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Chapter 3
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 will be explained below.
3.1 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(√h1 + √h2)(nm)
h1: Height (m) of radar scanner above sea level
h2: Height (m) of a target above sea level
Fig. 3.1-1 is 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.
Fig. 3.1-1
Chapter 3 TRUE AND FALSE ECHOES ON DISPLAY
3.1 RADAR WAVE WITH THE HORIZON
3
3-1
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