the trawl opening.
The biomass calculations in a Trawl echogram are not restricted by the bottom
detection. This means that the bottom echo will be included in the calculations
if it appears within the chosen range.
The echogram is only drawn when trawl position information is available.
Bottom TVG
Use this option to select up a specific Time Variable Gain (TVG) compensation for
the bottom detection.
The ES80 allows you to use different TVG compensation for the echoes from the
water column than from the bottom. By making the bottom echoes individually
adjustable, you can fine tune the presentation from the bottom to investigate the
bottom type and conditions. The
close to the bottom.
If you set
Bottom TVG
detected bottom depth. The TVG selected for the echogram is then used for the
entire depth range.
406273/C
Bottom TVG
to None there will be no gain change in the TVG at the
Functions and dialog boxes
adjustment has no effect on fish
427