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Posts Tagged "ephemeris"

In the wider world, an almanac is an annual publication dedicated to information such as weather forecasts, tide tables, lunar cycles etc. A typical almanac will contain tabular information covering a particular field or fields, and will be arranged according to the calendar. However, in the world of satellite navigation systems, the almanac is a regularly updated digital schedule of satellite orbital parameters for use by GNSS receivers. The almanac for any g...

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The ionosphere is the single largest error source in point positioning after the application of precise GNSS orbit and clock products, and there are a number of mathematical models that have been proposed to mitigate its effects. Of these, the model developed by John A Klobuchar is used by the GPS system and broadcast by every satellite. The Klobuchar model is something of a compromise between computational complexity and accuracy. However, it is reckoned to be capable of correcting up to 70% o...

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An ephemeris is quite simply a table giving the coordinates of a celestial body at specific times during a given period. The word comes from the same Greek root as “ephemeral”, which strictly means short-lived, but has come to mean inconsequential. However, in terms of GNSS systems, the ephemeris is certainly not inconsequential. Each GNSS satellite includes ephemeris data in the signal it transmits. This comprises a set of parameters that can be used to accurately calculate the loc...

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