Thursday, May 31, 2012

The Automatic Identification System: Then, now, and in the future.

Excerpt from U.S. Coast Guard Proceedings of the Marine Safety & Security Council magazine by Mr. Jorge Arroyo, program and management analyst, U.S. Coast Guard Office of Navigation Systems, Electronic Navigation Division.
Congress enacted the Oil Pollution Act of 1990 after the Exxon Valdez oil spill incident. This act made significant changes: It changed the way the nation deals with oil pollution prevention and response and made participation in Coast Guard vessel traffic services (VTS) mandatory. Another important provision in the law was the mandate to create a dependent surveillance system to monitor tankers navigating to and from Valdez, Alaska.

Room for Improvement
Prior to this incident, vessel traffic services typically provided vessel information by inquiring about vessels’ intentions and tracking their movement within the system via some manual plotting board or similar device. 

Though the inclusion of radar greatly enhanced the ability to track and monitor vessel movements, its range is limited, so the cost of providing full radar coverage throughout an entire VTS area and its approaches was prohibitive. 

Further, radar does not provide the ability to positively identify a vessel among other vessels or physical objects, such as ice. This limitation was always known, but became more evident after the Exxon Valdez disaster.

The U.S. Coast Guard Office of Vessel Traffic Management researched various means to improve vessel tracking, opting to modify the digital selective calling (DSC) communications protocol relied upon for Global Marine Distress Safety System alerts. 

DSC allows for scheduled broadcasts and the ability to poll for information, which led to a shipboard system that would allow specific very high frequency DSC messages composed of vessel identity and position for tracking purposes. 

Mandating Universal Standards 
In 2000, the International Maritime Organization mandated universal automatic identification system use on all tankers, passenger vessels of 150 gross tonnage or greater, and other ships of 300 gross tonnage or greater (500 gross tonnage or greater in domestic voyages).
Today we track more than 7,000 vessels a day via a shore-side network of Coast Guard VTS transceivers and AIS receiver stations through our nationwide automatic identification system. In addition to our land network, we have also received AIS reports from what was initially a Coast Guard project to receive and decode AIS from commercial satellites.
IS-SAT graphic courtesy of exactEarth Ltd. and the Environmental Systems Research Institute, Inc.
Full article is available at