Reference

Maritime domain awareness glossary

Plain-English definitions of the maritime domain awareness (MDA) and maritime OSINT terms used across MarineAware — the sensors, the evasion tactics, and the methods. 33 terms.

AIS & vessel tracking

AIS (Automatic Identification System): A VHF radio system by which ships broadcast their identity, position, course and speed. Mandated by SOLAS for most vessels over 300 gross tonnes on international voyages. It is cooperative and self-reported — which is exactly why it can be switched off or falsified.
Terrestrial vs satellite AIS (T-AIS / S-AIS): T-AIS is received by coastal base stations (near-instant but limited to ~40–100 km from shore). S-AIS is received by satellites over open ocean, arriving in bursts after each pass; it fills the gap terrestrial AIS cannot reach but suffers message collision in dense areas.
MMSI: Maritime Mobile Service Identity — a nine-digit number identifying an AIS transponder. Because it is set in the transponder, it can be duplicated, borrowed from a scrapped ship, or set to zero to obscure identity.
IMO number: A permanent seven-digit identifier assigned to a ship hull for its lifetime, unlike the MMSI. It is the anchor for resolving a vessel across registries even when its name, flag or MMSI change.
SOG / COG: Speed Over Ground and Course Over Ground — the reported velocity and heading in an AIS position message. Low SOG offshore is a core cue for loitering and ship-to-ship transfers.

Imagery & sensors

SAR (Synthetic Aperture Radar): A satellite radar that images the surface by its own microwave illumination, so it works in any weather, day or night. It sees a hull whether or not the transponder is on, making it the key non-cooperative sensor for dark-vessel detection. Copernicus Sentinel-1 is the open example; ICEYE, Umbra and Capella are commercial.
Electro-optical / Earth observation (EO): Optical imaging in visible and near-infrared light — a scene a human recognizes. High resolution but limited by cloud and darkness. Copernicus Sentinel-2 (10 m) is the open example.
Multispectral: Imaging across several discrete spectral bands beyond red-green-blue, typically adding near-infrared and shortwave-infrared. The extra bands carry information about material, not just shape — useful for oil sheens, flaring and vessel/cargo discrimination.
Hyperspectral: Imaging across hundreds of contiguous narrow spectral bands, so each pixel carries a near-continuous spectrum — effectively chemistry per pixel. Planet Tanager (426 bands, 380–2500 nm) and Pixxel are bringing it to the commercial catalog.
Revisit: How often a satellite (or constellation) images the same place. Open Sentinel-1 revisit is measured in days; large commercial constellations push it toward hours. Revisit is what determines whether you sample a chokepoint or watch it.
Tasking: Commissioning a satellite to image a specific place at a specific time, rather than using whatever the archive happens to hold. Commercial SAR and optical operators sell tasking; open datasets do not offer it.
Resolution (GSD): Ground sample distance — the real-world size of one pixel. Open Sentinel-1 is tens of metres; commercial SAR reaches 16–25 cm. Resolution bounds what you can classify: presence is easy, ship type is hard.
CFAR detection: Constant False Alarm Rate — the classic algorithm for finding bright point targets (like ships) against sea clutter in SAR imagery, adapting its threshold to local background noise.

Dark activity, sanctions & geography

Maritime Domain Awareness (MDA): Effective understanding of anything in the maritime domain that could affect security, safety, the economy or the environment — in practice, fusing vessel tracking, imagery, environment and identity data into an actionable picture.
OSINT (open-source intelligence): Intelligence built from publicly available sources. In the maritime context: open AIS, open satellite imagery, metocean, news and registries, fused and verified into a corroborated assessment. See the maritime OSINT guide.
Dark vessel / dark ship: A vessel present in imagery but not broadcasting AIS — a radar or optical detection with no matching transponder. The central object of dark-vessel detection and sanctions monitoring.
AIS gap: A period where a vessel stops transmitting AIS then reappears. A core evasion signal — but only once normalised against expected satellite coverage, since a thin-coverage patch produces the same pattern innocently.
AIS spoofing: Broadcasting false AIS data — a fake GNSS position (teleporting, circular or land-locked tracks) or a false identity (another ship’s MMSI, a scrapped ship’s MMSI, or a zero MMSI). A defining tactic of the shadow fleet.
Shadow fleet / dark fleet: The 600–800-ship fleet of ageing, often opaquely owned and under-insured tankers moving sanctioned oil while evading tracking through AIS gaps, spoofing and ship-to-ship transfers.
Ship-to-ship (STS) transfer: Transferring cargo between two vessels at sea rather than in port. Legitimate for many trades, but a hallmark of sanctioned-cargo laundering when done by dark or spoofing vessels in known transfer zones.
Loitering / rendezvous: A vessel holding at very low speed (loitering), or two vessels co-located at low speed offshore (rendezvous) — behavioural cues for a possible STS transfer, to be separated from holding station in heavy weather.
IUU fishing: Illegal, Unreported and Unregulated fishing. Detected in OSINT through AIS gaps in fishing grounds, SAR detections of non-broadcasting fishing vessels, and Global Fishing Watch effort data.
Chokepoint: A narrow, strategically critical maritime passage — Hormuz, Bab-el-Mandeb, the Suez and Panama canals, the Bosphorus, the Malacca and Taiwan straits — where a disruption ripples through global trade.
EEZ: Exclusive Economic Zone — the area, generally to 200 nautical miles from shore, where a coastal state has rights over marine resources. Central to fisheries enforcement and grey-zone disputes.

Environment

Metocean: Meteorological and oceanographic conditions — wind, waves, swell, currents, temperature, visibility. Essential context that separates intent (loitering) from circumstance (holding station in heavy seas).
Sea state / Beaufort: Standardised scales for wave conditions (sea state) and wind force (Beaufort). Used to translate raw metocean numbers into a transit read — favourable, marginal or degraded.
Bathymetry: The depth and shape of the seafloor. Open grids (GEBCO, EMODnet) bound routing and under-keel clearance and help distinguish plausible from impossible tracks.

Methods & AI

Sensor fusion: Combining multiple feeds — cooperative AIS, non-cooperative SAR/optical, metocean, registries — into one corroborated answer. The core discipline of MDA: value comes from fusion, not any single feed.
Foundation model: A large model pre-trained on broad data that is adapted to specific tasks. In maritime AI, geospatial and time-series foundation models provide a base that is then fine-tuned on vessel and sensor data.
Fine-tuning: Adapting a base model on labelled domain data — here, maritime imagery across SAR, optical and multispectral bands for the specific vessel classes and behaviours a mission cares about. It is what turns a generalist model from a plausible narrator into a dependable detector.
Agentic AI / tool-using agent: An AI system that plans and calls external tools and data feeds to answer a question, reasoning across the results. It makes on-demand, multi-feed fusion practical — the agent pulls whichever sources the question needs at investigation time.
Ground truth: Independently verified fact used to calibrate and validate a model or finding — for example, checking a detection against licensed AIS. Without it, confidence is guesswork.
Explainability: The property that every output ships with its evidence and reasoning, so a regulator, underwriter or watch officer can defend it. A non-negotiable for maritime decisions.

Maritime OSINT guide → Open datasets catalog → See it live ↗

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