exactEarth is often asked about the relationship between LRIT and Satellite AIS (S-AIS). I believe that the two technologies are complimentary not competitive.
AIS was developed for collision avoidance and LRIT was designed for the purpose of long range tracking. With LRIT the ship is required to broadcast a position report every six hours for a total of 4 reports every 24. Satellite AIS on the other hand will only report what is present, and detectable, in the satellite footprint. S-AIS does provide many position reports with every satellite pass, but it cannot guarantee that the ship will be detected with every pass.
What I find particularly useful for S-AIS are the various data applications well outside simple tracking of ships. By having multiple position reports for a given ship, and the possibility that the ship will be detected many times during a day, it is now possible to develop behavioral models for ships and ship traffic. This essentially extends maritime domain awareness well outside terrestrial AIS reception, allowing for applications ranging from protection of environmentally sensitive areas to understanding and alarming on abnormal behavior of a ship.
S-AIS does not guarantee a report from a ship at a definite interval and so therefore cannot replace LRIT. However the two technologies are complimentary, for example S-AIS can be used to identify non-complying ships under LRIT reporting obligations. In general, data quantity and quality provided by S-AIS is enabling dozens of use cases and applications all based on ship behavioral modeling that will benefit the maritime community for years to come.