Automatic Identification System
Also called: AIS · Topic: Remote Sensing, GIS and GNSS · NCERT: Beyond NCERT
Meaning
The Automatic Identification System (AIS) is a ship-tracking system that works by radio. Each vessel carries a transponder, a device that sends out signals on its own. The signals give the ship's name (identity), position, course and speed. The ship's satellite navigation receiver supplies the position, and the AIS unit broadcasts it to nearby ships, shore stations and satellites. In India, vessels longer than 20 metres must carry AIS. Smaller boats, which include most fishing boats, mostly do not have it. This leaves a big gap in watching the coast.
Example
A large cargo ship coming into Mumbai port shows up on AIS screens on shore with its name and route. A small fishing boat under 20 metres off the Gujarat coast often has no AIS. On radar it looks like any other boat, so a hostile boat can hide among fishing boats. For this reason, India is fitting small boats with transponders under the Vessel Communication and Support System. More than 36,000 transponders had been delivered by January 2025.
Don't confuse with
- Radar: Radar is an active sensor, meaning it sends out its own microwave pulses. It picks up any object from the echoes, even a boat that sends no signal. AIS only works if the ship itself broadcasts its details.
- GNSS (GPS, NavIC): GNSS satellites tell a receiver where it is. AIS takes that position and broadcasts it to others.