Time transfer describes methods for transferring reference clock synchronization from one point to another, often over long distances. Radio-based navigation systems are frequently used as time transfer systems.
In some cases, multiple measurements are made over a period of time, and exact time synchronization only determined retrospectively.
In particular time synchronization has been accomplished by using pairs of radio telescopes to listen to a pulsar, with the time transfer accomplished by comparing time offsets of the received pulsar signal.
See also