On the Adoption of a Terrestrial Reference Frame

1980 ◽  
Vol 56 ◽  
pp. 145-153
Author(s):  
Dennis D. McCarthy
Keyword(s):  
Reference Frame ◽  
Polar Motion ◽  
Center Of Mass ◽  
Terrestrial Reference Frame ◽  
Fixed Frame ◽  
The Earth ◽  
International Polar ◽  
Definition Of ◽  
Observational Techniques ◽  
Fixed System

AbstractThe report of the IAU Working Group on Nutation endorsed by Commissions 4, 8, 19 and 31 at the 1979 General Assembly points out that “… the complete theory of the general nutational motion of the Earth about its center of mass may be described by the sum of two components, astronomical nutation, commonly referred to as nutation, which is nutation with respect to a space-fixed coordinate system, and polar motion, which is nutation with respect to a body-fixed system …”. Unlike the situation for the space-fixed frame, there is not an adequate, formally accepted, body-fixed system for this purpose. The Conventional International Origin (CIO) as it is presently defined is no longer acceptable because of recent improvements in observational techniques. The effective lack of this type of terrestrial reference frame limits the complete description of the general nutational motion of the Earth. In the absence of a terrestrial reference frame suitable for specifying the orientation of the Earth, it is suggested that a body-fixed system could be represented formally in a manner analogous to that used to represent the space-fixed frame. This procedure would be quite similar to methods employed currently by the International Polar Motion Service and the Bureau International de l’Heure, and would allow for the use of observations from new techniques in the definition of a terrestrial reference frame to be used to specify the complete nutational motion of the Earth.

The Estimation and Prediction of Geocenter Motion Based on GNSS Weekly Solutions

2020 ◽  
Author(s):  
Chunmei Zhao ◽  
Lingna Qiao ◽  
Tianming Ma
Keyword(s):  
Reference Frame ◽  
Prediction Accuracy ◽  
Center Of Mass ◽  
Science Research ◽  
Terrestrial Reference Frame ◽  
Small Contribution ◽  
The Earth ◽  
Term Prediction ◽  
Geocenter Motion

<p>The development of satellite space geodesy technology makes the establishment of global terrestrial reference frame based on the Earth’s center of mass become reality. Precise and stable terrestrial reference frame is the foundation of the Earth science research, while determination and analysis of the position of the Earth's center of mass and its change is an important part to build high precision terrestrial reference frame. Based on GNSS weekly solutions provided by IGS, the geocenter motion (GM) time series between 2007 and 2017 are obtained by means of net translation method. Then the amplitude of the annual term of geocentric motion is 2.27mm, 1.84mm and 2.13mm in the direction of X, Y and Z respectively, and the amplitude of the half-year term is 0.1mm, 0.20mm and 0.15mm respectively. In addition, some other inter-annual changes with relatively small contribution rate are found. Finally, in order to get reliable GM prediction ,two kinds of methods are used, which are ARMA and SSA+ARMA. In the short-term prediction, the accuracy of the two methods is the same, both can reach the millimeter level of prediction accuracy, but SSA+ARMA is more stable. SSA+ARMA algorithm is much better in the medium and long-term scale, and it can provide 1mm medium term prediction accuracy and 1.5mm long term prediction accuracy.</p>

scholarly journals Relativistic effects in geodynamics

1986 ◽  
Vol 114 ◽  
pp. 241-253 ◽  
Author(s):  
C. Boucher
Keyword(s):  
Gravity Field ◽  
Reference Frame ◽  
Relativistic Effects ◽  
Terrestrial Reference Frame ◽  
The Earth ◽  
Lunar Laser ◽  
Time Variations ◽  
Satisfactory Answer ◽  
Definition Of ◽  
Theories Of Gravitation

Geodesy has now reached such an accuracy in both measuring and modelling that time variations of the size, shape and gravity field of the Earth must be basically considered under the name of Geodynamics. The objective is therefore the description of point positions and gravity field functions in a terrestrial reference frame, together with their time variations.For this purpose, relativistic effects must be taken into account in models. Currently viable theories of gravitation such as Einstein's General Relativity can be expressed in the solar system into the parametrized post-newtonian (PPN) formalism. Basic problems such as the motion of a test particle give a satisfactory answer to the relativistic modelling in Geodynamics.The relativistic effects occur in the definition of a terrestrial reference frame and gravity field. They also appear widely into terrestrial (gravimetry, inertial techniques) and space (satellite laser, Lunar laser, VLBI, satellite radioelectric tracking …) measurements.

Reference Coordinate System Requirements for Geophysics

1975 ◽  
Vol 26 ◽  
pp. 87-92
Author(s):  
P. L. Bender
Keyword(s):  
Coordinate System ◽  
Polar Motion ◽  
Main Part ◽  
Measurement Techniques ◽  
Reference Points ◽  
Angular Motion ◽  
Coordinate Systems ◽  
Axis Of Rotation ◽  
The Earth ◽  
Fixed System

AbstractFive important geodynamical quantities which are closely linked are: 1) motions of points on the Earth’s surface; 2)polar motion; 3) changes in UT1-UTC; 4) nutation; and 5) motion of the geocenter. For each of these we expect to achieve measurements in the near future which have an accuracy of 1 to 3 cm or 0.3 to 1 milliarcsec.From a metrological point of view, one can say simply: “Measure each quantity against whichever coordinate system you can make the most accurate measurements with respect to”. I believe that this statement should serve as a guiding principle for the recommendations of the colloquium. However, it also is important that the coordinate systems help to provide a clear separation between the different phenomena of interest, and correspond closely to the conceptual definitions in terms of which geophysicists think about the phenomena.In any discussion of angular motion in space, both a “body-fixed” system and a “space-fixed” system are used. Some relevant types of coordinate systems, reference directions, or reference points which have been considered are: 1) celestial systems based on optical star catalogs, distant galaxies, radio source catalogs, or the Moon and inner planets; 2) the Earth’s axis of rotation, which defines a line through the Earth as well as a celestial reference direction; 3) the geocenter; and 4) “quasi-Earth-fixed” coordinate systems.When a geophysicists discusses UT1 and polar motion, he usually is thinking of the angular motion of the main part of the mantle with respect to an inertial frame and to the direction of the spin axis. Since the velocities of relative motion in most of the mantle are expectd to be extremely small, even if “substantial” deep convection is occurring, the conceptual “quasi-Earth-fixed” reference frame seems well defined. Methods for realizing a close approximation to this frame fortunately exist. Hopefully, this colloquium will recommend procedures for establishing and maintaining such a system for use in geodynamics. Motion of points on the Earth’s surface and of the geocenter can be measured against such a system with the full accuracy of the new techniques.The situation with respect to celestial reference frames is different. The various measurement techniques give changes in the orientation of the Earth, relative to different systems, so that we would like to know the relative motions of the systems in order to compare the results. However, there does not appear to be a need for defining any new system. Subjective figures of merit for the various system dependon both the accuracy with which measurements can be made against them and the degree to which they can be related to inertial systems.The main coordinate system requirement related to the 5 geodynamic quantities discussed in this talk is thus for the establishment and maintenance of a “quasi-Earth-fixed” coordinate system which closely approximates the motion of the main part of the mantle. Changes in the orientation of this system with respect to the various celestial systems can be determined by both the new and the conventional techniques, provided that some knowledge of changes in the local vertical is available. Changes in the axis of rotation and in the geocenter with respect to this system also can be obtained, as well as measurements of nutation.

scholarly journals The permanent tide and the International Height Reference Frame IHRF

2021 ◽  
Vol 95 (9) ◽  
Author(s):  
Jaakko Mäkinen
Keyword(s):  
Reference Frame ◽  
International Association ◽  
Reference Value ◽  
Equipotential Surface ◽  
Terrestrial Reference Frame ◽  
Reference Level ◽  
Consistent Estimate ◽  
The Mean ◽  
Global Mean Sea Level ◽  
Definition Of

AbstractThe International Height Reference System (IHRS), adopted by International Association of Geodesy (IAG) in its Resolution No. 1 at the XXVI General Assembly of the International Union of Geodesy and Geophysics (IUGG) in Prague in 2015, contains two novelties. Firstly, the mean-tide concept is adopted for handling the permanent tide. While many national height systems continue to apply the mean-tide concept, this was the first time that the IAG officially introduced it for a potential field quantity. Secondly, the reference level of the height system is defined by the equipotential surface where the geopotential has a conventional value W0 = 62,636,853.4 m2 s–2. This value was first determined empirically to provide a good approximation to the global mean sea level and then adopted as a reference value by convention. I analyse the tidal aspects of the reference level based on W0. By definition, W0 is independent of the tidal concept that was adopted for the equipotential surface, but for different concepts, different functions are involved in the W of the equation W = W0. I find that, in the empirical determination of the adopted estimate W0, the permanent tide is treated inconsistently. However, the consistent estimate from the same data rounds off to the same value. I discuss the tidal conventions and formulas for the International Height Reference Frame (IHRF) and the realisation of the IHRS. I propose a simplified definition of IHRF geopotential numbers that would make it possible to transform between the IHRF and zero-tide geopotential numbers using a simple datum-difference surface. Such a transformation would not be adequate if rigorous mean-tide formulas were imposed. The IHRF should adopt a conventional (best) estimate of the permanent tide-generating potential, such as that which is contained in the International Earth Rotation and Reference Systems Service Conventions, and use it as a basis for other conventional formulas. The tide-free coordinates of the International Terrestrial Reference Frame and tide-free Global Geopotential Models are central in the modelling of geopotential for the purposes of the IHRF. I present a set of correction formulas that can be used to move to the zero-tide model before, during, or after the processing, and finally to the mean-tide IHRF. To reduce the confusion around the multitude of tidal concepts, I propose that modelling should primarily be done using the zero-tide concept, with the mean-tide potential as an add-on. The widespread use of the expression “systems of permanent tide” may also have contributed to the confusion, as such “systems” do not have the properties that are generally associated with other “systems” in geodesy. Hence, this paper mostly uses “concept” instead of “system” when referring to the permanent tide.

Overview and Proposition for a Modern Definition of the CEP

2000 ◽  
Vol 178 ◽  
pp. 571-584
Author(s):  
Nicole Capitaine
Keyword(s):  
Working Group ◽  
Polar Motion ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
The Earth ◽  
Conventional Models ◽  
Definition Of ◽  
Orientation Parameters ◽  
Observational Procedure

AbstractThe current IAU conventional models for precession and nutation are referred to the Celestial Ephemeris Pole (CEP). However, the concept corresponding to the CEP is not clear and cannot easily be extended to the most recent models and observations. Its realization is actually dependent both on the model used for precession, nutation and polar motion and on the observational procedure for estimating the Earth orientation parameters. A new definition of the CEP should therefore be given in order to be in agreement with modern models and observations at a microarsecond level. This paper reviews the various realizations of the pole according to the models and observations and discusses the proposals for a modern definition of the CEP that are under consideration within the work of the subgroup T5 entitled “Computational Consequences” of the “ICRS” IAU Working Group.

scholarly journals The Calculation of the Nutations

1974 ◽  
Vol 3 ◽  
pp. 221-222
Author(s):  
R. O. Vicente
Keyword(s):  
Working Group ◽  
Polar Motion ◽  
Financial Difficulties ◽  
The Earth ◽  
International Astronomical ◽  
Earth Models ◽  
International Polar ◽  
Rotation Of The Earth ◽  
Set Up ◽  
Original Observation

It is well known that the knowledge of precession and nutation is essential for the computation of astronomical coordinates and the comparison of values obtained at different dates. It is therefore important to compute the nutations from the best available observations.Unfortunately, there are not many long series of reliable observations that can be used for the calculation of the several nutations. Nowadays, we need more accurate values and, therefore, it is fundamental to have observations reduced in an homogeneous way. For this purpose, Commission 19 (Rotation of the Earth) set up a ‘Working Group on Pole Coordinates’, during the last IAU meeting in 1970 (Vicente, 1972), with the objective of reducing the 70 years of variation of latitude observations done by the International Latitude Service (called the International Polar Motion Service at the present time) that constitute a remarkable set of astronomical data. It is expected to obtain more reliable values for the coordinates of the pole and be able to calculate the nutations.The Working Group on Pole Coordinates is transferring to punched cards all the observations registered in the original observation books and that involves nearly 2 million cards. This work has been hampered by financial difficulties, but it should be supported by the international astronomical community in order to obtain the best results from so many years of observations, done by international cooperation.The theoretical researches done in the last decades have shown that the values of the nutations depend on the structure of the Earth (Jeffreys and Vicente, 1957). Lately, the researches done in seismology have resulted in a better knowledge about the structure of the Earth, leading to the setting up of many Earth models due to the availability of computers. This fact has led to the situation where one cannot propose better theoretical values for the nutations because they depend on the model adopted for the structure of the Earth.

scholarly journals Unconstrained Estimation of VLBI Global Observing System Station Coordinates

2021 ◽  
Vol 55 ◽  
pp. 23-31
Author(s):  
Markus Mikschi ◽  
Johannes Böhm ◽  
Matthias Schartner
Keyword(s):  
Reference Frame ◽  
Terrestrial Reference Frame ◽  
Baseline Length ◽  
Radio Telescopes ◽  
Earth Orientation Parameters ◽  
The Earth ◽  
Station Coordinates ◽  
International Vlbi Service ◽  
Orientation Parameters

Abstract. The International VLBI Service for Geodesy and Astrometry (IVS) is currently setting up a network of smaller and thus faster radio telescopes observing at broader bandwidths for improved determination of geodetic parameters. However, this new VLBI Global Observing System (VGOS) network is not yet strongly linked to the legacy S/X network and the International Terrestrial Reference Frame (ITRF) as only station WESTFORD has ITRF2014 coordinates. In this work, we calculated VGOS station coordinates based on publicly available VGOS sessions until the end of 2019 while defining the geodetic datum by fixing the Earth orientation parameters and the coordinates of the WESTFORD station in an unconstrained adjustment. This set of new coordinates allows the determination of geodetic parameters from the analysis of VGOS sessions, which would otherwise not be possible. As it is the concept of VGOS to use smaller, faster slewing antennas in order to increase the number of observations, shorter estimation intervals for the zenith wet delays and the tropospheric gradients along with different relative constraints were tested and the best performing parametrization, judged by the baseline length repeatability, was used for the estimation of the VGOS station coordinates.

The MARVEL gravity and reference frame mission proposal

2020 ◽  
Author(s):  
Jean-Michel Lemoine ◽  
Mioara Mandea ◽  
Keyword(s):  
Reference Frame ◽  
Terrestrial Reference Frame ◽  
Mass Change ◽  
Earth System ◽  
Polar Orbit ◽  
Laser Tracking ◽  
The Earth ◽  
Gravity Sensor ◽  
Mass Transfers ◽  
Leo Satellite

<p>The "MARVEL gravity and reference frame mission" proposal has been selected by CNES for the start of a pre-phase A study. <br>MARVEL aims at reaching in one single mission two major and complementary goals:<br>- The monitoring of mass transfers within the Earth system with increased precision,<br>- The realization, at the millimeter level, of the terrestrial reference frame.</p><p>In the nominal configuration, a LEO satellite (400 - 450 km) in polar orbit, acting as a gravity sensor, performs optical ranging measurements on two MEO satellites (7000 km) orbiting on the same plane. The MEO satellites are equiped with the four geodetic techniques (GNSS, SLR, DORIS, VLBI), in order to meet the GGOS Earth reference frame accuracy objectives.</p><p>We also propose two alternative (and less costly) configurations, where only the first goal is fully reached:<br>- one by replacing the MEO satellites by two or more cubesats on the same orbit,<br>- the second one by using specially equipped GNSS satellites as targets for the LEO optical ranging measurements.</p><p>In any case, the goal of monitoring mass change with enhanced precision is attained through the use of high-low SST laser tracking.</p><p>We will present in detail the different configurations proposed and present the simulation plan for this pre-phase A study.</p>

scholarly journals The Effects of the Reference Frames and of their Realization on the Earth Rotation Parameters Computed from Different Observational Techniques

1980 ◽  
Vol 56 ◽  
pp. 135-144
Author(s):  
Nicole Capitaine ◽  
Martine Feissel
Keyword(s):  
Reference Frame ◽  
Earth Rotation ◽  
High Frequency ◽  
Reference Frames ◽  
The Earth ◽  
Earth Rotation Parameters ◽  
Rotation Parameters ◽  
Using Data ◽  
Observational Techniques ◽  
Numerical Estimations

AbstractThe inaccuracies in the reference frames actually realized by the different techniques for measuring the Earth’s rotation are theoretically investigated. The intercomparison of the available series of measurements provides numerical estimations of these defects. Using data corrected for reference frame effects high frequency fluctuations of UT1 are detected.

scholarly journals Survey of Observational Techniques and Hipparcos Reanalysis

2000 ◽  
Vol 178 ◽  
pp. 237-250 ◽  
Author(s):  
Jan Vondrák ◽  
Cyril Ron ◽  
Ivan Pešek
Keyword(s):  
Polar Motion ◽  
Universal Time ◽  
Earth Orientation Parameters ◽  
The Past ◽  
The Earth ◽  
Celestial Pole ◽  
Hipparcos Catalogue ◽  
Individual Star ◽  
Observational Techniques ◽  
Orientation Parameters

AbstractPolar motion and Universal Time have been regularly determined since 1899 and 1956, respectively, at a number of observatories all over the world. Before the International Earth Rotation Service (IERS) was established in 1988, the classical astrometry instruments such as visual zenith-telescopes, PZTs, transit instruments, astrolabes etc. were used. The survey of all these instruments and the methods of observation used is described. The values of instantaneous latitude and UT0-UTC made at a set of selected observatories and based on individual star observations have been collected at the Astronomical Institute in Prague during the past years. They were recalculated using the most recent astronomical standards and the Hipparcos Catalogue, and used to determine the Earth orientation parameters (polar motion, celestial pole offsets and Universal Time). The most recent solution, based on about 4.5 million observations with 47 different instruments at 33 observatories, is described and the results of polar motion presented.

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