What is the automatic identification system AIS

AIS is the abbreviation for Automatic Identification System or Universal Automatic Identification System (UAIS). This is a (universal) automatic identification system which, through the exchange of navigation and other ship data, improves safety, e.g. for collision prevention and the control of ship traffic. It was adopted as a binding standard on December 6, 2000 by the International Maritime Organization (IMO).

Your own ship position and the position of the surrounding ships are displayed on a digital waterway map. Position, direction of travel and speed can be used to intuitively estimate whether your own course is safe or whether there is a risk of collision. High-quality devices can calculate the risk of collision and the remaining time until they meet, and suggest measures to prevent collisions.

Since the ship's data (ship name, MMSI number, etc.) are also transmitted, the skipper (e.g. captain, pilot or helmsman) can contact you directly via radio. AIS also works when there is flat land between two ships, for example behind a cape or behind a river curve. AIS shows ship movements exactly as they can be seen in reality (in contrast to radar observation in which the ship movement is represented relatively and is much more difficult to evaluate).

Equipment obligation

Since January 1, 2004, all commercial vessels over 300 GT on international voyages and since July 1, 2008 also those over 500 GT on national voyages are obliged to operate an AIS system. Ships that are longer than 20 m or have more than 50 passengers on board must also be equipped with an AIS unit. The equipment requirement was introduced for new ships on July 1, 2002 and for existing ships from 2004. [1] The IMO set different transition times for passenger ships, ferries, freighters and tankers.

Mandatory equipment for pleasure craft is currently being discussed in Turkey.

Since July 1, 2008, inland vessels (except for small vehicles) are required to be equipped with Inland AIS transponders on the Austrian part of the Danube between river kilometers 1880.2 and 2199.3 and some adjacent waters. [2]


Class A transponder - These are intended for commercial ships, for example cargo ships or large passenger ships. Class A transponders transmit with a higher VHF signal strength than class B transponders and can therefore be received by ships further away and also transmit more frequently. Class A transponders are mandatory on all vehicles over GT 300 on international journeys and on certain passenger ships that are subject to the SOLAS Convention. The transmitter adapts the repetition frequency of the transmission to the driving speed and the maneuvering situation.

Inland AIS transponder - Inland AIS transponders are compulsory for ships equipped with AIS transponders on the Rhine, unless they are ocean-going vessels. [3] The devices correspond to Class A transponders with extensions for inland navigation. [4]

Class B transponder - They are comparable to Class A transponders in many ways, but are usually cheaper due to less stringent performance requirements. Class B transponders transmit with a lower signal strength and a lower reporting rate. You can from all ships that do not require equipment, e.g. B. be used in the leisure sector and in fishing. Class B transponders use empty class A time slots.

AIS base stations - AIS base stations are used by marine traffic systems to monitor and control the transmission of AIS transponders.

AtoN transponder (Aids to Navigation) - AtoNs are transponders that are mounted on buoys and other possible dangers and obstacles for shipping, and transmit details of their position to ships in the vicinity.

AIS receiver - AIS receivers receive transmissions from Class A transponders, Class B transponders, AtoNs and AIS base stations, but do not transmit any information about the vessel on which they are installed.


AIS transmits alternately on two channels in the VHF marine radio range: [5]

- AIS 1 - 161.975 MHz
- AIS 2 - 162.025 MHz

The transmission of the AIS data takes place in a fixed time frame. 2250 time slots are available per minute to which an AIS transponder is synchronized via its integrated GPS receiver. Class A transponders automatically coordinate the slot assignment with others within radio range (SOTDMA = Self Organizing Time Division Multiple Access), while Class B transponders use free time slots to send their data (CSTDMA = Carrier Sense Time Division Multiple Access). Antenna any antenna tuned to the VHF marine radio band can be used. Special combined VHF / GPS antennas are particularly suitable for AIS, which contain both antennas required for an AIS transponder in one assembly. The AIS transponder receives dynamic ship data (LAT, LON, COG, SOG, UTC) from the integrated GPS receiver, in the case of Class A, also from the ship's navigation system. The course direction (heading) can be fed in from the compass as an HDG data record via a NMEA-183 interface.

Pilot Port - Ships requiring equipment must have Class A systems with a pilot port, a standardized data interface in accordance with EIA-422 at an easily accessible point. B. Permits pilots to access traffic situation and navigation data with their own equipment. Errors in the pin assignment of the plug that occur due to incorrect installation can usually be corrected by commercially available Untangler without interfering with the on-board installation.

Ship data

The AIS unit sends ship-specific data that can be received and evaluated by any AIS receiver within range:

Static ship data:
IMO number
Ship name
MMSI number
Type of ship (freighter, tanker, tugboat, passenger ship, SAR, pleasure craft, etc.)
Dimensions of the ship (distance of the GPS antenna from the bow, stern, port and starboard sides)

Dynamic ship data:
Navigational status (under machine, under sail, at anchor, moored, unable to maneuver, etc.)
Ship position (LAT, LON, in WGS 84)
Ship position time (seconds only)
Course over ground (COG)
Speed ​​over ground (SOG)
Pre-alignment (HDG)
Course Change Rate (RED)

Travel data:
current maximum static draft / dm
Dangerous goods class of the load (IMO)
Destination (UN / LOCODE) [6]
estimated time of arrival (ETA)

For inland AIS there is also:
ENI ship number
Association data (type ERI, length, width)
Dangerous goods class of the load
Draft / cm
Loading condition
Fairway side left / right (blue board)
max.height above water
Number of crew members
Number of passengers
Number of crew on the ship

The navigation status and the travel data must be updated manually by the WO. However, not all data have to be sent. Especially with class B transmitters used in recreational shipping, often only the ship's name, MMSI, position, course and ship size are transmitted.

Sending the AIS data

The AIS signals are transmitted on two VHF marine radio channels (usually on AIS1 and AIS2, i.e. VHF channels 87B and 88B with the frequencies 161.975 MHz and 162.025 MHz) with HDLC data protocol in a fixed time frame. The data is decoded and z. B. graphically represented as text information or similar in a radar image.

The intervals at which a ship sends out its data depend on the mobility, i. H. speed and rate of change of course.

Processing the AIS data

In addition to the transmitted data, the program also evaluates its own data.

The current traffic situation is displayed dynamically, every movement of the ship is visible on the screen. It also shows when exactly two ships that meet are the shortest distance from each other, how big it will be, and how long it will take until then.

The advantage of AIS compared to radar is, among other things, that the officer on watch knows the identity of other ships and changes in course and speed are automatically transmitted during maneuvers. This means that he can also make direct contact via marine radio and discuss necessary maneuvers.

With AIS, ship movements behind larger obstacles can also be recorded while sailing through the area; The radar is often overwhelmed in such situations, as ships are not detected in the radar shadow. The VHF signals of the AIS reach these shadow areas much better due to the longer wavelength. In inland waterways, transponders are set up in curves that are sealed off from radio signals, and they also transmit the AIS signals over mountains.

The ship data can be integrated directly into the electronic nautical chart (ECDIS, Electronic Chart Display and Information System) or processed by separate AIS software on the computer in order to display all ship movements including one's own position. Separate software often offers a clearer display, the display of additional data disseminated via AIS (in testing: weather reports, water levels) and better support in the event of a collision risk.

Smaller seagoing vessels that do not require equipment can use the AIS data passively with inexpensive AIS receivers and display the position, course and speed of the surrounding equipped vessels. The received data can be displayed on a small screen on the receiver, on an existing map plotter or with suitable software on a separate laptop / computer. In this way, you can initiate evasive maneuvers in good time if there is a risk of collision, especially when visibility is poor.

However, AIS cannot replace a radar system, as military vehicles, for example, often do not transmit AIS signals and many smaller vehicles are not equipped with an AIS transceiver.


Ultra-short waves have a range that only slightly exceeds the geometrical range of vision. For ship-to-ship connections, this is around 20 nautical miles (37 km). Coast stations receive signals from ships within a radius of 50−100 km, depending on the antenna height. Low-flying satellites should be able to receive the VHF signals, provided the antennas are also beaming upwards (omnidirectional). Orbcomm is equipping its new satellites with AIS receivers. If the test is successful, the system could record all ships worldwide.

In November 2009, an AIS receiving antenna was installed on the European part of the ISS, the COLUMBUS module. Since June 1, 2010, reception attempts with various AIS receivers have been carried out as part of an ESA study. Disturbing signal overlaps due to the great distance of the radio horizon are countered with special signal processing techniques. [7] [8).

Airplane, navigation mark, land station

In addition to ships, the following are also involved in the AIS:

- SAR aircraft
- Sea distress marker transmitter (AIS SART - Search and Rescue Transmitter)
- some navigation marks (Aids to Navigation / AtoN)
- Levels and weather stations
- Land traffic monitoring stations (VTS)

Short messages, traffic control

Short messages and free text messages specified by the IMO can also be transmitted via the AIS. For example, the automatic measuring stations on navigation signs can distribute current weather, water level and current data or route instructions can be sent to ships. On rivers and canals, in particular in the area of ​​locks and bottlenecks, the AIS is increasingly used to direct traffic, for example to indicate the opening of the lock.

Captains look around the corner

The "Leo Sympher" is a pilot project ship. The tour ship of the Wasser- und Schifffahrtsamt (WSA) Verden is one of around 100 ships that were equipped with the new AIS (Automatic Identification System) as part of a test run.

The Mittelweser between Bremen and Minden is the test area of ​​the project of the Federal Ministry of Transport.

The testers have transponders on board that transmit the ship's data to other road users - such as the name and dimensions, as well as the location and speed - and received the same information from them. What that means and what it should be good for is shown by a look at the bridge to skipper Karl-Heinz Gutsch. The large screen in front of Gutsch looks like a navigation system for ships. It shows the course of the Weser and the 2.80 meter deep fairway, the location of the "Leo Sympher" and other ships with transponders. Similar systems are already established in the coastal areas.

Since not all ships are yet equipped with the system, one cannot of course rely on AIS alone when sailing the Weser, explains Thomas Rumpf, Head of the Waterways and Shipping Office. But if, for example, two captains of different nationalities meet at one point who are not allowed to pass two ships at the same time (and there are a few between Bremen and Minden), it is helpful to know exactly where the other is. Unlike radar, the AIS can also be used to “look around the corner” and thus drive with foresight. more [304 KB]