Long Distance Propagation of 162-MHz Shipping Information Links Associated with Sporadic-E

Anomalous long distance reports of Automatic Identification System (AIS) shipping transmissions were received by a United States Coast Guard terrestrial monitoring network in the eastern United States and Puerto Rico. 6677 signals were identified from ships located over 1000-km from the ground stations between 13 and 14 July 2021, with almost no long-distance links received at night or at any time on 15 July. The cause appears to be sporadic-E layers identified by Digisonde and satellite radio occultation data. The density of these layers cannot be accurately determined, but might exceed 27 MHz, or 9x1012 el. m3. AIS transmissions potentially provide an excellent means of identifying dense sporadic-E layers globally.