GNSS Position Integrity Monitoring on KlaipėdaTraffic

Modern AIS tracking relies heavily on GNSS (GPS) positioning. While GNSS is normally reliable, in real-world maritime operations position data can occasionally become inaccurate, delayed, or physically impossible due to technical or environmental reasons.

To help users recognize and correctly interpret such situations, KlaipėdaTraffic operates a GNSS Position Integrity Monitoring system.

This system is designed to support situational awareness — not to judge vessels.

What the system does

The GNSS Position Integrity Monitor continuously evaluates AIS position updates and checks whether they are physically plausible.

• Time between AIS updates
• Distance between consecutive positions
• Implied speed required to make that movement
• Reported Speed Over Ground (SOG)

If a position update would require unrealistic speed or movement, the vessel’s GNSS position is marked as unreliable for a limited time.

What the system does not do

• ❌ It does not accuse vessels of wrongdoing
• ❌ It does not confirm hostile GNSS spoofing
• ❌ It does not replace radar, pilotage, or VTS decisions
• ❌ It does not judge navigation quality

The system answers only one question: “Can this reported position be trusted right now?”

Warning levels explained

🟡 Suspected
A single abnormal position detected. Commonly caused by brief GNSS glitches or delayed AIS updates. Usually harmless.
Operator guidance: Observe, no action required.

🟠 Likely
Repeated abnormal movements detected. Position accuracy may be degraded.
Operator guidance: Avoid using precise position for close-quarters decisions.

🔴 Confirmed
Position update is physically impossible (for example, hundreds of meters in seconds).
Operator guidance: Do not rely on displayed position for CPA, TCPA, or berth clearance.

Drift, wind, and current — handled correctly

The system fully accounts for normal maritime behavior, including:

• Difference between heading and COG
• Wind and current set and drift
• Swinging at anchor
• Low-speed maneuvering
• Minor GNSS jitter

These situations do not trigger warnings, because the resulting movements remain physically plausible.

Why warnings remain visible after recovery

When an abnormal event is detected, the warning remains visible for a short hold period (typically 10 minutes), even if later positions appear normal.

This provides operator awareness, context for recent anomalies, and protection against false confidence. This behavior mirrors professional ECDIS and VTS systems.