A Group of Terms Precession(Sun-Earth-Moon, Fixed! I ) Vernal Equinox moves towards west 50.26second. The difference between equinox calendar year and sidereal year 0. 014day Nutation: The oscillation withprespect to the inertial space is called nutation(Sun-Earth-Moon, Change! ! !) 1. Secular precession 2. Periodic nutation Polar motion: The oscillation with respect to the terrestrial system is named polar motion Chandler period: The period of the free motion amounts to about 430 days and is known as the Chandler period Ev Principles of the Global Positioning System 1. Conventional Celestial Reference System 1. Definition of CCRS CRF: Since this system is defined conventionally and the practical realization does not necessarily coincide with the theoretical system, it is called(conventional) Celestial Reference Frame(CRF oquasi-inertial"means a geocentric system is not rigorously inertial because of the accelerated motion of the earth around the sun o the International Earth Rotation Service (IERS) called /CRF EX Principles of the Global Positioning System
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Z-Axis PrAxis Point伸,0 Y- Axis Y-Axis ThreeDimensional Artesia Three- Dimensional Polar Coordinates X.Y.Z (中,e,r) wy Principles of the Global Positioning Syste 200534(13 Y-Axis Three- Dimensional Polar Coordinates Three- Dimensional Cartesian Coordinates x=rcos(中)c0s() 中)sin(0 rsin(中) rinciples of the Global Positioning System 2005-3-4
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Conventional Terrestrial Reference System Definition: Terrestrial Reference Frame(TRF) TRF: is defined by a set of terrestrial control stations erving as reference points. Most of the reference stations are equipped with Satellite Laser Ranging(SLR)or Very Long Baseline Interferometry (VLBD bilit o World Geodetic System 1984(WGS-84), 1500 o ITRF-94 established by the IErS, 180 points Principles of the Global Positioning System 2005-34(15 Geodetic Coordinates Geodetic Height of Point p Ellipsoid Semi Minor Axi Point p Semi Mayor Axis Equator Geodetic Longitude at Latitude at Point p Point p WE Principles of the Global Positioning System 200534(16
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