Furuno 1823C manual Interpreting the Radar Display, General, Minimum and maximum ranges

2. RADAR OPERATION

2.27Interpreting the Radar Display

2.27.1General

Minimum and maximum ranges

Minimum range

The minimum range is defined by the shortest distance at which, using a scale of

1.5or 0.75 nm, a target having an echoing area of 10 m2 is still shown separate from the point representing the antenna position. It is mainly dependent on the pulselength, antenna height, and signal processing such as main bang suppression and digital quantization. It is best to use the shortest possible range as long as the clarity and definition of the picture remain good.

Maximum range

The maximum detecting range of the radar, Rmax, varies considerably depending on several factors such as the height of the antenna above the waterline, the height of the target above the sea, the size, shape and material of the target, and atmospheric conditions.

Under normal atmospheric conditions, the maximum range is equal to the radar horizon or a little shorter. The radar horizon is longer than the optical one by about 6% because of the diffraction property of the radar signal. Rmax is given in the following equation.

Rmax = 2.2 x ( h1 + h2 )
where	Rmax:	radar horizon (nautical miles)
	h1:	antenna height (m)
	h2:	target height (m)

Radar horizon

Optical horizon

Radar horizon

For example, if the height of the antenna above the waterline is 9 meters and the height of the target is 16 meters, the maximum radar range is;

Rmax= 2.2 x ( 9 + 16 ) = 2.2 x (3 + 4) = 15.4 nm

It should be noted that the detection range is reduced by precipitation (which absorbs the radar signal).

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