The integrity of Global Navigational Satellite Systems (GNSS) is increasingly under threat, posing significant and immediate dangers to maritime safety, especially in geopolitical conflict zones. Gard, a prominent P&I club, highlights recent incidents and claims stemming from GNSS disruption, emphasizing the urgent need for enhanced awareness and countermeasures within the shipping industry. While multiple GNSS constellations exist (e.g., China’s BeiDou, Europe’s Galileo, Russia’s GLONASS), the focus remains primarily on GPS due to its widespread use and established infrastructure.
Causes and Manifestations of GPS Interference
GPS disruptions are a result of various factors, including natural phenomena like solar flares and equipment malfunctions such as faulty receivers or antennas. However, a rapidly increasing concern is deliberate interference, which has become a prominent feature of modern conflict and geopolitical tensions. States are actively employing GPS interference to:
- Deny adversaries access to critical positioning data.
- Protect critical infrastructure from potential attacks.
- Obscure military movements.
These deliberate operations frequently have collateral impact on civilian activities, particularly maritime navigation in nearby sea lanes. Recent examples of such defensive measures against drone and missile threats include the Israeli coast and the Red Sea during the Israel-Hamas conflict, as well as the Persian Gulf and Arabian Gulf. Throughout 2025, an increasing number of regions globally have experienced GNSS interference, underscoring the widespread nature of this challenge.
Beyond state actors, criminals are also increasingly utilizing GPS jammers to disable tracking systems on trucks, containers, and vessels, especially in and around ports and logistics hubs, thereby facilitating theft and other illicit activities.
GPS Jamming vs. Spoofing
It is crucial to differentiate between two commonly interchanged terms:
- GPS Jamming: This involves blocking or interfering with legitimate GPS signals by overwhelming them with stronger, unauthorized radio signals. It’s akin to overwhelming a conversation with noise, making the original signal inaudible. When jamming occurs, receivers typically lose signal lock and cannot determine position.
- GPS Spoofing: This is the more deceptive act of transmitting false GPS signals designed to trick a receiver into calculating an incorrect position, velocity, or time. Instead of blocking the signal, a spoofer imitates a legitimate GPS signal, making the vessel’s receiver believe it is real. The GPS display will show a position, but it will be inaccurate, potentially by a significant margin, without necessarily triggering alarms.
Recognizing the Signs of GPS Disruption
Mariners must maintain heightened vigilance for signs of GPS disruption, as many onboard systems—including ECDIS, Radar/ARPA, Gyro compass, course recorder, and autopilot—are heavily reliant on GPS input.
- Jamming Indications: Mariners may observe unusually high Horizontal Dilution of Precision (HDOP) values (e.g., greater than ‘4’), RAIM (Receiver Autonomous Integrity Monitoring) alerts entering caution or unsafe modes, or elevated Signal-to-Noise Ratio (SNR) values. On ECDIS, jamming can trigger sensor failure alarms, potentially leading to a switch to backup sensors or dead reckoning.
- Spoofing Indications: Spoofing poses a more deceptive threat as the GPS receiver might report an erroneous but seemingly valid position, often without RAIM detection. ECDIS can display incorrect positions, and radar/ARPA systems (when GPS-fed) will show erroneous data. Gyro compasses may also enter an alarm state if relying on GPS for drift stabilization.
A significant challenge is alarm fatigue during GPS signal loss, where numerous simultaneous alarms can lead to sensory overload. Furthermore, covert GPS failures can occur without triggering any alarms, making detection incredibly difficult. A near-grounding incident in the Great Barrier Reef, caused by a malfunctioning GPS antenna feeding incorrect data without alarms, underscores the dangers of relying solely on a single source of navigational data.
Responding to GPS Disruption and Countermeasures
Effective responses to GPS disruption involve both technical mitigation and critical operational decisions:
Technical Mitigating Measures:
- Referencing resources like Intertanko’s ‘Jamming and Spoofing of Global Navigation Satellite Systems’ is crucial.
- Switching to a secondary receiver that uses a different GNSS constellation (if available).
- Employing parallel indexing on radar or ECDIS.
- Utilizing RADAR overlay on ECDIS for position verification.
- Performing manual position plotting on ECDIS using traditional navigation techniques (e.g., visual bearings, radar ranges and bearings from conspicuous landmarks) where feasible. It’s noted that ECDIS user-friendliness for manual plotting varies significantly.
- Upon a GPS interference alarm, mariners must identify the root cause rather than simply silencing it.
Operational Decisions and Voyage Continuation: Beyond technical fixes, critical operational decisions become paramount:
- Reducing speed: This provides more time for assessment and lessens potential damage during incidents like grounding.
- Increasing bridge manning: Ensures sufficient personnel to manage the situation.
- Informed go/no-go decisions: Whether to proceed with the voyage should be guided by a comprehensive response plan considering:
- Complexity of the passage and room to maneuver.
- Availability and capability of pilots or local tug assistance.
- Reliability of buoys and fairway markings.
- Presence of safe anchoring points.
- Density of traffic.
- Effectiveness of Vessel Traffic Service (VTS) management.
- Visibility conditions.
- Geographic extent of the GPS disruption.
These integrated approaches, combining enhanced crew training, vigilant monitoring, and robust contingency planning, are essential to ensure maritime safety in an environment where GNSS interference is an increasingly prevalent and sophisticated threat.
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Source: Gard
