In brief: A Norwegian rescue helicopter and a small aircraft took off over Andøya in 2024, but the routes visible to satellite-navigation receivers told a different story. On tracking screens, the helicopter appeared to make a series of tight, overlapping turns. The plane seemed to trace sharp, unnatural patterns in the air. Neither display reflected the aircraft's actual flight path.
The false tracks were created as part of Jammertest, an annual Norwegian exercise that examines how equipment responds when satellite-navigation signals are disrupted or manipulated.
Held on the island of Andøya, roughly 300 kilometers north of the Arctic Circle, the event brings together engineers, public agencies, and companies that depend on Global Navigation Satellite Systems, or GNSS.
The exercise, scheduled for mid-September this year, has become more relevant as real-world satellite interference has intensified around Russia's war in Ukraine. An RAF aircraft encountered GPS jamming near the Russian border in May. In September 2025, Sweden's Transport Agency said it was dealing with interference every day. Experts also warned in June 2026 that Russian satellites had transmitted interference from orbit, briefly disrupting GPS signals across Europe.
Aviation offers the clearest example of the problem because the effects are visible immediately. But GNSS interference can extend far beyond a flight deck or a map display. Satellite networks such as GPS provide not only location data but also highly accurate time. That timing supports communications networks, power grids, transport systems, and financial markets, where systems must remain synchronized.
Jammertest is built around the possibility that a receiver may lose that signal or, more troublingly, accept a false one. Jamming overwhelms the signal so that a receiver cannot use it. Spoofing sends a stronger counterfeit signal that can make equipment report an incorrect position or time.
The difference is important for infrastructure operators. A sudden loss of satellite data may be detected quickly, allowing a system to switch to backup timing. Spoofing can be harder to catch. If equipment continues to receive what appears to be valid data, it may distribute inaccurate timing or location information before anyone recognizes the problem.
At the 2024 event, Harald Hauglin, chief engineer of time and frequency metrology at the Norwegian Metrology Service, and his team demonstrated that spoofing can be a slow-moving risk. They gradually increased the strength of a spoofing signal over about 40 minutes. As the decoy signal became more powerful, a map display shifted the test site's reported location away from its real position and into the Norwegian Sea.
The positional error was easy to see. Measuring the effect on time required a different setup. The team compared a GNSS-synchronized clock exposed to interference with a reference clock connected by fiber-optic cable to a receiver beyond the test area. The difference between the two was tracked in nanoseconds, revealing how a manipulated signal can slowly move a clock away from the correct time.
That is a particular concern for systems that need a common clock to operate. A power grid or mobile network can continue operating for some time after losing GNSS, but its ability to do so depends on the quality of its backup equipment. Local clocks, atomic references, and fiber-optic links can maintain precise timing, though building and maintaining them adds cost.
The more difficult scenario is a spoofing event that goes unnoticed. Rather than forcing a system to use its backup, it could continue feeding the system bad data. Over time, that may cause a wider synchronization problem across connected networks.
Jammertest is intended to identify these weaknesses before they appear in an actual disruption. Participants test commercial and industrial receivers in an open setting, then share results with other attendees. That approach differs from more tightly controlled US military tests, where information from the exercises is more restricted.
Norway and other governments are considering how much redundancy is needed as GNSS interference becomes a more regular feature of the security environment. Fiber-based timing networks and atomic clocks are among the options. Hauglin's White Rabbit patch refers to White Rabbit, a CERN-developed system that distributes time across fiber-optic networks with accuracy better than one nanosecond.
Such systems can reduce dependence on satellite signals, but they do not replicate every service GNSS provides. Dana Goward, co-founder of the Resilient Timing and Navigation Foundation, said the answer will require several layers of protection rather than one replacement technology. "There is no silver bullet, which is why you need a combination of systems," he told the BBC.