AIS (Automatic Identification System) overview | NATO Shipping Centre

AIS (Automatic Identification System) overview

The Automatic Identification System (AIS) is a short-range coastal tracking system currently used on ships. It was developed to provide identification and positioning information to both vessels and shore stations.

AIS (Automatic Identification System) is the mariner’s most significant development in navigation safety since the introduction of radar. This is a digital positional awareness system operating in the Very High Frequency (VHF) maritime band. Its purpose is to help identify ships, assist in target tracking, assist in search and rescue operation, simplify information exchange and provide additional information to assist situational awareness (International Maritime Organization (IMO), A 29/Res.1106). Originally developed as a collision avoidance tool to enable commercial vessels to ‘see’ each other more clearly in all conditions and improve the helmsman’s information about his surrounding environment. AIS does this by continuously transmitting a vessels identity, position, speed and course along with other relevant information to all other AIS equipped vessels within range. Combined with a shore station, this system also offers port authorities and maritime safety bodies the ability to manage maritime traffic and reduce the hazards of marine navigation.

The range of reception can be variable and is dependent on factors including signal propagation conditions, sea state, the height of the transmitting and receiving antenna and the strength of the vessel transmitter. Reception could be as little as 20 nautical miles, or as much as 350 nautical miles for powerful transmissions during appropriate atmospheric conditions. In the context of the factors that act to control AIS reception range it is considered likely that on average a 40 nautical mile reception radius will be achieved by the AIS receiver network. The same coverage assumptions do not apply to AIS-B which has a smaller power output with ranges of up to 10 nautical miles

How AIS Works:

AIS works by taking your position and movements via the vessels’ GPS system or an internal sensor built into an AIS unit. That information is then collated along with programmable information from the AIS unit (e.g. Maritime Mobile Service Identity (MMSI) number, vessel name, destination, cargo type) and is transmitted in the background at regular intervals whilst also receiving other vessels AIS information. The AIS unit can have its own separate antenna or an antenna splitter can be used from the antenna the VHF radio transmits from. If an antenna splitter is used, it must be an active splitter suitable for a VHF radio and AIS transponder.

SOLAS requirements: The IMO Convention for the Safety Of Life At Sea (SOLAS) Regulation V/19.2.4 requires all vessels of 300 GT and above engaged on international voyages and all passenger ships irrespective of size to carry AIS onboard.

Which ships use AIS:

The International Convention for the Safety of Life at Sea (SOLAS) is an international maritime treaty that sets the minimum safety standards in the construction, equipment, and operation of merchant ships. Regulation 19 of SOLAS Chapter V convention details the minimum carriage requirements for shipborne navigational systems and equipment.

AIS types:

Class A: Mandated for all vessels 300 GT and above engaged on international voyages as well as all passenger ships
Class B: Provides limited functionality and is intended for non-SOLAS vessels. Primarily used for vessels such as pleasure crafts

AIS operates principally on two dedicated frequencies or VHF channels:

AIS 1: Works on 161.975 MHz- Channel 87B (Simplex, for the ship to ship)
AIS 2: 162.025 MHz- Channel 88B (Duplex for the ship to shore)

DATA transmitted:

1. Static Information (Every 6 minutes and on request):

MMSI number
IMO number
Name and Call Sign
Length and Beam
Type of ship
Location of position fixing antenna

2. Dynamic Information (Depends on speed and course alteration)

Ship’s position with accuracy indication
Position timestamp (in UTC)
Course Over Ground (COG)

Maritime security

AIS enables authorities to identify specific vessels and their activity within or near a nation’s Exclusive Economic Zone. When AIS data is fused with existing radar systems, authorities are able to differentiate between vessels more easily. AIS data can be automatically processed to create normalized activity patterns for individual vessels, which when breached, create an alert, thus highlighting potential threats for more efficient use of security assets. AIS improves maritime domain awareness and allows for heightened security and control

AIS cannot be switched off, save for very few exceptions. According to IMO guidelines provided by Resolution A. 917(22), AIS should always be in operation when ships are underway or at anchor. A ship’s crew in singular circumstances may turn off its AIS broadcast for a variety of legitimate reasons, but this behavior may indicate that a vessel is hiding its location and identity to conceal illegal activities.