What is the meaning of epoch as it applies to GPS?

• A. A calendar time mark used for system updates.
• B. An interval of time.
• C. A moment when a single satellite is observed.
• D. The reference time for clock corrections.

Answer: (B)

In GPS, epoch refers to the time interval over which a specific set of navigation data (ephemeris and clock corrections) is valid. The satellite orbit parameters and clock information are computed for a given epoch and are meant to be used for a defined period, not just a single instant. This interval defines when the data apply, so receivers know when to update or refresh their calculations. Other options point to a single moment or a separate reference time, but the important idea is the span of time during which the ephemeris and clock data are valid.