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On the other hand, hulls made from wood
or fiberglass return much weaker echoes.
Vertical surfaces, such as a cliff, are good
targets provided they face the radar. Con-
versely, horizontal and smooth surfaces such
as mudbanks, sandy beaches, and gently
sloping hills make poor targets because they
disperse rather than reflect most of the en-
ergy that strikes them.
The strongest radar echoes known come
from built-up areas, docks, etc., because
these targets are less subject to changes in
aspect. These types of targets have three flat,
smooth surfaces mutually at right angles.
Some radar buoys are arranged this way so
as to deliberately increase their detection
range.
2.3 Range Resolution
Range resolution is a measure of the capa-
bility of a radar to display as separate pips
the echoes received from two targets which
are on the same bearing and are close to-
gether.
The main factor which affects range resolu-
tion is pulselength. Two targets on the same
bearing, close together, cannot be seen as
two distinct echoes on the display unless
they are separated by a distance greater than
one-half the pulselength.
Figure 2-2 Range resolution
2.4 Bearing Resolution
Bearing resolution is a measure of the capa-
bility of a radar to display as separate tar-
gets the echoes received from two targets
which are at the same range and are close
together.
The principal factor which affects bearing
resolution is horizontal beamwidth. Two tar-
gets at the same range must be separated by
more than one beamwidth to appear as sepa-
rate pips.
Figure 2-3 Bearing resolution
2.5 False Echoes
Occasionally false echoes appear on the
screen at positions where there is no target.
In some cases the effects can be reduced or
eliminated. The operator should familiarize
himself or herself with the appearance and
effects of these false echoes, so as not to
confuse them with echoes from legitimate
contacts.
Multiple echoes
Multiple echoes occur when a short range,
strong echo is received from a ship, bridge,
or breakwater. A second, a third or more ech-
Target
Transmitted
radar
pulse
Transmitted
radar
pulse
Target
Radar is able to display two
distinct target echoes.
Radar cannot display targets as
separate echoes because they
are within the pulselength.
Direction of
scanner rotation
Target
Horizontal
beamwidth
Direction of
scanner rotation
Horizontal
beamwidth
Radar is able to display two
distinct target echoes.
Radar cannot display targets as
separateechoes because they
are within the beamwidth.
Target