How AIS (Automatic Identification System) Is Replacing Conventional Radar In Marine Navigation

by Paul Rudo on 26/04/12 at 9:35 pm

The Automatic Identification System is a major component of vessel traffic services and assists the use of marine radar in identifying maritime dangers for ships and submarines at sea. As we will see, AIS tools are also used for navigation, AIS applications are used to provide information related to the position, course and speed of a ship as well as tracking movements of vessels which are delivering commercial shipments. All passenger ships and any ship traveling internationally carrying more than 300 tons is required to be equipped with an AIS ship tracking device.

How AIS works

An AIS configuration consists of a VHF transmitter, two VHF TDMA receivers, a VHF DSC receiver. These devices provide vessel information and voyage information, including MMSI numbers, IMO number, registration, navigation status, rate of turn, position accuracy, longitude, time stamp and ship dimensions. A ship transmit this information in 26.6 millisecond messages to an AIS station at the same time as it receives a new slot for the next message. These stations work continuously in order to synchronize the information, avoiding overlap of different ship transmissions. AIS systems have a range of about 15-20 nautical miles, although base stations with higher elevations can push that range up to 60 miles. Here are some of the major applications resulting from the widespread maritime adoption of automatic identification systems:

Avoiding collisions

This was the original use for AIS and it still stands as one of its primary functions. The first line of defense against collision are visual observation, audio transmissions and radar, but these three aren’t always completely reliable, especially on busy waters that may be encountering a lot of traffic. AIS information can be integrated into electronic charts and used to provide real-time updates about ship locations, thereby helping to avoid collisions even during poor weather, turbulent sea conditions, or overcrowded sea paths.

Vessel traffic services

The VTS is a marine traffic monitoring system which uses a variety of technologies in order to protect busy waters and harbors. These technologies include close circuit television, radar, VHF radiotelephony and AIS. Imagine vessel traffic services as being the sea-based equivalent of air traffic control, and AIS as being one of the principal tools in making sure avenues of travel do not get congested. Without AIS, the incidents of vessel collisions would be much higher.

Navigational assistance

One of the great advantages of AIS is that it can identify objects other than ships, which makes it extremely valuable for navigation. Reefs, shoreline rocks, even large sea mammals can be identified. It can be used to track marine objects from on shore as well as assess changing conditions, such as turbulent weather patterns and ocean currents. AIS is like a lighthouse that is not land-bound: it can reach out and track moving parts while also evaluating fluctuating factors. This makes it extremely useful during storms and even hurricanes.

Search and rescue

For several years now, many major search and rescue missions have utilized AIS tools. The International Electrotechnical Commission developed an AIS-SART Search and Rescue Transmitter to help locate distress signals and search marine waters for radar messages sent by troubled ships. This transmitter is a self-contained radio device that evolved from a GNSS receiver—the most obvious example being GPS—that sends out position and speed updates once every minute. In the aftermath of hurricanes, AIS transponders are often sent out to try and pinpoint the locations of survivors. AIS can also continually track an object or vessel that is adrift, providing rescue operations up to the minute information regarding current locations and likely directions for continued movement.

Maritime Domain Awareness

AIS is also seen as a primary tool for littoral states who wish to obtain information about any and all vessels that are functioning near their coasts. These ships, which are often mandated to carry AIS equipment, stream information related to its identity, position, and speed on a continuous basis. The U.S. Coast Guard, for instance, uses AIS as a principle component of creating maritime domain awareness and safety. The Coast Guard maintains that because of its ease as an on-shore tool AIS will likely replace racons, or radar beacons used at sea. AIS is also utilized by the Defense Department and the military.

AIS is not limited to these applications. It is integrated into a wide variety of interdisciplinary uses, including accident investigation, Homeland Security, space-based tracking, binary messaging, and online geo-location. AIS works independently as its own tool while also holding the potentiality of integration with other tools such as GPS, LORAN-C, and the gyrocompass. AIS could be used in space in much the same way as it’s used in bodies of water, helping space agencies keep track of the growing number of man-made satellites in orbit around the Earth.

Additionally, more advanced applications of AIS could be used in marine telecommunications, vessel simulations for training seminars, real-time databases, pollution detection, sea path algorithms that could help determine vessel arrival times. Neither the sea nor the sky is the limit with AIS.

About The Author: This guest article was contributed by Sam Peters, who writes about AIS ship tracking and maritime business intelligence. For more information on AIS, please visit portvision.com.