Displays

The demanding requirements of the global geodetic observing system (GGOS) necessitate appropriate changes to be made also in the field of geodetic/astrometric very long baseline interferometry (VLBI). The VLBI global observing system (VGOS) is the milestone step towards reaching the GGOS goals. This next-generation VLBI system has already reached an operationally stable international network and it continuously evolves into a truly global infrastructure, with the aim of delivering geodetic products and frame parameters with an unprecedented quality. Thanks to the enhanced measurement precision, increased observation density and improved tracking capabilities, VGOS provides also a great opportunity for extending the current VLBI research with new applications such as observations of geodetic satellites with VLBI. This requires also that a geodetic satellite transmits signals that can be observed by VLBI telescopes, and such ideas have been proposed over the last years. Although a variety of simulation studies have already been performed with the aim of addressing the usefulness of this concept for geodesy and few interesting aspects have been discussed, this topic has not been fully exploited, especially in connection with VGOS. Observations of natural radio sources (quasars) and dedicated geodetic satellites with the same instruments (radio telescopes) bring several benefits as well as new challenges related to the observing strategy and the technical feasibility of this concept. When observing satellites, VLBI gains an access to the set of geodetic parameters that are usually out of scope for conventional VLBI, e.g., satellite orbits or geocenter motion (observed directly). Besides the co-location in space and on the ground, the combined quasar-satellite solutions could also potentially result in an enhanced quality of common geodetic products such as Earth Rotation Parameters (ERP) or station positions. Lastly, the goal of a consistent determination of the terrestrial and celestial reference frames, Earth Orientation Parameters and satellite orbits could be also met in this case.
The following contribution provides a holistic view concerning the prospective VLBI observations of geodetic satellites in the era of GGOS and their impact on various geodetic products. The aspect of VGOS-type satellite observations in the GGOS era is investigated with the use of Monte-Carlo simulations carried out with the c5++ analysis software. The basis of our study form three-day VGOS schedules, which include both quasar and satellite observations. The latter are realized with the use of several Galileo satellites, which are located on different orbital planes. Both observation types are used to derive satellite orbits and estimate common station-based and global geodetic parameters.  The impact on classical geodetic parameters (station positions, ERP), caused by additional satellite observations and the orbit determination process, is investigated with the use of different satellite observation precision levels. We also provide insights concerning the quality of the determined satellite orbits and geocenter estimates. In addition, the scheduling aspects and the technical feasibility of the presented approach are also discussed.

How to cite: Klopotek, G., Haas, R., Hobiger, T., and Otsubo, T.: Satellite geodesy with VLBI in the GGOS era: observation concepts, geodetic products and the technical feasibility, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5922, https://doi.org/10.5194/egusphere-egu2020-5922, 2020.

Global terrestrial reference frames (TRFs), as one of the most important geodetic products, currently miss the imperative requirements of 1 mm accuracy and 1mm/decade long-term stability. In this study, the prospects of a future Global Navigation Satellite System (GNSS) to improve global TRFs is assessed by simulations. The future constellation, named “Kepler”, is proposed by the German Aerospace Center DLR in view of the next generation Galileo system. In addition to a contemporary Medium Earth Orbit (MEO) segment with 24 satellites in three orbital planes, Kepler consists of six Low Earth Orbit (LEO) satellites in two near polar planes, all carrying long-term stable optical clocks. The MEO satellites in one orbital plane and the LEO and MEO satellites in different planes are connected with optical two-way inter-satellite links (ISLs) as the innovative key feature. The ISLs allow very precise range measurements and time synchronization (at the picosecond-level) between the satellites. Different simulation scenarios are set up to evaluate the impact of the Kepler features on the TRF-defining parameters origin and scale as well as on the Earth rotation parameters (ERPs). The origin of a Kepler-only TRF improves considerably by factors of 8, 8, and 43 in X, Y, and Z direction, respectively, w.r.t. a Galileo-only solution. The scale realized by a Kepler-TRF shows improvements of 34% w.r.t. Galileo-only. In a combination with simulated observations of Very Long Baseline Interferometry the impact on multi-technique TRFs is assessed as well. The ERPs of both techniques are combined as global ties and benefits especially on the determination of UT1-UTC are expected.

How to cite: Glaser, S., Michalak, G., Koenig, R., Maennel, B., and Schuh, H.: On the prospects of a future GNSS constellation on the global terrestrial reference frame, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3620, https://doi.org/10.5194/egusphere-egu2020-3620, 2020.

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.

How to cite: Schreiner, P., Mammadaliyev, N., Glaser, S., Koenig, R., Neumayer, K. H., and Schuh, H.: Simulation studies on single-satellite space ties and their potential to achieve the Global Geodetic Observing System goals., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7991, https://doi.org/10.5194/egusphere-egu2020-7991, 2020.

The ITRF is realized through the combination of the individual solutions (station coordinates and velocities) of the four space geodetic techniques. This combination features two main aspects: 1) precise local ties, to establish the link among techniques, and 2) full variance-covariance information of each solution, to account for the accuracy of each technique. Although this approach strives to obtain accurate geodetic products, this combination is not entirely "rigorous'', especially when it comes to the Earth Orientation Parameters (EOPs). In the current realization of the ITRF only polar motion (x-pole and y-pole) are combined, whereas UT1-UTC and nutation offsets and rates are taken from the solution of a single technique (VLBI). Furthermore, parameters such as troposphere delays and clock offsets are not part of the combination strategy. Thus, a rigorous estimation of the ITRF, with consistent EOPs and with appropriate tropospheric and clock ties, is still a challenge to be met.

To achieve a rigorous combination, all parameter types common to more than one space geodetic observation technique should be combined including their full variance-covariance information as well as the corresponding ties. In particular, as both, GNSS and geodetic VLBI, are based on microwave frequencies, their physical models and their parameter types are closely related. These common parameters are the site coordinates and velocities, troposphere estimates, EOPs and (possibly) clock estimates. Thus, using the data from the CONT17 campaign as a case study, we discuss the processing scheme, the challenges and initial results of a rigorous combination of VLBI and GNSS observations, in order to estimate and densify EOPs, particularly diurnal and sub-diurnal variations for polar motion and UT1-UTC, and to realize an inter-technique tropospheric tie, thus remedying the deficiencies mentioned above. The results obtained constitute an important step towards the realization of a rigorous ITRF solution that is able to improve the accuracy and consistency of all geodetic products.

How to cite: Herrera Pinzón, I. D. and Rothacher, M.: A Study on Rigorous Combination of GNSS and VLBI Observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9193, https://doi.org/10.5194/egusphere-egu2020-9193, 2020.

We present a Celestial Reference Frame (CRF) based on the combination of independent, multi-frequency radio source position catalogs using nearly 40 years of Very Long Baseline Interferometry observations at the standard geodetic frequencies at S/X band and about 15 years of observations at higher frequencies (K and X/Ka). The final catalog contains 4617 sources.

The novelty in our approach is the combination of independent, multi-frequency radio source position catalogs through a rigorous combination by carrying over the full co-variance information of each catalog through the process of accumulation of normal equation systems instead of using only the positions themselves. Through the novel process of combination, a complete co-variance matrix of the entire set of sources across the three bands is provided. Special validation routines were used to characterize the random and systematic errors between the input reference frames and the combined one.

The resulting CRF contains precise positions of 4617 compact radio astronomical objects, 4536 measured at 8~Ghz, 824 sources being observed also at 24 GHz and 674 at 32 GHz. The frame is aligned with ICRF3 within ±3 μas and shows an average positional uncertainty of 0.1 mas in right ascension and declination. No significant deformations can be identified. Comparisons with Gaia-CRF remain inconclusive, nonetheless significant differences between all frames can be attested.

How to cite: Karbon, M. and Nothnagel, A.: A multi-frequency Celestial Reference Frame at S/X, K and X/Ka-band, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21503, https://doi.org/10.5194/egusphere-egu2020-21503, 2020.

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, that is, 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, such as pressure measurements, cable calibrations, and range biases. Performing the observation combination with atmospheric ties improves the combined solution, especially for sparse observing geometry, and facilitates the detection of unaccounted systematic errors.

How to cite: Balidakis, K., Glaser, S., Zus, F., Nilsson, T., Schuh, H., and Gross, R.: On the multi-technique combination with atmospheric ties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7818, https://doi.org/10.5194/egusphere-egu2020-7818, 2020.

Recent studies on troposphere delay in Satellite Laser Ranging (SLR) show that the compliance of horizontal gradients of troposphere delay reduces the observation residuals, as well as improves the consistency between SLR results and other space geodetic techniques, all of which are essential for the realization of the terrestrial reference frame. In this work, we examine 3 novel approaches of troposphere delay modeling in SLR, with respect to the standard Mendes-Pavlis approach. We test Potsdam Mapping Function (PMF) with mapping function coefficients and linear horizontal gradients which are based on ERA5 reanalysis provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) model with improved time and spatial resolution in comparison to ERA-Interim reanalysis. We also test a solution based on Vienna Mapping Function 3 for optical observations (VMF3o) which considers the separation of the mapping functions for hydrostatic and non-hydrostatic delays and horizontal gradients. Eventually, we test a solution based on Mendes – Pavlis model with a parameterized model for horizontal gradients based on the 16-year time series of horizontal gradients from PMF. To conduct this experiment, we use SLR observations to passive geodetic satellites LAGEOS-1 and LAGEOS-2. From differences of residual standard deviations for all proposed solutions, we observe an improvement of the SLR observation residuals, for low elevation angles above 10% and improvement of the consistency between estimated pole coordinates and the combined solution IERS-14-C04 series with respect to the currently recommended solutions that neglect the horizontal gradients in SLR solutions.

How to cite: Drożdżewski, M., Boisits, J., Zus, F., Balidakis, K., and Sośnica, K.: Recent studies on troposphere delay modeling for SLR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9378, https://doi.org/10.5194/egusphere-egu2020-9378, 2020.

Numerous active low Earth orbiters (LEOs) and Global Navigation Satellite System (GNSS) satellites, including the Galileo constellation, are equipped with laser retroreflectors used for Satellite Laser Ranging (SLR). Moreover, most of LEOs are equipped with GNSS receivers for precise orbit determination. SLR measurements to LEOs, GNSS, and geodetic satellites vary in terms of the number of registered normal points (NPs) or registered satellite passes. In 2016-2018, SLR measurements to LEOs constituted 81% of all NPs and 59% of all registered satellite passes, whereas 10% of NPs and 30% of satellite passes, respectively, were assigned to GNSS. The remaining SLR measurements were completed by geodetic satellites, including LAGEOS-1/2, and LARES-1.

In this study, we show that the SLR observations to Galileo, passive geodetic and active LEO satellites together with precise GNSS-based orbits of LEOs and Galileo, can be used for the determination of global geodetic parameters, such as geocenter coordinates (GCC) and Earth rotation parameters (ERPs), i.e. pole coordinates, and length-of-day parameter.

GCC are typically determined using SLR observations to passive geodetic satellites, such as LAGEOS-1/2. Also, the SLR observations to LAGEOS-1/2 together with GNSS and Very Long Baseline Interferometry data are used for the determination of ERPs. Here, we use SLR observations to Galileo, LAGEOS-1/2, LARES-1, Sentinel-3A, SWARM-A/B/C, TerraSAR-X, Jason-2, GRACE-A/B satellites to investigate whether they can be applied for the reference frame realization and for deriving high-quality global geodetic parameters.

We present various types of solutions to investigate the best solution set-up. The studied solutions differ in terms of solution lengths, the combination of different sets of satellites and the relative weights for the variance scaling factors of technique and satellite-specific normal equations. We compare our results with the standard LAGEOS-based solutions, the combined EOP-14-C04 products and show the consistency of the results.

How to cite: Strugarek, D., Sośnica, K., Arnold, D., Jäggi, A., Bury, G., and Zajdel, R.: Determination of global geodetic parameters based on integrated SLR measurements to LEO, geodetic, and Galileo satellites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-486, https://doi.org/10.5194/egusphere-egu2020-486, 2020.

The development of satellite space geodesy technology makes the establishment of global terrestrial reference frame based on the Earth’s center of mass become reality. Precise and stable terrestrial reference frame is the foundation of the Earth science research, while determination and analysis of the position of the Earth's center of mass and its change is an important part to build high precision terrestrial reference frame. Based on GNSS weekly solutions provided by IGS, the geocenter motion (GM) time series between 2007 and 2017 are obtained by means of net translation method. Then the amplitude of the annual term of geocentric motion is 2.27mm, 1.84mm and 2.13mm in the direction of X, Y and Z respectively, and the amplitude of the half-year term is 0.1mm, 0.20mm and 0.15mm respectively. In addition, some other inter-annual changes with relatively small contribution rate are found. Finally, in order to get reliable GM prediction ,two kinds of methods are used, which are ARMA and SSA+ARMA. In the short-term prediction, the accuracy of the two methods is the same, both can reach the millimeter level of prediction accuracy, but SSA+ARMA is more stable. SSA+ARMA algorithm is much better in the medium and long-term scale, and it can provide 1mm medium term prediction accuracy and 1.5mm long term prediction accuracy.

How to cite: Zhao, C., Qiao, L., and Ma, T.: The Estimation and Prediction of Geocenter Motion Based on GNSS Weekly Solutions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2504, https://doi.org/10.5194/egusphere-egu2020-2504, 2020.

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.

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.

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.

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.

How to cite: Lengert, L., Hellmers, H., Flohrer, C., Thaller, D., and Kehm, A.: Combination of GNSS and VLBI data for consistent estimation of Earth Orientation Parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4722, https://doi.org/10.5194/egusphere-egu2020-4722, 2020.

Accurate quantification and analysis of geocenter motion are of great significance to the construction and maintenance of the international terrestrial reference frame and its geodetic and geophysical applications. Here, the time series of 13-year geocenter motion coordinates (from 2006 to 2019) is determined by using the network shift approach from Satellite Laser Ranging (SLR) observations to Lageos1 / 2. Then, the geocenter motion time series is analyzed by using singular spectrum analysis. The principal components of geocenter motion are determined with the w-correlation criterion and two principal components with large w-correlation are regarded as the periodic signals. The results show that the annual periodic terms are clearly detectable in all out of three coordinate components, whereas the semi-annual term is only detected in the X-component. Moreover, weak periodic oscillations of 3 to 4 months exist in the X- and Y-components. Besides weak periodic signals with periods of about 8 months and 1 month for the X- and Y-components, respectively, a significant periodic signal of about 2.8 years exists in the  Z-component. Compared to the geocenter motion signals derived by the Center for Space Research (CSR) and Wrocław University of Environmental and Life Sciences (WUELS), both amplitude and phase agree well, with a better consistency with those from CSR, especially for the X- and Y-components.

How to cite: Yu, H., Sośnica, K., and Shen, Y.: Geocenter motion determination and analysis from SLR observations to Lageos1/2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10097, https://doi.org/10.5194/egusphere-egu2020-10097, 2020.

A unique architecture of Sentinel-3A and Sentinel-3B satellites includes the shared ultra stable oscillator (USO) by DORIS and GPS receiver. This concept enables to apply GPS estimates of onboard clocks in DORIS processing and to substitute DORIS polynomial clock model by GPS epochwise model.  Such an approach is particularly profitable for the mitigation of South Atlantic Anomaly effect (SAA), affecting the short-term frequency stability of USO oscillator in South America and South Atlantic region.  GPS clock modeling precisely maps the SAA effect and enables us to demonstrate a difference between Sentinel-3A and Sentinel-3B USO sensitivity to SAA. Moreover, we present an impact on 3Dpositioning, where SAA-related bias reaches in extreme cases a decimeter level.  We also determine an effect of the precise clock modeling on the Earth rotation parameters estimation. Elimination of SAA effect also gives us an opportunity to get an SAA free DORIS solution of Sentinel-3A and Sentinel-3Bsatellites. Using this solution as a reference, we estimate an SAA effect on the DORIS positioning by satellites Jason-2, Jason-3, Sentinel, Cryosat-2 and Hy-2A and the efficiency of SAA mitigation strategies for these satellites. 

How to cite: Stepanek, P., Duan, B., Hugentobler, U., and Filler, V.: DORIS positioning from Sentinel-3A and Sentinel-3B data applying GPS onboard clock modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18527, https://doi.org/10.5194/egusphere-egu2020-18527, 2020.

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 (x_r,y_r), 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  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.

How to cite: Richard, J.-Y., Karbon, M., Bizouard, C., Lambert, S., and Becker, O.: NEW EOP, TRF and CRF determination by GNSS & VLBI COMBINATION, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19169, https://doi.org/10.5194/egusphere-egu2020-19169, 2020.

In the correction for polar motion, terrestrial gravimetry and 3-D positioning follow different conventions. The 3-D positions are corrected to refer to the "mean pole" (IERS Conventions 2010) or to the "secular pole" (IERS update working version since 2018). In any case, the pole reference evolves in time and describes the track of secular or low-frequency polar wander. However, in terrestrial gravimetry the gravity values are corrected to refer to the IERS Reference Pole, a fixed quantity. This may lead to discrepancies when for instance gravity change rates from absolute gravity measurements are compared with vertical velocities from GNSS. I discuss the size and geographical distribution of the possible discrepancies.

How to cite: Mäkinen, J.: The correction for polar motion in gravimetry and in 3-D positioning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11837, https://doi.org/10.5194/egusphere-egu2020-11837, 2020.

International Terrestrial Reference Frame (ITRF) is the realization of the International Terrestrial Reference System (ITRS), which can be used for the variety applications such as earth research, surveying and mapping. 2000 National Geodetic Coordinate System (CGCS2000) has been established and widely applied as a long-term reference frame in China, however, a software for short-term reference frame establishment is also developed to provide high accuracy applications based on the fusion of GNSS/SLR/VLBI/DORIS. We analyzed the covariance from sinex format of the GNSS/SLR/VLBI/DORIS and the quality of local ties. The errors between the local ties and the ITRF2014 within 1cm was 89% in north direction and 85% east direction. We used inner constraints as the method of datum realization and Helmert variance component estimation for giving the weight of different space geodetic GNSS/SLR/VLBI/DORIS. Finaly, short-term terrestrial reference frame realization software can produce the weekly, monthly and annual frame products for high accuracy applications.

How to cite: Xu, C., Cheng, Y., and Dang, Y.: Short-Term Realization of the ITRS with GNSS/SLR/VLBI/DORIS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21088, https://doi.org/10.5194/egusphere-egu2020-21088, 2020.

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.

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.

How to cite: Wang, J., Balidakis, K., Ge, M., Heinkelmann, R., and Schuh, H.: GNSS and VLBI integrated processing at the observation level, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5749, https://doi.org/10.5194/egusphere-egu2020-5749, 2020.

The exceptional situation of simultaneously observing a dedicated near-Earth orbiting satellite via the four main space geodetic techniques opens the unique opportunity to investigate the additional benefits on the realization of global terrestrial reference frame using co-location in space. Applying co-location in space requires a precise orbit determination (POD) of dedicated satellites for all techniques. In this regard, current VLBI infrastructure is extended by the observation to satellites and the impact of such observation concept on the VLBI estimates is assessed. Thus the main geodetic products including the terrestrial reference frame are investigated within the GGOS-SIM-II project. In this study, the potential influence of orbital errors on the estimates and capability of VLBI observations to satellites within the POD are investigated for different scenarios with varying networks, observation time and measurement noise.  

How to cite: Mammadaliyev, N., Schreiner, P., Glaser, S., Neumayer, K. H., Koenig, R., Heinkelmann, R., and Schuh, H.: Simulations of VLBI observations to satellites enabling co-location in space , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20227, https://doi.org/10.5194/egusphere-egu2020-20227, 2020.

Multipath is a largely unmodelled source of error and causes large range errors in Global Navigation Satellite System (GNSS) observations. The effects have strong site-specific characteristics and impact each receiver differently. Multipath errors can propagate and can cause in-situ position and velocity biases and are also contributing to the pervasive draconitic harmonic signals. We employ an empirical approach to reducing the effects of multipath by stacking one-way post-fit carrier phase residual observations by applying an appropriate averaging scheme. Our processing is based on static multi-GNSS observations using various scientific GNSS software packages (Bernese GNSS Software, NAPEOS, GAMIT-GLOBK, PRIDE and GINS). Our multipath stacking (MPS ) uses the stacking of individual residuals generated by variable azimuth cell size (congruent cells) by allocating carrier phase residuals in each cell, unlike fixed azimuth cell resolution in the standard MPS approaches. This reduces the binning of fewer residuals at higher elevation angles. Before stacking, we also apply rigorous statistical outlier screening tests for each one-way post-fit carrier phase residual assigned to each of the congruent cells. We thus correct the multipath effects by subtracting the stacked multipath map from the post-fit carrier phase residual. Using this technique we produce a model available in the form of the Antenna Exchange (ANTEX) file format, that can potentially be implemented in routine GNSS analysis with no or little additional overhead for individual analysis centers (ACs).

In this study, we assess the feasibility and applicability of the MPS maps as an International GNSS Service (IGS) product for routine GNSS analysis. We have selected a subset of IGS stations with and without known multipath issues in different climatic zones. We demonstrate the multipath stacking technique to result in a significant reduction of the variation in the one-way post-fit carrier phase residuals. For GPS-only solutions, the MPS technique shows a decrease of up to 30% in the RMS value of the one-way post-fit carrier phase residuals. We have also tested our MPS for other constellations such as GLONASS, Galileo and BeiDou, and combinations of these .

How to cite: Hunegnaw, A., Ejigu, Y. G., Teferle, F. N., and Elgered, G.: On the Feasibility and Applicability of Multipath Mitigation Maps as an IGS Product, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7787, https://doi.org/10.5194/egusphere-egu2020-7787, 2020.