GNSS Interference Is Now Persistent: What Offshore Survey Must Do Next

What The Report Documents

The Secure World Foundation’s annual Global Counterspace Capabilities 2026 report, released in April 2026, documents a year in which GNSS interference shifted from an episodic threat to a persistent feature of conflict zones on multiple continents. For positioning engineers, that shift is the operational headline: what was once a sporadic jamming problem is now a recurring planning assumption, particularly in maritime regions.

In the Baltic, European data showed aircraft GNSS interference cases over Poland rising from 1,908 in October 2024 to 2,732 by January 2025. Estonia announced in July 2025 that Russia had moved additional jamming equipment to a site near Kingisepp, roughly 20 kilometres from its border, and stated that GPS jamming had caused over €500,000 in damage to its internal security sector in the preceding three months. Sweden has accused Russia of widespread, near-daily GNSS disruption over the Baltic Sea, with the affected area spreading geographically.

During the June 2025 Iran–Israel conflict, GNSS jamming and spoofing intensified across the Middle East. The Maritime Information Cooperation and Awareness Center estimated that around 970 vessels per day experienced GPS interference in the Strait of Hormuz in mid-June 2025, with operators reporting reduced and more cautious transits through a strait that carries roughly a fifth of global seaborne oil. In May 2025, India’s Operation Sindoor (7–10 May) involved electronic-warfare GNSS jamming in the South Asian theatre. The report also notes GPS spoofing of Starlink ground terminals during protests in Iran in January 2026.

The regulatory response has been measured. In October 2025, ICAO passed a resolution condemning interference attributed to Russia and North Korea. In November 2025, the ITU’s Radio Regulations Board, at its 100th meeting, urged Russia to cease harmful interference to safety services affecting receivers in Estonia, Finland, Latvia and Lithuania.

Why This Matters For Offshore Positioning

Offshore positioning systems are generally designed around the assumption that GNSS is continuously available: DP leans on DGPS, hydrographic surveys on RTK or PPP, and subsea construction on a surface reference position. The SWF data forces a different baseline. RF interference is now a planning input, especially in the Baltic, the eastern Mediterranean, the Strait of Hormuz and South Asian waters, and the practical question is whether a vessel’s positioning suite will function at all in those areas.

DP guidance such as IMCA’s reference-system recommendations accounts for factors like multipath and ionospheric delay, but those provisions assume the underlying GNSS signal exists. Deliberate, sustained RF denial is a different problem, and clients often discover the gap between design assumption and field reality only once the vessel is on station.

The Reality On Deck

RF interference is not one failure mode but two, and they behave very differently. Jamming removes the fix outright: the receiver loses lock, integrity alarms fire, and the DP or survey system fails over to its secondary tier in a way that is at least visible to the operator. Spoofing is the harder problem. A spoofed signal produces a plausible but wrong position, and a DP or survey suite can accept it silently, holding station or logging soundings against a counterfeit fix with no alarm raised. The defence against spoofing is not fall-back but cross-check: continuously comparing the GNSS solution against an independent source, inertial or acoustic, and rejecting the GNSS fix when the two diverge beyond a defined threshold. A contingency plan written only for loss of signal does not cover the poisoned-signal case, and in the contested waters documented above both are now in play.

That matters because the secondary tier, inertial and acoustic, is rarely specified as a primary long-duration solution. A DP2 vessel entering the Baltic with a standard DGPS suite and inertial backup looks adequately redundant on paper, but when the band is denied the GNSS receivers fail together and the work falls to systems that were never sized to carry it.

The same constraint applies to survey accuracy. IHO S-44 defines survey orders in terms of total horizontal and total vertical uncertainty, and the tighter orders depend on RTK-grade corrections to be met. RTK typically delivers horizontal accuracy at the few-centimetre level; without corrections, that performance is simply not available, and the achievable order drops accordingly. Subsea work is harder still. USBL positioning of a vehicle inherits the uncertainty of the surface vessel. If the surface position degrades to unaided inertial drift, that error propagates straight down to the vehicle and grows with time.

Where Clients Get It Wrong

1. Assuming Interference Is Episodic Rather Than Persistent

Clients still ask whether interference could affect operations, as though it were a remote scenario. The SWF data indicates that in contested waters, interference is closer to the rule than the exception. The better question is not whether GNSS could be lost, but how many hours per day it is likely to be unavailable and what the contingency plan is. Treating persistent denial as a rare event leads to under-specified positioning suites, schedules built on optimistic GNSS availability, and force majeure clauses that quietly ignore RF denial.

2. Conflating DP Class With Positioning Availability

Some clients assume a DP class designation guarantees positioning performance regardless of conditions. It does not. DP class defines redundancy against equipment and systems failure, not performance in a denied RF environment. A DP3 vessel with four DGPS receivers and two inertial units still loses its GNSS references together when the band is jammed. The class is unchanged; the operational capability under those conditions is not.

3. Treating Alternative Positioning As An Add-On Rather Than Primary Capability

Specifications often name GNSS as the primary method with “alternative systems as required by conditions”. In high-interference environments the priority should invert: acoustic or mechanical references become primary, with GNSS used opportunistically when available. Carrying acoustic positioning as a secondary afterthought leads to poorly aligned transponders, rushed array calibration and operator unfamiliarity when those systems must carry the work.

4. Underestimating Mobilisation Time When GNSS Is Unavailable

A typical allowance of one to two days for setup and verification assumes GNSS is available and only needs a single check. Where acoustic positioning must instead be deployed and calibrated, three to five days is more realistic: transponder deployment, array calibration, sound-velocity profiling and end-to-end testing each take time. A two-day plan in a denied environment starts behind schedule on day one.

5. Misunderstanding Force Majeure Coverage

Force majeure clauses typically cover war, government action and events beyond the contractor’s control. Persistent GNSS interference in a conflict zone looks like a candidate, but most clauses require the event to be unforeseeable. When public reporting, including SWF assessments, documents interference in specific waters months in advance, and when ICAO and ITU have formally addressed it, an unforeseeability argument is weak. The risk shifts back toward the party that should have planned for it.

What Actually Works In Denied Environments

In a denied environment, acoustic and mechanical references should be treated as primary, not as backup. LBL transponder arrays provide coordinates that are unaffected by RF interference; a well-configured array can hold relative accuracy in the decimetre range, and in good geometry better, which is adequate for most subsea construction and pipeline inspection work, independent of the surface GNSS state. USBL positions a vehicle relative to the surface vessel, with an error that scales with slant range, commonly on the order of a fraction of a percent of range, so depth and offset add metres of uncertainty in deep water before any surface error is counted. It also inherits whatever uncertainty that surface position carries, so in a denied environment the surface vessel itself needs a non-GNSS measurement source feeding its DP system, for example a taut wire or a laser/fanbeam sensor referenced to a fixed structure. DP is the station-keeping controller, not a position reference in its own right; it can only hold the vessel as well as the relative sensor it is fed.

Inertial systems bridge short GNSS outages but are not a persistent-denial solution. Even a navigation-grade IMU, with unaided position drift on the order of a nautical mile per hour, walks well beyond survey tolerance within minutes once the GNSS aiding is gone, and the error only compounds over a multi-day operation. They are valuable for transient dropouts, not for sustained interference. Route planning should assume GNSS will be unavailable: establish safe positions from which acoustic positioning can be initialised before entering known interference zones, and treat inertial-only transits from the last GNSS fix as good for hours, not days.

Recommendations For Project Teams

Check project areas against the SWF report and comparable assessments of active RF interference. If you are operating in an interference zone, make acoustic or mechanical positioning the primary system rather than a backup, and plan a three- to five-day mobilisation rather than one to two. For DP in interference zones, specify the minimum station-keeping and position-measurement approach that must work without GNSS: the relative reference that feeds DP, such as taut wire for a lifting platform or acoustic and laser referencing for a construction vessel, and, where applicable, a mooring mode such as anchoring for a drilling rig that removes dependence on a dynamic GNSS fix altogether. Do not rely on DP class alone, since it does not guarantee positioning performance.

For hydrographic surveys, define the minimum accuracy required and identify the point at which loss of RTK corrections renders the survey order unachievable. For some tasks, DGPS or PPP accuracy is sufficient; for others it is not. Settle that before mobilisation, not on station.

Update force majeure clauses to reflect that persistent RF interference is no longer an unforeseen event. Plan redundancy against interference, not only against equipment failure, which means diversity of technology, acoustic alongside GNSS, rather than simply more GNSS receivers. Account for transponder counts, calibration time and the operational procedures that acoustic positioning demands. Persistent GNSS interference is the emerging normal in contested waters, and design specifications and positioning layouts should be set accordingly.

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Based on: GNSS Interference Now a Constant of Modern Conflict, SWF Annual Report Finds