WAYPOINT - Staying alert to jamming and spoofing

George Shaw from the Royal Institute of Navigation explores how GNSS can become vulnerable to jamming and spoofing and what mariners can do to stay on course

GNSS are principal sources of maritime positioning. However, they are all vulnerable to signal interference – both natural and deliberate (jamming). Unlike aviation’s provision of alternative electronic positioning inputs independent of GNSS (eg radio beacons, ILS, high-grade INS), maritime versions have limited backup systems.

A vessel’s GNSS-derived position and course, portrayed so precisely by ECDIS, remains a compelling indication for mariners even if GNSS errors are suspected. Positioning resilience for safe passage during GNSS disturbance is primarily dependent on mariners’ alertness and frequent cross-checks combined with manual intervention using traditional navigation skills.

The world is seeing increasing instances of geopolitical conflicts. As a result, GNSS jamming at sea is becoming more commonplace in some regions such as the Middle East and eastern Europe, which raises severe risks to shipping. Several years ago, live GPS jamming trials using Trinity House vessels revealed shocking effects that can still be experienced today. Relatively low power jamming, insufficient to deny GPS fully, induced a slow increase in position errors that went undetected and grew sufficiently to affect the autopilot and alter the vessel‘s course. This was all without any alarms sounding on the bridge. At higher jamming power levels, GPS was fully denied and the crew were alerted by the receiver triggering alarms.

GNSS JAMMING AT SEA IS BECOMING MORE COMMONPLACE IN SOME REGIONS SUCH AS THE MIDDLE EAST AND EASTERN EUROPE, WHICH RAISES SEVERE RISKS TO SHIPPING

Errors and alarms

Responses of vessels’ systems to jamming vary, as even type-approved receivers can behave differently. When GNSS is denied, the displayed position may freeze or be extrapolated by Dead Reckoning (with errors growing significantly due to inertial drift). Digital bridge systems are becoming increasingly integrated, meaning that undetected erroneous PNT information can be fed instantly to multiple applications, and affect AIS reports. In live trials, GPS denial caused multiple bridge systems (eg stabilisation of the Radar display) to alert in rapid succession, with a cacophony of alarms sounding, temporarily overwhelming mariners’ cognition.

Additionally, the threat of GNSS spoofing is expanding, particularly in areas such as the Red Sea, Gulf and Black Sea. Counterfeit signals can take over the receiver’s tracking from genuine signals, gradually offsetting the position solution without being detected by the ship’s systems or being readily noticeable to the mariner. This is a more insidious effect than AIS spoofing, which typically introduces more obvious position errors.

GNSS jamming and spoofing are becoming more widespread, with emerging evidence of some malicious transmissions from satellites. Regulatory action for future type-approved receivers is underway to counter these threats, but most vessel implementation is years away. Longer term, cross-sectoral solutions are being explored, some necessitating extensive ground infrastructure: dedicated Low Earth Orbit PNT satellites or innovative PNT applications of existing LEO communications signals (eg Starlink).

For the foreseeable future, mariners must hone traditional navigation skills (ideally with bridge simulator training safely providing a wider experience of threats) and navigate using all available data sources. Mariners should monitor possible discrepancies of ECDIS portrayed position and track when cross-referenced in coastal waters with radar overlay and regular visual bearings. Always consider that GNSS can present hazardously misleading positions even if no alarms are raised.