44
Interpreting The Probe’s Forward
Display
The Interphase Probe 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 Probe
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 is
converted into a small electrical signal and processed for
display on the Probe’s LCD.
Since the Probe 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 Probe 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 sketch at right.
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.
Strong Return from
Up-sloping Bottom
Weak Return From Far-Forward
Strong Return from Wall Far-Forward
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