scholarly journals Indirect linking of the Hipparcos catalog to extragalactic reference frame via Earth orientation parameters

1996 ◽  
Vol 172 ◽  
pp. 491-496
Author(s):  
J. Vondrák
Keyword(s):  
Time Series ◽  
Reference Frame ◽  
Indirect Method ◽  
Reference Frames ◽  
Slow Rotation ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Vlbi Observations ◽  
Orientation Parameters

The indirect method of linking the Hipparcos reference frame to the frame defined by extragalactic sources is described. To this end, two independent time series of Earth orientation parameters observed by two different techniques with respect to the two reference frames are used: a) Optical astrometry observations (referred to Hipparcos stars), b) VLBI observations (referred to extragalactic objects). The parallel use of both techniques during the last decade enables to determine the orientation of the two reference frames at a fixed epoch and their mutual slow rotation with precision of at least 1mas and 1mas/year, respectively. In order not to raise confusion, the potentiality of the method is demonstrated on the example based on the star catalogues originally used at the participating observatories, not on any of the existing preliminary versions of the Hipparcos catalog.

scholarly journals Estimation of EOP from VLBI: Direct Approach

2000 ◽  
Vol 180 ◽  
pp. 254-258 ◽  
Author(s):  
L. Petrov
Keyword(s):  
Time Series ◽  
Harmonic Component ◽  
Segment Length ◽  
Physical Parameters ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Alternative Approach ◽  
Two Stages ◽  
Orientation Parameters ◽  
Raw Earth

AbstractThe currently adopted strategy of EOP estimation from VLBI is to estimate six parameters: UT1, UT1 rate, pole positions and nutation offsets for each 24-hour session independently. Then the resulting time series of raw Earth orientation parameters are filtered and a regression analysis is performed in order to obtain nutation coefficients, polhode of the pole and other physical parameters. Thus, the latter parameters are obtained indirectly in two stages. An alternative approach of direct estimation of the final Earth orientation parameters is presented. Pole coordinates and UT1 are considered as a sum of three components: the low-period component which is modeled by a cubic spline, the harmonic component which includes forced nutation, precession and sub-daily variations of EOP, and the stochastic component which is modeled by a linear spline with segment length 1-2 hours. All parameters are obtained in a single LSQ solution using all available data.

scholarly journals Consistency of CDP and IRIS VLBI Earth orientation results

1988 ◽  
Vol 128 ◽  
pp. 187-192 ◽  
Author(s):  
A. Mallama ◽  
T. A. Clark ◽  
J. W. Ryan
Keyword(s):  
Data Centers ◽  
Reference Frames ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
The Past ◽  
The Earth ◽  
Formal Error ◽  
Orientation Parameters ◽  
Iris Data

This study compares the earth orientation results obtained by the NASA CDP and the NGS IRIS experiments. The results agree at about one combined formal error (two milliarcseconds) after small biases (one to three milliarcseconds) have been removed from each component. Furthermore the biases are found to correspond to small rotations between the reference frames, principally the terrestrial frame, for the two sets of experiments. In the past the CDP data has not been used in combined solutions of earth orientation parameters prepared by the data centers at the U.S.N.O. and the B.I.H. The authors propose that these data should be included because they are distinct from the IRIS data and represent an important supplement to those data. We also point out that the total number of observations is about equal in the CDP and IRIS experiment sets.

A preliminary assessment of the accuracy of the VGOS geodetic products: implications for the terrestrial reference frame and Earth orientation parameters

2021 ◽  
Author(s):  
Dhiman Mondal ◽  
Pedro Elosegui ◽  
John Barrett ◽  
Brian Corey ◽  
Arthur Niell ◽  
...  
Keyword(s):  
Reference Frame ◽  
Mixed Mode ◽  
Daily Basis ◽  
Terrestrial Reference Frame ◽  
Preliminary Assessment ◽  
Earth Orientation Parameters ◽  
Vlbi Observations ◽  
International Vlbi Service ◽  
Single Baseline ◽  
Orientation Parameters

<p>The next-generation VLBI system called VGOS (VLBI Global Observing System) has been designed and built as a significant improvement over the legacy geodetic VLBI system to meet the accuracy and stability goals set by the Global Geodetic Observing System (GGOS). Improved geodetic products are expected as the VGOS technique transitions from demonstration to operational status, which is underway. Since 2019, a network of nine VGOS stations has been observing bi-weekly under the auspices of the International VLBI Service for Geodesy and Astrometry (IVS) to generate standard geodetic products. These products, together with the mixed-mode VLBI observations that tie the VGOS and legacy networks together will be contributions to the next realization of the International Terrestrial Reference Frame (ITRF2020). Moreover, since 2020 a subset of 2 to 4 VGOS stations has also been observing in a VLBI Intensive-like mode to assess the feasibility of Earth rotation (UT1) estimation using VGOS. Intensives are daily legacy VLBI observations that are run on a daily basis using a single baseline between Kokee Park Geophysical Observatory, Hawaii, and Wettzell Observatory, Germany, made with the goal of near-real-time monitoring of UT1. In this presentation, we will describe the VGOS observations, correlation, post-processing, and preliminary geodetic results, including UT1. We will also compare the VGOS estimates to estimates from legacy VLBI, including estimates from mixed-mode observations, to explore the precision and accuracy of the VGOS products.</p>

scholarly journals Baseline-dependent clock offsets in VLBI data analysis

2021 ◽  
Vol 95 (12) ◽  
Author(s):  
Hana Krásná ◽  
Frédéric Jaron ◽  
Jakob Gruber ◽  
Johannes Böhm ◽  
Axel Nothnagel
Keyword(s):  
Data Analysis ◽  
Reference Frames ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Long Baseline ◽  
Station Coordinates ◽  
Vlbi Data ◽  
Group Delays ◽  
The Impact ◽  
Orientation Parameters

AbstractThe primary goal of the geodetic Very Long Baseline Interferometry (VLBI) technique is to provide highly accurate terrestrial and celestial reference frames as well as Earth orientation parameters. In compliance with the concept of VLBI, additional parameters reflecting relative offsets and variations of the atomic clocks of the radio telescopes have to be estimated. In addition, reality shows that in many cases significant offsets appear in the observed group delays for individual baselines which have to be compensated for by estimating so-called baseline-dependent clock offsets (BCOs). For the first time, we systematically investigate the impact of BCOs to stress their importance for all kinds of VLBI data analyses. For our investigations, we concentrate on analyzing data from both legacy networks of the CONT17 campaign. Various aspects of BCOs including their impact on the estimates of geodetically important parameters, such as station coordinates and Earth orientation parameters, are investigated. In addition, some of the theory behind the BCO determination, e.g., the impact of changing the reference clock in the observing network on the BCO estimate is introduced together with the relationship between BCOs and triangle delay closures. In conclusion, missing channels, and here in particular at S band, affecting the ionospheric delay calibration, are identified to be the dominant cause for the occurrence of significant BCOs in VLBI data analysis.

scholarly journals An Optimum Strategy for Producing Precise GPS Satellite Orbits using Double-Differenced Observations

2018 ◽  
Vol 24 (9) ◽  
pp. 109
Author(s):  
Oday Yaseen Mohamed Zeki Alhamadani
Keyword(s):  
Reference Frame ◽  
Double Difference ◽  
Satellite Orbits ◽  
Special Importance ◽  
Satellite Clock ◽  
Earth Orientation Parameters ◽  
Orbital Parameters ◽  
Earth Orientation ◽  
Gnss Positioning ◽  
Orientation Parameters

Both the double-differenced and zero-differenced GNSS positioning strategies have been widely used by the geodesists for different geodetic applications which are demanded for reliable and precise positions. A closer inspection of the requirements of these two GNSS positioning techniques, the zero-differenced positioning, which is known as Precise Point Positioning (PPP), has gained a special importance due to three main reasons. Firstly, the effective applications of PPP for geodetic purposes and precise applications depend entirely on the availability of the precise satellite products which consist of precise satellite orbital elements, precise satellite clock corrections, and Earth orientation parameters. Secondly, the PPP processing strategy has been employed by the International GNSS Service (IGS) and IGS analysis centers to evaluate their products in terms of homogeneity and precision over a long period of time. Thirdly, the precise positions, which are determined using PPP technique, and are referenced directly to the geodetic reference frame of the satellite orbital parameters. Thus, the definition of the geodetic datum of the site coordinates using different strategies plays an enormous role in the process of generation satellite orbital parameters which have to be compatible with the corresponding satellite clock corrections and the Earth orientation parameters. This study focuses on producing uninterrupted series of satellite orbit and clock products using different criteria and assesses these products using PPP. The double-difference processing technique was used to achieve the goal of this study by Bernese GPS software version 5.0. Twenty-two globally distributed IGS stations were selected to run PPP based on the generated products and then compare the results with corresponding PPP results which were created based on the IGS rapid products. The comparison pointed to a significant improvement in the generated precise products which have considerably increased the precision of positions. What is more, this study stated that there is an observable agreement between the horizontal positions accuracies which are generated using different techniques for modeling the reference frame.  

scholarly journals The First Decade of the IERS

2000 ◽  
Vol 178 ◽  
pp. 201-213 ◽  
Author(s):  
Ivan I. Mueller
Keyword(s):  
Reference Frame ◽  
Reference System ◽  
Terrestrial Reference Frame ◽  
Point Of View ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Time Space ◽  
International Astronomical ◽  
Celestial Reference System ◽  
Orientation Parameters

AbstractThe International Earth Rotation Service (IERS) was established in 1987 by the International Astronomical Union (IAU) and the International Union of Geodesy and Geophysics (IUGG), and it began operation on 1 January 1988. The primary objectives of the IERS are to serve the astronomical, geodetic and geophysical communities by providing the following: •The International Celestial Reference System (ICRS) and its realization, the International Celestial Reference Frame (ICRF).•The International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF).•Earth orientation parameters required to study Earth orientation variations and to transform between the ICRF and the ITRF.•Geophysical data to interpret time/space variations of the ITRF with respect to the ICRF, i.e., of the Earth orientation parameters, and to model such variations.•Standards, constants and models (i.e., conventions) encouraging international adherence.This presentation primarily covers the first three IERS functions from the operational point of view.

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