Radar Line-Of-Sight Range - JRC JMA-7710-6 Instruction Manual

6.1
The role of the radar operator is to analyze pictures on the screen and to help maneuvering the ship as much
as possible.
For the purposes, the operator have to fully understand the merits and demerits of the radar before observing
the screen.
To analyze pictures on the screen, it is important to get many experiences of comparing targets in sight with
their pictures on the screen by operating the radar on sunny days.
The radar is mainly used to monitor courses of the own ship and other ships in open sea, to check buoys and
other navigation marks when entering ports, to measure own ship position in coastal waters on the chart to
take distances to and bearings of land and island and to observe positions and motions of targets appeared on
the screen in heavy rain. Explanations on radar screen will follow hereunder:
6.1

Radar Line-of-sight Range

Radar wave has the characteristic to propagate along the curved surface of the earth. This characteristic
varies with the character of air layer through which the wave propagates. In the normal propagation, the
radar line-of-sight range (D) can be expressed as follows though the distance is generally said about 10%
longer than the distance to the optical line-of-sight range (see Fig. 6.1).
D = 2.23
Fig. 6.2 shows how to radar line-of-sight range in normal wave propagation.
Radar
( )
(nm)
h + h
1 2
h1 : Height of radar scanner above sea level (m)
h2 : Height of target above sea level (m)
D
Earth
Fig. 6.1
6 – 1
Target