Interpreting The Twinscope's Forward Vertical (Probe) Display - Interphase Twinscope Operation Manual

Strong Return from
Up-sloping Bottom
Weak Return From Far-Forward
Strong Return from Wall Far-Forward
Interpreting The Twinscope's
Forward Vertical (Probe) Display
The Interphase 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
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) to
receive 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 and
processed for display on the Twinscope's LCD.
Since the Twinscope knows the direction in which it sent
the transmit pulse and the time it took to receive the
return echo, it can determine the location of the object or
bottom that created the return echo. As the Twinscope
sequentially steps the acoustic beam from the bottom to
the area ahead of the vessel, 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 diagram at the 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 diagram at left indicates.
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