ANALYSIS OF ADVANCED EARTH ROTATION PARAMETERS MODELS AND THEIR EFFECT ON GEODETIC POSITION DETERMINATION

Abstract

A new field in the geophysical sciences has recently emerged, namely space geodesy. An integral part of geodesy has always been the definition and realization of a terrestrial reference frame, celestial reference frame, and determination of the earth rotation parameters that link these two reference frames. The term "earth orientation" refers to the direction of earth's axis in space, with respect to the earth's crust. Such orientation is usually measured using five quantities commonly: two angles which identify the direction of the earth's rotation axis within the earth (polar motion); an angle describing the earth rotation variation rate (length of day or universal time); and two angles which characterize the direction of the earth's rotation axis in space (Precession and Nutation). With these five quantities, the orientation of the earth in space is fully described. Whoever, celestial nutations and precession are primarily products of earth's interactions with other celestial bodies, and define the orientation of the rotation axis with respect to the celestial sphere, and are largely periodic. Such celestial orientation is considered outside the scope of present investigation. The earth rotation parameters include the polar motion and rotation variation rate (length of day or universal time). This research will focuses on the earth rotation parameters because, it has proceeded rapidly over time. In this research, the different coordinates systems used in geodetic positioning, such as: terrestrial, celestial, and satellite orbital coordinates systems, and their interrelationships with earth rotation variations parameters, will be studied, and the recent monitoring systems of the earth rotation variations like satellite laser ranging (SLR), very long baseline interferometry (VLBI), lunar laser ranging (LLR), and the global positioning system (GPS), are studied. The polar motion and rotation rate variation are considered complex oscillations, consisting of sum of several components. These components are different in amplitude, period and phase. The variations of periods, amplitudes and phases of the each component of the parameters under investigation, will be studied. Decomposition of earth rotation variation into separated components, is a useful way to describe the variation in the measured data. This can help to understand the behavior of this phenomenon. Understanding the l behavior of these phenomena, which will help in producing and developing a more

accurate and reliable prediction models for these parameters. Decomposition of earth rotation variation based on the spectral analysis of the up to date records of both polar