Radar Observer · ARPA — Target Swap
When two tracked targets pass close to each other, an ARPA may suffer 'target swap,' meaning:
- ABoth targets are deleted
- BThe tracker exchanges the two targets' history/vectors, briefly producing wrong course and speed for each✓ Correct
- CThe radar loses power
- DThe targets merge permanently into one
Explanation
If two targets' echoes nearly coincide, the tracking gates can swap, so each target inherits the other's past track — giving erroneous vectors until the tracker re-settles. Operators must be alert to sudden unexplained changes in a target's computed course/speed near a passing situation.
Authority: IMO Performance Standards for ARPA; Bowditch
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