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>

Earth Orientation Parameter Estimation by Integrating VLBI and GNSS on the Observation Level

2021 ◽  
Author(s):  
Jungang Wang ◽  
Kyriakos Balidakis ◽  
Maorong Ge ◽  
Robert Heinkelmann ◽  
Harald Schuh
Keyword(s):  
Polar Motion ◽  
Reference Frames ◽  
Global Navigation Satellite Systems ◽  
Satellite Systems ◽  
Earth Orientation ◽  
Long Baseline ◽  
Space Geodetic Techniques ◽  
Global Navigation Satellite ◽  
The Impact ◽  
Globally Distributed

<p>The terrestrial and celestial reference frames are linked by the Earth Orientation Parameters (EOP), which describe the irregularities of the Earth's rotation and are determined by the space geodetic techniques, namely, Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). The satellite geodetic techniques (SLR, GNSS, and DORIS) cannot determine the UT1-UTC or celestial pole offsets (CPO), rendering VLBI the only technique capable of determining full EOP set. On the other hand, the GNSS technique provides precise polar motion estimates due to the continuous observations from a globally distributed network. Integrating VLBI and GNSS provides the full set of EOP and guarantees a superior accuracy than any single-technique solution.</p><p>In this study we focus on the integrated estimation of the full EOP set from GNSS and VLBI. Using five VLBI continuous observing campaigns (CONT05–CONT17), the GNSS and VLBI observations are processed concurrently in a common least-squares estimator. The impact of applying global ties (EOP), local ties, and tropospheric ties, and combinations thereof is investigated. The polar motion estimates in integrated solution are dominated by the huge GNSS observations, and the accuracy in terms of weighted root mean squares (WRMS) is ~40 μas compared to the IERS 14 C04 product, which is much better than that of the VLBI-only solution. The UT1-UTC and CPO in the integrated solution also show slight improvement compared to the VLBI-only solution. Moreover, the CPO agreement between the two networks in CONT17, i.e., the VLBA and IVS networks, shows an improvement of 20% to 40% in the integrated solution with different types of ties applied.</p>

scholarly journals GNSS RTK Positioning Augmented with Large LEO Constellation

2019 ◽  
Vol 11 (3) ◽  
pp. 228 ◽  
Author(s):  
Xingxing Li ◽  
Hongbo Lv ◽  
Fujian Ma ◽  
Xin Li ◽  
Jinghui Liu ◽  
...  
Keyword(s):  
Low Earth Orbit ◽  
Global Navigation Satellite Systems ◽  
Convergence Time ◽  
Current Status ◽  
Initial Assessment ◽  
Satellite Systems ◽  
Long Baseline ◽  
Leo Satellites ◽  
Global Navigation Satellite ◽  
Long Baselines

It is widely known that in real-time kinematic (RTK) solution, the convergence and ambiguity-fixed speeds are critical requirements to achieve centimeter-level positioning, especially in medium-to-long baselines. Recently, the current status of the global navigation satellite systems (GNSS) can be improved by employing low earth orbit (LEO) satellites. In this study, an initial assessment is applied for LEO constellations augmented GNSS RTK positioning, where four designed LEO constellations with different satellite numbers, as well as the nominal GPS constellation, are simulated and adopted for analysis. In terms of aforementioned constellations solutions, the statistical results of a 68.7-km baseline show that when introducing 60, 96, 192, and 288 polar-orbiting LEO constellations, the RTK convergence time can be shortened from 4.94 to 2.73, 1.47, 0.92, and 0.73 min, respectively. In addition, the average time to first fix (TTFF) can be decreased from 7.28 to 3.33, 2.38, 1.22, and 0.87 min, respectively. Meanwhile, further improvements could be satisfied in several elements such as corresponding fixing ratio, number of visible satellites, position dilution of precision (PDOP) and baseline solution precision. Furthermore, the performance of the combined GPS/LEO RTK is evaluated over various-length baselines, based on convergence time and TTFF. The research findings show that the medium-to-long baseline schemes confirm that LEO satellites do helpfully obtain faster convergence and fixing, especially in the case of long baselines, using large LEO constellations, subsequently, the average TTFF for long baselines has a substantial shortened about 90%, in other words from 12 to 2 min approximately by combining with the larger LEO constellation of 192 or 288 satellites. It is interesting to denote that similar improvements can be observed from the convergence time.

NEW EOP, TRF and CRF determination by GNSS & VLBI COMBINATION

2020 ◽  
Author(s):  
Jean-Yves Richard ◽  
Maria Karbon ◽  
Chrsitian Bizouard ◽  
Sebastien Lambert ◽  
Olivier Becker
Keyword(s):  
Global Navigation Satellite Systems ◽  
Polar Coordinates ◽  
Normal Equation ◽  
Satellite Systems ◽  
Earth Orientation ◽  
Long Baseline ◽  
Time Period ◽  
Station Coordinates ◽  
The Individual ◽  
Global Navigation Satellite

<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 Very Long Baseline Interferometry (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) and the quasar coordinates constituting the celestial frame (CRF). 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 2000-2020 are presented and the resulting  EOP, station positions (TRF) and quasars coordinates (CRF) are analysed and evaluated, differences w.r.t. the individual solutions and the IERS time-series investigated.</p>

On the multi-technique combination with atmospheric ties

2020 ◽  
Author(s):  
Kyriakos Balidakis ◽  
Susanne Glaser ◽  
Florian Zus ◽  
Tobias Nilsson ◽  
Harald Schuh ◽  
...  
Keyword(s):  
Systematic Errors ◽  
Global Navigation Satellite Systems ◽  
Normal Equation ◽  
Local Ties ◽  
Satellite Systems ◽  
Long Baseline ◽  
Station Coordinates ◽  
Uncertainty Estimates ◽  
Space Geodetic Techniques ◽  
Atmospheric Delays

<p align="justify"><span>We explore a new strategy to combine geodetic observations employing the existing and future systems. Imposing atmospheric ties on the combination at either the observation or normal equation level introduces a physical interpretation to the estimated atmospheric delay parameters, </span><span>that is, </span><span>zenith delays and gradients. In essence, besides combining station coordinates via local ties, we combine atmospheric delays via atmospheric ties. The purpose of this work is to assess the advantages and caveats of such a combination approach, on legacy, state-of-the-art, and next generation geodetic systems. We simulate 10 years of observations of all space geodetic techniques that currently contribute to the realization of the international terrestrial reference system; that is, very long baseline interferometry (VLBI), satellite laser ranging (SLR), global navigation satellite systems (GNSS), and Doppler orbitography and radiopositioning integrated by satellite (DORIS). The noise we inject in the simulated observations is technique-specific and - besides a thermal contribution - stems from three-state clock models and ray-traced delays from the latest ECMWF reanalysis, ERA5. To make the simulations more realistic, we estimate the probability of potential observations being successful by utilizing ERA5 fields, for example cloud fields for SLR. To avoid overoptimistic uncertainty estimates, we have accounted for the correlation between observations based on ERA5 fields. In a bias-free setup, we find that the improvement of employing atmospheric ties in addition to local ties to fuse multi-sensor observations, on the combined station coordinates and atmospheric delays is statistically significant for all techniques except for GNSS. We attribute the latter to the relatively good observing geometry. We also find that employing atmospheric ties reveals unaccounted systematic errors stemming from erroneous auxiliary data that are necessary for the reduction of geodetic observations, </span><span>such as </span><span>pressure </span><span>measurements, </span><span>cable </span><span>calibrations, </span><span>and range biases. Performing the observation combination with atmospheric ties improves the combined solution, </span><span>especially </span><span>for sparse observing geometry, and facilitates the detection of unaccounted systematic errors.</span></p>

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>

The Contribution of LARES to Global Climate Change Studies With Geodetic Satellites

2015 ◽  
Author(s):  
Giampiero Sindoni ◽  
Claudio Paris ◽  
Cristian Vendittozzi ◽  
Erricos C. Pavlis ◽  
Ignazio Ciufolini ◽  
...  
Keyword(s):  
Reference Frame ◽  
Earth Science ◽  
Global Climate ◽  
Temporal Variations ◽  
Terrestrial Reference Frame ◽  
Global Navigation Satellite Systems ◽  
Satellite Systems ◽  
Long Baseline ◽  
Geophysical Processes ◽  
Global Navigation Satellite

Satellite Laser Ranging (SLR) makes an important contribution to Earth science providing the most accurate measurement of the long-wavelength components of Earth’s gravity field, including their temporal variations. Furthermore, SLR data along with those from the other three geometric space techniques, Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS) and DORIS, generate and maintain the International Terrestrial Reference Frame (ITRF) that is used as a reference by all Earth Observing systems and beyond. As a result we obtain accurate station positions and linear velocities, a manifestation of tectonic plate movements important in earthquake studies and in geophysics in general. The “geodetic” satellites used in SLR are passive spheres characterized by very high density, with little else than gravity perturbing their orbits. As a result they define a very stable reference frame, defining primarily and uniquely the origin of the ITRF, and in equal shares, its scale. The ITRF is indeed used as “the” standard to which we can compare regional, GNSS-derived and alternate frames. The melting of global icecaps, ocean and atmospheric circulation, sea-level change, hydrological and internal Earth-mass redistribution are nowadays monitored using satellites. The observations and products of these missions are geolocated and referenced using the ITRF. This allows scientists to splice together records from various missions sometimes several years apart, to generate useful records for monitoring geophysical processes over several decades. The exchange of angular momentum between the atmosphere and solid Earth for example is measured and can be exploited for monitoring global change. LARES, an Italian Space Agency (ASI) satellite, is the latest geodetic satellite placed in orbit. Its main contribution is in the area of geodesy and the definition of the ITRF in particular and this presentation will discuss the improvements it will make in the aforementioned areas.

Co-location of SLR and GNSS techniques onboard Galileo and GLONASS satellites

2021 ◽  
Author(s):  
Grzegorz Bury ◽  
Krzysztof Sośnica ◽  
Radosław Zajdel ◽  
Dariusz Strugarek ◽  
Urs Hugentobler
Keyword(s):  
Orbital Plane ◽  
Terrestrial Reference Frame ◽  
Global Navigation Satellite Systems ◽  
Navigation Systems ◽  
Local Ties ◽  
Satellite Systems ◽  
The Impact ◽  
Space Ties ◽  
Gnss Observations

<p>All satellites of the Galileo and GLONASS navigation systems are equipped with laser retroreflector arrays for Satellite Laser Ranging (SLR). SLR observations to Global Navigation Satellite Systems (GNSS) provide the co-location of two space geodetic techniques onboard navigation satellites.</p><p>SLR observations, which are typically used for the validation of the microwave-GNSS orbits, can now contribute to the determination of the combined SLR+GNSS orbits of the navigation satellites. SLR measurements are especially helpful for periods when the elevation of the Sun above the orbital plane (β angle) is the highest. The quality of Galileo-IOV orbits calculated using combined SLR+GNSS observations improves from 36 to 30 mm for β> 60° as compared to the microwave-only solution. </p><p>Co-location of two space techniques allows for the determination of the linkage between SLR and GNSS techniques in space. Based on the so-called space ties, it is possible to determine the 3D vector between the ground-based co-located SLR and GNSS stations and compare it with the local ties which are determined using the ground measurements. The agreement between local ties derived from co-location in space and ground measurements is at the level of 1 mm in terms of the long-term median values for the co-located station in Zimmerwald, Switzerland.</p><p>We also revise the approach for handling the SLR range biases which constitute one of the main error sources for the SLR measurements. The updated SLR range biases consider now the impact of not only of SLR-to-GNSS observations but also the SLR observations to LAGEOS and the microwave GNSS measurements. The updated SLR range biases improve the agreement between space ties and local ties from 34 mm to 23 mm for the co-located station in Wettzell, Germany.</p><p>Co-location of SLR and GNSS techniques onboard navigation satellites allows for the realization of the terrestrial reference frame in space, onboard Galileo and GLONASS satellites, independently from the ground measurements. It may also deliver independent information on the local tie values with full variance-covariance data for each day with common measurements or can contribute to the control of the ground measurements as long as both GNSS and SLR-to-GNSS observations are available.</p>

Validating the impact of various ionosphere correction on mid to long baselines and point positioning using GPS dual-frequency receivers

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Alaa A. Elghazouly ◽  
Mohamed I. Doma ◽  
Ahmed A. Sedeek
Keyword(s):  
Geomagnetic Storms ◽  
Global Navigation Satellite Systems ◽  
Electron Content ◽  
Assessment Procedure ◽  
Vertical Total Electron Content ◽  
Dual Frequency ◽  
Total Electron ◽  
Satellite Systems ◽  
Point Positioning ◽  
The Impact

Abstract Due to the ionosphere delay, which has become the dominant GPS error source, it is crucial to remove the ionospheric effect before estimating point coordinates. Therefore, different agencies started to generate daily Global Ionosphere Maps (GIMs); the Vertical Total Electron Content (VTEC) values represented in GIMs produced by several providers can be used to remove the ionosphere error from observations. In this research, An analysis will be carried with three sources for VTEC maps produced by the Center for Orbit Determination in Europe (CODE), Regional TEC Mapping (RTM), and the International Reference Ionosphere (IRI). The evaluation is focused on the effects of a specific ionosphere GIM correction on the precise point positioning (PPP) solutions. Two networks were considered. The first network consists of seven Global Navigation Satellite Systems (GNSS) receivers from (IGS) global stations. The selected test days are six days, three of them quiet, and three other days are stormy to check the influence of geomagnetic storms on relative kinematic positioning solutions. The second network is a regional network in Egypt. The results show that the calculated coordinates using the three VTEC map sources are far from each other on stormy days rather than on quiet days. Also, the standard deviation values are large on stormy days compared to those on quiet days. Using CODE and RTM IONEX file produces the most precise coordinates after that the values of IRI. The elimination of ionospheric biases over the estimated lengths of many baselines up to 1000 km has resulted in positive findings, which show the feasibility of the suggested assessment procedure.

An Advanced Receiver Autonomous Integrity Monitoring (ARAIM) Ground Monitor Design to Estimate Satellite Orbits and Clocks

2020 ◽  
Vol 73 (5) ◽  
pp. 1087-1105
Author(s):  
Yawei Zhai ◽  
Jaymin Patel ◽  
Xingqun Zhan ◽  
Mathieu Joerger ◽  
Boris Pervan
Keyword(s):  
Measurement Errors ◽  
Satellite Orbit ◽  
Global Navigation Satellite Systems ◽  
Estimation Accuracy ◽  
Satellite Orbits ◽  
Integrity Monitoring ◽  
Satellite Systems ◽  
Receiver Autonomous Integrity Monitoring ◽  
The Impact ◽  
Advanced Receiver

This paper describes a method to determine global navigation satellite systems (GNSS) satellite orbits and clocks for advanced receiver autonomous integrity monitoring (ARAIM). The orbit and clock estimates will be used as a reference truth to monitor signal-in-space integrity parameters of the ARAIM integrity support message (ISM). Unlike publicly available orbit and clock products, which aim to maximise estimation accuracy, a straightforward and transparent approach is employed to facilitate integrity evaluation. The proposed monitor is comprised of a worldwide network of sparsely distributed reference stations and will employ parametric satellite orbit models. Two separate analyses, covariance analysis and model fidelity evaluation, are carried out to assess the impact of measurement errors and orbit model uncertainty on the estimated orbits and clocks, respectively. The results indicate that a standard deviation of 30 cm can be achieved for the estimated orbit/clock error, which is adequate for ISM validation.

The Status, Development and Future Role of Radiobeacon Differential GNSS

1998 ◽  
Vol 51 (2) ◽  
pp. 152-158 ◽  
Author(s):  
N. Ward
Keyword(s):  
Global Navigation Satellite Systems ◽  
Current Status ◽  
Automatic Identification ◽  
Future Role ◽  
Satellite Systems ◽  
Advantages And Disadvantages ◽  
The Status ◽  
Differential Corrections ◽  
Global Navigation Satellite

Marine radiobeacons have been used to broadcast differential corrections for global navigation satellite systems (DGNSS) for nearly a decade. The method has become the accepted international standard for maritime applications. The background to the development of the system is described and the current status of radiobeacon DGNSS services around the world reported. The applications are discussed, including the function of radiobeacon DGNSS as the position sensor within integrated systems, together with the performance requirements imposed by associated systems such as ECDIS and Automatic Identification Systems. The advantages and disadvantages of the radiobeacon system in regulatory, administrative and technical terms are discussed and the potential for development of the system is considered. The future role of radiobeacon DGNSS in the overall mix of systems is assessed taking into account the introduction of geo-stationary overlays, and possibly Loran-C, for provision of DGNSS corrections.

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