Furuno FR-8122, FR-8252 Radar Observation, General, Minimum and maximum ranges, Minimum range

2.RADAR OBSERVATION

2.1General

2.1.1Minimum and maximum ranges

Minimum range

The minimum range is defined by the shortest distance at which, using a scale of 1.5 or 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 pulse length, antenna height, and signal processing such as main bang suppression and digital quantization. It is a good practice to use a shorter range scale as far as it gives favorable definition or clarity of picture. This series of radars satisfy the requirement of IEC 62252 5.14.1 (Class A).

Maximum range

The maximum detecting range of the radar, Rmax, varies considerably depending on several fac- tors 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 the 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. The 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

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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