Interphase iScan V90, Руководство по эксплуатации

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Transducer
Sidelobes
Main Beam
False
Echoes
Main Beam
Sidelobe
“False” Bottom
Echoes Caused by
Sidelobe Returns.
Besides the bottom conditions, water conditions will also
affect the iScan V90’s performance. For example, surface
chop, temperature inversion layers (thermoclines) and
muddy water may degrade performance.
Noise and Sensitivity Adjustments
The
iScan V90 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 far forward
bottom readings and too much gain will cause an increase in
screen noise and a possible display of unwanted transducer
sidelobe readings.
Transducer Sidelobe Effect
The
iScan V90’s transducer, like all acoustic transducers,
does not form a perfect beam of acoustic energy. Some of
the acoustic energy is contained in an area called the
sidelobes. In conventional downlooking depthsounders, the
sidelobes create little problem except to distort the size of the
actual beam angle; however, in scanning sonars they can
create echoes that are not placed on the LCD screen in their
proper position (also known as false echoes).
As the
iScan V90 sends off its acoustic beam in a specific
direction, it assumes that any return echoes are within the
main beam. However, if the sidelobe energy (which is not
within the main beam) strikes a large object (i.e. the bottom)
and creates a strong return echo, the
iScan V90 has no way
of knowing that this “false” echo was not created by the
main beam and will go ahead and show it on the display as if
it was located within the main beam. The most typical
display of the sidelobe echoes appears as an arc at the same
distance as the bottom depth , and in the worst case, from the
bottom below to the surface ahead. After using the
iScan V90 in different situations, with different gain
settings, you should become proficient in identifying the
bottom echoes caused by the transducer’s sidelobes. To
minimize the sidelobe effect, the gain should be reduced.