scholarly journals The use of astronomy VLBA campaign MOJAVE for geodesy

2021 ◽  
Vol 95 (9) ◽  
Author(s):  
Hana Krásná ◽  
Leonid Petrov
Keyword(s):  
Baseline Length ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Long Baseline ◽  
Station Coordinates ◽  
The Difference ◽  
Very Long Baseline Array ◽  
Orientation Parameters ◽  
Source Structure ◽  
Selection Of

AbstractWe investigated the suitability of the astronomical 15 GHz Very Long Baseline Array (VLBA) observing program MOJAVE-5 for estimation of geodetic parameters, such as station coordinates and Earth orientation parameters. We processed a concurrent dedicated VLBA geodesy program observed at 2.3 GHz and 8.6 GHz starting on September 2016 through July 2020 as reference dataset. We showed that the baseline length repeatability from MOJAVE-5 experiments is only a factor of 1.5 greater than from the dedicated geodetic dataset and still below 1 ppb. The wrms of the difference of estimated Earth orientation parameters with respect to the reference IERS C04 time series are a factor of 1.3 to 1.8 worse. We isolated three major differences between the datasets in terms of their possible impact on the geodetic results, i.e. the scheduling approach, treatment of the ionospheric delay, and selection of target radio sources. We showed that the major factor causing discrepancies in the estimated geodetic parameters is the different scheduling approach of the datasets. We conclude that systematic errors in MOJAVE-5 dataset are low enough for these data to be used as an excellent testbed for further investigations on the radio source structure effects in geodesy and astrometry.

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.

Earth Orientation Parameters determination by GNSS & VLBI Combination at Normal Equation Level

2021 ◽  
Author(s):  
Jean-Yves Richard ◽  
Christian Bizouard ◽  
Sebastien Lambert ◽  
Olivier Becker
Keyword(s):  
Global Navigation Satellite Systems ◽  
Polar Coordinates ◽  
Normal Equation ◽  
Earth Orientation Parameters ◽  
Satellite Systems ◽  
Earth Orientation ◽  
Long Baseline ◽  
Station Coordinates ◽  
The Individual ◽  
Orientation Parameters

<p>The Earth orientation parameters (EOP), the regular products of IERS Earth Orientation Centre, are computed at daily bases by combination of EOP solutions using different astro-geodetic techniques. At SYRTE we have developed a strategy of combination of the <strong>Global Navigation Satellite Systems</strong> (GNSS) and <strong>Very Long Baseline Interferometry</strong> (VLBI) techniques at normal equation level using Dynamo software maintained by CNES (France). This approach allows to produce the EOP at the daily bases, which contains polar coordinates (x,y) and their rates (x<sub>r</sub>,y<sub>r</sub>), universal time UT1 and its rate LOD, and corrections from IAU2000A/2006 precession-nutation model (dX,dY), and in the same run station coordinates constituting the terrestrial frame (TRF). The recorded EOP solutions obtained from GNSS and VLBI combination at weekly bases is recently maintained by SYRTE.</p><p>The strategy applied to consistently combine the IGS and IVS solutions provided in Sinex format over the time period 2000-2021 are presented and the resulting EOP, station positions (TRF) are analysed and evaluated, differences w.r.t. the individual solutions and the IERS time-series investigated.</p>

scholarly journals Testing impact of the strategy of VLBI data analysis on the estimation of Earth Orientation Parameters and station coordinates

2016 ◽  
Vol 101 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Agata Wielgosz ◽  
Monika Tercjak ◽  
Aleksander Brzeziński
Keyword(s):  
Reference Frame ◽  
Terrestrial Reference Frame ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Long Baseline ◽  
Station Coordinates ◽  
Vlbi Data ◽  
Weighting Strategy ◽  
Orientation Parameters

Abstract Very Long Baseline Interferometry (VLBI) is the only space geodetic technique capable to realise the Celestial Reference Frame and tie it with the Terrestrial Reference Frame. It is also the only technique, which measures all the Earth Orientation Parameters (EOP) on a regular basis, thus the role of VLBI in determination of the universal time, nutation and polar motion and station coordinates is invaluable. Although geodetic VLBI has been providing observations for more than 30 years, there are no clear guidelines how to deal with the stations or baselines having significantly bigger post-fit residuals than the other ones. In our work we compare the common weighting strategy, using squared formal errors, with strategies involving exclusion or down-weighting of stations or baselines. For that purpose we apply the Vienna VLBI Software VieVS with necessary additional procedures. In our analysis we focus on statistical indicators that might be the criterion of excluding or down-weighting the inferior stations or baselines, as well as on the influence of adopted strategy on the EOP and station coordinates estimation. Our analysis shows that in about 99% of 24-hour VLBI sessions there is no need to exclude any data as the down-weighting procedure is sufficiently efficient. Although results presented here do not clearly indicate the best algorithm, they show strengths and weaknesses of the applied methods and point some limitations of automatic analysis of VLBI data. Moreover, it is also shown that the influence of the adopted weighting strategy is not always clearly reflected in the results of analysis.

scholarly journals Geodetic VLBI Analysis at the National Geographic Institute of Spain

Proceedings ◽  
2019 ◽  
Vol 19 (1) ◽  
pp. 2
Author(s):  
Víctor Puente ◽  
Esther Azcue ◽  
Susana García-Espada ◽  
Yaiza Gómez-Espada
Keyword(s):  
Earth Orientation Parameters ◽  
Technical Aspects ◽  
National Geographic ◽  
Earth Orientation ◽  
Geodetic Vlbi ◽  
Software Packages ◽  
Station Coordinates ◽  
Set Up ◽  
Orientation Parameters ◽  
Troposphere Delays

National Geographic Institute of Spain has a strong background concerning technical aspects of geodetic VLBI. As a step forward in this field, a VLBI analysis team has been set up and tests with different software packages have been carried out. In this sense, two VLBI software packages have been used for experimentation activities in order to compare and validate IGE capability to produce accurate and consistent geodetic products, specifically Earth Orientation Parameters, station coordinates and troposphere delays. The purpose of this contribution is to present the results of these analyses, including some tests to use GNSS-based troposphere delay in VLBI processing and the study of gravitational deformation in Yebes radiotelescope.

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.

Combination of GNSS and VLBI data for consistent estimation of Earth Orientation Parameters

2020 ◽  
Author(s):  
Lisa Lengert ◽  
Hendrik Hellmers ◽  
Claudia Flohrer ◽  
Daniela Thaller ◽  
Alexander Kehm
Keyword(s):  
Normal Equation ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Starting Point ◽  
Station Coordinates ◽  
Space Geodetic Techniques ◽  
Vlbi Data ◽  
Gnss Data ◽  
The Impact ◽  
Orientation Parameters

<p>We present the current activities of the Federal Agency for Cartography and Geodesy (BKG) towards a combined processing of VLBI and GNSS data.  The main goal of the combined analyses of the two different space-geodetic techniques is the improvement of the consistency between the techniques through common parameters, as Earth Orientation Parameters (EOPs), but also station coordinates and tropospheric parameters through local ties and atmospheric ties, respectively.</p><p>The combination of GNSS data with VLBI 24-hour sessions and VLBI Intensive sessions is studied in detail w.r.t. EOPs to exploit he combination benefit to its maximum extend. We analyse the impact of the combination on the technique-specific parameters (e.g. dUT1), but also on common parameters (e.g. LOD, polar motion, station coordinates). When using GNSS data in combination with VLBI Intensive sessions, we can demonstrate an accuracy improvement of the dUT1 time series.</p><p>We also study the combination of troposphere parameters, focusing first on the validation of the technique-specific troposphere parameters at VLBI-GNSS co-located sites and on the modelling of the corresponding atmospheric ties.</p><p>BKGs primary interest is the combination of GNSS and VLBI data on the observation level. However, the current combination efforts are based on the normal equation level using technique-specific SINEX files as a starting point.</p>

scholarly journals Estimation of VGOS Station Coordinates

2020 ◽  
Author(s):  
Markus Mikschi ◽  
Johannes Böhm ◽  
Matthias Schartner
Keyword(s):  
Global Solution ◽  
Very Long Baseline Interferometry ◽  
A Priori ◽  
Terrestrial Reference Frame ◽  
Normal Equation ◽  
Earth Orientation Parameters ◽  
Long Baseline ◽  
Station Coordinates ◽  
Definition Of ◽  
Orientation Parameters

<p>With the number of available VGOS (VLBI Global Observing System) sessions rising, precise coordinates for the participating stations become more important. While station coordinates can be estimated during the VLBI (Very Long Baseline Interferometry) analysis, the definition of the geodetic datum via Not-Net-Rotation (NNR) and No-Net-Translation (NNT) conditions requires at least three participating stations with precise a priori coordinates. The VGOS station network is currently independent of the International Terrestrial Reference Frame (ITRF), as none of the stations have participated in a solution for the ITRF in VGOS mode. By estimating the VGOS station coordinates based on ITRF coordinates, originating from local surveying and solutions of S/X observations by now converted stations, a link to the ITRF can be established. First a global solution, which is the combination of individual sessions on the normal equation level, of the five VGOS CONT17 sessions was calculated. The datum was defined by WESTFORD, ISHIOKA and WETTZ13S whereby the coordinates of the first two stations are known from S/X observations and of the latter from local surveying. With velocities from adjacent stations, the estimated coordinates were used to calculate a global solution of the 2019 VGOS sessions. The obtained coordinates were assessed on basis of formal errors, coordinate repeatability and comparisons of estimated Earth Orientation Parameters (EOP) time series with fixed station coordinates to the 14 C04 a priori dataset.</p>

scholarly journals Earth orientation and its excitations by atmosphere, oceans, and geomagnetic jerks

2015 ◽  
pp. 59-66 ◽  
Author(s):  
J. Vondrák ◽  
C. Ron
Keyword(s):  
Very Long Baseline Interferometry ◽  
Broad Band ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Long Baseline ◽  
The Earth ◽  
Rapid Changes ◽  
Celestial Pole ◽  
Geomagnetic Jerks ◽  
Orientation Parameters

In addition to torques exerted by the Moon, Sun, and planets, changes of the Earth orientation parameters (EOP) are known to be caused also by excitations by the atmosphere and oceans. Recently appeared studies, hinting that geomagnetic jerks (GMJ, rapid changes of geomagnetic field) might be associated with sudden changes of phase and amplitude of EOP (Holme and de Viron 2005, 2013, Gibert and Le Mou?l 2008, Malkin 2013). We (Ron et al. 2015) used additional excitations applied at the epochs of GMJ to derive its influence on motion of the spin axis of the Earth in space (precession-nutation). We demonstrated that this effect, if combined with the influence of the atmosphere and oceans, improves substantially the agreement with celestial pole offsets observed by Very Long-Baseline Interferometry. Here we concentrate our efforts to study possible influence of GMJ on temporal changes of all five Earth orientation parameters defining the complete Earth orientation in space. Numerical integration of Brzezi?ski's broad-band Liouville equations (Brzezi?ski 1994) with atmospheric and oceanic excitations, combined with expected GMJ effects, is used to derive EOP and compare them with their observed values. We demonstrate that the agreement between all five Earth orientation parameters integrated by this method and those observed by space geodesy is improved substantially if the influence of additional excitations at GMJ epochs is added to excitations by the atmosphere and oceans.

scholarly journals Scheduling And Simulation Of VLBI Measurements For The Determination Of Earth Orientation Parameters

2015 ◽  
Vol 5 (1) ◽  
pp. 61-68 ◽  
Author(s):  
S. Nistor ◽  
A. S. Buda
Keyword(s):  
Very Long Baseline Interferometry ◽  
Terrestrial Reference Frame ◽  
Point Of View ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Long Baseline ◽  
Celestial Sphere ◽  
Orientation Parameters ◽  
Primary Space

Abstract The article aims to present the results obtain from the scheduling and simulation of VLBI measurements in October 2010 for a period of three days for 24 hour continuous observations. To be sure that we will obtain good VLBI observation we have to do an optimization of the network. This can be done quite accurately by using the new modules that are part of the VLBI processing software’s, the modules scheduling and simulation. This can be considered the first step in preparation of the VLBI experiment. Very Long Baseline Interferometry (VLBI) it is a primary space-geodetic technique that it is able to determine precise coordinates on the Earth, by monitoring the variable of Earth orientation parameters (EOP) with high precision. Also Very Long Baseline Interferometry plays an important role for determination of celestial and terrestrial reference frame. It is also a technique that each year is more developed form a software and hardware point of view. To obtain the scans we used a set of eight different VLBI antennas and as a source we used different quasars. In the scheduling we used the source based strategy contrary to the station based approach and the radio sources where from updated catalogues according to the requirements of the VLBI2010 system, which means that we are able to obtain a best coverage of the celestial sphere. The results show that scheduling and simulation are very good tools in preparing real VLBI experiments.

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