Interphase iScan V90, Руководство по эксплуатации

Страница: 29 / 40

29
Interpreting The Forward Vertical
Display
The Interphase
iScan V90 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 iScan V90 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 iScan V90’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
iScan V90 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 iScan V90 will show level or
shallowing bottom contours for a distance forward of between
3X to 5X the depth below the transducer. Obstructions in the
water, such as walls, mud banks, etc. may be seen at greater
distances, subject to the depth below the transducer and the
1,200 ft. maximum forward range.
Strong Return from
Up-sloping Bottom
Weak Return From Far-Forward
Strong Return from Wall Far-Forward