GNSS interference stopped being an exotic threat around 2022 and became operational weather: tens of thousands of flights along NATO's eastern flank log jamming every month, ships see phantom positions, and drone operators in the Baltics treat GPS loss as a when, not an if. If your aircraft's plan for "GPS acting strange" is a shrug, this guide is the fix.
Know your enemy: three flavours of trouble
| Threat | Mechanism | Receiver symptom | Danger level |
|---|---|---|---|
| Jamming | Noise overpowers weak satellite signals | C/N0 collapse, lost fix | Moderate — detectable |
| Meaconing/rebroadcast | Recorded real signals replayed | Position/time offset, plausible-looking | High |
| Spoofing | Synthesised fake constellation | Confidently wrong position/time, healthy-looking fix | Highest |
Scale matters: satellite signals arrive at roughly −130 dBm — a one-watt jammer kilometres away wins. That asymmetry is why resilience is an architecture question, not a better-antenna question.
What interference does inside your aircraft
The flight stack's EKF fuses GNSS with inertial sensors (see the sensor suite guide). Under jamming, GNSS innovations explode and a healthy configuration rejects the source — the aircraft coasts on IMU+baro with growing drift. Under spoofing, the poison arrives inside tolerance: position walks off smoothly, the EKF follows, and a position-hold aircraft physically follows the lie. Time is the sneaky casualty — GNSS disciplines your timestamps, and mapping payloads or synchronised sensors inherit spoofed time silently. RTK helps against crude spoofing (corrections won't match) but is equally jammable.
The resilience ladder
Climb only as high as your operation needs — each rung costs money and integration effort:
- Configuration hygiene (free). Multi-constellation, multi-band receivers; EKF innovation gating and GNSS-weight parameters actually tuned; sane GNSS-loss failsafe per mission phase — dead-reckon briefly, then altitude-hold descent or inertial return, never blind position-hold.
- Detection and alerting. Log and alarm on C/N0 collapse, fix-type changes, position-vs-inertial divergence and receiver interference flags (modern u-blox class receivers report jamming/spoofing indicators). Crews who see "GNSS degraded" act; crews who don't, file incident reports.
- Sensor cross-checks. Dual dissimilar receivers, GNSS heading vs magnetometer disagreement alarms, barometer/rangefinder sanity checks — cheap redundancy that unmasks most spoofing.
- Hardened antennas. Controlled-reception-pattern antennas (CRPA) null jammers directionally — long a military staple, now appearing in compact civil form factors. Effective against jamming; partial against smart spoofing.
- GNSS-denied navigation. Visual-inertial odometry, terrain-relative navigation from onboard cameras (an AI integration workload), UWB/beacon systems at fixed sites, or radio-based alternatives. This is the destination for operations that must survive denial, and a serious engineering programme.
Operational practice for the interference era
- Plan for it: check interference reports for your region (public maps aggregate ADS-B-derived jamming data), brief the degraded-nav procedure, and rehearse manual recovery in ATTI-style modes — the skill atrophies fastest exactly where it's needed most.
- Log everything: C/N0 per satellite, fix type, innovations. A month of baseline logs is what makes "this site is being jammed" a statement instead of a hunch — and your BVLOS safety case increasingly gets asked how the operation handles interference.
- Mind the paperwork: jamming your own test range is illegal in essentially all of Europe — resilience testing happens with record-and-replay simulators on the bench, or in licensed facilities.
Treat GNSS as a sensor with a threat model, not as ground truth. An aircraft that notices when satellites lie, says so, and lands safely on its remaining senses is achievable at rung 2–3 prices — and it's rapidly becoming the difference between operators who fly near interference and operators who explain incidents.
Frequently asked questions
What happens to a drone when GPS is jammed?
The receiver's signal-to-noise ratios collapse and the position fix degrades or drops. A well-configured drone detects this, stops trusting GNSS, and falls back to altitude-hold or inertial dead reckoning with a defined behaviour; a badly configured one may drift, toilet-bowl or fly away following a corrupted estimate.
How is spoofing different from jamming?
Jamming shouts over the satellites so the receiver loses lock — obvious and detectable. Spoofing whispers convincingly: it broadcasts fake satellite signals so the receiver computes a confidently wrong position and time. Spoofing is far more dangerous because everything looks healthy while the aircraft is being steered by lies.
How can a drone detect GNSS spoofing?
Cross-checks: GNSS position jumping against inertial prediction, implausible time steps, carrier-to-noise patterns too uniform across satellites, single-antenna direction anomalies, and disagreement between dual receivers or GNSS heading versus compass. Modern receivers (u-blox F9/F10 class) also flag suspected spoofing directly.