DP Mini Guide: GNSS — Jamming and Spoofing

Crew Connect DP Academy · Mini Guide 04

GNSS — Jamming and Spoofing

Topic: Position Reference Systems · Sub-topic: GNSS/DGNSS  ·  Level: DPO / Senior DPO  ·  Read time: 9 min

1. What / Why / How

GNSS position depends on satellite signals and, usually, differential correction data. Jamming/denial means loss or degradation of signal; spoofing means plausible-looking but false position data being received instead. They look and behave differently, and call for different reasoning.

2. Recognition / Risk / But

Watch for: simultaneous loss of same-principle sources, loss of corrections, abnormal quality indicators, inconsistent speed/position, or a mismatch against an independent (non-GNSS) PRS.

But: onboard equipment faults, an antenna change, shielding or reflection, and ordinary environmental effects can all resemble external interference. Don't reach for "jamming" as the explanation before ruling out the vessel's own systems.

3. Now / What next / Decision / Why

Validate using genuinely independent-principle sources and vessel checks. Identify which of your references actually share the suspected failure path (usually: anything GNSS-based). Apply your approved response/reporting procedure and any resulting operational limits.

4. Consequence / Reassess / Escalate

A second GNSS source starts to look credible again — but it's moving coherently with the first, suspect one. Reassess the common-cause assumption rather than treating "two sources agree" as automatic confirmation, and reassess activity acceptability against your ASOG.

5. Recover / Verify / Human factor

Restore GNSS-based references only once source integrity and configuration are demonstrated per your procedure — not the moment the numbers look normal again. Trap: anchoring on the first narrative ("it must be jamming") and stopping the investigation there, when the real cause might be closer to home.

Sources: IMCA M252, IMCA DPE 04/20 and current DP event learning on onboard interference, IMO MSC.1/Circ.1580 (PRS diversity requirements). This guide is educational content, not a substitute for accredited DP training, vessel-specific FMEA/ASOG, or full-mission simulator assessment. Crew Connect never infers compliance with a specific vessel's applicable requirements — always verify against your own approved documents.