Introduction

Satellite detection of AIS messages has been requested by administrations. In response, studies were made that were documented in Report ITU-R M.2084 – Satellite detection of automatic identification system messages. The report considered the operational and technical characteristics of the shipborne AIS and the requirements and limitations of reception of AIS messages from satellites. Further studies were proposed to deal with the technical limitations that hinder detection of AIS-equipped target ships in high-traffic areas (e.g. the Dover Straits, Singapore, North East United States of America, and the northern Gulf of Mexico) on the designated AIS VDL (VHF Data Link). The technical limitations specifically cited were:

1 the length of the AIS message in the time slot (insufficient time buffer for the satellite detection range);

2 the large number of messages in the satellite antenna footprint (excess reuse of the time slots in the VDL as detected by the satellite);

3 the difficulty satellite AIS has in distinguishing signals between AIS messages and communications from terrestrial services within the satellite antenna footprint (coverage pattern).

This report on further studies shows the need for a special AIS message that is shortened in length and can be transmitted on a special reporting schedule on two other frequencies when those frequencies are designated. Accordingly, a new Recommendation ITU-R M.1371 AIS message (Message 27) and new Radio Regulations (RR) Appendix 18 (AP18) frequencies for this service are proposed.