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81238_1.book Page 143 Thursday, September 16, 2004 2:49 PM
Appendix B: Radar
Standard range scales
Standard ranges that can be selected are shown in the following table:
Maximum range
*The maximum range depends on scanner type.
The number of range rings shown in the table is the number to the selected range.
Additional range rings are displayed to the edge of the radar picture, at the
standard ring interval for the current range, and are visible when the center is
offset.
Interpreting the radar picture
Navigational echoes may be large, small bright or faint, depending not only on
the size of the object but also on its orientation and surface. Different objects
reflect the radar signals in different ways. For example, vertical objects such as
cliffs reflect signals better than sloping ones such as sandbanks.
High coastlines and mountainous coastal regions can be observed at the longest
radar range. However, the first sight of land may be a mountain several miles
inland from the coastline. The actual coastline may not appear on the radar until
the boat is close to the line of sight distance.
The radar indication may not be similar to your visual observation; a nearby small
object may appear to be the same size as a distant large object on the radar.
Number of range
(nm)
rings (nm)
0.125
2
0.25
2
0.5
4
0.75
3
1.5
6
3
6
6
6
12
6
24*
6
48*
6
72*
6
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Range ring interval
(nm)
0.0625
0.125
0.125
0.25
0.25
0.5
1
2
4
8
12
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