True And False Echoes On Display; Radar Wave With The Horizon - JRC JMA-7133-SA Instruction Manual

JMA-7100 Instruction Manual
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
h
h
Fig 6-2 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.
h Radar
1
>

6.TRUE AND FALSE ECHOES ON DISPLAY

)
h h
+ [NM]
1 2
: Height (m) of radar scanner above sea level
1
: Height (m) of a target above sea level
2
D
Earth
Fig 6-1: RADAR wave with the horizon
6－ 1
>
6.1 RADAR WAVE WITH THE HORIZON
Targets
6
h
2