JRC JMA-5912-6, Instruction Manual

Page: 306 / 466

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.
6.1
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( h2 h1
+
)(nm)
h1: Height (m) of radar scanner above sea level
h2: Height (m) of a target above sea level
Figure 6.1 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.
6-1