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to be a coastline and the closet edge is put
into memory as a map of the area.
This land outline is used to inhibit further ac-
quisition and tracking of ship sized echoes
beyond the closest coast outline. 5 consecu-
tive scans of coastal outline are retained in
memory to allow for signal variation. All
smaller echoes are declared to be ship sized
and the middle of the leading edge is used to
provide precise range and bearing coordi-
nates of each echo on every scan. This
range/bearing data is matched to previous
data and analyzed from scan-to-scan for con-
sistency. When it is determined to be as con-
sistent as a real target, automatic acquisition
occurs and tracking is initiated.
Continued tracking and subsequent calcula-
tion 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 up-
dated 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 acquisi-
tion rings are used instead of the limit lines.
Auto acquisition rings work as suppression
lines when viewed from the opposite direc-
tion. The should be placed clear of a land-
mass 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 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, de-
pending 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 recov-
ers quickly.