The benefits for ITRF2020 from multi-technique combination at the observation level (COOL) processing

2020 ◽  
Author(s):  
Michiel Otten ◽  
Tim Springer ◽  
Francesco Gini ◽  
Volker Mayer ◽  
Erik Schoenemann ◽  
...  
Keyword(s):  
Reference Frames ◽  
Observation Level ◽  
Three Solutions ◽  
Satellite Transmitter ◽  
Rigorous Approach ◽  
Gps Satellites ◽  
Significant Step ◽  
Space Geodetic Techniques ◽  
Combination Approach ◽  
Space Ties

<p>For the previous ITRF calls for participation ESOC reprocessed the historic data from the IDS, IGS, and ILRS. Our three solutions were computed with a single software package (NAPEOS), running on the same machine and using, as far as possible, identical settings. Any systematic differences between the technique dependent reference frame solutions must therefore be caused by the techniques themselves, and not because of model differences or errors. Our three technique dependent solutions gave us a good understanding of the technique dependent effects, helping us to improve our models.</p><p>At ESOC we have now made a significant step forward by including all satellite geodetic techniques (SLR, DORIS and GNSS) into one solution. This allows us to combine the ILRS, IDS and IGS reference frames by using “space ties”. Of course these space ties are not perfectly known but they still allow for a rigorous combination of the different reference frames. Furthermore, and very important for the GNSS technique, they allow for the direct estimation of the GNSS satellite transmitter phase centre offset. We solve not only for integer ambiguities of the GPS satellites but also for those of the LEO satellites, which is also providing GPS phase observations on two frequencies. </p><p>Our poster presents an overview of this multi-technique combination approach at observation level (COOL). We have included all observations provided by the following satellites in a single parameter estimation process: GNSS, JASON, SPOT, Sentinels, GRACE, LAGEOS and Etalon satellites. We demonstrate the benefits of such a rigorous approach compared to processing the various space geodetic techniques separately.</p>

scholarly journals Satellite Scheduling with VieSched++ : current status and future plans

2020 ◽  
Author(s):  
Helene Wolf ◽  
Matthias Schartner ◽  
Johannes Böhm ◽  
Andreas Hellerschmied
Keyword(s):  
Reference Frames ◽  
Very Long Baseline Interferometry ◽  
Satellite Observations ◽  
Current Status ◽  
Long Baseline ◽  
Automatic Mode ◽  
Space Geodetic Techniques ◽  
Satellite Scheduling ◽  
Space Ties ◽  
Future Plans

<p>Observing extragalactic radio sources is an integral part of Very Long Baseline Interferometry (VLBI) but observing satellites also provides a variety of new possibilities. Interesting scientific applications can be found in providing space ties instead of using local ties for connecting reference frames of different space-geodetic techniques. To generate schedules including observations to satellites a dedicated module has been implemented in the new scheduling software VieSched++.</p><p><br>This newly developed module determines possible satellite observations considering several observation conditions, such as the visibility from the selected station network and antenna slew rates. A schedule including observations to quasars and satellites can be generated in a semi-automatic mode. The scheduling of the satellite scans is done manually by the user who can select and adjust the possible satellite observations before adding them to the schedule. The remaining part of the schedule is filled automatically by the software VieSched++ using the general optimization algorithm with observations to quasars. In this poster an overview of the current status of the satellite scheduling module in VieSched++ is given, as well as an outlook to highlight future plans. </p>

Simulation studies on single-satellite space ties and their potential to achieve the Global Geodetic Observing System goals.

2020 ◽  
Author(s):  
Patrick Schreiner ◽  
Nicat Mammadaliyev ◽  
Susanne Glaser ◽  
Rolf Koenig ◽  
Karl Hans Neumayer ◽  
...  
Keyword(s):  
Reference Frame ◽  
Precise Orbit Determination ◽  
Terrestrial Reference Frame ◽  
German Research Foundation ◽  
Station Coordinates ◽  
Earth Rotation Parameters ◽  
German Research ◽  
Space Geodetic Techniques ◽  
The Impact ◽  
Space Ties

<p>The German Research Foundation (DFG) project GGOS-SIM-2, successor of project GGOS-SIM, is a collaboration between the Helmholtz Center Potsdam - German Research Center for Geosciences (GFZ) and the Technische Universität Berlin (TUB). The project aims at investigating the feasibility of meeting the requirements specified by the Global Geodetic Observing System (GGOS) for a global terrestrial reference frame (TRF) with the help of simulations. In GGOS-SIM-2 the potential of so-called space ties is examined in relation to the GGOS targets, 1 mm accuracy in position and 1 mm / decade long-term stability, which have not yet been achieved by the recent International Terrestrial Reference Frame (ITRF). Space ties are provided by a satellite that carries two, three or all the four main space-geodetic techniques, i.e. DORIS, GPS, SLR and VLBI. This allows for a quantification of the impact of systematic errors on the derived orbits and subsequent results of the dynamic method as the TRF. Proposed co-location in space missions such as GRASP and E-GRASP anticipate such a scenario. We therefor simulate the space-geodetic observations based on Precise Orbit Determination (POD) with real observations from various missions and evaluate their potential for determining a TRF. So far, we simulated DORIS and SLR observations to six orbit scenarios, including a GRASP-like and an E-GRASP-like one, and generated TRFs based on each scenario either technique-wise or combined via the space-ties or in combination with ground data. We quantify the effect on the TRF in terms of changes of origin and scale and of formal errors of the ground station coordinates and of the Earth rotation parameters.</p>

scholarly journals Visibility study of Galileo satellites from a VLBI network

2021 ◽  
Author(s):  
Helene Wolf ◽  
Johannes Böhm ◽  
Matthias Schartner ◽  
Urs Hugentobler
Keyword(s):  
Reference Frames ◽  
Direct Determination ◽  
Satellite Constellation ◽  
Long Baseline ◽  
Space Geodetic Techniques ◽  
Satellite Scheduling ◽  
Observation Geometry ◽  
The Impact

<p>Over the last years, ideas have been proposed to install a Very Long Baseline Interferometry (VLBI) transmitter on one or more satellites of the Galileo constellation. Satellites transmitting signals that can be observed by VLBI telescopes provide the opportunity of extending the current VLBI research with observations to geodetic satellites. These observations offer a variety of new possibilities such as high precision tying of space geodetic techniques but also the direct determination of the absolute orientation of the satellite constellation with respect to the International Celestial Reference Frame (ICRF) and have implications on the determination of long-term reference frames. </p><p>This contribution provides a visibility study of the Galileo satellites from a VLBI network. The newly developed satellite scheduling module in VieSched++ is used to determine the time periods during which a satellite is observable from a VLBI network. The possible satellite observations are evaluated through the number of stations from which a satellite is observable. Moreover, the impact on determining the orientation of the satellite constellation, caused by the observation geometry, is investigated with using the UT1-UTC Dilution of Precision (UDOP) factor.</p>

Validation of tropospheric ties at the test setup GNSS co-location site in Potsdam

2021 ◽  
Author(s):  
Chaiyaporn Kitpracha ◽  
Robert Heinkelmann ◽  
Markus Ramatschi ◽  
Kyriakos Balidakis ◽  
Benjamin Männel ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Reference Frames ◽  
Meteorological Data ◽  
In Situ Measurements ◽  
Zenith Delay ◽  
Terrestrial Reference Frames ◽  
Space Geodetic Techniques ◽  
Set Up ◽  
Weather Models

<p>Atmospheric ties are induced by differences between the set-up of observing geodetic systems at co-location sites, are mainly attributed to frequency and position, and are usually quantified by zenith delay and gradient component offsets derived by weather models or in situ instuments.. Similar to local ties, they could be applied to combine datasets from several space geodetic techniques, thus contributing to the improvement of the realization of terrestrial reference frames (TRF). Theoretically, atmospheric ties are affected only by the height differences between antennas at the same site and meteorological conditions. Therefore, atmospheric ties could be determined analytically based on meteorological information from in situ measurements or weather models. However, there is often a discrepancy between the expected zenith delay differences and those estimated from geodetic analysis, potentially degrading a combined atmospheric ties solution should tight constraints be used. In this study, we set up a GNSS experiment campaign on the rooftop of a building in Telegrafernberg that offers unobscured data coverage for one month. We compared the estimated zenith delay and gradients from GNSS stations in this experiment, applying atmospheric ties from (1) meteorological data from the Global Pressure and Temperature model 3 (GPT3), (2) ERA5 reanalysis, and (3) in-situ measurements, as well as corrections derived from ray tracing (Potsdam Mapping Functions, PMF). The results show that atmospheric ties employing GPT3, ERA5, in-situ measurements, and ray tracing has an excellent and comparable performance in term of bias mitigation, but not in term of standard deviation, for zenith delay. Moreover, the unexpected bias in zenith delay was identified in the antenna with radome installation. A significantly large bias was identified in estimated gradients; the source of this discrepancy has been traced back to unmitigated multipath effects in this experiment.</p>

Assessment on atmospheric parameters at co-location sites

2020 ◽  
Author(s):  
Chaiyaporn Kitpracha ◽  
Kyriakos Balidakis ◽  
Robert Heinkelmann ◽  
Harald Schuh
Keyword(s):  
Reference Frames ◽  
Meteorological Data ◽  
Tropospheric Delay ◽  
Atmospheric Parameters ◽  
Local Ties ◽  
Zenith Delay ◽  
Terrestrial Reference Frames ◽  
Weather Model ◽  
Space Geodetic Techniques ◽  
Seasonal Signals

<p>Atmospheric ties are affected by the differences of atmospheric parameters of space geodetic techniques at co-location sites. Similar to local ties, they could be applied along with local ties for a combination of space geodetic techniques to improve the realization of terrestrial reference frames (TRF). Theoretically, atmospheric ties are affected by the height differences between antennas at the same site and meteorological conditions. Therefore, atmospheric ties could be determined by analytical equation based on meteorological information from in situ measurements or weather model. However, there is often a discrepancy between the expected zenith delay differences and those estimated from geodetic analysis, thus potentially degrading a combined atmospheric ties solution. In this study, we analyse the time series of zenith delays from co-located GNSS antennas at Wettzell (height differences below 3 meters), for 11 years (2008–2018). GNSS observations were analyzed with Bernese GNSS software version 5.2 with double-differencing technique and relative tropospheric delay and gradients were estimated with L1, L2, and the ionosphere-free (L3) linear combination thereof. Atmospheric ties were derived analytically employing meteorological data from Global Pressure and Temperature model 3 (GPT3) and ERA5 reanalysis, as well as corrections derived from ray tracing (Potsdam Mapping Functions, PMF). The comparison shows that zenith delay differences are dominated by equipment changes. The discrepancies between atmospheric ties and estimated zenith delay differences are frequency dependent, with the L1 solutions being the least biased. For these small vertical differences, seasonal signals are not significant for all frequencies.</p>

GNSS and VLBI integrated processing at the observation level

2020 ◽  
Author(s):  
Jungang Wang ◽  
Kyriakos Balidakis ◽  
Maorong Ge ◽  
Robert Heinkelmann ◽  
Harald Schuh
Keyword(s):  
Reference Frames ◽  
Global Navigation Satellite Systems ◽  
Current Status ◽  
Normal Equation ◽  
Observation Level ◽  
Satellite Systems ◽  
Navigation Data ◽  
Long Baseline ◽  
Integrated Processing ◽  
The Impact

<p>The terrestrial and celestial reference frames, which serve as the basis for geodesy and astronomy, are mainly determined and maintained by space geodetic techniques such as Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite). These techniques are also used together to determine the Earth Orientation Parameters (EOP), which are very important for precise positioning, navigation and timing. Currently, the combination of all these techniques is done on the parameter level (ITRF) or on the normal equation level (DTRF), which are well-known and convenient methods but may suffer from some inconsistency.</p><p>Unlike the combination on the parameter or normal equation levels, the integrated processing at the observation level exploits the lengths and unique features of different techniques, and is valuable in determining homogeneous reference frames and EOP, and to connect the terrestrial, celestial, and dynamic frames. We are applying the integrated GNSS, VLBI and SLR data processing in the current Positioning And Navigation Data Analyst (PANDA) software, which aims on processing multi-geodetic techniques on the observation level. We present the strategy and current status of the integrated GNSS and VLBI processing and demonstrate the benefit of integrating GNSS for VLBI using 14 years of VLBI intensive sessions (2001-2014) and five CONT campaigns (2005-2017). We discuss the impact of applying tropospheric tie and local tie in the integrated processing.</p>

scholarly journals THE VALIDATION OF THE TRANSFORMATION BETWEEN AN OLD GEODETIC REFERENCE FRAME AND A MODERN REFERENCE FRAME, BY USING EXTERNAL SPACE TECHNIQUES SITES: THE CASE STUDY OF THE HELLENIC GEODETIC REFERENCE SYSTEM OF 1987

2017 ◽  
Vol 23 (3) ◽  
pp. 434-444 ◽  
Author(s):  
Ioannis D. Doukas ◽  
Dimitrios Ampatzidis ◽  
Vassileios Kampouris
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Dynamic Change ◽  
Geodetic Reference System ◽  
Bias Estimation ◽  
Rigorous Approach ◽  
Systematic Effects ◽  
Tectonic Motion ◽  
Geodetic Reference Frame

Abstract: Many of the old geodetic reference frames which realized in the previous decades using classical observations carry biases. These biases are mainly caused due to the problematic observations and/or the tectonic motion. That is the case of the official Greek geodetic reference frame which consists of classical and satellite observations. Herein, we present a rigorous approach of the reconstruction of the Greek official reference frame based on the modern geodetic reference frames and their ability to express the spatial position and the dynamic change of the stations. We applied the rigorous approach to ninety stations located in Greece and we compare it with the officially accepted procedure. We found a consistency at 59.4cm between the rigorous and the officially accepted approaches, respectively. The associated mean bias estimation was estimated at 51.4 cm, indicating the resistance of a rather large amount of systematic effects. In addition, the observed discrepancies between the two approaches show great inhomogeneity all over the country.

scholarly journals A review of the lunar laser ranging technique and contribution of timing systems

2016 ◽  
Vol Volume 112 (Number 3/4) ◽  
Author(s):  
Cilence Munghemezulu ◽  
Ludwig Combrinck ◽  
Joel O. Botai ◽  
◽  
◽  
...  
Keyword(s):  
Reference Frames ◽  
Laser Pulses ◽  
Relativity Theory ◽  
Earth Tides ◽  
Laser Ranging ◽  
The Moon ◽  
Lunar Laser Ranging ◽  
Factors Affecting ◽  
Lunar Laser ◽  
Space Geodetic Techniques

Abstract The lunar laser ranging (LLR) technique is based on the two-way time-of-flight of laser pulses from an earth station to the retroreflectors that are located on the surface of the moon. We discuss the ranging technique and contribution of the timing systems and its significance in light of the new LLR station currently under development by the Hartebeesthoek Radio Astronomy Observatory (HartRAO). Firstly, developing the LLR station at HartRAO is an initiative that will improve the current geometrical network of the LLR stations which are presently concentrated in the northern hemisphere. Secondly, data products derived from the LLR experiments – such as accurate lunar orbit, tests of the general relativity theory, earth–moon dynamics, interior structure of the moon, reference frames, and station position and velocities – are important in better understanding the earth–moon system. We highlight factors affecting the measured range bias such as the effect of earth tides on station position and delays induced by timing systems, as these must be taken into account during the development of the LLR analysis software. HartRAO is collocated with other fundamental space geodetic techniques which makes it a true fiducial geodetic site in the southern hemisphere and a central point for further development of space-based techniques in Africa. Furthermore, the new LLR will complement the existing techniques by providing new niche areas of research both in Africa and internationally.

Establishment of State-of-the-Art Geodesy Village in India: Current status and Outlook

2021 ◽  
Author(s):  
Sujata Dhar ◽  
Ashutosh Tiwari ◽  
Nagarajan Balasubramanian ◽  
Balaji Devaraju ◽  
Onkar Dikshit ◽  
...  
Keyword(s):  
Reference Frames ◽  
State Of The Art ◽  
Simulation Modelling ◽  
Current Status ◽  
Site Location ◽  
Earth Orientation Parameters ◽  
Earth Gravity ◽  
Core Site ◽  
Space Geodetic Techniques

<p>National Centre for Geodesy (NCG) has been established in IIT Kanpur, India with the vision of acting as a hub of excellence in geodetic research at the National and International level. Working towards its mission, it has initiated this state-of-the- art establishment for improving the space geodetic infrastructure of the country and encouraging more researches in the geodesy field. The presentation will discuss the current status of the planned core site and its future establishments. It will provide detailed description of all the facilities installed in the site right now, and the future extensions. This new core-site will house facilities for three technologies – Space, Time and Earth gravity domain. The main purpose of establishing this site is for improving the realization of terrestrial and celestial reference frames, Earth Orientation Parameters (EOPs) and other data products essential for understanding the Earth’s environment. This co-located site with four space geodetic techniques will help in the International campaign for determination of TRF with 1mm accuracy and 0.1 mm/yr. stability. Moreover, this site location will improve the uniformity in geographical distribution of the ITRF observatories and the necessity of this station has been confirmed by simulation modelling.</p><p>Keywords: NCG, India, Core site, TRF, stability, uniformity.</p>

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