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Tarvet Propertics
As a genpral nile nf
thiimta,
largor largets
can
bQ soen oA tho radar display
at
greater
ranges,
providecl
Jine-of-sight
exists belween
Ihe scanner and
target.
llowever, a large target wlth poor reflecting properties may not be
detected as easily as a smaller target with better reflecting properties.
bince one of tJie main funetions of radar is to detect other ships,
the com-
position of a target ships'
huli affeets the detection range.
A ship whose
huli
is
made
of
oonducting
materials,
such
as
a
steel,
return
relativel y
strong echoes.
On the other hånd,
hulis made from wood or fiberglass return mueh weaker
echoes.
Vertical surfaces,
sucli as a cliff,
are good targels provided they face the
radar-
Inverscly,
horisontal and
smouith surfaues such
as mudbanKS,
sandy
beaches,
and
gently sloping hilis make poor targets because they disperse
rather than reflect most of the energy that strikes them.
The
strengest
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.
This type
or arrangement
is
used
on
some
radar
buoys
to increase
their
detection
range.
INTERPRETING THE DISPLAY
In the previous section
some of the characteristics and limitations
of
radar
were discussed-
Now its time to take a look at what you can expect to see
on
the
radar screen.
What shows up
on the screen isn't Hkely to match
Gxactly
what is seen on a navigation chart.
A
radar cannot see through
a
itiounlain in
the path between your boat and
the harbor,
nor can it see a
small boat directly
behind
a large ship,
since both
the mountain and
the
larger vessel effeetively shield the radar from the desired target.
To aid you in target identification,
the echoes appearing on the display are
quantized
in
four
level s,
according
to
their
inlensity-
The
brightest
intensity
cchoeo
are
probably
from
Steel
ships,
or
piers,
or
other
"good"
targets.
Poor
targets,
for example wooden boats,
appear in the
weakest
intensities.
The ability to interpret a radar picture comes through practice and exper-
ience.
Practice should be done during clear weather in daytime,
since you
can compare the picture with v</hat you actually see around you.
Go to an
area you are familiar with and compare the way coastliaes, buoys and other
targets
are
displayed
on
the
screen
and
the
way
they
are
drawn
on
a
navigation chart.
To observe the movement of an echo in relation to your
position, try running your boat at various speeds and headings.
LAND TARGETS
Landmasses
are
readily
recognizable
because
of
tne
generally
steady
briiliance of the relatively large areas painted on the display.
Knowledge of
the ship's navigational position will also tell you where land should be-
On
relative
motion
displays
(this radar) ,
landmasses
move in
directions and
at
rates opposite and
equal to the
actual motion of your own ship.
Various
41
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