Anritsu RA77OUA, Instruction Manual

Page: 21 / 52

3.2
Echo Strength and Incident Angle of Target
The strength
of
an echo pulse, arriving at the radar
receiver from
a
target,
is
dependent not only upon the
distance to the target, its height above sea level and
size, but also upon the target configuration and
material.
large target is not always strong; a strong echo may
return
from
a
low
target,
if
its surface is comparatively
vertical (and
smooth) with respect to the
transmitted
radiowaves.
A s
the angle of incidence
of
radiowaves, with
respect to the decreases beyond a
certain angle, the intensity of the echo signal decreases
greatly. Intensities of echo signals reflected from
gradually sloped surfaces such as sandy beaches or
cone-shaped lighthouses are very faint. Echoes from
locations considerably removed from a coastline may, at
times, be displayed on the screen as if they are a
coastline (Fig. 3 - 3 ) .
You
must train yourself not to
mistake such echoes for coastline.
Accordingly, an echo signal reflected from a high,
Echoes appear on screen
A c t u a l
Coastline
(invisible)
Visible
on
.
Screen
I I
.
Targets Visible
on Screen
,
Invisible on Screen
Fig.
3 - 3 .
Echo Strength and Incident Angle of Target
3 . 3 Shadow Zones
Radar radiowaves travel in a straight line in much
the same manner as light. A local, partial
or total
shadow zone may be produced a funnel, mast, or a
derrick post near the antenna or a high target or
mountain at a short distance. In extreme cases, shadows
may be produced at long ranges and no
echoes are
displayed on the screen in their presence.
can when the antenna is installed.
These can be reduced by changing the location
of
the antenna installation.
Local shadow zones, produced by funnels, masts, etc
3 - 3