timberland boots size 5 Automatic Radar Plotting Aid
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An Automatic Radar Plotting Aid (ARPA) provides an interface between visually oriented radar displays and or marine navigation computers.
The ARPA device is, itself, a computer, usually a component inside the radar set rather than an external device; it supplements the traditional radar display. For each target, ARPA computes the actual position using GPS information. It stores the target positions between successive radar observations, so it can compute course and speed.
An ARPA message may include information either manually entered, or available from other sources such as the Automatic Identification System, the name of the target.
AIS, which relies on a GPS signal transmitted from the other target, is generally more accurate than ARPA; if the positions differ, a cautious seaman verifies both. Ideally, one’s own chartplotter, ARPA, and AIS should either take information from the same GPS source, or separate GPS should periodically be checked.