How fibre-optic gyrocompass systems combat jamming and spoofing

How FOG systems combat jamming and spoofing

Sperry’s new generation of FOG has a “built-in layer of security against jamming” said Mr Magner. When GNSS jamming or spoofing is detected, Sperry’s compass management system alerts navigators and issues a call for action to ensure the vessel’s safety.

Several generations of Sperry’s FOG units have been installed on thousands of commercial ships and can be upgraded to reduce the risk of GNSS jamming impacting ship navigation. “It is straightforward to upgrade existing ships with this solution without ripping out the entire system,” said Mr Magner.

Its Navigat 2500 attitude and heading-reference system gyrocompass provides a defence against jamming and “is robust to rough GNSS spoofing once it is correctly aligned,” he adds.  

It is DNV MED type-approved and available free of export controls, which could affect ordering military-grade INS units that can also support navigation when GNSS is jammed or spoofed.

Mr Magner said Navigat 2500 FOG is robust enough to ensure ship headings are sufficiently accurate to maintain safe operations without GNSS. 

“Alertness training is therefore critical, but so is training for knowing what to do next"

Sperry’s navigation systems for commercial ships are integrated and set up so collision avoidance remains fully functional during a fullscale GPS jamming attack.  

“The accuracy of heading, rate of turn, roll, pitch, yaw or acceleration data does not offer the position fixes or velocity calculations to support ECDIS position information during GNSS disruptions,” Mr Magner said, “but it is sufficient to support ARPA functions and autopilot control.”

GPS anomalies cause FOG units to prompt crew that heading data may be false, so they can consider whether and how far to offset ECDIS displays against radar overlay, he added.

“Alertness training is therefore critical, but so is training for knowing what to do next and how to use other means to navigate safely when a technology that you rely on is not available,” said Mr Magner. “Crew working in open seas with no visual reference points often do not easily recognise that spoofing is underway, or how long they have been exposed. If something goes wrong and they ask for help, their risk is compounded if the wrong position is being reported. Security is increasingly critical to realising the full benefits of a modern compass system.” 

Sperry Marine has researched the extent of GNSS jamming and spoofing to understand the issues ships face when navigating areas prone to these crimes. It found references to GNSS interference around the Black Sea, Red Sea, eastern Mediterranean, Arabian Gulf and Baltic Sea.  

In July 2023, the NATO Shipping Centre was reporting regular disruption in the eastern Mediterranean.  

On 4 April 2024, Lloyd’s List Intelligence reported 227 cargo ships in the Black Sea as located at multiple sites inland and 117 ships in the Mediterranean as in position at Beirut-Rafic Al Hariri airport, in Lebanon.  

Information from Windward AI indicated tracking on 890 vessels experienced interference off the coast of Sudan in Q2, up from 180 incidents in Q1 (and from zero in Q4 2024).  

A similar trend occurred in the Baltic Sea, where the number of affected ships rose from 1,225 in Q1 2025 to more than 5,800 in Q2.  

Windward also reported “970 ships per day” on average as affected by GPS jamming in the Arabian Gulf and Strait of Hormuz over a four-day period in June. Windward puts the average distance vessels jump when AIS is jammed as having increased tenfold from 600 km in Q4 2024, to 6,300 km in Q1 of 2025. 

An unnamed satellite service provider recently reported that, while calls concerning the unavailability of GPS from ships came in at a rate of around once every two weeks in July 2024, more than 150 reports were received in a single day in mid-July 2025. 

Riviera is hosting the When GPS lies and AIS goes dark: rethinking navigation resilience with AI webinar on 8 September 2025. Use this link to register for this free webinar.