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An uneven bottom which is covered with rocks or coral produces a complex display; the
bottom image is irregular, with long tails pointing upward. A wreck produces a similar
image.
Notice that the lower layer of the image is shown as a lighter gray, indicating a weaker
echo. This could mean that the upper layer is soft; some sound waves may get through this
layer and be reflected by a more solid layer below.
It is also possible that the sound waves are making two complete trips - hitting the bottom,
bouncing off the boat, the reflecting off the bottom again. This can happen if the water is
shallow, the bottom is hard, or gain is set high.
Displaying targets
When a target is detected, it is displayed on the sonar screen as a mark. The size and shape
of this mark is influenced by a combination of factors:
Boat speed
The shape of a target changes along with the boat speed. Slower speeds return flatter,
more horizontal marks. As your boat's speed increases, the target will tend to thicken and
arch slightly; until at fast speeds the mark resembles a double vertical line.
Target depth
The closer the target to the surface, the larger the mark on the screen. Individual target
depths can be displayed using the Target Depth ID function.
Target size
The larger the target, the larger the return on the sonar display. However, the size of a fish
target is dependent upon the size of the fish's swim bladder rather than it's overall size.
Swim bladder size varies from fish to fish.
Transducer frequency
The same target will appear differently when the transducer frequency is changed. The
lower the frequency, the broader the mark.
Factors that can impair an image
Although weaker than bottom or other echoes, your sonar picture may be impaired by
echoes received from floating or submerged debris, air bubbles or even your boats
movement. This is known as 'background noise 'or 'clutter' and is controlled by the gain
Ray Tech RNS V5.0 - User's Manual
D7059_1
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