Interpreting The Display; Land Targets - Furuno 1751 Operator's Manual

3. APPLICATION
IntQrpreting the Display
Interpreting the Display
In the previous section some of the characteristics and limitations of radar were discussed.
Now its time to take a look at what you can expect to see on the radar screen. What shows
up on the screen isn't likely to match exactly what is seen on a navigation chart. A radar
cannot see through a mountain in the path between your boat and the harbor, nor can it see
a small boat directly behind a large ship, since both the mountain and the larger vessel
effectively shield the radar from the desired target.
To aid you in target identification, the echoes appearing on the display are quantized in eight
levels according to their intensity. The brightest intensity echoes are probably from Steel
ships, or piers, or other "good" targets. Poor targets, for example, wooden boats, appear in
the weakest intensities.
The ability to interpret a radar picture comes through practice and experience. Practice
should be done during clear weather in daytime, since you can compare the picture with what
you actually see around you. Go to an area you are familiar with and compare the way
coastlines, buoys and other targets appear on the screen and the way they are drawn on a
navigation chart. To observe the movement of an echo in relation to your position, try
running your boat at various speeds and headings.
Land targets
Landmasses are readily recognizable because of the generally steady brilliance of the
relatively large areas painted on the display. Knowledge of the ship's navigational position
will also tell you where land should be. On relative motion displays (this radar), landmasses
move in directions and at rates opposite and equal to the actual motion of your own ship.
Various factors such as distortion from beamwidth and pulselength make identification of
specific features difficult. However, the following may serve as an aid to identification.
1) High, steep, rocky and barren landmasses provide good reflecting surfaces.
2) Low, vegetation covered lands make poor radar targets.
3) Submerged objects do not produce echoes.
4) Mud flåts, marshes, sandspits, and smooth, clear beaches make poor targets because they
have almost no area that can reflect energy back to the radar.
5) Smooth water surfaces such as lagoons and inland lakes appear as blank areas on the
display—smooth water surfaces return no energy.
6) Although you might expect an object as large as a lighthouse to be a good radar target, in
actuality the return echo is weak since the conical shape difftises most of the radiated
energy.
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