Simrad ES70 Operator's Manual page 112

Simrad ES70
You can adjust the TVG setting using the
on the menu.
Active
Because the strength of the echoes will become weaker with increasing depth, the echo
sounder will automatically amplify the deepest echoes more than the shallower echoes.
In fact, the gain will increase proportional to how long the echo sounder "waits" for the
echoes. When you choose the TVG setting you can either switch it off (which we do
NOT recommended), or you can choose settings
The various settings control the gain algorithms, how much gain to be applied when
the depth increases. When you choose the
the depth more rapidly than if you choose the
individual fishes emit smaller echoes than a school, and this makes them more difficult to
detect. In the equation the character R means "Range".
The illustration shows how
the gain close to the bottom
(B) is larger than just below
the transducer (A). The echoes
from the fish close to the
bottom will then be shown with
the same strength (colour) as
echoes from pelagic fish.
The left vessel uses the
setting. Due to the increasing
R
beam width (C), single fishes
are shown larger and larger with
increasing depth, even though
they may be of identical size.
The right vessel uses the
setting. The size of the fish
R
will still appear to grow larger
as the range increases, but the echo is compensated differently to offer a more uniform
echo strength (colour in the echogram).
When you are looking for schools these will fill the entire beam, just as the bottom
normally does. A lot of gain is then not necessary. The
acceptable echo strength.
110
Echogram
40 log R
Figure 37 TVG principle
20 log
40 log
(CD010217-004)
or functions. Both are located
TVG
or
20 log R 40 log R
setting, the gain will increase with
setting. This is simply because
20 log R
20 log R
A
setting will provide an
20 log R
.
40 log R
A
343539/B