The Statutory Instrument authorising the GLA to provide AIS as an Aid to Navigation was approved by the UK Parliament in July 2006. The introduction of AIS is a major development in the provision of AtoNs.
Vessel traffic information outside the Humber estuary recorded from the Trinity House Flamborough AIS base station
The AIS base station is able to send messages to each of these vessels. Normally the AIS return (above figure), will be combined with the radar return so that the mariner can not only see that there is a vessel moving across infront of them, but also who it is and where they are going etc. AIS is a system to enhance safety and the service provided. It may eventually make it possible to reduce the provision of some conventional AtoN services. It can provide the following information:
Static information - Name, call sign, MMSI, Dimensions, Type
Voyage related information - Draught, Cargo type, Destination, ETA
Dynamic information - Position - LAT/LNG, Course and speed over ground, Heading, Rate of turn
AIS Transmissions use Self Organising Time Division Multiple Access (SOTDMA). Each AIS unit has two receivers and a single transmitter. The transmitter, under normal operation, will transmit on both AIS1 and AIS2 VHF frequencies (161.97 Mhz and 162.025 Mhz) as indicated in the figure below.
This transmission format allows for two second update rates with any one AIS channel carrying only half the load. This is done to allow for simultaneous vessel to vessel communications. The SOTDMA frame length is 2250 slots with 256 bits per slot. Each frame consumes one minute of airtime.
