Table of Contents
Advertisement
124
disappear momentarily. Buoys and small boats often resemble each other, but boats
can usually be distinguished 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 presentation
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 operator, through observation,
practice, and experience, can generally detect these conditions very quickly. These
effects can usually be minimized using the radar controls.
Side lobes
Main lobe
Side lobe
Arc
True echo
Side lobe
Antenna
Side echoes
D7051_1
RayTech RNS V5.0 - User's Manual
Side lobe patterns are produced by small amounts of
energy from the transmitted 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.
Advertisement
Table of Contents
