JRC JMR-7230-S - Section 7 True and False Echoes on Display

7-1 Section 7 True and False Echoes on Display
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付録
Section 7 True and False Echoes on
Display
The radar operator has a role of interpreting the radar displays to provide his best aid in maneuvering
the ship.
For this purpose, the operator has to observe the radar displays after fully understanding the
advantages and disadvantages that the radar has.
For better interpretation of radar display, it is important to gain more experiences by operating the radar
equipment in fair weathers and comparing the target ships watched with the naked eyes and their
echoes on the radar display.
The radar is mainly used to monitor the courses of own ship and other ships in open seas, to check
buoys and other nautical marks when entering a port, to measure own ship’s position in the coastal
waters relative to the bearings and ranges of the shore or islands using a chart, and to monitor the
position and movement of a heavy rain if it appears on the radar display.
Various types of radar display are explained below.
7.1 Radar Wave with the Horizon
Radar beam radiation has the nature of propagating nearly along the curved surface of the earth. The
propagation varies with the property of the air layer through which the radar beam propagates. In the
normal propagation, the distance (D) of the radar wave to the horizon is approximately 10% longer
than the distance to the optical horizon. The distance (D) is given by the following formula:
D = 2.23
(
NM)
h
1
: Height (m) of radar antenna above sea level
h
2
: Height (m) of a target above sea level
The following figure illustrates a diagram for determining the maximum detection range of a target that
is limited by the curve of the earth surface in the normal propagation.
Radar Wave with the Horizon