Definition
Low earth orbit satellites carry AIS receivers whose footprint spans hundreds of nautical miles, extending coverage well beyond terrestrial range. The wide footprint causes message collisions in busy sea areas because SOTDMA only deconflicts locally, so detection is probabilistic and updates may be hours apart. Two channels, 156.775 and 156.825 MHz, are allocated for long range AIS to help. Commercial tracking websites blend satellite and shore-station feeds.
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