FLIR RAYMARINE A75 WiFi - Interpreting Objects; Maximum Radar Range

Sea
clutter
off
Sea
clutter in
auto
Interference
When two or more Radar-equipped vessels are
operating within range of each other mutual Radar
interference can occur. This usually appears as a
spiral of small dots from the display centre This type
of interference is most noticeable at long ranges.
This interference can be suppressed using the
interference rejection settings. The images in the
table below show how the Interference rejection
settings can clear up some of this interference:
Interfer-
ence re-
jection
off
Interfer-
ence re-
jection
on
Interpreting objects
The size of a target on screen is dependent on many
factors and may not be proportional to its physical
size. Nearby objects may appear to be the same
size as distant larger objects. With experience,
the approximate size of different objects can be
determined by the relative size and color / brightness
of the echoes.
The size of onscreen targets are affected by:
• The physical size of the reecting object
• The material from which the object is made
(Metallic surfaces reect signals better than
non-metallic surfaces.)
• Vertical objects such as cliffs reect signals better
than sloping objects such as sandbanks
• High coastlines and mountainous coastal regions
can be observed at longer Radar ranges.
Therefore, the rst sight of land may be a mountain
several miles inland from the coastline. Although
the coastline may be much nearer, it may not
appear on the Radar until the vessel is closer to
shore.
• Some targets, such as buoys and small vessels
difcult to discern, because they do not present a
consistent reecting surface as they bob and toss
about in the waves. Consequently these echoes
tend to fade and brighten, and at times disappear
momentarily.
• Buoys and small vessels resemble each other, but
vessels can often be distinguished by their motion.
Maximum Radar range
The usable range of the Radar is limited by factors
such as the height of the scanner, and height of the
target.
Maximum Radar range is essentially line-of-sight, so
is limited by the height of the scanner and the height
of the target as illustrated below:
Item Description
1 Radar equipped vessel.
2
Curvature of the earth.
3
Target (Cliff).
a
1
Radar horizon of antenna.
a
2
Radar horizon of target.
R
max
Maximum Radar range in
nautical miles.
R
max
= a
1
+ a
2
h Radar antenna height in
metres.
H Target height in metres.
The table below shows typical maximum Radar
ranges for various Radar antenna heights and target
heights. Remember that although the Radar horizon
is greater than the optical horizon, the Radar can
only detect targets if a large enough target is above
the Radar horizon.
Radar application
251