MARINE GNSS Guard

Can the ship trust its satellite position? Every second, ten checks decide, and when the answer is no the ship keeps navigating on dead reckoning, radar, depth soundings and other aids. Set in the Gulf of Finland, Baltic Sea.

Bridge view

For navigators and pitches: ship status, instructions, the ten checks and a live map. Pick a scenario (jamming, spoofing, receiver failure) and a correction method, then press Play.
Teaching website

How it works: signal inspector, check cards, playbooks with sources, maps, a briefing and the derivations behind every number.

How a problem is diagnosed

Flow chart: the ten checks run in order every second and the first one that fails decides the verdict. The full list is given below the chart. — Every second the checks run in this order; the first that answers “yes” decides:

Noise floor: background radio noise far above normal → JAMMING

Satellite count: too few satellites or no position → LOST

Signal strength drop: all satellites much quieter → JAMMING

Signal spread: satellites all equally strong → SPOOFING

Signal strength rise: satellites louder than possible → SPOOFING

Clock consistency: receiver clock jumped → SPOOFING

Position vs dead reckoning: the ship cannot have moved there → SPOOFING

Position on water: GNSS position on land → SPOOFING

Depth vs chart: sounder disagrees with the chart → SPOOFING

Position agreement: noisy but possible → DEGRADED (blend with dead reckoning)

All checks pass → GNSS is trusted.