JMA-2343/2344 - ProNav
JMA-2343/2344 - ProNav
JMA-2343/2344 - ProNav
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4 How to Interpret the PPI Screen<br />
4.1 Height of and the Distance to the Target<br />
The maximum distance to a target that can be observed with a radar depends not only on<br />
the power of the radar's transmitter, beam width of the scanner unit, and the receiver's<br />
sensitivity but also on height of a target, distance to a target and height of scanner unit line<br />
etc. This is because the radio wave emitted by a radar runs straight, undergoing no<br />
influence by the curvature of the earth surface.<br />
a1=2.23√h1<br />
a2=2.23√h2<br />
a1 + a2=2.23 (√h1 + √h2 )<br />
a1, a2:Unit [Nautical miles]<br />
h1, h2:Unit [Meters]<br />
[Distance and Target]<br />
For example, when the scanner unit lies 3 meters above the sea level, the radar can<br />
detect and display an island with a height of 10 meters at a distance 10 NM away from<br />
the scanner unit position but cannot detect and display an island with a height of 5<br />
meters at the same distance. This is theoretically true but does not always hold,<br />
depending on weather conditions.<br />
For a target located 10 NM away to be displayed on a radar, it theoretically needs to be<br />
7.6 meters or higher. Any targets lower than 7.6 meters cannot be displayed on a radar.<br />
• The target may be unable to be observed when the height of a scanner unit or an target is low.<br />
Island not displayed on the screen<br />
10 NM<br />
10 NM<br />
h1(meters)<br />
Scanner unit height<br />
a1+a2(NM)<br />
Distance<br />
207<br />
h2(meters)<br />
Target height