Furuno Marine Radar - Manual (Page 12)

Radar Picture and Marks
The Radar display shows you not only echoes but also
marks and information. This section describes the Radar
picture and marks you will see on the display.
Measuring Range
The range from own ship to target can be measured in three
ways: by range rings, by cursor, and by VRM.
By Range Rings:
The RINGS key shows/hides the range rings and adjusts
their brilliance. To measure range by the range rings, count
the number of rings between the center of the display and
the echo. Check the range ring interval at the top of the
display and judge the distance of the echo from the inner
edge of the nearest ring.
By Cursor:
The cursor provides a more accurate measurement of range
to targets. Set the cursor intersection on the inner edge of
the target. The range from own ship to target appears on the
display.
By VRM:
The VRM, like the cursor, provides a more accurate
measurement of the range to targets. Display a VRM and
adjust it so that it rests on the inner edge of the target. The
range to target appears on the VRM readout.
Figure 10 - How to measure range
Measuring Bearing
The relative bearing from own ship to targets can be
measured by the cursor and by the EBL. With gyrocompass
connection, you can display true bearing.
By Cursor:
Set the cursor intersection on the center of the echo. The
bearing from own ship to target appears on the display.
By EBL:
Display an EBL and adjust it so that it bisects the
target. The bearing to the target appears on the
EBL readout. Bearing relative to heading is relative
bearing, while bearing relative to North is true
bearing.
Figure 11: Comparison of true and relative bearing
No Gyrocompass Connection:
You can determine true bearing by adding relative
bearing to your compass reading. If the sum is over
360 degrees, subtract 360 from the number.
Gyrocompass connection:
Select the true bearing display, north-up mode.
Measure the bearing by the EBL and check the EBL
readout.
How to Suppress Sea Clutter
The effect of echoes with waves changes with wave
size, sea conditions, weather and antenna height above
the sea surface. Sea clutter can be suppressed by not
only the A/C SEA controls but also by a combination
of A/C RAIN and GAIN controls.
General Procedure:
Turn the A/C SEA control fully counterclockwise
(down). Turn the GAIN control fully clockwise (up).
Slowly turn the GAIN control counterclockwise
(down) to reduce sea clutter and distinguish targets.
Note that echoes that are weaker than the sea clutter
will not appear.
If this action does not remove sea clutter near own
ship, gradually turn the A/C SEA control clockwise
(up) to reduce sea clutter.
NOTE: The A/C RAIN control is also effective in
suppressing sea clutter. It is most effective when the
echo of the target is larger than that of the sea clutter.
Its main advantage over the A/C SEA control is that,
when used to suppress sea clutter, it does not shrink
small echoes.
How to Suppress Rain Clutter
Echoes from precipitation cover a much wider area on
the display than echoes from waves. However, since
they are not as strong as those from waves, they can
be suppressed by adjusting the A/C RAIN and GAIN
controls.
Example 1: Drizzle over a wide area
If using the A/C RAIN control shrinks or erases
echoes, turn the GAIN control clockwise (up) until
rain clutter just appears on the display.
Example 2: Density of rain different from area to
area
In this instance you usually reduce the clutter in the
area of light rain by adjusting the A/C RAIN control.
Be careful not to remove the clutter completely;
weak echoes may be missed. If strong clutter appears
in the area of heavy rain, turn the GAIN control
counterclockwise (down) a little.
10 11
AIS provides real-time information about AIS-equipped vessels on your
AIS-ready chart plotter, navigation software or Radar. This information is
presented graphically, allowing you to monitor and avoid AIS equipped ves-
sels in the area. Since AIS targets can be received even if they are not within
line of sight, the system greatly enhances situational awareness in congested
waterways, limited visibility or heavy sea conditions, and gives the navigator much
more information about AIS equipped vessels. Some common AIS symbols are:
An ARPA target is measured by range and bearing from
own ship and located on the Radar PPI. When ARPA
and AIS are combined and their symbols are within an
operator-set criteria, the ARPA symbol is merged with the
AIS symbol. Some common ARPA symbols are: