Distance Forward; Noise And Sensitivity Adjustments; Transducer Sidelobe Effect - Interphase Proble Operation Manual

Distance Forward

Under typical conditions, the Probe 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.
Besides the bottom conditions, water conditions will also
affect the Probe's performance. For example, surface chop,
temperature inversion layers (thermoclines) and muddy water
may degrade performance.

Noise and Sensitivity Adjustments

The Probe features an AUTO sensitivity feature where it
continuously adjusts the sensitivity to achieve the optimum
picture quality. The sensitivity can also be adjusted manually
to allow for a reduction in sensitivity to minimize the effect of
screen noise, or to increase the sensitivity to show weaker
targets.
In the forward scanning modes, the sensitivity setting is
especially important as too little sensitivity will cause a loss
of far forward bottom readings and too much sensitivity will
cause an increase in screen noise and a possible display of
unwanted transducer sidelobe readings.

Transducer Sidelobe Effect

The Probe'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 Probe 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 Probe 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 Probe in different
situations, with different gain settings, you should become
proficient in identifying the bottom echoes caused by the
transducer's sidelobes.
Display Depicting Forward Range
Approximately 5 X Current Depth
Display Depicting Forward
Range Approximately 6X
Depth
Transducer
False
Echoes
45
Sidelobes
Main Beam
Sidelobe
Main Beam