Crappy Class A AIS data, some stats
I’m still hoping someone will tell us more about the FCC and Class B AIS, but in the meantime Dan sent a great link to The Nautical Institute’s AIS Forum. It’s not a forum in the usual sense but rather a collection of Reported Problems and Technical Feedback papers. An interesting piece in the latter section is a PDF called Automatic Identification System (AIS): A Human Factors Approach, which strongly confirmed my notion that lots of user entered data is bogus. For instance, of nearly 31,000 AIS transmissions examined in one study 49% “showed obvious errors in the fields of destination and ETA.” Which reminded me of the screen shot Russ sent a while back, showing BoatingSF’s neat AIS tracker on Feb. 8, more than a month after the Pilot Vessel Golden Gate’s ETA! The boat, a violet target headed SW toward its namesake bridge, is also going 22 knots even though its Navigation Status is “moored”.
The good news is that user entered data isn’t very important (unless maybe you’re filtering targets based on their nav status), but the paper also confirms a rumor I’d heard that certain Class A transponders can broadcast a default MMSI in certain circumstances, leading to possible duplicates that really mess up the System. Well, it’s true, the MMSI is 1193046, and there’s a link to details about the units, causes, and remedies. We need to remember that AIS is a relatively young technology (and Class B is an infant).