Radar Observation; General; Minimum And Maximum Ranges - Furuno FR-8062 Operator's Manual

2.

RADAR OBSERVATION

2.1

General

2.1.1

Minimum 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 m
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.
R = 2.2 x ( h1 + h2 )
max
where Rmax: radar horizon (nautical miles)
h1: antenna height (m)
h2: target height (m)
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;
R = 2.2 x ( 9 + 16 ) = 2.2 x (3 + 4) = 15.4 nm
max
It should be noted that the detection range is reduced by precipitation (which absorbs the radar
signal).
2
is still shown separate from the point representing the
Radar horizon
Optical horizon
2-1