Furuno FR-10, Operator'S Manual

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3. HOW TO INTERPRET THE RADAR DISPLAY
3-3
3.1.3 Bearing accuracy
One of the most important features of the radar is how accurately the bearing of a tar-
get can be measured. The accuracy of bearing measurement depends on the narrow-
ness of the radar beam. The bearing is taken relative to the heading of the ship.
Correct adjustment of the heading line at installation is important to get accurate bear-
ings. To minimize the error when you measure the bearing of a target, put the target
echo at the extreme position on the screen by selecting a suitable range.
3.1.4 Range measurement
Measurement of the range to a target is important function of the radar. There are
three methods of measuring range: the fixed range rings, the Variable Range Marker
(VRM), and the cursor (if set to measure range and bearing). The fixed range rings
appear on the screen with a given interval and provide a rough estimate of the range
to a target. The diameter of VRM is increased or decreased so that the marker touches
the inner edge of the target. The VRM is a more accurate range measurement than
the fixed range rings.
3.2 False Echoes
The echo signals can appear on the screen at positions where there is no target or
disappear when there are targets. These false echoes are shown below.
3.2.1 Multiple echoes
Multiple echoes occur when a transmitted pulse returns from a solid object like a large
ship, bridge, or breakwater. A second, a third or more echoes can be seen on the dis-
play at double, triple or other multiples of the actual range of the target as shown be-
low. You can reduce and remove the multiple reflection echoes with the sea clutter
function.
Your ship
Target
True
echo
Multiple
echoes