Navigation General · Radar Plotting & CPA
On a relative-motion radar display (head-up, unstabilized), the trail of a target represents:
- AThe true course and speed of the target vessel
- BThe motion of the target vessel relative to own ship✓ Correct
- CThe track made good by own ship over the ground
- DThe predicted future position of the target
Explanation
In relative motion mode, all echoes are plotted relative to own ship (which appears stationary at the display center). Therefore a target's trail (or vector) shows its relative motion — how the target appears to move from own ship's perspective. To determine the target's true course and speed, a radar plot or ARPA true-vector mode is needed.
Authority: Radar Navigation Manual (Pub. 1310), Ch. 4
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