Position Integrity Monitoring for AIS Traffic in Klaipėda Port and Approaches
KlaipėdaTraffic has expanded its Position Integrity Monitor (PIM) from individual AIS position checks into a geographic monitoring tool covering Klaipėda Port and its seaward approaches.
The update is designed to make position-integrity information easier to interpret within a live traffic picture.
Instead of only highlighting an anomaly on an individual vessel, KlaipėdaTraffic can now provide a quick overview of whether position-integrity anomalies are currently being detected in the areas most relevant to vessels approaching, entering, leaving or operating inside the port.
The feature remains an experimental situational-awareness aid and is not intended for navigation.
The original Position Integrity Monitor and its detection logic are described in the February article: GNSS Position Integrity Monitoring on KlaipėdaTraffic .
Two operational monitoring areas
The Position Integrity Monitor now separates detections into two geographic areas.
Klaipėda Port covers vessels operating inside the defined port monitoring area.
Klaipėda Approaches adds a new seaward monitoring sector extending approximately 20 nautical miles from the port entrance.
This distinction is useful because a position-integrity anomaly detected before a vessel reaches the port may remain operationally relevant as that vessel continues toward Klaipėda.
Where the two monitoring areas meet, the port area has priority. Once a vessel enters the defined port boundary, it is classified as being within Klaipėda Port.
A compact PIM status on the live AIS map
A new PIM status indicator is displayed in the lower-right corner of the KlaipėdaTraffic live AIS map.
It provides a compact overview of current and recently detected position-integrity anomalies within the monitored areas.
The colour gives an immediate indication of the current situation:
- Green - no active or recent PIM indications
- Amber - a recent anomaly, suspected anomaly or likely anomaly is present
- Red - at least one confirmed position-integrity anomaly is present
Selecting the indicator opens a more detailed view showing the affected vessels and whether each indication is associated with Klaipėda Port or the Klaipėda Approaches.
The PIM display can also be switched on or off from Layers / Tools and is enabled by default.
This keeps the feature available when needed without forcing an additional information layer onto every user.
Recent anomalies remain visible as CAUTION
One important part of the update is the treatment of vessels whose positions have recently returned to normal.
When an active anomaly clears, the vessel does not immediately disappear from the integrity picture.
For a limited period it can remain visible as:
CAUTION · recent anomaly
This provides useful operational context.
A vessel may once again be transmitting physically plausible position information, while the user can still see that its reported position was questionable only a few minutes earlier.
After the hold period expires, the CAUTION indication clears automatically if no further anomaly is detected.
This short memory prevents the traffic picture from changing instantly from a significant integrity warning to apparently normal conditions with no indication of what happened moments earlier.
From individual warnings to an area picture
The original KlaipėdaTraffic Position Integrity Monitor was primarily vessel-oriented.
Individual AIS position reports were evaluated for physical plausibility, and an affected vessel could be highlighted when its reported movement or position appeared inconsistent.
The new implementation adds another level.
The system can now help answer not only:
“Is this vessel reporting a plausible position?”
but also:
“Are position-integrity anomalies currently affecting traffic in Klaipėda Port or its approaches?”
That creates a simple area-level integrity picture alongside the normal AIS traffic display.
For a local maritime traffic monitoring system, this wider context can be more useful than treating every vessel warning as an isolated event.
A single affected vessel may indicate an individual problem. Several indications appearing within the same geographic area may deserve closer attention.
PIM does not attempt to explain why that situation exists, but it makes the pattern easier to see.
Why monitor the approaches?
Position-integrity monitoring becomes particularly interesting before a vessel reaches confined port waters.
For this reason, KlaipėdaTraffic now includes the seaward approaches rather than limiting PIM to the port boundary.
A vessel detected with questionable position information offshore may subsequently continue toward the entrance and into the port.
Retaining this information provides continuity between what happens in the approaches and the traffic picture later seen inside Klaipėda.
It can also help show whether anomalies appear as isolated vessel events or whether several vessels are being affected within the same general area.
The approximately 20 NM approach sector therefore gives the monitoring system time and geographic context before traffic reaches the entrance itself.
What PIM is - and what it is not
KlaipėdaTraffic PIM evaluates the integrity and physical plausibility of position information derived from AIS data.
It does not determine the cause of an anomaly.
An abnormal position can have different technical, environmental, transmission, reception or positioning-related causes.
For that reason, PIM deliberately reports position-integrity anomalies rather than attempting to attribute them to a particular cause.
The system should therefore not be interpreted as proof of GNSS interference, spoofing, equipment failure or any other specific explanation.
It identifies that the observed AIS position information deserves additional caution.
PIM is designed to add another layer of awareness to the live AIS picture. It does not replace professional navigation systems, radar, VTS information, pilotage procedures or the navigator's own assessment.
Building a more resilient local traffic picture
KlaipėdaTraffic began as a local AIS traffic display, but the same live data can support more than vessel symbols on a map.
Position Integrity Monitoring is one example.
By combining:
live AIS + geographic monitoring areas + anomaly classification + recent-event memory + a clear visual status
the system can help users recognize when the traffic picture itself deserves additional caution.
The important change is not simply another warning symbol.
It is the transition from monitoring isolated vessel reports to maintaining a small geographic picture of position integrity across the port and its approaches.
For KlaipėdaTraffic, the next stage is straightforward: keep the system operating, collect real operational observations and evaluate how PIM behaves over time in Klaipėda Port and the 20 NM approaches.
That operational experience will be more valuable than trying to make conclusions from individual events alone.
Disclaimer
KlaipėdaTraffic Position Integrity Monitor is an experimental situational-awareness aid based on AIS data. It is not a navigation system and must not replace official charts, approved navigation equipment, radar, VTS information, pilotage procedures or professional judgment.
A PIM indication identifies an observed position-integrity anomaly. It does not determine its cause. AIS data may itself be delayed, incomplete, inaccurate or incorrectly transmitted.