Automatic Identification System (AIS)

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Maritime Information Management System (MIMS)

AIS provided by the San Francisco Marine Exchange

AIS Overview

What is the Automatic Identification System (AIS)?

Picture a shipboard radar or an electronic chart display that includes a symbol for every significant ship within radio range, each as desired with a velocity vector (indicating speed and heading). Each ship "symbol" can reflect the actual size of the ship, with position to GPS or differential GPS accuracy. By "clicking" on a ship symbol, you can learn the ship name, course and speed, classification, call sign, registration number, MMSI, and other information. Maneuvering information, closest point of approach (CPA), time to closest point of approach (TCPA) and other navigation information, more accurate and more timely than information available from an automatic radar plotting aid, can also be available. Display information previously available only to modern Vessel Traffic Service operations centers can now be available to every AIS - user as seen below.

Marine Exchange Management System (MIMS)

With this information, you can call any ship over VHF radiotelephone by name, rather than by "ship off my port bow" or some other imprecise means. Or you can dial it up directly using GMDSS equipment. Or you can send to the ship, or receive from it, short safety-related email messages.

The AIS is a shipboard broadcast system that acts like a transponder, operating in the VHF maritime band, that is capable of handling well over 4,500 reports per minute and updates as often as every two seconds. It uses Self-Organizing Time Division Multiple Access (SOTDMA) technology to meet this high broadcast rate and ensure reliable ship-to-ship operation.

Transponders aboard vessels coupled with computer software allow users to graphically view vessels and their associated information within Bay waters. Future enhancements and development point to the system becoming a fixture locally and globally.

AIS is this and much more. It not only provides a display to all the system users of the physical vessel traffic situation; it also provides key navigational and operational information as per the requirements of the users. For example all the users can display static information of each display target such as the name, type and size of vessel data that is not usually available through standard radar. They can also obtain real time information such as the speed over ground (SOG), course over ground (COG) and the destination of other vessels. In short, AIS is a system that provides each user a picture of the navigational information that all other participants are using.

How does the basic AIS perform this task? It starts with the Global Positioning System (GPS). The GPS is a network of many satellites that are in orbit around the earth and they transmit a signal similar to a pulse or a clock. The shipboard GPS transponder/radio receives that signal and calculates the time differences between the various satellites pulses, at least six for accuracy within 10 meters, to determine an exact location of the vessel in longitude and latitude. That data is then directly input into the ship?s AIS computer. The AIS computer combines the GPS location information with other vessel related data such as name, course and speed and transmits it, via VHF radio, to the AIS Vessel Traffic Controller (VTC). The VTC is a communications hub, normally located on an appropriate mountain peak (Mt.Tamalpais in the San Francisco Bay Area) that receives, organizes and combines all the transmissions of all the AIS vessels and then rebroadcasts the data back out so that all the vessels share the same data. When the AIS vessel receives the data from the VTC, it then displays it on the computer monitor with an Electronic Navigation Chart (ENC). If for any reason the VTC site fails to work properly, all the AIS vessel transponders automatically shift to work in ship-to-ship mode."

Current Enhanced SF-AIS Organization

The Marine Exchange controls the controls the Mt. Repeater and also delivers VTS Radar and PORTS data, that is collected from the internet, to the Repeater (via dedicated phone line) for distribution to the Vessel Operators.

Proposed 1371-1 SF-AIS Organization

The VTS Controls the repeater site (s) The Marine Exchange delivers PORTS Data to and collects AIS Data from the repeater site for infusion with and distribution to the web