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Errors and Accuracy Issues
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
Their relationship is as follows. The master control station gathers the GPS satellites’ data from monitoring stations around the world. After processing, this information is uploaded back to each satellite to become the broadcast ephemeris, broadcast clock correction, and so on. The actual specification for GPS time demands that it be within one microsecond of UTC as determined by USNO, without consideration of leap seconds. Leap seconds are used to keep UTC correlated with the actual rotation of the earth, but they are ignored in GPS time. In GPS time, it is as if no leap seconds have occurred at all in UTC since 00:00:00 h, January 6, 1980. And in practice, GPS time is much closer than the microsecond specification; it is usually within about 25 ns of UTC, except leap seconds. Each independent satellite clock should match exactly with the GPS system time, however, in practice, they are often deviated. Similar time-related problems also occur for GLONASS, Galileo, and BeiDou.
Miscellaneous topics
Published in Michael Talbot-Smith, Audio Engineer's Reference Book, 2012
GPS disseminates time data as Universal Coordinated Time (UTC), in a form capable of being used for time synchronization throughout the world. UTC is a composite form of time, having data inputs from both atomic clocks and a time scale derived from the rotation of the earth with respect to the sun (UT1). Atomic clock time, International Atomic Time (TIA), is highly accurate, being derived from atomic standards held in 50 timing laboratories in different countries, and computed by the Bureau International des Poids et Mesures (BIPM) in Paris to give a statistically definitive time. It is sometimes called a `Paper Time' since it is not kept by a physical clock. Irregularities in the earth's orbit, variations in the tilt of the equator and polar wobble result in the length of solar days (and hence of hours, minutes and seconds) varying. These are compensated for to give UT1, which defines the actual orientation of the ECEF coordinates with respect to space and celestial bodies. There are also variations in the rotational speed of the earth and, as a consequence, solar time (UT1) is irregular. Since navigation and both civil and military timekeeping depend on having a uniform time scale, these variations are computed out by the International Earth Rotation Service (IERS) to form UTC, which has seconds of equal length to
Cultural Communication Issues and Effective e-Leadership
Published in Margaret R. Lee, Leading Virtual Project Teams, 2021
When setting guidelines for time zones for a virtual team, it is important to recognize Coordinated Universal Time (UTC). UTC follows the International Atomic Time with an exact offset of an integer number of seconds, changing only when a leap second is added to keep clock time synchronized with the rotation of the earth. UTC was previously called Greenwich Mean Time (GMT) and UTC is sometimes written informally as GMT. Time zones around the world are expressed as positive or negative offsets from UTC. Many Internet and World Wide Web standards, computer servers, online services, flight plans and air traffic control, weather forecasts and maps, and radio operators use UTC to avoid confusion with time zones and daylight savings time.
Clock synchronisation: the establishment of Coordinated Universal Time (UTC) through the work of Louis Essen
Published in The International Journal for the History of Engineering & Technology, 2023
Louis Essen published his research in 140 papers and three small books.76 His work on Coordinated Universal Time (UTC), clock synchronisation and time signals appeared in only ten percent of his published papers. Nevertheless, it is this aspect of his work that is still most relevant today. Essen’s close cooperation with US astronomers and physicists made it easy to establish a prototype UTC time service in 1960. UTC remains the primary time standard by which the world regulates clocks and time. The unit of time is defined in terms of a natural property of the caesium atom as measured by Essen and Markowitz in the 1950s. And the idea of the ‘leap second’ (a one-second adjustment that is occasionally applied to UTC) was first proposed by Louis Essen and Gernot Winkler (USNO Head of Time Services, 1966–1996) in 1968. Their recommendation was accepted by the International Bureau of Weights and Measures in 1972.77 The National Physical Laboratory – where Essen worked for 43 years – now has responsibility for the UK national time and frequency service (Figure 13).