Interpreting The Vertical Display; Distance Forward - Interphase Color Twinscope Operation Manual

Strong Return from
Up-sloping Bottom
Weak Return From Far-Forward
Strong Return from Wall Far-Forward
Interpreting The Forward Vertical
Display
The Interphase Color Twinscope provides a display which
shows acoustic echo returns from the underwater area beneath
and ahead of the vessel. The Phased Array Transducer steers
an acoustic beam over an arc which can be adjusted from
approximately 12 to 90 degrees. As the Color Twinscope
steers the beam to different positions, it transmits a pulse of
energy and then waits a defined period of time (depending on
the range selected) and listens for any return echoes. As the
energy from this acoustic beam strikes underwater objects or
the bottom, a small portion of the energy is reflected as an
echo back to the transducer. When the echo is received at the
transducer, it's converted into a small electrical signal,
processed and displayed on the Color Twinscope's LCD.
The unit knows the direction in which it sent the transmit
pulse and the time it took to receive the return echo, so it can
determine the location of the object or bottom that created the
return echo. As the Color Twinscope sequentially steps the
acoustic beam from directly forward to the bottom, the LCD
display shows a continuously updated display of the return
echoes in their approximate position in relation to the vessel.
Because the LCD display is only showing the acoustic echoes
that are returned to the transducer, it can not show forward
bottom conditions that are hidden from its field of view or are
hidden due to obstructions in the acoustic beam's path
through the water. In addition, smooth bottom conditions far
forward of the vessel are difficult to see as very little of the
acoustic energy is reflected back as an echo. See the sketch at
left.
Bottoms that are rough and rocky or are sloping upwards will
reflect more acoustic energy back to the transducer and will
show up better far-forward of the vessel than bottoms that are
very smooth or slope downward. However, even though the
bottom may be smooth and does not show up far forward,
large obstructions (sea wall, large rocks, underwater shelves,
etc.) will typically send back strong echoes that can be seen
far forward, as the sketch at left indicates.

Distance Forward

Under typical conditions, the Color Twinscope will show
level or shallowing bottom contours for a distance forward of
between 4X to 6X the depth below the transducer.
Obstructions in the water, such as walls, mud banks, etc. may
be seen at much greater distances, subject to the depth below
the transducer and the 1,200 ft. maximum forward range.
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