Automatic Identification System

Contents

Introduction            3

1 Applications and limitations         4

     1.1 Collision avoidance         4

     1.2 Vessel traffic services        4

     1.3 Aids to navigation         4

     1.4 Search and rescue         5

     1.5 Accident Investigation        5

     1.6 Binary messages         5

     1.7 Computing and networking        5

     1.8 AIS data on the Internet        6

     1.9 Range limitations and space-based tracking     6

     1.10 Type Testing and Approval       7

2 How AIS works            8

     2.1 Basic overview         8

     2.2 Message Types         9

     2.3 Detailed description: Class A units       9

     2.3.1 Broadcast information        11

     2.4 Detailed description: Class B units       12

     2.4.1 Message 14: Safety Related Message

     2.4.2 Message 18: Standard Class B CS Position Report

     2.4.3 Message 19: Extended Class B Equipment Position Report

     2.4.4 Message 24: Class B CS Static Data Report

     2.5 Detailed description: AIS Receivers      13

Summary                                                                                        14

Attachement           16

Vocabulary            20 
 
 
 
 
 
 
 
 
 
 
 

Introduction

The Automatic Identification System (AIS) is an automated tracking system used on ships and by Vessel Traffic Services (VTS) for identifying and locating Vessels by electronically exchanging data with other nearby ships and VTS stations. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport.

Information provided by AIS equipment, such as unique identification, position, course, and speed, can be displayed on a screen or an ECDIS. AIS is intended to assist a vessel's watchstanding officers and allow maritime authorities to track and monitor vessel movements. AIS integrates a standardized VHF transceiver with a positioning system such as a LORAN-C or GPS receiver, with other electronic navigation sensors, such as a gyrocompass or rate of turn indicator. Ships outside AIS radio range can be tracked with the Long Range Identification and Tracking (LRIT) system with less frequent transmission.

The International Maritime Organization's (IMO) International Convention for the Safety of Life at Sea (SOLAS) requires AIS to be fitted aboard international voyaging ships with gross tonnage (GT) of 300 or more tons, and all passenger ships regardless of size. It is estimated that more than 40,000 ships currently carry AIS class A equipment. In 2007 the new Class B AIS standard was introduced which enabled a new generation of low cost AIS transceivers. This has triggered multiple additional national mandates from Singapore, China, Turkey and North America affecting hundreds of thousands of vessels.

The Automatic Identification System (AIS) was originally developed to aid the Vessel Traffic Services (VTS) by use of a VHF transponder working on Digital Selective Call (DSC) at VHF CH70, and is still in use along the UK coastal areas and others. Some time later the IMO developed a Universal AIS using the new sophisticated technology called Self-Organized Time Division Multiple Access (SOTDMA) based on a VHF Data Link (VDL). The system operates in three modes – autonomous (continuous operation in all areas), assigned (data transmission interval remotely controlled by authority in traffic monitoring service) and polled (in response to interrogation from a ship or authority). It is synchronized with GPS time to avoid conflict among multiple users (IMO minimum 2000 reports per minute and IEC requires 4500 reports on two channels). The VHF channels 87B and 88B are commonly used and in addition there are local AIS frequencies. Shipborne AIS transponders exchange various data as specified by the IMO and ITU on either frequency automatically set up by the frequency management telecommand received by the DSC receiver on ship. 

1. Applications and limitations^[1]

1.1 Collision avoidance

AIS is used in navigation primarily for collision avoidance. Due to the limitations of VHF radio communications, and because not all vessels are equipped with AIS, the system is meant to be used primarily as a means of lookout and to determine risk of collision rather than as an automated collision avoidance system, in accordance with the International Regulations for Preventing Collisions at Sea (COLREGS).

When a ship is navigating at sea, the movement and identity of other ships in the vicinity is critical for navigators to make decisions to avoid collision with other ships and dangers (shoal or rocks). Visual observation (unaided, binoculars, night vision), audio exchanges (whistle, horns, VHF radio), and radar or Automatic Radar Plotting Aid (ARPA) are historically used for this purpose. However, a lack of positive identification of the targets on the displays, and time delays and other limitation of radar for observing and calculating the action and response of ships around, especially on busy waters, sometimes prevent possible action in time to avoid collision.

While requirements of AIS are only to display a very basic text information, the data obtained can be integrated with a graphical electronic chart or a radar display, providing consolidated navigational information on a single display.

1.2 Vessel traffic services ^[5]

In busy waters and harbors, a local Vessel Traffic Service (VTS) may exist to manage ship traffic. Here, AIS provides additional traffic awareness and provides the service with information on the kind of other ships and their movement.

1.3 Aids to navigation

AIS was developed with the ability to broadcast positions and names of objects other than vessels, like navigational aid and marker positions. These aids can be located on shore, such as in a lighthouse, or on the water, on platforms or buoys. The US Coast Guard suggests that AIS might replace RACON, or radar beacons, currently used for electronic navigation aids.

The ability to broadcast navigational aid positions has also created the concepts of Synthetic AIS and Virtual AIS. In the first case, an AIS transmission describes the position of physical marker but the signal itself originates from a transmitter located elsewhere. For example, an on-shore base station might broadcast the position of ten floating channel markers, each of which is too small to contain a transmitter itself. In the second case, it can mean AIS transmissions that indicate a marker which does not exist physically, or a concern which is not visible (i.e. submerged rocks, or a wrecked ship). Although such virtual aids would only be visible to AIS equipped ships, the low cost of maintaining them could lead to their usage when physical markers are unavailable.

1.4 Search and rescue ^[4]

For coordinating resources on scene of marine search and rescue operation, it is important to know the position and navigation status of ships in the vicinity of the ship or person in distress. Here AIS can provide additional information and awareness of the resources for on scene operation, even though AIS range is limited to VHF radio range. The AIS standard also envisioned the possible use on SAR Aircraft, and included a message (AIS Message 9) for aircraft to report position. To aid SAR vessels and aircraft in locating people in distress a standard for an AIS-SART AIS Search and Rescue Transmitter is currently being developed by the International Electrotechnical Commission (IEC), the standard is scheduled to be finished by the end of 2008 and AIS-SARTs will be available on the market from 2009.

1.5 Accident Investigation

AIS information received by VTS is important for accident investigation to provide the accurate time, identity, position by GPS, compass heading, course over ground (COG), Speed (by log/SOG) and rate of turn (ROT) of the ships involved for accident analysis, rather than limited information (position, COG, SOG) of radar echo by radar.

The maneuvering information of the events of the accident is important to understand the actual movement of the ship before accident, particularly for collision, grounding accidents.

A more complete picture of the events could be obtained by Voyage Data Recorder (VDR) data if available and maintained onboard for details of the movement of the ship, voice communication and radar pictures during the accidents. However, VDR data are not maintained due to the limited 12 hours storage by IMO requirement.

Other reference:

Automatic Identification System (AIS): A Human Factors Approach

1.6 Binary messages

The Saint Lawrence Seaway uses AIS binary messages (message type 8) to provide information about water levels, lock orders, and weather. The Panama Canal uses AIS type 8 messages to provide information about rain along the canal and wind in the locks.

1.7 Computing and networking

Several computer programs have been created for use with AIS data. Some programs (such as ShipPlotter and gnuais) use a computer to demodulate the raw audio from a modified marine VHF radio telephone when tuned to the AIS broadcast frequency (Channel 87 & 88) into AIS data. Some programs can re-transmit the AIS information to a local or global network allowing the public or authorized users to observe vessel traffic from the web. Some programs display AIS data received from a dedicated AIS receiver onto a computer or chartplotter. Most of these programs are not AIS transmitters, thus they will not broadcast your vessel's position but may be used as an inexpensive alternative for smaller vessels to help aid navigation and avoid collision with larger vessels that are required to broadcast their position. Ship enthusiasts also use receivers to track and find vessels to add to their photo collections.

1.8 AIS data on the Internet

AIS position data are available on the Internet through many privately operated geographic information systems. In December 2004, the International Maritime Organization's (IMO) Maritime Safety Committee condemned the Internet publication of AIS data as follows:

In relation to the issue of freely available automatic identification system (AIS)-generated ship data on the world-wide web, the publication on the world-wide web or elsewhere of AIS data transmitted by ships could be detrimental to the safety and security of ships and port facilities and was undermining the efforts of the Organization and its Member States to enhance the safety of navigation and security in the international maritime transport sector.

Others have countered that AIS provides the same information that can be obtained with a pair of binoculars and that ships have the option of turning off AIS when they are in areas with security concerns.

1.9 Range limitations and space-based tracking

Shipboard AIS transponders have a horizontal range that is highly variable but typically only about 74 kilometers (46 miles). They reach much further vertically, up to the 400 km orbit of the International Space Station (ISS). Space-based AIS is referred to as S-AIS.

On April 28, 2008, Canadian company COM DEV International, became the first company to launch a space-based AIS nano-satellite designed to detect AIS signals from space^[4], and is currently deploying a full micro-satellite constellation, global ground network and centralized data processing center in order to offer global AIS data services. The service is operational and available worldwide as of mid-2010 through exactEarth, COM DEV's data services subsidiary. Exact Earth uses a patent-pending ground and space-based processing technology to minimize interference of collided AIS signals, therefore dramatically improving detection compared with all other satellite-based systems. As more satellites are launched, refresh rates will continue to increase as well.

In November 2009, the STS-129 space shuttle mission attached two antennas - an AIS VHF antenna, and an Amateur Radio antenna to the Columbus module of the ISS. Both antennas were built in cooperation between ESA and the ARISS team (Amateur Radio on ISS). Starting from May 2010 the European Space Agency is testing two different AIS receivers, one from Luxspace (GdL), one from FFI (Norway) in the frame of technology demonstration for space-based ship monitoring. This is a first step towards a satellite-based AIS-monitoring service.

In June of 2008, ORBCOMM launched six new low-earth orbit (LEO) satellites for their machine-to-machine communications constellation. These new satellites were also equipped with the capability to collect AIS data. Unfortunately, during the next 18 months all but one of these six satellite failed on orbit and the the final satellite was declared a total constructive loss for insurance purposes. Additionally, ORBCOMM plans to incorporate the ability to receive, collect and forward AIS data in the design of the next 18 ORBCOMM Generation 2 (0G2) satellites under development. As additional satellites are launched, ORBCOMM will increase its capability by providing greater redundancy and more frequent updates of AIS data. In 2009, LUXSPACE, a Grand Duchy of Luxembourg based company has launched PathFinder2, (ex-Rubin) and is now the only European company to have an operational system in orbit providing data from all over the world on a daily basis. The satellite is operated in cooperation with SES ASTRA and REDU Space Services. In 2007, a previous test of space-based AIS tracking by the U.S. TacSat-2 satellite suffered from signal corruption because the many AIS signals interfered with each other.