How To Suppress Sea Clutter; How To Reduce Sea Clutter Automatically; How To Reduce Sea Clutter Manually - Furuno FCR-21x9-BB Operator's Manual

2. RADAR, CHART RADAR OPERATION
2.7

How to Suppress Sea Clutter

Echoes from waves cover the central part of the display with random signals known
as sea clutter. The higher the waves, and the higher the antenna above the water, the
further the clutter will extend. When sea clutter masks the picture, suppress it with the
A/C SEA control (or [SEA] on the Status bar), either manually or automatically.
When both sea clutter and rain clutter are reduced, the sensitivity is decreased more
than when only one is adjusted. For that reason adjust them carefully.
The echo average is useful for reducing reflections from the sea surface. However,
high-speed targets are harder to detect than stationary ones when the echo average
is active.
2.7.1

How to reduce sea clutter automatically

Auto A/C SEA allows for fine-tuning of the A/C SEA circuit, within ±20 dB. Accordingly,
with the bar reading set to 100, gain is not lowered to minimum as with manual A/C
SEA on close-in ranges. Further, the auto A/C SEA level is low because the average
value of the original input echo is low in areas where there are no sea surface reflec-
tions. For example, when the ship is alongside a quay and the radar picture shows
echoes from both land and sea, you can observe the size of echoes because the STC
curve is different depending size of echoes.
To get automatic adjustment of sea clutter, do one of the following:
Control Unit: Push the A/C SEA control to display
[AUTO] on the [SEA] mode indication on the Status
bar.
Trackball module: Click the [SEA] mode indication
to display [AUTO].
2.7.2

How to reduce sea clutter manually

The A/C SEA control reduces the ampli-
fication of echoes at short ranges (where
clutter is the greatest) and progressively
increases amplification as the range in-
creases, so amplification will be normal
at those ranges where there is no sea
clutter.
The proper setting of the A/C SEA
should be such that the clutter is broken
up into small dots, and small targets become distinguishable. If the setting is set too
low, targets will be hidden in the clutter, while if the setting is too high, both sea clutter
and targets will disappear from the display. In most cases adjust the control until clut-
ter has disappeared to leeward, but a little is still visible windward.
Be careful not to remove all sea clutter, because you may erase weak echoes. Fur-
ther, the possibility of losing weak echoes is greater when you use both A/C SEA and
A/C RAIN to reduce clutter.
To reduce sea clutter manually, do one of the following:
2-8
SEA mode indication
Sea clutter at A/C SEA adjusted; sea
screen center clutter suppressed