Very Long Baseline Interferometry Stations Research Articles

On the improvement of the sensitivity levels of VLBI solutions from a combination with GNSS

Very Long Baseline Interferometry (VLBI) is the only technique that connects the celestial and the terrestrial reference frames. Because of its essential role, it is important to investigate the quality of VLBI observations and their effect on the estimated parameters. The fundamental goal of the quality assessment using the sensitivity is to find out to what level VLBI can detect station displacements in the adjusted coordinates. However, the global VLBI station network is worse in terms of the number and global distribution of stations when compared to the GNSS station network. In this study, we aim to improve the capacity of VLBI to detect station displacements through an inter-technique combination with GNSS. The effect of the selection of co-location sites in the inter-technique combination is investigated with four scenarios and we investigate how the sensitivity is affected by the assumed standard deviations of the local ties. The lower the standard deviations of the local ties, the higher the obtained sensitivity level. When larger standard deviations are assumed, the sensitivity levels of the VLBI stations are obtained up to 3 mm. When a smaller deviation is assumed for a local tie having various standard deviations obtained from different local tie observations, the sensitivity levels change too. If local ties with standard deviations of 1 cm and more are excluded, the detection capacities of the VLBI stations based on the gross errors improve by around 1 mm. When smaller standard deviations are assumed among the local ties, which are used in the inter-technique combination, the sensitivity levels drop below 2 mm. Hence, this study quantifies how important the selection of the co-location sites and the standard deviations of the local ties are for the accuracy of geodetic products obtained by inter-technique combination.

The importance of co-located VLBI Intensive stations and GNSS receivers

Frequent, low-latency measurements of the Earth’s rotation phase, expressed as UT1-UTC critically support the current estimate and short-term prediction of this highly variable Earth orientation parameter (EOP). Very long baseline interferometry (VLBI) Intensive sessions provide the required data. However, the Intensive UT1-UTC measurement accuracy depends on the accuracy of numerous models, including the VLBI station position. Intensives observed with the Maunakea (Mk) and Pie Town (Pt) stations of the Very Long Baseline Array (VLBA) illustrate how a geologic event (i.e., the M_w 6.9 Hawai‘i Earthquake of May 4th, 2018) can cause a station displacement and an associated offset in the values of UT1-UTC measured by that baseline, rendering the data from the series useless until it is corrected. Using the nonparametric Nadaraya–Watson estimator to smooth the measured UT1-UTC values before and after the earthquake, we calculate the offset in the measurement to be 75.7 ± 4.6 upmu s. Analysis of the sensitivity of the Mk-Pt baseline’s UT1-UTC measurement to station position changes shows that the measured offset is consistent with the 67.2 ± 5.9 upmu s expected offset based on the 12.4 ± 0.6 mm total coseismic displacement of the Maunakea VLBA station determined from the displacement of the co-located global navigation satellite system (GNSS) station. GNSS station position information is known with a latency on the order of tens of hours and thus can be used to correct the a priori position model of a co-located VLBI station such that it can continue to provide accurate measurements of the critical EOP UT1-UTC as part of Intensive sessions. In the absence of a co-located GNSS receiver, the VLBI station position model would likely not be updated for several months, and a near real-time correction would not be possible. This contrast highlights the benefit of co-located GNSS and VLBI stations in support of the monitoring of UT1-UTC with single-baseline Intensives.

Tropospheric Delay Correction of VLBI Stations for the Real‐Time Trajectory Determination of the Chang'E‐5 Spacecraft

AbstractThe Chang'E‐5 (CE‐5) spacecraft was launched on 24 November 2020 with the purpose to implement unmanned lunar surface sampling and return. Very long baseline interferometry (VLBI) technique played an important role in real‐time precise trajectory determination and attitude determination of the CE‐5 spacecraft in the Earth to Moon transfer, circumlunar, landing, and ascending phases. However, tropospheric delay is one of the main error sources for VLBI observations which has to be corrected accurately for precise trajectory determination. To deal with this error properly, a prediction model (TRO_P) and a method with Global Navigation Satellite System observations (TRO_G) are proposed for tropospheric zenith delay correction for real‐time and 30 min latency trajectory determination of the CE‐5 spacecraft, respectively. The results demonstrate that the mean root mean square (RMS) of residual error of VLBI delay and delay rate for TRO_P are 0.62 ns and 0.75 ps/s at low elevation angle, respectively. Moreover, the improvement for the mean RMS of VLBI delay using TRO_G is 39.5% meaning from 0.43 to 0.26 ns compared with that using the method with meteorological data (TRO_S) at low elevation angle. This study can provide a reference for tropospheric delay calibration for trajectory determination of the spacecraft using VLBI or other techniques.

The Role of Spatial Gradient on Vertical Total Electron Content Extraction From Geodetic Very Long Baseline Interferometry Observation: Case Study CONT08 to CONT17‐L1

AbstractGeodetic very long baseline interferometry (VLBI) observations are carried out, with the legacy system, using two well‐separated frequency bands in order to determine first‐order ionospheric delay corrections corresponding to the combined effect of total electron content (TEC) at two stations forming a baseline. On the other hand, it is possible to obtain the vertical TEC (VTEC) above the VLBI antennas from VLBI data. This research intends to investigate the role of the ionospheric spatial gradient on VTEC which is derived from VLBI observations based on the latest four Continuous VLBI Campaigns (CONT08 to CONT17‐L1). For this purpose, station‐based VTEC values were computed in two modes, with and without spatial gradients. Then, these two approaches were evaluated by comparison to global ionospheric maps (GIMs). The differences between the GIM‐based VTEC values and the VLBI VTEC values derived using two parameterization approaches were used to compute the Root Mean Square Error (RMSE) for each VLBI station during the CONTs. In addition, the improvement percentages of the VLBI VTEC's error were calculated to understand the spatial gradient role. Based on the obtained results, the role of spatial gradient is more significant on the equatorial region as compared to the polar area. Using the ionospheric spatial gradient decreases the RMSE values of VLBI‐derived VTEC values from CONT08, CONT11, CONT14, and CONT17‐L1 by 26.4%, 37.6%, 32.4%, and 27.4%, respectively. In addition, it is also shown that this parameter reduces the RMSE values during the high solar activity, as in 2011 and 2014.

Short-baseline interferometry local-tie experiments at the Onsala Space Observatory

We present results from observation, correlation and analysis of interferometric measurements between the three geodetic very long baseline interferometry (VLBI) stations at the Onsala Space Observatory. In total, 25 sessions were observed in 2019 and 2020, most of them 24 h long, all using X band only. These involved the legacy VLBI station ONSALA60 and the Onsala twin telescopes, ONSA13NE and ONSA13SW, two broadband stations for the next-generation geodetic VLBI global observing system (VGOS). We used two analysis packages: nu Solve to pre-process the data and solve ambiguities, and ASCOT to solve for station positions, including modelling gravitational deformation of the radio telescopes and other significant effects. We obtained weighted root mean square post-fit residuals for each session on the order of 10–15 ps using group-delays and 2–5 ps using phase-delays. The best performance was achieved on the (rather short) baseline between the VGOS stations. As the main result of this work, we determined the coordinates of the Onsala twin telescopes in VTRF2020b with sub-millimetre precision. This new set of coordinates should be used from now on for scheduling, correlation, as a priori for data analyses, and for comparison with classical local-tie techniques. Finally, we find that positions estimated from phase-delays are offset sim +3 mm in the up-component with respect to group-delays. Additional modelling of (elevation dependent) effects may contribute to the future understanding of this offset.

A broadband VLBI system using transportable stations for geodesy and metrology: an alternative approach to the VGOS concept

We have developed a broadband VLBI (very long baseline interferometry) system inspired by the concept of the VLBI Global Observing System (VGOS). The new broadband VLBI system was implemented in the Kashima 34 m antenna and in two transportable stations utilizing 2.4 m diameter antennas. The transportable stations have been developed as a tool for intercontinental frequency comparison but are equally useful for geodesy. To enable practical use of such small VLBI stations in intercontinental VLBI, we have developed the procedure of node-hub style VLBI: In joint observation with a large, high sensitivity ‘hub’ antenna, the closure delay relation provides a virtual delay observable between ‘node’ stations. This overcomes the limited sensitivity of the small diameter node antennas, while error sources associated with large diameter antennas, such as gravitational deformation and delay changes in necessarily long signal cables, are eliminated. We show that this scheme does not result in an increased sensitivity to radio source structure if one side of the baseline triangle is kept short. We have performed VLBI experiments utilizing this approach over both short range and intercontinental distance. This article describes the system components, signal processing procedure, experiment, and results in terms of baseline repeatability. Our measurements reveal signatures of structure effects in the correlation amplitude of several of the observed radio sources. We present a model of the frequency-dependent source size for 1928+738 derived from correlation amplitude data observed in four frequency bands.

Intercontinental comparison of optical atomic clocks through very long baseline interferometry

The comparison of distant atomic clocks is foundational to international timekeeping, global positioning and tests of fundamental physics. Optical-fibre links allow the most precise optical clocks to be compared, without degradation, over intracontinental distances up to thousands of kilometres, but intercontinental comparisons remain limited by the performance of satellite transfer techniques. Here we show that very long baseline interferometry (VLBI), although originally developed for radio astronomy and geodesy, can overcome this limit and compare remote clocks through the observation of extragalactic radio sources. We developed dedicated transportable VLBI stations that use broadband detection and demonstrate the comparison of two optical clocks located in Italy and Japan separated by 9,000 km. This system demonstrates performance beyond satellite techniques and can pave the way for future long-term stable international clock comparisons. Very long baseline interferometry is used to compare two optical clocks located in Japan and Italy through the observation of extragalactic radio sources. This approach overcomes limitations of the performance of satellite transfer techniques.

Evaluation of VLBI Observations with Sensitivity and Robustness Analyses

Very Long Baseline Interferometry (VLBI) plays an indispensable role in the realization of global terrestrial and celestial reference frames and in the determination of the full set of the Earth Orientation Parameters (EOP). The main goal of this research is to assess the quality of the VLBI observations based on the sensitivity and robustness criteria. Sensitivity is defined as the minimum displacement value that can be detected in coordinate unknowns. Robustness describes the deformation strength induced by the maximum undetectable errors with the internal reliability analysis. The location of a VLBI station and the total weights of the observations at the station are most important for the sensitivity analysis. Furthermore, the total observation number of a radio source and the quality of the observations are important for the sensitivity levels of the radio sources. According to the robustness analysis of station coordinates, the worst robustness values are caused by atmospheric delay effects with high temporal and spatial variability. During CONT14, it is determined that FORTLEZA, WESTFORD, and TSUKUB32 have robustness values changing between 0.8 and 1.3 mm, which are significantly worse in comparison to the other stations. The radio sources 0506-612, NRAO150, and 3C345 have worse sensitivity levels compared to other radio sources. It can be concluded that the sensitivity and robustness analysis are reliable measures to obtain high accuracy VLBI solutions.

Geodetic VLBI for precise orbit determination of Earth satellites: a simulation study

Recent efforts of tracking low Earth orbit and medium Earth orbit (MEO) satellites using geodetic very long baseline interferometry (VLBI) raise questions on the potential of this novel observation concept for space geodesy. Therefore, we carry out extensive Monte Carlo simulations in order to investigate the feasibility of geodetic VLBI for precise orbit determination (POD) of MEO satellites and assess the impact of quality and quantity of satellite observations on the derived geodetic parameters. The MEO satellites are represented in our study by LAGEOS-1/-2 and a set of Galileo satellites. The concept is studied on the basis of 3-day solutions in which satellite observations are included into real schedules of the continuous geodetic VLBI campaign 2017 (CONT17) as well as simulated schedules concerning the next-generation VLBI system, known as the VLBI Global Observing System (VGOS). Our results indicate that geodetic VLBI can perform on a comparable level as other space-geodetic techniques concerning POD of MEO satellites. For an assumed satellite observation precision better than 14.1 mm (47 ps), an average 3D orbit precision of 2.0 cm and 6.3 cm is found for schedules including LAGEOS-1/-2 and Galileo satellites, respectively. Moreover, geocenter offsets, which were so far out of scope for the geodetic VLBI analysis, are close to the detection limit for the simulations concerning VGOS observations of Galileo satellites, with the potential to further enhance the results. Concerning the estimated satellite orbits, VGOS leads to an average precision improvement of 80% with respect to legacy VLBI. In absolute terms and for satellite observation precision of 14.1 mm (47 ps), this corresponds to an average value of 17 mm and 7 mm concerning the 3D orbit scatter and precision of geocenter components, respectively. As shown in this study, a poor satellite geometry can degrade the derived Earth rotation parameters and VLBI station positions, compared to the quasar-only reference schedules. Therefore, careful scheduling of both quasar and satellite observations should be performed in order to fully benefit from this novel observation concept.

M2 constituent of ocean tide loading displacements from VLBI CONT14 hourly sessions

Several studies prove that ocean tide loading (OTL) displacements can be observed with space geodetic techniques. In this study, the amplitudes and Greenwich phase lags for each coordinate component, i.e., radial, west, and south of the principal lunar semidiurnal tide, M 2 of OTL displacements were estimated at the very long baseline interferometry (VLBI) sites of the 15 days long continuous VLBI campaign, CONT14, carried out by the International VLBI Service for Geodesy and Astrometry (IVS). In the estimation of the amplitudes and Greenwich phase lags of the M 2 tidal constituent, hourly VLBI station coordinate time series were used as observations derived through analyzing 1 hour VLBI sessions of the CONT14 campaign. In the analysis of hourly sessions of the CONT14 campaign, to derive accurate hourly station coordinates, troposphere delays estimated from daily sessions were reduced from the observations a priori to the analysis. The estimated amplitudes and Greenwich phase lags of the M 2 constituent of OTL displacements were compared with the predictions the state-of-the-art ocean tide models, among others, FES2012 [Lyard et al., 2006; Carrere et al., 2012], FES2014 [Carrere et al., 2016], and TPXO8 [Egbert and Erofeeva, 2002; Egbert et al., 2010]. Both the amplitudes and the phases between CONT14 estimates and ocean tide models agree well for the M 2 tide at all the sites and in most of the coordinate components. The RMS misfits of the M 2 tide of OTL displacements in all coordinate components between CONT14 and ocean tide models over coastal sites are found about two times larger than those of inland sites. This result confirms the modeling insufficiencies in shallow waters of ocean tide models which cause an accuracy restriction of OTL displacement predictions around coastal regions.

A New Very Long Baseline Interferometry Method Based on the Uplink Signal

Very long baseline interferometry (VLBI) is widely used for astronomical observations and navigation of deep space receivers. To solve the problems of the downlink signal being excessively weak to be received and the excessively large acquisition time, a new VLBI measurement method based on the uplink signal is proposed. Deep space ground stations can provide radio measurement signals for deep space spacecraft via the uplink. The range, Doppler and VLBI can be determined by the spacecraft through signals from multiple ground stations. In this manner, a higher signal to noise ratio (SNR) can be obtained. This study involves the development of a prompt acquisition algorithm for high dynamic deep space signals. Furthermore, the measurement and tracking of the phases of multiple VLBI stations by deep space receiver employing the uplink are analyzed. The use of the algorithms reduce the acquisition time for deep space receiver, and high precision results can be obtained for the VLBI measurement. Compared with the traditional VLBI method, the ranging error on the same distance is effectively improved, and the angle measurement accuracy is better than delta differential one way ranging ( $\Delta $ DOR). Because multiple spacecraft are not needed, there are fewer limitations than same beam interferometry (SBI).

Determination of the tectonic plates motion parameters based on SLR, DORIS and VLBI stations positions

Abstract On the base of International Terrestrial Reference Frame 2008 (ITRF2008) a new global plate model of station positions and velocities with accuracy 1–3 mm and 1 mm per year respectively was established. Next, this model was used in our paper for plate motion parameters estimation for the major plates as Eurasian, North American, Pacific and small plates as Australian, African and Antarctic on the base of the observation campaigns for three techniques: Satellite Laser Ranging (SLR), Doppler Orbitography by Radiopositioning Integrated on Satellite system (DORIS) and Very Long Baseline Interferometry (VLBI), each technique was analyzed separately. Investigation for GNSS technique is scheduled to take place in the future. The plate motion parameters were adjusted using least squares method and sequential solution. In the first stage, the plate motion parameters were determined for two selected stations and next stations were added until stability of the solution was observed. Final results of our solution were compared with the APKIM 2005 IGN model by H. Drewes. Agreement of solutions is order 2 degrees or better.

Delta-DOR Observations Using VLBI Antennas

Delta-DOR (differential one-way ranging) is a technique which addresses the problem of orbit determination of a target deep-space spacecraft, in particular by determining its angular position in the sky. This can be achieved by means of analyzing both quasar signals, using this radio source as a calibrator, and a proper signal transmitted by the target spacecraft. These signals should be received by two or more stations, possibly set at a large distance from each other. Nowadays, European Space Agency (ESA) can count only on a few stations, more precisely the largest ones, since large signal-to-noise ratios are required to acquire the faint transmissions involved. This study has the aim to exploit a different set of stations, the ones belonging to the very long baseline interferometry (VLBI) network, to perform Delta-DOR measurements. VLBI antennas have in general the right hardware requirements but lack a proper recording output; therefore, a software translation of the recorded signal is required. As a proof-of-concept of the proposed technique, a shadow pass, involving an Italian VLBI station, of a standard ESA Delta-DOR session has been scheduled. The recorded data were successfully translated and analyzed by means of the ESA’s software correlator, showing the feasibility of this innovative procedure.

Calibration of ALMA as a Phased Array. ALMA Observations During the 2017 VLBI Campaign

We present a detailed description of the special procedures for calibration and quality assurance of Atacama Large Millimeter/submillimeter Array (ALMA) observations in Very Long Baseline Interferometry (VLBI) mode. These procedures are required to turn the phased ALMA array into a fully calibrated VLBI station. As an illustration of these methodologies, we present full-polarization observations carried out with ALMA as a phased array at 3 mm (Band 3) and 1.3 mm (Band 6) as part of Cycle-4. These are the first VLBI science observations conducted with ALMA and were obtained during a 2017 VLBI campaign in concert with other telescopes worldwide as part of the Global mm-VLBI Array (GMVA, April 1–3) and the Event Horizon Telescope (EHT, April 5–11) in ALMA Bands 3 and 6, respectively.

Improving dUT1 from VLBI intensive sessions with GRAD gradients and ray-traced delays

Exact knowledge of the angle of Earth rotation UT1 with respect to coordinated time UTC, dUT1, is essential for all space geodetic techniques. The only technique which is capable of determining dUT1 is Very Long Baseline Interferometry (VLBI). So-called Intensive VLBI sessions are performed on a daily basis in order to provide dUT1. Due to the reduced geometry of Intensive sessions, there is however no possibility to estimate tropospheric gradients from the observations, which limits the accuracy of the resulting dUT1 significantly. This paper deals with introducing the information on azimuthal asymmetry from external sources, thus attempting to improve the dUT1 estimates. We use the discrete horizontal gradients GRAD and the empirical horizontal gradients GPT3 as well as ray-traced delays from the VieVS ray-tracer for this purpose, which can all be downloaded from the VMF server of TU Wien (http://vmf.geo.tuwien.ac.at). The results show that this strategy indeed improves the dUT1 estimates when compared to reference values from multi-station VLBI stations, namely by up to 15%. When converted to length-of-day (LOD), the estimates can be compared to LODs from global analyses of Global Navigation Satellite Systems (GNSS). Here, the improvement amounts to up to 7% compared to neglecting a priori information on azimuthal asymmetry.

Venus Express radio occultation observed by PRIDE

Context. Radio occultation is a technique used to study planetary atmospheres by means of the refraction and absorption of a spacecraft carrier signal through the atmosphere of the celestial body of interest, as detected from a ground station on Earth. This technique is usually employed by the deep space tracking and communication facilities (e.g., NASA’s Deep Space Network (DSN), ESA’s Estrack). Aims. We want to characterize the capabilities of the Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique for radio occultation experiments, using radio telescopes equipped with Very Long Baseline Interferometry (VLBI) instrumentation. Methods. We conducted a test with ESA’s Venus Express (VEX), to evaluate the performance of the PRIDE technique for this particular application. We explain in detail the data processing pipeline of radio occultation experiments with PRIDE, based on the collection of so-called open-loop Doppler data with VLBI stations, and perform an error propagation analysis of the technique. Results. With the VEX test case and the corresponding error analysis, we have demonstrated that the PRIDE setup and processing pipeline is suited for radio occultation experiments of planetary bodies. The noise budget of the open-loop Doppler data collected with PRIDE indicated that the uncertainties in the derived density and temperature profiles remain within the range of uncertainties reported in previous Venus’ studies. Open-loop Doppler data can probe deeper layers of thick atmospheres, such as that of Venus, when compared to closed-loop Doppler data. Furthermore, PRIDE through the VLBI networks around the world, provides a wide coverage and range of large antenna dishes, that can be used for this type of experiments.

Modernizing and Expanding the NASA Space Geodesy Network to Meet Future Geodetic Requirements.

NASA maintains and operates a global network of Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Global Navigation Satellite System (GNSS) ground stations as part of the NASA Space Geodesy Program. The NASA Space Geodesy Network (NSGN) provides the geodetic products that support Earth observations and the related science requirements as outlined by the US National Research Council (NRC 2010, 2018). The Global Geodetic Observing System (GGOS) and the NRC have set an ambitious goal of improving the Terrestrial Reference Frame (TRF) to have an accuracy of 1 millimeter and stability of 0.1 millimeters per year, an order of magnitude beyond current capabilities. NASA and its partners within GGOS are addressing this challenge by planning and implementing modern geodetic stations co-located at existing and new sites around the world. In 2013, NASA demonstrated the performance of its next-generation systems at the prototype next-generation core site at NASA's Goddard Geophysical and Astronomical Observatory in Greenbelt, Maryland. Implementation of a new broadband VLBI station in Hawaii was completed in 2016. NASA is currently implementing new VLBI and SLR stations in Texas and is planning the replacement of its other aging domestic and international legacy stations. In this article, we describe critical gaps in the current global network and discuss how the new NSGN will expand the global geodetic coverage and ultimately improve the geodetic products. We also describe the characteristics of a modern NSGN site and the capabilities of the next-generation NASA SLR and VLBI systems. Finally, we outline the plans for efficiently operating the NSGN by centralizing and automating the operations of the new geodetic stations.

A balloon-borne very long baseline interferometry experiment in the stratosphere: Systems design and developments

The balloon-borne very long baseline interferometry (VLBI) experiment is a technical feasibility study for performing radio interferometry in the stratosphere. The flight model has been developed. A balloon-borne VLBI station will be launched to establish interferometric fringes with ground-based VLBI stations distributed over the Japanese islands at an observing frequency of approximately 20 GHz as the first step. This paper describes the system design and development of a series of observing instruments and bus systems. In addition to the advantages of avoiding the atmospheric effects of absorption and fluctuation in high frequency radio observation, the mobility of a station can improve the sampling coverage (“uv-coverage”) by increasing the number of baselines by the number of ground-based counterparts for each observation day. This benefit cannot be obtained with conventional arrays that solely comprise ground-based stations. The balloon-borne VLBI can contribute to a future progress of research fields such as black holes by direct imaging.

On the impact of local ties on the datum realization of global terrestrial reference frames

Local ties (LTs) at co-located sites are currently used to combine different single-technique solutions to determine global terrestrial reference frames (TRFs). We assess by simulations the impact of different LT standard deviations, biased LTs and a selection of LTs on the datum realization of global TRFs. The simulations are based on Global Positioning System (GPS), Satellite Laser Ranging, and Very Long Baseline Interferometry (VLBI) observations covering the time span 2008–2014. We find that LT standard deviations of 1 cm and better yield differences in the TRF-defining parameters below 1 mm. VLBI is most affected by altering the LT standard deviations, especially in the translations since VLBI is inherently not sensitive to the origin of the TRF. Altering the standard deviations of the LTs applied in ITRF2005, ITRF2008, ITRF2014 results in small differences reaching a maximum of 0.6 mm at the VLBI stations. Simulating technique-wise biased LT stations shows the largest differences in the TRF-defining parameters of more than 2 mm, if all GPS LT stations are biased by 1 cm, proving that GPS plays the major role in the connection of the three techniques. Simulating single biased LT stations by 1 cm in either the north, east, or height component indicates small differences of less than 0.8 mm in the TRF-defining parameters, the largest differences result at LT stations located on the southern hemisphere. The selection of LTs demonstrates that the southern hemisphere LTs are very important, especially for the realization of the scale.

On the long-term stability of terrestrial reference frame solutions based on Kalman filtering

The Global Geodetic Observing System requirement for the long-term stability of the International Terrestrial Reference Frame is 0.1 mm/year, motivated by rigorous sea level studies. Furthermore, high-quality station velocities are of great importance for the prediction of future station coordinates, which are fundamental for several geodetic applications. In this study, we investigate the performance of predictions from very long baseline interferometry (VLBI) terrestrial reference frames (TRFs) based on Kalman filtering. The predictions are computed by extrapolating the deterministic part of the coordinate model. As observational data, we used over 4000 VLBI sessions between 1980 and the middle of 2016. In order to study the predictions, we computed VLBI TRF solutions only from the data until the end of 2013. The period of 2014 until 2016.5 was used to validate the predictions of the TRF solutions against the measured VLBI station coordinates. To assess the quality, we computed average WRMS values from the coordinate differences as well as from estimated Helmert transformation parameters, in particular, the scale. We found that the results significantly depend on the level of process noise used in the filter. While larger values of process noise allow the TRF station coordinates to more closely follow the input data (decrease in WRMS of about 45%), the TRF predictions exhibit larger deviations from the VLBI station coordinates after 2014 (WRMS increase of about 15%). On the other hand, lower levels of process noise improve the predictions, making them more similar to those of solutions without process noise. Furthermore, our investigations show that additionally estimating annual signals in the coordinates does not significantly impact the results. Finally, we computed TRF solutions mimicking a potential real-time TRF and found significant improvements over the other investigated solutions, all of which rely on extrapolating the coordinate model for their predictions, with WRMS reductions of almost 50%.