Space-based AIS : theoretical considerations and system parameter optimization
The recently introduced Universal Automatic Identification System (AIS) is a ship-to-ship and ship-to-shore reporting system based on broadcasting of messages in the maritime VHF band. The AIS messages could also be received from space, and this report studies the behaviour of such a space-based AIS system with respect to the relevant parameters. The necessary theory is developed, and a method for optimizing the system with respect to ship detection probability, observation time, and number of ships that the system can handle is presented. Results show that the system can be optimized to handle 10 000 ships within the field of view with a ship detection probability of 99% if the ship reporting interval is set to 5.5 min, and the observation time is at least 36 min. In principle, the system could be optimized to handle any number of ships if the appropriate ship reporting interval is chosen, and the observation time is sufficiently long.