Radar Observer · ARPA — Vectors
A relative vector displayed by an ARPA shows:
- AThe target's actual course and speed over the ground
- BHow the target is moving relative to own ship — i.e., whether it will pass clear or close✓ Correct
- COnly the target's range
- DThe compass error
Explanation
A relative vector points along the relative-motion line and indicates the developing risk (a vector aimed at own ship means small CPA). A true vector instead shows the target's actual course and speed. The navigator should know which mode is selected.
Authority: Radar Navigation — ARPA Vectors
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