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The number of range rings shown in the table is the number to the selected
range. Additional range rings are displayed to the edge of the radar
picture, at the standard ring interval for the current range, and are visible
when the center is offset.
B.5 Interpreting the radar picture
Navigational echoes may be large, small bright or faint, depending not only
on the size of the object but also on its orientation and surface. Different
objects reflect the radar signals in different ways. For example, vertical
objects such as cliffs reflect signals better than sloping ones such as
sandbanks.
High coastlines and mountainous coastal regions can be observed at the
longest radar range. However, the first sight of land may be a mountain
several miles inland from the coastline. The actual coastline may not
appear on the radar until the boat is close to the line of sight distance.
The radar indication may not be similar to your visual observation; a nearby
small object may appear to be the same size as a distant large object on
the radar. However, with experience the approximate size of different
objects can be determined by the relative size and brightness of the echoes.
Some targets, such as buoys and small boats, can be difficult to differen-
tiate, since they bob and toss about in the waves and do not represent a
consistent reflecting surface. Consequently, these echoes have a tendency
to fade and brighten, and at times, to disappear momentarily. Buoys and
small boats often resemble each other, but boats can usually be distin-
guished by their motion.
Not all radar echoes are produced by hard navigational items. Some echoes
may be received from irregularities on the surface of the water, particularly
at close range (sea clutter), or from rain or snow either around the boat or
in the distance. In addition, some echoes may be indirect reTurns to the
radar scanner, providing false echoes or multiple echoes.
The effects of many false echoes can be minimized, and the target presen-
tation clarified.
Identifying false echo returns
Not all echoes are direct reTurns to the radar antenna. Occasionally signals
appear at positions where there is no actual target. These are called false
echoes, and may be caused by side lobes, ghost images, indirect echoes or
multiple echoes.
This section briefly describes the echo patterns that can be produced by
false echoes and the likely cause. It should be noted that the radar oper-
ator, through observation, practice, and experience, can generally detect
these conditions very quickly. These effects can usually be minimized using
the radar controls.
156 RayTech RNS V6.0 - Users Guide
Side lobes
Side lobe patterns are produced by small amounts of energy from the trans-
mitted pulses that are radiated outside the narrow main beam.
The effects of side lobes are most noticeable with targets at short ranges
(normally below 3nm), and in particular with larger objects. Side lobe
echoes form either arcs on the radar screen similar to range rings, or a
series of echoes forming a broken arc.
Indirect echoes
There are several types of indirect echoes or ghost images. These some-
times have the appearance of true echoes, but in general they are
intermittent and poorly defined.
Multiple echoes
Multiple echoes are not very common but can occur if there is a large
target with a wide vertical surface at a comparatively short range. The
transmitted signal will be reflected back and forth between the target and
your own boat, resulting in multiple echoes, displayed beyond the range of
the true target echo, but on the same bearing.
True echo Side echoes
Main lobe
Antenna
Arc
Side lobe Side lobe
D7051_1
False echo
True echo
Passing
ship
True echo
False echo
Mast
or funnel
D7052_1