Читать книгу Global Navigation Satellite Systems, Inertial Navigation, and Integration - Mohinder S. Grewal - Страница 65

The timescale to which GPS signals are referenced is referred to as GPS time. GPS time is derived from a composite or “paper” clock that consists of all operational monitor station and satellite atomic clocks. Over the long run, it is steered to keep it within about 90 nanoseconds (1σ) of UTC, as maintained by the master clock at the US Naval Observatory, ignoring the UTC leap seconds. At the integer second level, GPS time equaled UTC in 1980. However, due to the leap seconds that have been inserted into UTC, GPS time was ahead of UTC by 18 seconds after September 2019.