Radar Observation; General; Minimum Range; Maximum Range - Furuno FAR-2218-BB Operator's Manual

2.

RADAR OBSERVATION

2.1

General

2.1.1

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
point representing the antenna position.
It is mainly dependent on the pulselength, antenna height, and signal processing such
as main bang reduction 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.
The IMO Resolution MSC.192(79) requires the minimum range to be less than 40 m,
respectively. This series of radars satisfy this requirement.
2.1.2

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 the atmospheric
conditions.
Under normal atmospheric conditions, the maximum range is equal to the radar hori-
zon 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 follow-
ing equation.
D = 2.2 x ( h1 + h2)
where D: 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).
Optical horizon
Globe
2
D: Radar horizon
is still shown separate from the
2-1