Navigation Resilience: Procedures for GNSS-Denied Environments in Ukraine

Navigation resilience refers to the ability of air, sea, and ground vehicles to maintain safe, accurate navigation when Global Navigation Satellite System (GNSS) signals are unavailable, degraded, or spoofed. The Russia-Ukraine conflict has transformed navigation resilience from a theoretical planning consideration into an operational imperative: GNSS denial and spoofing are routine features of the operating environment, forcing military and civilian operators to develop and employ backup navigation capabilities. The lessons emerging from this environment are reshaping international standards and best practices for navigation system design across aviation, maritime, and military domains.

IMO Guidelines for GNSS-Denied Maritime Navigation

The International Maritime Organization has progressively strengthened guidance for GNSS-denied navigation following incidents attributed partly to over-reliance on electronic navigation. IMO Resolution A.1115(30) and related circulars address backup navigation, requiring vessels to maintain proficiency in traditional navigation techniques including manual radar fixes, celestial navigation, and dead reckoning independent of GNSS. The IMO's e-Navigation strategy explicitly addresses cyber resilience and GNSS denial scenarios, calling on states to ensure navigation infrastructure and vessel competence can sustain safe navigation without GNSS.

Black Sea shipping companies have adapted IMO guidance to their specific context: requiring double-watch procedures during GNSS-anomaly-suspect periods, maintaining paper chart plotting parallel to electronic charts, and requiring bridge officers to demonstrate manual radar navigation competency in annual training assessments. The Ukrainian maritime authority has issued national guidance reinforcing IMO requirements with Ukraine-specific threat context, acknowledging explicit Russian electronic warfare as the threat rather than treating GNSS anomalies as hypothetical.

Inertial Navigation System Backup for UAVs

Inertial Navigation Systems (INS) derive position from accelerometers and gyroscopes that measure acceleration and rotation, integrating these measurements from a known starting position to compute current position. INS requires no external signals—it is entirely self-contained, making it immune to jamming and spoofing. The limitation is position drift: small measurement errors accumulate over time, producing position error that grows with navigation duration (approximately 1-2 km per hour for commercial MEMS-based INS, and 10-100 meters per hour for military-grade ring laser gyroscope INS).

For tactical military UAVs with mission durations of 30-90 minutes and GPS unavailable for portions of flight, MEMS INS backup may be acceptable—position error of 1-3 km from INS drift could still allow course corrections based on visual landmarks or target acquisition. For longer-range strike UAVs flying several hundred kilometers, INS-only navigation produces unacceptable terminal accuracy degradation; these systems require supplementary navigation (terrain matching, visual navigation, or periodic GPS re-acquisition where signal is available) to achieve acceptable strike accuracy.

Navigation Backup System Comparison

Ukrainian Drone Operator Anti-Jam Training

The Ukrainian military has developed training programs for UAV operators specifically addressing GPS denial environments. Training curricula include: recognition indicators for GPS jamming (sudden fix loss, position jumps, high-HDOP readings), recognition of GPS spoofing (position inconsistency with visual landmarks, compass heading divergence from GPS track), manual navigation procedures using terrain recognition and visual waypoint identification, and emergency recovery procedures when GPS is lost during mission. CERT-UA and the armed forces have documented that Russian electronic warfare systems create predictable patterns—certain areas and altitudes are more consistently jammed—allowing operators to plan missions to reduce jamming exposure during critical mission phases.

International Aviation GNSS Resilience Standards

International Civil Aviation Organization (ICAO) has accelerated work on GNSS resilience standards following the documented spoofing and jamming incidents near conflict zones. The Frequency Spectrum Protection Panel and GNSS Panel have been tasked with developing new monitoring requirements, improving RAIM algorithms to detect spoofing rather than only jamming, and establishing requirements for backup navigation capability at airports in regions with elevated GNSS interference risk. Airlines operating in affected regions have preemptively adopted crew training enhancements before formal regulatory requirements are updated, training crews in VOR/DME and ILS-only approach procedures that had been partially de-emphasized as GNSS obviated much traditional radio navigation proficiency.

FAQ

What is dead reckoning and how reliable is it for maritime navigation under GNSS denial?

Dead reckoning derives current position by applying known course and speed from a last-known position, producing an estimated position that degrades in accuracy over time with current, leeway, and measurement uncertainties. For a vessel traveling at 15 knots, dead reckoning error with careful manual plotting may be 1-3 nautical miles after several hours—adequate for open-ocean navigation but potentially hazardous near coastal obstacles or traffic separation schemes. Combined with regular radar fixes from identifiable shore features or buoys, dead reckoning provides acceptable position maintenance for periods of GNSS outage in most maritime environments.

How does TERCOM terrain-following navigation work in Ukrainian strike drones?

TERCOM (Terrain Contour Matching) correlates radar or barometric altimeter readings against a pre-loaded digital elevation model to derive position by matching measured terrain profile against reference maps. The drone measures its altitude above sea level versus altitude above terrain as it flies, and specialized algorithms match this signature against the stored database to derive a position fix. TERCOM performance depends on terrain variability (flat terrain provides fewer distinctive features for matching) and database update currency. Western cruise missiles like the Tomahawk have used TERCOM for decades; Ukraine has incorporated terrain correlation navigation into domestically developed long-range strike UAVs.

Can commercial drones be retrofitted with anti-jam GPS for Ukrainian military use?

Commercial DJI and similar consumer drones use standard civilian GPS receivers with no anti-jam features and cannot be practically retrofitted with military anti-jam capabilities—the required controlled reception pattern antennas (CRPA) are physically too large and heavy for most consumer drone form factors, and the signal processing electronics would require complete GPS system replacement. Practical adaptations for commercial drones in contested GNSS environments include adding secondary multi-constellation receivers (Galileo + GPS increases jamming threshold), visual navigation aids, and software-level spoofing detection, which can improve resilience without requiring classified hardware.

What does ICAO recommend for pilots experiencing GPS spoofing during approach?

ICAO and EASA guidance advises pilots who suspect GPS spoofing to immediately cross-check GPS-derived position against inertial reference position (available in modern aircraft as IRS position), and against traditional radio navigation (VOR/DME position fix if available). If discrepancy is confirmed, pilots should not use GPS for navigation and should inform ATC immediately. In the approach environment, pilots should request a non-GNSS approach (ILS, VOR, or radar) and, if inside the final approach fix with GPS corrupted, should execute a missed approach unless visual conditions allow continuation without GPS guidance.

How long can a military aircraft navigate purely by INS before position error becomes critical?

Military aircraft with ring laser gyroscope INS can typically navigate for 1-2 hours with position errors remaining below 200-500 meters—adequate for transit navigation but potentially limiting for precision strike in the terminal phase. Fighter aircraft in high-performance maneuvers accumulate INS error faster than steady-state cruise. Most modern military aircraft blend GNSS and INS (GPS/INS integration) where GPS provides frequent position corrections to reset INS accumulated drift, extending the effective INS-only navigation period to however long before the drift exceeds mission-required accuracy—which with regular GPS availability is indefinitely, and in GPS-denied conditions is the raw INS performance period.

Sources

1. IMO — "Maritime Cyber Risk Management in Safety Management Systems," IMO Resolution MSC-FAL.1/Circ.3/Rev.2, 2022
2. ICAO — "Manual on Global Navigation Satellite System (GNSS)," Doc 9849, 4th Edition 2013 (under revision)
3. NATO STANAG 4430 — "Navigation in GPS Degraded/Denied Environments," (unclassified summary cited in NATO ACT papers)
4. EASA — "NPA 2023-14: GNSS Resilience and Interference Monitoring," easa.europa.eu 2023
5. The MITRE Corporation — "Resilient Navigation: A Framework for Analyzing and Mitigating Navigation Vulnerabilities," mitre.org 2020