ADS-B

Unlike traditional secondary surveillance radar, which determines an aircraft's position by interrogating its transponder from a ground station and measuring the response, ADS-B has the aircraft determine and broadcast its own position, derived from its onboard GNSS receiver, without waiting to be asked. Ground stations and other equipped aircraft within range receive this broadcast directly, and space-based ADS-B receivers extend that reception well beyond any ground station's range, providing surveillance coverage over oceans and remote regions that radar has never been able to cover.

The surveillance capability gain ADS-B delivers is most significant precisely where radar coverage has always been weakest or entirely absent — oceanic and remote continental airspace — because space-based ADS-B reception doesn't depend on ground infrastructure density the way radar fundamentally does, closing a surveillance gap that radar could never economically address regardless of investment. In airspace that already has radar coverage, ADS-B is typically deployed as a complement providing finer-grained, more frequent position updates rather than a wholesale radar replacement, since regulators generally maintain radar as a backup surveillance method precisely because ADS-B depends on the aircraft's own equipment functioning and broadcasting correctly — a radar system observes an aircraft regardless of whether the aircraft's own systems are cooperating, which ADS-B by design cannot do. For CE aviation operations, ADS-B equipage is now a practical requirement for accessing controlled airspace in most jurisdictions, and space-based ADS-B specifically is what has made continuous, radar-independent surveillance of oceanic and polar routes operationally realistic for the first time.