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

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.

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A Terrestrial Reference Frame (TRF), coordinates and velocities for South American stations: contributions to Central Andes geodynamics

Advances in Geosciences ◽

10.5194/adgeo-22-181-2009 ◽

2009 ◽

Vol 22 ◽

pp. 181-184 ◽

Cited By ~ 1

Author(s):

M. V. Mackern ◽

M. L. Mateo ◽

A. M. Robin ◽

A. V. Calori

Keyword(s):

Reference Frame ◽

Central Andes ◽

Terrestrial Reference Frame ◽

Global Navigation Satellite Systems ◽

South American ◽

Good Precision ◽

Positioning Systems ◽

Satellite Systems ◽

Satellite Positioning ◽

Global Navigation Satellite

Abstract. Satellite positioning systems allow the fixing of the location of a point on the Earth's surface with very good precision and accuracy. To do this, however, it is necessary to determine the point coordinates taking account the reference system and the movements that affect them because of tectonic plate movements. These reference systems are materialized by a significant number of continuous measurement stations in South America. In SIRGAS (Sistema de Referencia Geocéntrico para las Américas), there are four Analysis Centers that process the data collected from satellites of the Global Navigation Satellite Systems (GNSS), with the primary purpose to maintain the international terrestrial reference frame through calculation of the coordinates and velocities of the continuous GNSS stations of the SIRGAS-CON Network. In this work, we demonstrate the quality of the solutions from CIMA, one of the SIRGAS official processing centers operating in Mendoza, Argentina, in comparison with other South American processing centers. The importance of precise calculations of coordinates and velocities in a global frame is also shown. Finally, we give estimations of velocities from stations located within deformation zones in the Central Andes.

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Preparations for the ITRF2020 at TU Wien

10.5194/egusphere-egu2020-8712 ◽

2020 ◽

Author(s):

Anna Zessner-Spitzenberg ◽

David Mayer ◽

Andreas Hellerschmied ◽

Markus Mikschi ◽

Sigrid Böhm

Keyword(s):

Terrestrial Reference Frame ◽

Global Navigation Satellite Systems ◽

Final Phase ◽

Satellite Systems ◽

Long Baseline ◽

Atmospheric Loading ◽

Space Geodetic Techniques ◽

International Vlbi Service ◽

The Individual ◽

Global Navigation Satellite

The next International Terrestrial Reference Frame (ITRF), ITRF2020, will be released in early 2021 and preparations are entering the final phase. It will be realized by using the observations of the space geodetic techniques Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). The Vienna VLBI group is planning to contribute to the ITRF2020. This poster will present the goals, the methodology and preparations for our contribution. In order to analyse the VLBI observation sessions, the Vienna VLBI and Satellite Software (VieVS) will be used. The poster will focus on the influence of applying the gravitational deformation and the atmospheric loading on the individual solutions and the ITRF. &#160;For this purpose, a selected list of more than 800 sessions of the last 40 years, which was released by the International VLBI Service for Geodesy and Astrometry (IVS) to verify the latest changes in the implementation, will be analysed and the results will be presented.

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GNSS RTK Positioning Augmented with Large LEO Constellation

Remote Sensing ◽

10.3390/rs11030228 ◽

2019 ◽

Vol 11 (3) ◽

pp. 228 ◽

Cited By ~ 6

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.

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Determination of UT1 by VLBI

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310008859 ◽

2009 ◽

Vol 5 (H15) ◽

pp. 216-216

Author(s):

Harald Schuh ◽

Johannes Boehm ◽

Sigrid Englich ◽

Axel Nothnagel

Keyword(s):

Satellite Orbit ◽

Global Navigation Satellite Systems ◽

Length Of Day ◽

Satellite Systems ◽

Long Baseline ◽

Geodetic Technique ◽

Set Up ◽

Global Navigation Satellite ◽

Space Geodetic Technique

AbstractVery Long Baseline Interferometry (VLBI) is the only space geodetic technique which is capable of estimating the Earth's phase of rotation, expressed as Universal Time UT1, over time scales of a few days or longer. Satellite-observing techniques like the Global Navigation Satellite Systems (GNSS) are suffering from the fact that Earth rotation is indistinguishable from a rotation of the satellite orbit nodes, which requires the imposition of special procedures to extract UT1 or length of day information. Whereas 24 hour VLBI network sessions are carried out at about three days per week, the hour-long one-baseline intensive sessions (‘Intensives’) are observed from Monday to Friday (INT1) on the baseline Wettzell (Germany) to Kokee Park (Hawaii, U.S.A.), and from Saturday to Sunday on the baseline Tsukuba (Japan) to Wettzell (INT2). Additionally, INT3 sessions are carried out on Mondays between Wettzell, Tsukuba, and Ny-Alesund (Norway), and ultra-rapid e-Intensives between E! urope and Japan also include the baseline Metsähovi (Finland) to Kashima (Japan). The Intensives have been set up to determine daily estimates of UT1 and to be used for UT1 predictions. Because of the short duration and the limited number of stations the observations can nowadays be e-transferred to the correlators, or to a node close to the correlator, and the estimates of UT1 are available shortly after the last observation thus allowing the results to be used for prediction purposes.

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Performance Analyses of a RAIM Algorithm for Kalman Filter with GPS and NavIC Constellations

Sensors ◽

10.3390/s21248441 ◽

2021 ◽

Vol 21 (24) ◽

pp. 8441

Author(s):

Susmita Bhattacharyya

Keyword(s):

Kalman Filter ◽

Measurement Errors ◽

Weighted Least Squares ◽

Temporal Variations ◽

Global Navigation Satellite Systems ◽

Model Parameters ◽

Integrity Monitoring ◽

Satellite Systems ◽

Performance Analyses ◽

Global Navigation Satellite

This paper evaluates the performance of an integrity monitoring algorithm of global navigation satellite systems (GNSS) for the Kalman filter (KF), termed KF receiver autonomous integrity monitoring (RAIM). The algorithm checks measurement inconsistencies in the range domain and requires Schmidt KF (SKF) as the navigation processor. First, realistic carrier-smoothed pseudorange measurement error models of GNSS are integrated into KF RAIM, overcoming an important limitation of prior work. More precisely, the error covariance matrix for fault detection is modified to capture the temporal variations of individual errors with different time constants. Uncertainties of the model parameters are also taken into account. Performance of the modified KF RAIM is then analyzed with the simulated signals of the global positioning system and navigation with Indian constellation for different phases of aircraft flight. Weighted least squares (WLS) RAIM used for comparison purposes is shown to have lower protection levels. This work, however, is important because KF-based integrity monitors are required to ensure the reliability of advanced navigation methods, such as multi-sensor integration and vector receivers. A key finding of the performance analyses is as follows. Innovation-based tests with an extended KF navigation processor confuse slow ramp faults with residual measurement errors that the filter estimates, leading to missed detection. RAIM with SKF, on the other hand, can successfully detect such faults. Thus, it offers a promising solution to developing KF integrity monitoring algorithms in the range domain. The modified KF RAIM completes processing in time on a low-end computer. Some salient features are also studied to gain insights into its working principles.

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Asynchronous RTK Method for Detecting the Stability of the Reference Station in GNSS Deformation Monitoring

Sensors ◽

10.3390/s20051320 ◽

2020 ◽

Vol 20 (5) ◽

pp. 1320

Author(s):

Yuan Du ◽

Guanwen Huang ◽

Qin Zhang ◽

Yang Gao ◽

Yuting Gao

Keyword(s):

Real Time ◽

Reference Frame ◽

Deformation Monitoring ◽

Global Navigation Satellite Systems ◽

Reference Station ◽

Monitoring Station ◽

Landslide Monitoring ◽

Satellite Systems ◽

Local Reference ◽

Global Navigation Satellite

The real-time kinematic (RTK) positioning technique of global navigation satellite systems (GNSS) has been widely used for deformation monitoring in the past several decades. The RTK technique can provide relative displacements in a local reference frame defined by a highly stable reference station. However, the traditional RTK solution does not account for reference stations that experience displacement. This presents a challenge for establishing a near real-time GNSS monitoring system, as since the displacement of a reference station can be easily misinterpreted as a sign of rapid movement at the monitoring station. In this study, based on the reference observations in different time domains, asynchronous and synchronous RTK are proposed and applied together to address this issue, providing more reliable displacement information. Using the asynchronously generated time difference of a reference frame, the proposed approach can detect whether a measured displacement has occurred in the reference or the monitoring station in the current epoch. This allows for the separation of reference station movements from monitoring station movements. The results based on both simulated and landslide monitoring data demonstrate that the proposed method can provide reliable displacement determinations, which are critical in deformation monitoring applications, such as the early warning of landslides.

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Linking the optically bright Gaia frame to the third International Celestial Reference Frame

10.5194/egusphere-egu21-8604 ◽

2021 ◽

Author(s):

Susanne Lunz ◽

James Anderson ◽

Ming H. Xu ◽

Robert Heinkelmann ◽

Oleg Titov ◽

...

Keyword(s):

Reference Frame ◽

European Space Agency ◽

Global Navigation Satellite Systems ◽

Satellite Systems ◽

The Third ◽

Long Baseline ◽

Data Release ◽

Radio Frequencies ◽

Celestial Reference Frame ◽

Radio Stars

The new data release of the Gaia satellite operated by the European Space Agency recently published its 3rd data release (Early Data Release 3, EDR3). The dataset contains astrometric data of about 1.8 billion objects detected at optical frequencies and therefore it outperforms any catalog of astrometric information up to date. The reference frame defined by Gaia EDR3 is aligned to the International Celestial Reference System by referring to counterparts in its realization, the third International Celestial Reference Frame (ICRF3), which is calculated from very long baseline interferometry (VLBI) observations of extragalactic objects at radio frequencies. The Gaia dataset is known to be magnitude-dependent in terms of astrometric calibration. As the objects in ICRF3, although bright at radio frequencies, are mostly faint at optical frequencies, the optically bright Gaia frame has to be linked to ICRF3 by additional counterparts besides objects in ICRF3. The non-rotation of the optically bright Gaia frame is especially important as optically bright objects can, besides astrophysical studies, be used for navigation in space, where other geodetic systems like global navigation satellite systems are out of reach. Suitable additional counterparts are radio stars which are observed by VLBI relative to extragalactic objects in ICRF3. We discuss the orientation and spin differences between the optically bright Gaia EDR3 and VLBI data of radio stars and their impact on the Gaia data usage.

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

10.5194/egusphere-egu21-616 ◽

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

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.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&#8211;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&#160;&#956;as 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.

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

10.5194/egusphere-egu2020-19169 ◽

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

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 Global Navigation Satellite Systems (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 (xr,yr), 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.The strategy applied to consistently combine &#160;the IGS and IVS &#160;solutions provided &#160;in Sinex format over the time period 2000-2020 are presented and the resulting &#160;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.

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Survey Of GNSS Coordinates Systems

European Scientific Journal ESJ ◽

10.19044/esj.2016.v12n24p33 ◽

2016 ◽

Vol 12 (24) ◽

pp. 33

Author(s):

Martina Szabova ◽

Frantisek Duchon

Keyword(s):

Coordinate System ◽

Reference Frame ◽

Local Coordinate System ◽

Local Area ◽

Global Navigation Satellite Systems ◽

Positioning Systems ◽

Satellite Systems ◽

Satellite Positioning ◽

Cadastral Surveying ◽

Global Navigation Satellite

The use of satellite positioning systems to determine position in reference frame can introduce serious practical difficulties. The problem can be in the fields of navigation, map revision or cadastral surveying. It arises because in local area the local coordinate system were used. The problem can be solved by transformation between coordinates frame. Global navigation satellite systems (GNSS) don’t use same reference frame and it is important to know transformation between this systems. This paper works with information of many international organizations and their documents. It contains information about reference coordinate system of GNSS, information about local coordinates system used in North America, UK, and Europe.

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