26,639 saved AIS position reports from 200 vessels form this Santa Barbara Channel view for June 15, 2023. They are broadcasts, not radar detections.
Range rings are 10 nautical miles apart, north up. The sweep makes one turn per UTC day in 45 seconds. A report waits for its bearing unless the sweep has passed; then it appears on arrival. This reveal is not sighting time. Blips fade to a faint trace over 20 data minutes.
NOAA / MarineCadastre AIS_2023_06_15, public U.S. government data. The 74,362-report box extract was reduced to 26,639 reports for 200 vessels with at least eight reports each; long tracks are thinned.
Distances use a local planar approximation. Blip color shows vessel class; the selected track is yellow. Reference squares mark ports and islands. Arrows select vessels; up/down steps UTC hours. Coverage and broadcast intervals are uneven.
Code: Luke Steuber, MIT. Data Poems.