Introduction To The Auto Plotter - Furuno GP-280 Operator's Manual

12.2 Introduction to the Auto Plotter

This series of video plotters can accommodate an optional ARP (Automatic Radar Plotter)
module. With the optional ARP circuit board ARP-10 (GP/GD-280) or ARP-17 (GP/GD-380,
GP/GD-680) fitted in the display unit, the equipment will automatically acquire 10 targets
(GP/GD-280) or 20 targets (GP/GD-380, GP/GD-680) coming into the acquisition area. Once a
target is acquired automatically or manually it is automatically tracked within 0.1 to 32 nm,
whether inside or outside the acquisition area. Heading signal is required to use the Auto Plotter.
12.2.1 Criteria of tracking
A target measuring 800 m or more in the radial or circumferential direction is regarded as a
landmass and not acquired or tracked. Echoes smaller than 800 m are regarded as targets to be
tracked.
The FURUNO ARP video processor detects targets in the midst of noise and discriminates radar
echoes on the basis of their size. Target whose echo measurements are greater than those of
the largest ship in range or tangential extent are usually land and are displayed only as normal
radar video. All smaller ship-sized echoes which are less than this dimension are further
analyzed and regarded as ships and displayed as small circles superimposed over the video
echo.
When a target is first displayed, it is shown as having zero true speed but develops a course
vector as more information is collected. In accordance with the International Marine Organization
Automatic Radar Plotting Aid (IMO ARP) requirements, an indication of the motion trend should
be available within 20 scans of antenna and full vector accuracy within 60 scans. The FURUNO
ARPs/ATAs comply with these requirements.
12.2.3 Acquisition and tracking
A target which is hit by five consecutive radar pulses is detected as a radar echo.
Auto acquisition is not defined in paints but in time, which should be less than three seconds of
initial stage.
Manual acquisition is done by designating a detected echo with the trackball. Automatic
acquisition is done in the acquisition area when a target is detected 5-7 times continuously
depending upon the congestion. Tracking is achieved when the target is clearly distinguishable
on the display for five consecutive or alternate paints out of 10 consecutive scans whether
acquired automatically or manually.
Targets not detected in five consecutive scans become "lost targets."
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