Install the radar
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15
In this example, the scanner is installed on the vessel at a height of 3 m (10 ft) above sea level
(h1). Island A is 10 m (33 ft) high (h2) and for comparison, island B is 5 m (16.4 ft) high (h2).
Both islands are at a distance (D) of 10 nautical miles from the vessel.
Calculations using the formula show that, at this distance, the radar can only detect objects that
are more than 7.6 m (25 ft) high, which means that island A is shown on the radar but island B
is not shown.
Remember that:
•
The maximum detection range of the radar is limited by the curvature of the earth's surface
under normal conditions of wave propagation.
•
Bad weather conditions can reduce the maximum detection range.
3.6
How to find the optimum height for the scanner
The optimum height for the scanner is as close as possible to the A-B line for best performance.
How to find the A-B Line:
The vertical extent of the radar beam is 2
θ
°, so most of the radar beam is concentrated within
this angle, meaning that outside of this angle, the radar beam will be very weak.
Scanner model
θ
° value (half the -3 dB beam width)
2 kW
15
4 kW
12.5
An example of an A-B Line is shown in the picture. If you install the scanner below the A-B line,
the scanner will be too low. It will be difficult to acquire distant targets and the superstructure
will be more likely to impede the passage of the beam and generate false echoes. If the scanner
is installed too high above the A-B line, the beam will miss close targets and increase sea clutter
return.
You can find the A-B line for any vessel as follows:
•
Using a scaled drawing of the vessel, lay a rule along the line of the main deck and
continue this forwards as a dashed line extending beyond the bow.
•
Using a protractor, measure the
θ
° value (for your scanner model) below the dashed line
at the bow and draw in a new line along this angle.
•
Extend the new line back beyond the bow of the vessel. This is the A-B line.
Summary of Contents for 2kW
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