Navigation General · AIS
A vessel observes an AIS target on the display whose position does not match the corresponding radar echo. The navigator should:
- ATrust the AIS position because GPS is more accurate than radar bearings
- BTrust the radar echo because AIS positions can be erroneous due to GPS error, incorrect data entry, or sensor failure on the target vessel✓ Correct
- CDisregard both and rely solely on visual observation
- DCall the target vessel on AIS to request a GPS position update
Explanation
AIS data can be incorrect due to GPS errors on the target, manually entered erroneous data, equipment malfunction, or deliberate falsification. Radar echo positions are independently derived and more reliable for collision avoidance. Best practice is to cross-check AIS against radar and visual observation; significant discrepancies require heightened caution.
Authority: Bowditch (Pub. 9), Ch. 13
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