Finding dark ships: AIS over SAR
Maritime monitoring needs two answers at once: who is where, and what is actually on the water. Neither AIS nor SAR gives both — but together they do, and the useful signal is exactly where they disagree.
Two half-answers
AIS transponders broadcast a vessel's name, position and heading — but only for ships that carry and enable them, and the message can be switched off or falsified. Synthetic Aperture Radar images every vessel's radar return regardless of weather, darkness or cloud, but it doesn't know any names.
The mismatch is the intelligence
Overlay live AIS tracks on enhanced Sentinel-1 SAR and cooperative vessels line up with their radar signature. The revealing cases are the exceptions: a strong SAR return with no AIS nearby is a candidate dark ship — illegal fishing, sanctions evasion, smuggling — while an AIS report with no radar return can indicate spoofing or a relayed position.
Because SAR is all-weather and refreshes on the Sentinel-1 cadence across coasts, seas and the main shipping routes, this runs as continuous surveillance at national or basin scale, without tasking — the economics that keep it out of reach for one-off high-resolution collection.