Make space for AIS:
The Automatic Identification System could be the next
electronics item mandated onto your ship by
SOLAS
By as early as 2002, vessels over 300 grt may be required, under a revised Chapter 5 of the SOLAS convention, to carry AIS equipment. AIS stands for Automatic Identification System. Essentially, it uses VHF to automatically transmit information--for example identification data, or location data--to another AIS. That other AIS could be on board a ship, or could form a part of a VTS (vessel traffic system) network.
Development of standards for what is more specifically a Universal Shipborne Automatic Identification System--Universal AIS--is being carried out under the auspices of the ITU (International Telecommunications Union), the IALA (International Association of Lighthouse Authorities) and other bodies. A key date in the development process will be IMO's NAV45 meeting in September next year, when AIS proponents hope they can lay the groundwork for carriage of AIS to become mandatory under SOLAS.
Universal AIS is sometimes referred to as "the 4S system": Ship-to-Ship and Ship-to-Shore identification and communication system.
According to GP&C Sweden, a subsidiary of the Swedish Space Corporation, implementation of Universal AIS will substantially enhance general safety at sea, as well as giving ships and VTS operators improved control and surveillance of vessel traffic.
KNOWN TECHNOLOGY,
NEW COMBINATIONThe technology behind this, explains GP&C Sweden, is "Self-Organized Time Division Multiple Access--SOTDMA"
This combines several known technologies in a unique way. Three main components--a GPS receiver, a VHF receiver and a computer--are combined in a single transponder unit. The GPS-receiver provides accurate position and navigation data, the computer packages this information together with the vessel's speed, name, heading, course over ground etc. and broadcasts the data on a digital data link via the VHF-transceiver. All ships within VHF range, equipped with an AIS transponder, can receive this message, unpack it and plot the position of the other ship and its speed, name, heading, course over ground etc. on an Electronic Chart Display.
This means that every ship within VHF radio coverage may be plotted on the bridge ECD. [Presumably, if the ship is not ECD-equipped, the information can be displayed on some other display, such as radar].
Differential corrections for enhanced GPS accuracy can be obtained from shore based stations, via the same AIS data link, and from ship mounted beacon receivers.
FINLAND AND SWEDEN MOVE AHEAD
Sweden and Finland have made significant progress in the development of a new Universal AIS. The Finnish Maritime Administration and Finnish electronics manufacturer VTT Technologies have recently completed in depth studies of the use of AIS, using GP&C's SOTDMA approach, in conjunction with VTS. The studies were carried out as part of the European Union Poseidon project and the findings have been presented to the EU.
Poseidon's objectives are to establish the principles, standards and architecture for the interoperability of VTS at local, regional and European level by the integration of VTS with advanced vessel communications, information and tracking technologies.
The Finnish and Swedish maritime administrations have already encouraged leading shipowners to invest in AIS equipment and the technology examined in the Finnish Poseidon project is regarded as being ready for large scale use. Sweden has started to set up a network of coastal AIS stations. Finland will start putting in its own network of coastal stations before the end of the year 2001.
Interest in and work on AIS has increased in intensity since July 1998 when standards for AIS were announced by the ITU. These are the standards being used by Sweden and Finland.
SINGAPORE, TOO
GP&C Sweden has recently been awarded a contract for a pilot installation of AIS transponders by Brown Automation and Consulting Engineering. The end customer is the Marine and Port Authority of Singapore, which is introducing AIS transponders, based on the SOTDMA technology in Singapore waters.
ITU ALLOCATES TWO VHF CHANNELS
The ITU has already decided to allocate two VHF channels worldwide to AIS applications. The frequencies are AIS channel 1 on frequency 161.975 MHz and AIS channel 2 on frequency 161.025 MHz. As a supplement, some countries are planning to use INMARSAT for data transmission.
Although an AIS set can be configured specifically ally as a base station or a mobile station, data communication is totally independent of any onshore base station network. Once two or more AIS devices are within radio range of each other, a data link is set up immediately--whether ship-to-ship or ship-to-shore. This facilitates identification on the open ocean just as easily as within range of an onshore base station.
The Finnish project uses GP&C's R3 AIS, which integrates GPS receiver, processor components and a VHF radio in a single package. The GPS receiver is used both for positioning and for receiving the precise time reference that the system requires.
The position data are sent by VHF to all AIS instruments within range. The transmission is automatic and takes place every few seconds. The position data contain identification and coordinates as well as information on the vessel's speed and course over ground. If the necessary input from the ship's sensors are provided to it, the AIS equipment also transmits the heading and rate of turn as part of the position message. Separate transmissions, at less frequent intervals, give information such as the vessel's name and main measurements, the position of the on-board location antenna, vessel type, draft and port of destination.
The system also also allows transmission of freely composed messages, in text form up to 80 characters in length, or the equivalent amount of binary data. The capacity of the system is over 2,000 signals per minute.
While the AIS equipment automatically handles the the transmission and reception of signals, it does not itself display their contents. That requires AIS-compatible computer software. Since the most important AIS application is associated with the identification and location of objects, the usual interface is with an electronic chart display application. The AIS equipment interface meets NMEA-0183 standard.
In what follows, we look at some AIS functions that are currently in use:
Forecast display of ship movement parameters
Using the ship movement parameters received, a curved speed vector can be plotted for each AIS subject on a chart monitor, indicating the course over ground of the vessel as well as turning and its predicted location in 1-2 minutes.
Changes of planned routes
Today's integrated navigation systems use numerical route plans that can be monitored by various automatic control systems. AIS allows a vessel to transmit data to other shipping on its route plan so that its intentions are known to others in advance. Encounter situations, for example, can thus be planned in more detail ahead of time.
Transmitting objects under radar surveillance
As a permanent radar installation, a VTS radar network provides unbroken and wider coverage than can be achieved with shipboard radar. The location and identification data of the objects identified and tracked in VTS radar monitoring can be transmitted via AIS just as if the radar targets were AIS subjects. As a result, objects need to be identified only once, by VTS, and other parties will be able to receive the object in ready-identified form.
Exchange of text messages
A planned communication protocol, based on standardized short messages, will support a multilingual service in which the user can output a message in a language of his own choice, using the text signal transmission capability of AIS.
Transmitting differential corrections
This is a function built into the system. If required, a GPS correction signal can be transmitted on the AIS network. A DGPS accuracy of positioning can thus be achieved on vessels without a differential receiver. This correction signal, which is transmitted on VHF, is also insensitive to weather interference, so it can be used as a backup on vessels which normally use other differential receivers.
Further information:
http://www.fma.fi/radionavigation
http://hermes.civil.auth.gr/poseidon/ poseidon.html