AIS - much more than an Automatic Identification System
By Captain Robert McCabe
AIS from conception to birth
Marine casualty reports are littered with instances of vhf assisted collisions. There are few mariners who haven't at some time picked up a radio to call 'ship on my port bow'. What were our thoughts as we waited for the reply. How many ships within vhf range heard that call? Will the ship I have in mind be the ship that replies? Will I agree a course of action with a wrong ship causing chaos many miles away? Why can't there be a system that lets me know the name of the other ships in my area?
In 1988 that simple and practical thought eventually found its way to IALA (the International Association of Marine Aids to Navigation and Lighthouse Authorities), and a study was commenced to provide a solution. Some ten years later the IMO (International Maritime Organisation) approved performance standards for a Universal Automatic Identification System and AIS as we know it today was born. Class A AIS has been mandatory on vessels over 300 tons since July 2004. Class B AIS for the non mandatory sector has also been developed and was brought to market in 2006.
Like any child of the late 1990s AIS is choc full of technology and does much more than the simple function its name suggests. So as well as the traffic identification tool that we dreamed of on the bridge many years ago AIS can also provide-
• ship to ship identification and information exchange
• ship to shore identification and information exchange
• short safety related messages (SSRM)
• binary messages (texts)
• aids to navigation functions
• meteorological and hydrological information
• differential GNSS services
• search and rescue transmitters
• Search and rescue aircraft tracking
Through these functions AIS can facilitate collision avoidance, safe navigation, ships routing, automatic reporting, search and rescue operations, security screening, and traffic analysis. Future long range identification and tracking (IRIT) will give virtually full global coverage.
All of these functions have the potential to improve safety at sea and protect life and property.
How does AIS work?
The key to AIS operation is precise timing provided by GPS, and a technique known as TMA (time division multiple access) which supports a high volume of short messages. Shipborne AIS units transmit and receive on two reserved frequencies in the vhf band. With message slots of 26.6 microseconds, 4,500 slots are available in any one minute, removing concerns regarding potential overload of the system.
Ships transmit static information such as MMSI, call sign, name, IMO number, length, beam, ship type, and antenna location; dynamic information such as position, course over ground, heading, speed, rate of turn, and status; and voyage related information such as draught, cargo, persons on board, destination, estimated time of arrival and route plan. Shore stations and aid to navigation stations use the same frequencies but slightly different TDMA techniques. All of the information can be networked and stored or retransmitted.
Irish Lights and AIS
Irish Lights has been to the forefront of AIS development since its conception. Involvement in inter General Lighthouse Authority/Maritime and Coastguard Agency trials in Southampton led to a user trial in Dublin. An EU Interreg IIIA funded project has allowed us to provide trial aid to navigation AIS and base station coverage for all of our buoys of primary navigational significance on the north and north-east coast and to trial innovative techniques for meteorological text messaging and remote installation assessment. This project is now being extended to Killybegs.
AIS as an aid to navigation can be real AIS where there is an AIS transmitter on the aid; synthetic AIS where a nearby base station transmits the message but it appears to the mariner to have come from the aid; or virtual AIS where there is no physical aid to navigation on the water but a message is transmitted from a shore station which appears on the ship's receiver as an AIS target.
The aids to navigation system replacing the Coningbeg Lightfloat will be the first full aid to navigation AIS system provided in Ireland and Great Britain. AIS will confirm to the mariner that the aids are in position and are functioning correctly. A combination of real and synthetic AIS will be used.
Roll out of further AIS aids to navigation and base stations is planned over the next five years.
As well as providing additional functionality for existing aids to navigation AIS can offer a tool for early marking of new dangers or wrecks. Virtual aid to navigation AIS can be used in circumstances where a physical aid to navigation cannot be established.
The future
AIS is still very young and in a constant state of development. It will play a key role in the development of eNavigation for many years to come. Over reliance on GPS may be overcome by use of eLoran as an alternative source of timing and position in the event of GPS unavailability.
Further information
This has been a brief layman's introduction to AIS. Further more detailed information is available on the Irish Lights website www.cil.ie and specific queries may be e-mailed to aisproject@cil.ie.
Captain Robert McCabe is Local Aids to Navigation Inspector in the Marine Department of Irish Lights, and also has special responsibilities for radio navigation affairs.
Marine casualty reports are littered with instances of vhf assisted collisions. There are few mariners who haven't at some time picked up a radio to call 'ship on my port bow'. What were our thoughts as we waited for the reply. How many ships within vhf range heard that call? Will the ship I have in mind be the ship that replies? Will I agree a course of action with a wrong ship causing chaos many miles away? Why can't there be a system that lets me know the name of the other ships in my area?
In 1988 that simple and practical thought eventually found its way to IALA (the International Association of Marine Aids to Navigation and Lighthouse Authorities), and a study was commenced to provide a solution. Some ten years later the IMO (International Maritime Organisation) approved performance standards for a Universal Automatic Identification System and AIS as we know it today was born. Class A AIS has been mandatory on vessels over 300 tons since July 2004. Class B AIS for the non mandatory sector has also been developed and was brought to market in 2006.
Like any child of the late 1990s AIS is choc full of technology and does much more than the simple function its name suggests. So as well as the traffic identification tool that we dreamed of on the bridge many years ago AIS can also provide-
• ship to ship identification and information exchange
• ship to shore identification and information exchange
• short safety related messages (SSRM)
• binary messages (texts)
• aids to navigation functions
• meteorological and hydrological information
• differential GNSS services
• search and rescue transmitters
• Search and rescue aircraft tracking
Through these functions AIS can facilitate collision avoidance, safe navigation, ships routing, automatic reporting, search and rescue operations, security screening, and traffic analysis. Future long range identification and tracking (IRIT) will give virtually full global coverage.
All of these functions have the potential to improve safety at sea and protect life and property.
How does AIS work?
The key to AIS operation is precise timing provided by GPS, and a technique known as TMA (time division multiple access) which supports a high volume of short messages. Shipborne AIS units transmit and receive on two reserved frequencies in the vhf band. With message slots of 26.6 microseconds, 4,500 slots are available in any one minute, removing concerns regarding potential overload of the system.
Ships transmit static information such as MMSI, call sign, name, IMO number, length, beam, ship type, and antenna location; dynamic information such as position, course over ground, heading, speed, rate of turn, and status; and voyage related information such as draught, cargo, persons on board, destination, estimated time of arrival and route plan. Shore stations and aid to navigation stations use the same frequencies but slightly different TDMA techniques. All of the information can be networked and stored or retransmitted.
Irish Lights and AIS
Irish Lights has been to the forefront of AIS development since its conception. Involvement in inter General Lighthouse Authority/Maritime and Coastguard Agency trials in Southampton led to a user trial in Dublin. An EU Interreg IIIA funded project has allowed us to provide trial aid to navigation AIS and base station coverage for all of our buoys of primary navigational significance on the north and north-east coast and to trial innovative techniques for meteorological text messaging and remote installation assessment. This project is now being extended to Killybegs.
AIS as an aid to navigation can be real AIS where there is an AIS transmitter on the aid; synthetic AIS where a nearby base station transmits the message but it appears to the mariner to have come from the aid; or virtual AIS where there is no physical aid to navigation on the water but a message is transmitted from a shore station which appears on the ship's receiver as an AIS target.
The aids to navigation system replacing the Coningbeg Lightfloat will be the first full aid to navigation AIS system provided in Ireland and Great Britain. AIS will confirm to the mariner that the aids are in position and are functioning correctly. A combination of real and synthetic AIS will be used.
Roll out of further AIS aids to navigation and base stations is planned over the next five years.
As well as providing additional functionality for existing aids to navigation AIS can offer a tool for early marking of new dangers or wrecks. Virtual aid to navigation AIS can be used in circumstances where a physical aid to navigation cannot be established.
The future
AIS is still very young and in a constant state of development. It will play a key role in the development of eNavigation for many years to come. Over reliance on GPS may be overcome by use of eLoran as an alternative source of timing and position in the event of GPS unavailability.
Further information
This has been a brief layman's introduction to AIS. Further more detailed information is available on the Irish Lights website www.cil.ie and specific queries may be e-mailed to aisproject@cil.ie.
Captain Robert McCabe is Local Aids to Navigation Inspector in the Marine Department of Irish Lights, and also has special responsibilities for radio navigation affairs.