Factors Affecting Arpa Functions - Furuno FR-2125V Operator's Manual

determined to be as consistent as a real target, automatic acquisition occurs and tracking
is initiated. Continued tracking and subsequent calculation develop the relative course
and speed of the target.
The true course and speed of own ship are computed from own ship's gyro and speed
inputs, and the resulting course and speed of each tracked target are easily computed by
vector summing of the relative motion with own ship's course and speed. The resulting
true or relative vector is displayed for each of the tracked targets. This process is updated
continually for each target on every scan of the radar.
5.18.3 Automatic acquisition areas and suppression lines
Performance of auto-acquisition is enhanced by controlling the limit lines (suppression
line) in the former series of FURUNO ARPAs. In this new series of ARPAs, the automatic
acquisition rings are used instead of the limit lines.
Auto acquisition rings work as suppression lines when viewed from the opposite direction.
They should be placed clear of a landmass or shoreline. The acquisition areas may be a
full 360 degree circle or sector of any angles are gyro stabilize.
5.18.4 Qualitative description of tracking error
The FURUNO ARPA accuracy complies with or exceed IMO standards.
Own ship maneuvers
For slow turns there is no effect. For very high turning rates (greater than 150 /minute,
depending on gyro), there is some influence on all tracked targets which last for a minute
or two and then all tracked targets revert to full accuracy.
Other ship maneuvers
Target ship courses lag 15 to 30 seconds at high relative speed, or three to six seconds at
low (near 0) relative speed. It is less accurate during a turn due to lag, but accuracy
recovers quickly.

5.19 Factors Affecting ARPA Functions

Sea returns
If the radar anti-clutter control is adjusted properly, there is no serious effect because
distant wave clutter, not eliminated by this control, is filtered out by more than one bang
correlation and scan-to-scan matching of data.
Rain and snow
Clutter can be acquired and tracked as targets. Adjust the [A/C RAIN] control. If it is heavy
rain, switch to S-band if provided, or switch on the interference rejector on the radar. If
heavy clutter still exists, switch to manual acquisition. Accuracy can be affected.
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