Kongsberg Flexview, Reference Manual

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You can change the physical size of the sonar view by clicking on the left view border,
then dragging it to create a smaller or larger window. You can also make the sonar
view full screen by clicking
Display
→
Full Screen
or by clicking the
Show Full Screen
button in the tool bar.
Interpreting the sonar view
The sonar view is a map of the echo returns over the scanned area.
A sequence of colours is used to show the relative strengths of the echo returns. Several
colour scale options are available. Most of them use darker colours to indicate weak
returns, and brighter colours to indicate stronger returns.
Bright spots in the image indicate strong sonar targets. Generally, bright spots indicate
a hard, highly reflective surface. Dark spots in the image indicate either areas of low
reflectivity (soft areas), or possibly an acoustic shadow zone behind a target.
Most targets will block the transmission of sound — either by reflecting it, or absorbing
it. This will leave a shadowed area behind the target that is not ensonified and therefore
will not generate any echoes. This is very similar to the shadow formed when an object is
illuminated with a single light source. The shadow behind a target can often yield more
information about the target than the reflections from the target itself. The shadow will
often reveal the shape of the target, but you must remember that the shape will usually be
distorted according to the position of the Sonar Head relative to the target and the bottom,
and according to the slope of the bottom. It is often possible to estimate the height of a
bottom target based on the length of the shadow and the known height of the Sonar Head.
Noise and interference
Acoustic noise and bubble interference can affect the quality of the sonar view image.
It is usually easy to recognize interference from other acoustic sources such as echo
sounders, pingers, and other sonars. These sources all produce pulses at regularly timed
intervals and will therefore tend to create a regular or symmetrical pattern of blips on the
screen. Mechanical noise sources such as propellers, hydraulic pumps, and thrusters, are
usually more directional and tend to show up only when the sonar is pointed directly
at them.
In addition, sonar signals are easily blocked by air or gas bubbles in the water or on the
transducer face. As an example, the aeration present in the wake of a vessel will often
last for ten to twenty minutes and effectively mask out most sonar returns on the far
side. The aeration partially blocks the outgoing pulses as well as any returns. Another
source of gas bubbles can be found when a sea bottom containing decomposing organic
matter is disturbed by dredging or ploughing.
Flexview Reference Manual