Not all AIS data is received equally. Depending on where a vessel is sailing - and what decision you need to make - relying on just one type of tracking data can leave massive blind spots.

How it works: Land-based VHF antenna towers along coastlines and ports.

Range: ~15–40 nautical miles (Line-of-Sight).

Update Speed: Ultra-fast / Near real-time (every few seconds).

Best Use Cases: Port operations, Vessel Traffic Services (VTS), harbor maneuvering, and coastal collision avoidance.

Limitation: Complete blind spot once a vessel leaves coastal waters.

How it works: Low Earth Orbit (LEO) satellites picking up VHF signals from space.

Range: Global coverage — including deep oceans and polar routes.

Update Speed: Intermittent (tied to satellite pass intervals and pass-over frequency).

Best Use Cases: Long-haul voyage monitoring, commodity trade flow analytics, sanctions/dark fleet detection, and global fleet management.

Limitation: Signal collisions (congestion) in dense waterways and ports (e.g., English Channel).

How it works: Onboard transceivers broadcasting VHF signals directly ship-to-ship and to nearby receivers.

Direct Purpose: Tactical, ship-to-ship collision avoidance integrated into bridge ECDIS and radar displays.

Modern Evolution (Shipborne Relay): Vessels act as floating roaming AIS nodes, relaying neighbor data via satellite links to bridge coverage gaps in high-density offshore shipping lanes.

Best Use Cases: Navigational safety, emergency maneuvering, and augmenting offshore visibility.