-2.3-
Continued tracking and subsequent calculation develop the relative course and speed of the target
just as a man would do when plotting the relative course and speed of the target on the scope with
a grease pencil.
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 is 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.
Automatic acquisition areas and suppression lines
Performance of auto-acquisition is enhanced by controlling the limit lines (suppression lines) in the
former series of FURUNO ARPAs. In the ATA, 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. They are gyro stabilized.
Qualitative description of tracking error
The FURUNO ARPA or ATA 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 3 to 6 seconds at low (near 0)
relative speed. It is less accurate during a turn due to lag, but accuracy recovers quickly.
