To compensate this a master clock frequency of nominal 10.23 MHz has actual 10. "Due to several relativistic effects, the atomic clocks in the GPS satellites run a little faster, they gain 445 picoseconds per second. After that TAI corresponds to the time at mean sea level. The differences between atomic clocks on earth on different gravitational potentials are compensated since 1977. So GPS and TIA clocks are not strictly coupled, but the differences are kept very small. The GPS ground stations monitors all atomic clocks of the GPS system and UTC for that purpose." "Atomic clocks on earth could be synchronized using GPS to less than 10 nanoseconds difference." To acheive this, the atomic clocks of GPS satellites and ground stations are synchronized to less than 20 nanoseconds and the GPS time to UTC time to less than 100 nanoseconds. The long term difference between GPS and UTC time should be held less than 1 microsecond (disregarding leap seconds). However, except for those who need milliarcsecond pointing accuracy, treating GPS time as being offset from TAI by exactly 19 seconds is more than good enough.įrom the book GPS Satellitennavigation by Frank Schröder ISBN 3-7723-6692-1: "GPS has it own time scale, it starts with the week 0 at 6th January of 1980. (18) where n represents the integer number of seconds. The end result is that GPS time and TAI are not separated by exactly 19 seconds. The relation between these time scales can be summarized as follows: TAI UTC +10s +n. As the most accurate atomic clocks currently are those maintained by the US Naval Observatory, those clocks get more weight as to what constitutes TAI. Global Positioning System (GPS) GPS - UTC. This addresses issues such as tidal effects and subtle changes in elevation. SIM Time (SIMT) Coordinated Universal Time (UTC) International Atomic Time (TAI) TAI - UTC. To best represent this ideal, time as ticked by atomic clocks worldwide are averaged over the course of a year, weighted by the accuracies of those clocks. TAI is an ideal time scale as opposed to an operational time scale. The GPS satellite atomic clocks are updated regularly, roughly once per day, to satisfy the promised accuracy of GPS receivers. The smallish atomic clocks on the GPS satellites aren't as accurate as are the very large atomic clocks maintained by the US Naval Observatory. While this is the goal, it is not the reality. The goal is to have the tick rate of a GPS satellite as observed from a receiver at sea level be equal to the tick rate of the best atomic clocks, adjusted to sea level. To compensate for these effects, the GPS satellites' atomic clocks are intentionally made to tick at a slightly slower rate than is standard (the standard being "9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom"). The gravitational (general relativistic) effects result from the altitude at which GPS satellites orbit. The special relativistic effects result from the relative motion of the GPS satellites and a clock on the surface of the Earth. The atomic clocks on GPS satellites are subject to both special relativistic and gravitational effects. Each GPS satellite contains an atomic clock, but with a tick rate that deviates slightly from the standard definition of "9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom". They assume a perfect succession from one second to the next, without any leaps ever occurring. Unix timestamps do not account for leap seconds. It is illogical to think of a Unix timestamp as being in any particular time zone. Both differ from UT1, time as ticked by the Earth's rotation (this is the source of leap seconds), and because of how they represent time, they also differ very slightly from one another. Unix timestamps are always based on UTC ( otherwise known as GMT ). TAI and GPS time both attempt to represent time as ticked by an ideal clock at mean sea level on the surface of the Earth. Print 'Synchronizing system time.TL DR: For all practical purposes except milliarcsecond radio astronomy, TAI and GPS time are separated by exactly 19 seconds. # Connects to your GPS-Dongle and synchronize systemtime with GPS-UTC-time.
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