Operational Guide · Registers & Logbooks

# Electronic Navigation and GNSS Resilience

Satellite positioning can no longer be taken for granted: GNSS jamming and spoofing have grown to the point of prompting an unprecedented joint warning from IMO, ICAO and ITU.

GNSS jamming spoofing electronic navigation

## Operational Explanation

Interference with global satellite positioning systems (GNSS, of which GPS is the best known) has grown significantly since 2022, with thousands of ships reported as affected in 2025 in specific high-geopolitical-risk areas. Two phenomena are distinguished: jamming (signal disruption that prevents reception) and spoofing (transmission of a false signal that causes the receiver to calculate an incorrect position, often with no obvious sign of malfunction).

In March 2025, ICAO, ITU and IMO issued a joint warning expressing "grave concern" that GNSS jamming and spoofing disruptions constitute an urgent threat to public safety, telecommunications networks and international trade.

Real resilience is achieved through multi-band (L1/L2/L5) receivers capable of maintaining an accurate position even when one or two frequency bands are completely disrupted, integrated with CRPA (Controlled Reception Pattern Antenna) antennas, RAIM (Receiver Autonomous Integrity Monitoring) systems and, where available, signal authentication. In high-risk areas, the bridge team must be able to fall back on alternative positioning sources: inertial navigation systems (INS), celestial navigation, radar parallel indexing and visual fixes on known coastal points.

## Regulatory Reference

No single IMO instrument is dedicated exclusively to GNSS resilience; the topic falls within the general requirements of SOLAS Chapter V on navigational equipment and within the operational guidance issued by individual flag Administrations (e.g. the RMI) following the joint ICAO/ITU/IMO warning of March 2025. Technical reference: applicable ECDIS/GPS performance standards and industry good practice on redundant navigation.

## Scope of Application

Every ship operating in geographic areas known for active GNSS interference (jamming/spoofing), including routes near areas of conflict or geopolitical tension.

## Procedure / How to Complete It

1. During passage planning, identify areas known for active GNSS interference along the intended route, consulting up-to-date bulletins and notices to mariners.
2. Verify the availability and functionality of multi-band GNSS receivers and any signal-integrity monitoring systems (RAIM) on board.
3. Constantly keep the position updated using alternative methods (radar parallel indexing, visual fixes, celestial navigation) during transit through risk areas, not merely as a theoretical backup.
4. Train the bridge team to recognise the signs of possible spoofing (position inconsistent with other sensors, implausible position jumps) and not only the absence of signal typical of jamming.
5. Report detected interference episodes in accordance with Company procedures and, where applicable, to the competent Administrations.

## Practical Example

Management example: during transit through an area known for active GNSS spoofing, the bridge team maintains continuous radar parallel-indexing plotting and constantly verifies the consistency between the displayed GNSS position and radar fixes on known coastal points, promptly detecting a discrepancy indicative of possible spoofing before the incorrect position is used for course decisions.

## Real Cases

The joint warning from ICAO, ITU and IMO in March 2025 was prompted by the significant growth, from 2022 onwards, in GNSS interference episodes in specific geographic areas, with thousands of ships reported affected in 2025 alone, evidence that the phenomenon has moved from a theoretical risk to a daily operational threat to commercial navigation in certain areas.

## Common Mistakes Mistake Library

Mistake | Consequence | How to avoid it
--- | --- | ---
Exclusive reliance on GNSS position without cross-checking against other sensors in areas of known risk | Use of a position incorrect due to spoofing without timely detection | Always maintain active cross-checking (radar, visual fixes) in areas known for interference
Bridge team training focused only on jamming (absence of signal), not on spoofing (a plausible false signal) | Failure to recognise a false but apparently normal position | Train specifically on recognising spoofing signals, not only jamming
Passage planning that does not consider areas known for GNSS interference along the route | No specific preparation of the bridge team before entering the risk area | Always integrate areas known for GNSS interference into the appraisal phase of passage planning

## PSC Observations

The topic is not yet subject to a standardised specific PSC verification, but falls within the general assessment of bridge team competence and the availability of redundant, functioning navigation equipment required by SOLAS Chapter V.

## Operational Tips

- Always maintain active cross-checking between GNSS and other sensors (radar, visual fixes) in areas known for interference.
- Train the bridge team to recognise even the subtle signs of spoofing, not just the absence of signal typical of jamming.
- Integrate areas known for GNSS interference into the appraisal phase of passage planning, not merely as a generic note.

## Checklist

- Areas known for GNSS interference identified during passage planning
- Multi-band receivers and RAIM monitoring systems verified as functioning
- Alternative positioning methods kept active during transit through risk areas
- Bridge team trained to recognise jamming and spoofing
- Detected interference episodes reported in accordance with applicable procedures

## FAQ

What is the difference between GNSS jamming and spoofing?
Jamming disrupts the signal, preventing reception, with an evident loss of fix; spoofing transmits a false signal that causes the receiver to calculate an incorrect but apparently plausible position, often with no obvious sign of malfunction.
What did ICAO, ITU and IMO state in March 2025?
A joint warning of grave concern that GNSS jamming and spoofing disruptions constitute an urgent threat to public safety, telecommunications networks and international trade.
What alternative positioning sources are recommended in GNSS-risk areas?
Inertial navigation systems (INS), celestial navigation, radar parallel indexing and visual fixes on known coastal points, to be kept active during transit, not merely as a theoretical backup.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

ECDIS (Electronic Chart Display and Information System)Passage Planning in Polar Waters

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