Top GNSS/GPS-Denial Questions Answered

Modern military, aviation, and maritime operations are critically dependent on precise Positioning, Navigation, and Timing (PNT) data. For decades, the Global Positioning System (GPS) and other Global Navigation Satellite Systems (GNSS) have served as the backbone of these capabilities, enabling everything from aircraft navigation and drone guidance to vessel tracking and synchronized global communications. However, as GPS denial and deception events become more frequent and geographically widespread, the need for resilient, assured PNT (A-PNT) solutions has become urgent. Ensuring operational continuity requires a clear understanding of the causes of GNSS disruption, who is most affected, how navigation can be sustained without it, and how technologies such as A-PNT can provide protection and redundancy.

The following GPS/GNSS-denial questions outline the key dimensions of this challenge: the sources of GPS disruption, the sectors and regions most exposed, operational fallback procedures, and the A-PNT technologies and strategies designed to safeguard navigation and timing in an increasingly contested GPS environment.

Q1. What Causes GPS Disruption?

Disruption can arise from unintentional interference, deliberate hostile actions, or natural environmental factors; all of which can degrade, deny, or corrupt the signal in ways that directly impact mission assurance and operational safety.

Unintentional interference remains a common source of disruption, particularly in congested environments, like major shipping ports, airspace hubs, and coastal regions. Overpowered or poorly shielded radio frequency transmitters, such as cellular base stations, radar systems, or satellite uplinks, can unintentionally saturate or desensitize GNSS receivers. Faulty amplifiers, including “personal privacy devices” (PPDs) used illegally in vehicles to block tracking, also generate wideband noise that can overwhelm nearby receivers.

Intentional interference, including jamming and spoofing, poses a more severe and rapidly escalating threat. In the military domain, jamming may occur during electronic warfare or combat operations. Criminal organizations also exploit GPS and GNSS vulnerabilities for illicit purposes such as cargo theft, illegal fishing, or sanctions evasion using low cost jammers and spoofers to conceal location or manipulate tracking data. In aviation and maritime operations, such interference can mislead autopilot systems, distort route data, and undermine collision avoidance and surveillance systems like ADS-B and AIS, potentially leading to incidents that pose a threat to life.

Environmental and natural factors further complicate GPS reliability. Solar flares and ionospheric disturbances can alter signal transmission, particularly at high latitudes or during periods of intense space weather, resulting in signal delays or complete loss of lock.  Multipath reflections from large metallic structures, such as port cranes, vessel superstructures, or urban skyscrapers, can also distort signals and create false positional data. These effects are particularly acute in confined environments like harbors or dense airspace corridors, where reflected signals can be mistaken for valid GPS information.

Detection and characterization of GPS/GNSS disruption requires a combination of technical and procedural measures. RF power monitoring and direction finding equipment can help locate the source of interference, while incident mapping and space weather alerts support broader situational awareness. Crowdsourced interference reporting and data sharing between civil and military authorities enhance detection coverage and enable trend analysis across regions.

Q3. How do Pilots, Mariners, and Military Personnel Navigate Without GPS?

In aviation, when GPS is unavailable, aircraft revert to more traditional navigation systems and navigation aids that must be maintained as essential backups. The backbone is the Inertial Reference System (IRS)  and Inertial Navigation System (INS), which uses accelerometers and gyroscopes to continuously estimate position, velocity, and attitude. However, inertial systems suffer from drift – small sensor errors accumulate over time. To constrain that drift, pilots use periodic corrections from ground-based radio aids such as DME (Distance Measuring Equipment), VOR (VHF Omnidirectional Range), or radar updates from Air Traffic Control. When GPS integrity is lost, pilots may revert to conventional airways and non-GNSS instrument procedures, fly under visual flight rules if weather allows, or rely on approaches guided by the Instrument Landing System (ILS), NDB (Non-Directional Beacon), or local ground-based navigation aids. The FAA explicitly retains a VOR MON (Minimum Operational Network) concept to ensure aircraft can navigate via conventional VOR paths during GPS outages.

In maritime and offshore operations, GNSS denial is a severe vulnerability, particularly for dynamic positioning vessels and precise stationkeeping tasks, so ships rely on a suite of fallback systems. A gyrocompass, Doppler log, and radar-bearing fixes provide coarse navigation and heading references in coastal waters. Electronic Chart Display and Information Systems (ECDIS) allow manual plotting of fixes, and in more extended open ocean transits, celestial navigation or celestial fixes remain usable (albeit with skill). Some operators are evaluating the revival of terrestrial radio systems like eLORAN, which transmit low frequency signals over land that are much harder to jam and can serve as a GNSS backup in restricted regions.

For military operations in contested or GPS-denied environments, reliance on GNSS is particularly fragile, so hybrid navigation is essential. The U.S. Army has actively pursued pseudolite networks (ground-based “pseudo-satellites”) to preserve position information when GPS is denied. Pseudolites broadcast local ranging signals that, when integrated with an INS, give troops a reliable local positioning layer with far higher received power than spaceborne signals and therefore much better resistance to jamming at the tactical scale.

These alternative methods, however, are not without vulnerabilities or trade-offs. Inertial systems drift and must be regularly corrected; radio aids can be jammed, degraded, or decommissioned, vision-based systems fail in low visibility or featureless terrain, and acoustic or pseudolite systems have limited coverage or require infrastructure. This is why cross-training crews in traditional navigation techniques, sensor fusion architectures, and frequent calibration of INS and navigation sensors remains essential. Maintaining up to date navigation charts, ground aids, and fallback databases all help to ensure operational continuity when GNSS is degraded or denied.

Q5. How Is Iridium PNT Improving Navigational Resilience for GPS-denied Territories?

For military and security users, this shift offers critical operational advantages. LEO-PNT services delivered via the Iridium constellation provide encrypted and regionally tailored positioning, navigation, and timing data that can penetrate indoors, under canopy, or through moderate jamming. Iridium’s PNT service leverages Iridium’s 66-satellite global mesh operating in the L-band, distinct from GPS frequencies, making it far harder to disrupt with conventional jamming equipment. Because the Iridium system is already operational and uses cross-linked satellites for global coverage, it provides real time assured timing and location integrity even in contested or denied regions such as the Arctic, the Indo-Pacific, or urban RF-dense zones.

Satellite proximity to the Earth and signal strength alone, however, are not enough to secure PNT. Thus, the Iridium PNT service also incorporates cryptographic authentication to protect against spoofing and tampering. Every navigation and timing message is digitally signed, and receiving devices verify the integrity of those signatures before using the data. Unauthorized or falsified signals are rejected, ensuring that systems operate only on trusted information, delivering a far more robust and resilient service than GPS.

For commercial shipping and aviation, these LEO-based services introduce an accessible layer of resilience. In hybrid navigation, Iridium PNT works alongside GNSS and INS, enabling devices to seamlessly shift or blend inputs as signal conditions change. In maritime environments, where GPS spoofing has been documented in the Black Sea and Eastern Mediterranean, Iridium-based A-PNT can sustain dynamic positioning operations. Similarly, aviation operators can use A-PNT to maintain flight management system synchronization and prevent false positional data from compromising navigation displays.

In practice, A-PNT serves as a critical additional layer of navigation for military, maritime, and aviation operations, allowing personnel, aircraft, ships, and unmanned systems to maintain mission continuity when GNSS is compromised. The resilient and secure design of A-PNT provides operational assurance, mitigating the single point vulnerabilities of space-based GNSS and GPS navigation, and is increasingly becoming recognized for resilient navigational planning in both defense and commercial sectors.

Q7. What are the Early Warning Signs of GNSS Interference?

Early warning signs of GNSS interference are critical for maintaining operational safety across military, aviation, and maritime platforms. Onboard receivers may show a sudden loss of satellite lock, unexpected position or time jumps, or RAIM/integrity alerts in aircraft, all of which indicate potential jamming or spoofing. Unusually high or low signal-to-noise ratios, discrepancies between redundant receivers, or inconsistencies with INS, radar, Doppler logs, or visual bearings, or an Iridium PNT feed, are additional red flags.

In hybrid GNSS + INS + Iridium PNT architectures, the system can continuously compare GNSS against Iridium PNT’s independent time/location. Divergence beyond thresholds, for example, GNSS position drifting while STL-referenced dead reckoning and ship sensors remain coherent, provides early, positive indication of spoofing or severe degradation, enabling alarms, de-weighting of GNSS, or automatic failover/blending to maintain navigation continuity.

At the system level, automated controls may generate alerts: aircraft autopilots or ship dynamic positioning systems may show deviations from expected performance without an apparent environmental cause. Slowly drifting positions or erratic movements that do not match the platform’s true course may suggest spoofing rather than outright jamming. Environmental indicators, such as unusual RF activity in GNSS frequency bands or corroborating reports from nearby vessels or aircraft, can confirm the presence of interference.

In Summary

The vulnerabilities of GPS and GNSS represent a critical operational risk across military, aviation, and maritime domains. Their inherently weak signals are easily disrupted by intentional jamming, spoofing, or even natural phenomena such as solar flares and ionospheric disturbances. Real world incidents from the Black Sea to the Eastern Mediterranean and Arctic corridors have repeatedly demonstrated that overreliance on GNSS can jeopardize mission integrity, navigational safety, and the continuity of operations. To mitigate these threats, both defense forces and commercial operators should invest in A-PNT to further strengthen resilience by providing high-power, encrypted, and timing and positioning data.

The strategic imperative is clear: GNSS dependence must evolve toward a multi-layered ecosystem, integrating terrestrial and PNT technologies, procedural training, and robust reporting chains. For decision makers in defense, aviation, and commercial shipping, building resilience into PNT infrastructure has become an operational necessity for maintaining control, safety, and strategic advantage in an increasingly contested environment.