Interpreting And Adjusting The Sounder Image; Target Indications - Raymarine DSM300 User Manual

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5.2 Interpreting and Adjusting the Sounder Image

The DSM300 uses sound waves to find fish and show bottom structure. The
transducer sends high-frequency sound waves into the water; these sound waves
strike fish, the bottom, or other objects in the water and return as echoes. The
DSM300 interprets these echoes to present an image of the fish and bottom.
The strength of echoes is indicated by different colors (or shades of gray in
monochrome displays). You can use this information to determine the size of fish
and the bottom structure. Other objects in the water, such as debris and air
bubbles, also return echoes; these echoes are generally weaker than the fish or
bottom echoes and produce background noise or clutter on the display.
The digital sounder provides controls to reduce the background noise and to
adjust the way in which echoes of different strengths are displayed. The color
displays also let you select the background color and remove the display colors for
weaker echoes.
The sounder provides a White Line feature which helps to distinguish between the
bottom and fish (or other objects such as weed) that are close to the bottom.

Target Indications

When the sounder detects a target echo such as a fish, it displays a representative
image on the LCD. The shape and size of this image is influenced by a combination
of factors:
Boat speed
The shape of the target changes along with your speed. Slower speeds return
flatter, more horizontal images. As your boat's speed increases, the image will
tend to thicken and arch slightly.
The depth of the target
The closer the target to the surface the larger the image on screen.
To display the depth of individual targets, switch on the TARGET DEPTH ID from
the menu, as described on page 44.
The size of the target
The larger the target, the larger the return on the fishfinder display. The size of a
fish target is however dependent upon the size of the fish's swim bladder rather
than its overall size. This swim bladder will vary in size between different breeds of
fish.
DSM300 Operation with PLUS Series Displays