Interpreting The Horizontal Display - Interphase Color Twinscope Operation Manual

100 ft Forward Range, Water Depth of 14.7 Ft
Bait
Bait Ball
Plane of Forward Scan is Angled 10 Degrees
Downward From Surface. Forward beam will reach
bottom at approx. 5 times depth
Interpreting The Forward Horizontal
Display
In the Horizontal display, the Color Twinscope scans from
left to right across the boats bow. The forward scanning
elements in the transducer are positioned so that the plane of
the horizontal scan is angled downward approximately 10
degrees from the water's surface (see sketch at left). This
downward angle is designed to help reduce the effects of
surface noise clutter when the water is choppy and to allow
easier mounting of the transducer to the transom of smaller
boats.
As the acoustic sound beam is projected away from the boat,
the cross-sectional diameter of the beam increases. At a
range of approximately 5 to 6 times the depth of the water
the sound beam will begin intersecting the bottom and some
of the sound energy that intersects the bottom will be
reflected back and will appear on the dislay as bottom echos.
It is important to understand that when the Color
Twinscope is in the Horizontal display mode, in shallow
water - it will typically show the bottom on the forward
display. This display information can be used to help
understand the structure of the bottom ahead of the boat, but
the bottom echos can also mask or be confused as fish
targets.
Bottom
The top picture and resulting screen display shows a boat in
Echos
14.7 feet of water. The Color Twinscope's forward range is
set to 100 Ft. Notice that the bottom is just starting to show
at about 75 forward.. A school of fish or bait is shown about
50 feet to the right and forward of the ship's bow.
On the following page, two bottom situations are shown
along with the resulting Color Twinscope Display.
Noise and Sensitivity Adjustments
The Color Twinscope features an AUTO gain feature
where it continuously adjusts the gain to achieve the
optimum picture quality. The gain can also be adjusted
manually to allow for a reduction in gain to minimize the
effect of screen noise, or to increase the gain to show weaker
targets.
In the forward scanning modes, the gain setting is especially
important as too little gain will cause a loss of target
detection and too much gain will cause an increase in screen
noise. In the AUTO mode, the Color Twinscope increases
the forward gain until there is a certain density of targets on
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