An AIS identity mismatch is a disagreement between displayed data and transmitted fields, which may be unavailable or wrong. This error misleads target association and requires verification through external checks.
AIS static identity fields include MMSI, call sign and name, IMO number, vessel dimensions and ship type; several are set during installation and require amendment when vessel identity or configuration changes. Official guidance documents identity fields that require updating and invalid or duplicated MMSIs that can confuse target association, so one mismatch can have more than one data-quality explanation and does not establish deliberate spoofing.
USCG guidance records that invalid or duplicated MMSIs occur and that reports from vessels using the same MMSI can appear as one target jumping between positions on a graphical display. AIS can assist identification by name, call sign, ship type and navigational status, but received accuracy is only as good as the transmitted information and faulty input can mislead other vessels.
MCA guidance says the simplest check on own-ship transmitted identity, position and movement information is to contact another vessel or shore station. This verification step ensures that the underlying data quality issues are identified without assuming malicious intent behind the discrepancy.
