A vessel goes dark. Its AIS transponder stops transmitting, or it keeps transmitting — but from the wrong place. The first scenario is a dark period. The second is spoofing. Both are investigatively significant. Both are also frequently innocent. The discipline required to tell the difference is what separates a defensible finding from a speculative one — and it is the discipline that MAR-003 is designed to build.
AIS gaps are among the most commonly misread signals in maritime OSINT. A transponder that goes silent for four hours off the coast of West Africa is not the same as one that goes silent for four hours in the middle of a known ship-to-ship transfer zone, reappears 200 nautical miles from its last position, and shows a speed history that no vessel of its class could physically achieve. The first is probably a relay gap. The second requires explanation. The methodology in this card tells you how to make that determination — and how to document it to evidentiary standard.
MAR-003 covers the eight-step workflow for dark vessel analysis: establishing a baseline AIS track, identifying and classifying gap periods, applying the speed plausibility test, cross-referencing across independent AIS platforms, requesting and interpreting Sentinel-1 SAR imagery, using VIIRS nighttime detection data, assessing spoofing indicators, and completing the chain of custody. It builds on MAR-001 (AIS and MMSI tracking) and MAR-002 (ownership research) and is the third card in the Signal & Shadow Maritime Intelligence series.
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