Furuno 1830 - Position Fixing with Radar; By Radar Range; By Range and Bearing to a Point of Land

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
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