Grades: observed own-recorded live from terrestrial AIS (aisstream.io network) · reported counted by a named body · modelled derived by an algorithm, never quotable as a measurement.
Own-recorded AIS at eight US container gateways, filtered to merchant vessels — AIS ship-type 70–79 and 150 m or longer, which excludes tugs and workboats. AIS cannot separate container ships from bulkers, so this is a proxy, not a measurement. A ship we cannot hear is indistinguishable from a ship that is not there — see the method.