Kongsberg Simrad SN90 Reference Manual page 613

Only echoes detected and interpreted as single fish are shown. The echoes are
compensated for their physical position in the beam (beam compensation).
This means that fish in the outer region of the beam are adjusted to correct
size even though their echoes are weaker.
Target mix (40 log R)
This setting uses the same TVG compensation as Fish (40 log R), but
additional beam compensation is implemented. Echoes detected and
interpreted as single fish are adjusted to their correct size according to their
physical position in the beam.
User
This setting allows you to define your own TVG curve. To choose your own
TVG curve, use the dedicated function in the
Echogram Type
Use this function to select what kind of echogram you wish to see in the current
(active) view.
Surface
A Surface echogram is mainly used when you wish to look at the entire water
column starting from the sea surface and down to the sea bottom. Since this
echogram is referenced to the sea surface, the sea bottom contour will vary
with the actual depth. If you set up the
the sea bottom contour at the lower end of the echogram, you will have good
opportunity to study the echoes from the water column.
In the surface echogram, all calculations are made from the sea surface
and down to the detected sea bottom. Use this echogram type to obtain
correct calculation of the biomass. It will also provide valid data for the
Size Distribution information pane.
Bottom
A Bottom echogram is mainly used when you want to examine the echoes
from fish close to the sea bottom. Since this echogram is referenced to the
sea 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 sea bottom.
You can investigate the sea 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 ping rate is increased.
381294/E
Functions and dialog boxes
dialog box.
Echogram
and
Start Range Range
depths to place
611