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2022 | OriginalPaper | Buchkapitel

3. Reference Systems in GNSS Geodesy

verfasst von: Clement A. Ogaja

Erschienen in: Introduction to GNSS Geodesy

Verlag: Springer International Publishing

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Abstract

Accurate and well-defined time and coordinate reference systems are the basis for GNSS geodesy, where positions are computed from radio signal travel time measurements and provided as a set of coordinates. This chapter contains a review of the time systems and coordinate systems (and reference frames). The aim is to provide only the necessary background information, and references for a more detailed understanding of the pertinent concepts and equations are provided.
Fußnoten
1
We all have 86,400 seconds a day.
 
2
SI second is the time it takes a Cesium-133 atom at the ground state to oscillate exactly 9,192,631,770 times [4].
 
3
The continuing requirement for a time scale approximating UT is due to its wide application in surveying and navigation. A compromise solution had, therefore, to be found which retains the advantage of uniform time scale generation by atomic clocks and still follows the variations of the Earth’s rotation [18].
 
4
A one-second adjustment that is occasionally applied to UTC in order to keep its time of day close to the mean solar time as realized by UT1.
 
5
The work to generate UTC is performed at the BIPM in France. The staff doing the work is composed of several international timing experts who frequently interact with, and obtain timing data from, the rest of the world’s time and frequency community. The leap second steps are determined by the IERS, which operates out of the Paris Observatory and which collects the Earth’s rotation data from numerous observatories and radio telescopes around the globe.
 
6
Potential GPS week rollover issues would include (1) UTC timing displayed and/or time tags of receiver data containing PNT information could jump by 19.7 years and (2) associated time tags of GPS solutions could be incorrect, causing problems such as GPS receiver engine failure or loss of data.
 
7
The national estimate of UTC generated by the timing entity in Russia.
 
8
Galileo/GPS time of week is the number of seconds that have occurred since the transition from the previous week. It covers an entire week from 0 to 604,799 seconds and is reset to zero at the end of each week.
 
9
BeiDou seconds of week is the number of seconds that have occurred since the last Sunday, 00:00:00 BDT. It covers an entire week from 0 to 604,799 seconds and is reset to zero at the end of each week.
 
10
A datum is defined when points are positioned with reference to a particular ellipsoid whose shape, size, position, and orientation relative to the Earth’s surface are known. The position and orientation of an ellipsoid may be defined using physical point(s) located on the Earth’s surface, through assigned latitude and longitude.
 
11
A datum defined using an ellipsoid whose center and the origin of its associated Cartesian coordinate system coincide but are non-geocentric.
 
12
Projects such as road constructions, pipes, and drainage systems rely on orthometric heights (elevations) which determine the direction of flow of water and liquids based on gravity potential differences.
 
13
The ICRF was defined and adopted by the International Astronomical Union (IAU) on January 1, 1998. It was determined using radio positions of 212 extragalactic radio sources determined through very long baseline interferometry (VLBI).
 
14
What is the ellipsoid associated with the realizations of ITRS? The ITRF solutions do not directly use an ellipsoid. ITRF solutions are specified by Cartesian equatorial coordinates X, Y, and Z. If needed, they can be transformed to geographical coordinates (Longitude, Latitude, and Height) referred to an ellipsoid. GRS80 ellipsoid is recommended. (http://​itrf.​ensg.​ign.​fr/​).
 
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Metadaten
Titel
Reference Systems in GNSS Geodesy
verfasst von
Clement A. Ogaja
Copyright-Jahr
2022
DOI
https://doi.org/10.1007/978-3-030-91821-7_3