Furuno ARP-17 manual Automatic acquisition areas and suppression lines, Own ship maneuvers

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.

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