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An Erratum to this paper has been published: https://doi.org/10.1134/S1064226924550011

Abstract

Smartphone-based location-based services (LBS) require enhanced horizontal position accuracy with integrity. Due to the mass-market nature and compact design of smartphones, they utilize low-cost antennas and receivers, making them susceptible to multipath effects and other errors, which complicates the differentiation between reliable and unreliable measurements. To address these challenges, this paper explores the application of an adaptive Kalman filter technique to improve smartphone positioning accuracy. Adaptive Kalman filters adjust parameters such as process noise covariance or measurement noise covariance to modify the filter gain. When augmented with outlier detection mechanisms, the filter becomes more robust. This paper introduces a robust adaptive Kalman filter to enhance smartphone position accuracy. Outliers are detected using standardized innovations as a learning statistic, and a t-test is applied to these statistics to identify and mitigate outliers and adapt the measurement noise covariance accordingly. While previous research used empirical values for thresholds to adapt measurement noise covariance matrix, this study derives thresholds from t-tests, contingent on the normal distribution of learning statistics. By eliminating clock reset effects, innovations are transformed from bimodal to a normal distribution. Testing across multiple datasets demonstrates reductions of up to 42% in horizontal positioning root mean square error, with 50th, 68th, and 95th percentile statistics showing improvements of up to 53%, 41%, and 61%, respectively.

Abstract

Groundwater withdrawal and recharge lead to changes in terrestrial hydrological loads, which in turn cause surface deformation. Based on poroelastic response and elastic loading theory, the 24 Global Positioning System (GPS) stations on the North China Plain (NCP) and the Gravity Recovery and Climate Experiment mission and its follow-on (GRACE/GRACE-FO) are first integrated to quantify the spatial–temporal changes in surface deformation and groundwater storage (GWS) during 2011–2022. The results show that the trends of GWS in the three periods of 2011–2017, 2018–2020, and 2021–2022 were  − 2.56 ± 0.33 mm/yr,  − 4.72 ± 1.74 mm/yr, and 11.76 ± 4.18 mm/yr, respectively. Most of the GPS stations showed a significant negative correlation between GWS and surface deformation under the elastic loading theory. In 2021, surface subsidence of more than 5 mm was experienced by 94% of the GPS stations, and 58% experienced more than 10 mm, further confirming that the South-to-North Water Diversion (SNWD) effectively replenishes groundwater resources in the NCP. The SNWD, precipitation, and human activity were the three principal factors influencing the groundwater in the NCP. SNWD effectively mitigated the continuous decrease of groundwater in the NCP.

Abstract

Satellite signals from the Global Navigation Satellite System (GNSS) are refracted as they pass through the troposphere, owing to the variable density and composition of the atmosphere, causing tropospheric delay. Typically, tropospheric delay is treated as an unknown parameter in GNSS data processing. Given the growing need for real-time GNSS applications, accurate tropospheric delay predictions are crucial to improve Precise Point Positioning (PPP). In this paper, time-series of tomography data are used for wet refractivity prediction employing Machine Learning (ML) techniques in both Poland and California, under extreme weather conditions including sweeping rain bands and storms. The predicted wet refractivity is implemented for tropospheric delay determination through ray-tracing technique. PPP processing is conducted in both static and kinematic modes using different setups. These are: (1) common PPP, called Com-PPP, (2) Ray-PPP, which applies obtained tropospheric delay on GNSS observations and thus eliminates tropospheric parameters from unknowns, and (3) Dif-PPP, which applies the difference of estimated tropospheric delay from ray-tracing and GNSS measurements to compensate for the remaining tropospheric delay in the observations. The results show that Dif-PPP reduces the Mean Absolute Error (MAE) of the Three-Dimensional (3-D) component between 8 and 33% in static mode compared to the Com-PPP method. Additionally, it can improve the convergence time of the up component in the kinematic mode by between 6 and 17%.

Abstract

For precise orbit determination (POD) and precise applications with POD products, one of the critical issues is the modeling of non-conservative forces acting on satellites. Since the official publication of Galileo satellite metadata in 2017, analytical models including the box-wing model and thermal thrust models have been established to absorb a substantial amount of solar radiation pressure (SRP) and thermal thrust. These models serve as the foundation for the best overall modeling approach, combining the analytical box-wing model and thermal thrust model with parameterization of the remaining non-conservative perturbing forces using various optimized Empirical CODE Orbit Models (ECOMs) of the Center for Orbit Determination in Europe (CODE). Firstly, we have demonstrated the significance of the second-order signals in the D direction and the first-order signals in the B direction through spectral analyses of the pure box-wing model, which are consistent with the currently recommended 7-parameter Empirical CODE Orbit Model 2 (ECOM2). In spite of this, we still found that degradation in orbit accuracy frequently occurs during deep eclipse seasons when using the ECOM2 model. We confirm a high-frequency signal existing in the fluctuating orbit overlap differences through the spectral analysis. Considering this, the ECOM2 force model should be extended to higher order and adapted to absorb the remaining effects of potential perturbing forces. After extending the ECOM2 force model to the sixth order in the Sun direction, we demonstrated the significance of fourth- and sixth-order sine terms for deep eclipses. Due to the higher-order periodic terms, the averaged RMS values of orbit overlap difference over deep eclipses can be reduced from 5.3, 10.8, and 23.8 cm to 3.2, 3.9, and 9.9 cm for in-orbit validation (IOV) satellites, from 5.0, 8.6, and 17.7 cm to 3.0, 3.0, and 7.1 cm for the first generation of full operational capability (FOC-1) satellites, and from 5.4, 8.6, and 19.0 cm to 3.6, 3.6, and 7.4 cm for the second generation of FOC (FOC-2) satellites, in the radial, cross-track, and along-track directions, respectively. Fluctuations with a peak amplitude of approximately 0.4 nm/s2 in the bias in the solar panel axis (Y) direction (Y-bias) are effectively mitigated by the higher-order terms. Due to the higher-order terms, the vertical positioning errors during kinematic precise point positioning (PPP) convergence can be improved from 42.3 to 37.1 cm at the 95.5% confidence level. Meanwhile, a low correlation level of up to 0.02 is found between the newly introduced higher-order parameters and earth rotation parameters (ERPs).

Abstract

The European Galileo High Accuracy Service (HAS) started to provide freely and openly accessible real-time precise satellite orbit, clock and code bias products to global users on January 24, 2023. Combined with the already running BeiDou PPP-B2b service, the launch of a variety of satellite-based PPP services provided more choices to users. However, different satellite-based PPP services provide services for different GNSS systems, which hamper users to make full use of multi-GNSS systems. Therefore, the combination of different satellite-based products can further improve the availability of corrections, usage of multi-GNSS observation data and positioning performance. This paper proposes to combine HAS and PPP-B2b products by the Helmert coordinate transformation method. To validate the algorithm, HAS and PPP-B2b products of day of year (DOY) 308–317 in 2023 were collected in Zhengzhou, China. First, they are evaluated in terms of correction availability, orbit and clock quality. Then the HAS and PPP-B2b products are combined by the Helmert coordinate transformation method. Two combination strategies are proposed. The first strategy is integrating BDS satellites of PPP-B2b products into HAS products (denoted as C_H), while the second strategy is integrating Galileo satellites of HAS products into PPP-B2b products (denoted as C_B). Finally, the combined strategies are evaluated with static and kinematic data. Based on the static data of 18 Multi-GNSS Experiment (MGEX) stations in China and its surrounding areas, the results show that, when separately using HAS and PPP-B2b products for PPP, the average accuracy in horizontal and vertical directions are (2.4, 2.7 cm) and (2.4, 2.0 cm), respectively. The average accuracy of C_H strategy is 2.1 and 1.7 cm, which was improved by 31.3% compared with separately using the products. Similarly, the average accuracy of C_B strategy is 2.1 and 1.9 cm, corresponding to improvements of 29.6%. When comparing the two combined strategies, it is noted that the C_B strategy converges faster. Based on the data from vehicle platform, the results show that the horizontal and vertical accuracy of the C_B strategy is 8.6 and 15.7 cm respectively. The accuracy improvement of C_B is better than that of C_H strategy, and the average accuracy is 68.4% better than that of separately using the products. The above results show that the two combined strategies can improve positioning accuracy. In addition, the improvements in accuracy and convergence speed of C_B strategy are more significant. Users are advised to use C_B strategy for the combination of HAS and PPP-B2b products, which will greatly expand the application of HAS and PPP-B2b services.

Abstract

In recent decades, Global Navigation Satellite System-Interferometric Reflectometry (GNSS-IR) environmental parameters inversion has become a research hotspot in the field of GNSS. Among them, sea/water level inversion has become one of the applications with better inversion performance because of its clear mathematical relationship and horizontal reflection surface. Among the many sources of error in GNSS-IR sea level inversion, sea surface height variation is the most significant source of error. The key to correcting this error is the accurate estimation of the rate of change of sea surface height. However, the estimation of the rate of change is difficult to be accurate, making it difficult to correct this error precisely. Theoretically, the retrieval error results in an offset in the initial phase parameter in the signal-to-noise ratios (SNR) oscillation sequence. Therefore, the error can also be corrected by estimating the phase. However, the phase determined during parameter fitting is between − π and π. When the error affects the phase offset magnitude greater than 2π, the integer cycle of it is not available, resulting in the phase-based correction model not being able to correct the error. In other words, the integer cycle ambiguity that exists in GNSS positioning also exists in SNR phase determination. In this article, a method for integer cycle determination based on the assistance of the traditional sea surface height variation error model is proposed, and an error correction method based on SNR phase and a multi-mode multi-frequency combination inversion method are also proposed. Two GNSS sites with different tidal amplitudes are selected to carry out the experiments. The results show that the phase-based error correction method improves the sea-level retrieval accuracy by about twice as much as that obtained using the traditional correction method. Meanwhile, this paper analyses the adaptability of the phase-based error correction method: good results can be achieved in the lower elevation angle interval, while the results are poor in the higher elevation angle interval. This study provides another solution idea for GNSS-IR error correction based on phase parameters, and the accuracy improvement achieved by this method is significant.

Abstract

The SMILE (Solar wind Magnetosphere Ionosphere Link Explorer) mission is a joint space science mission between the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS), aiming to understand the interaction of the solar wind with the Earth’s magnetosphere in a global manner. The mission was adopted by CAS in November 2016 and by ESA in March 2019 with a target launch in 2025. The SMILE mission successfully passed the join mission Preliminary Design Review in 2020 and the joint spacecraft and mission Critical Design Review in June 2023. The SMILE spacecraft Flight Model is now in the final stage of Assembly, Integration and Test campaign which will be carried out at ESTEC in September 2024. It will then be shipped to the Kourou Space Centre in French Guiana for launch. This paper summarizes the SMILE mission development, design and status as of June 2024.

Abstract

The least squares method is still commonly employed in traditional global navigation satellite system (GNSS) velocity estimation, but this method is easily biased by outliers from various sources. Random sample consensus (RANSAC) and solution separation (SS) algorithms have been employed in the domain of GNSS velocity estimation to identify and eliminate faults in the GNSS propagation process, yielding favorable outcomes. However, these algorithms are generally applied in single-epoch velocity estimation applications and use a single threshold for inspection and elimination, lacking adaptability to the observation environment. Therefore, a residual-based multithreshold constraint algorithm (RMCA) is proposed to improve the iterative results and obtain a time series solution of the GNSS velocity model. In the RMCA, the importance of residuals in the least squares approach is considered, and errors are directly expressed. Second, rather than employing a predetermined single threshold for exclusion, flexible threshold regulation is applied across various levels. Finally, the RMCA leverages the historically optimized velocity to establish sensible constraints on the current velocity estimation. Moreover, a mutual detection mechanism between GNSS velocity models is established. An experimental analysis of two groups of urban vehicles reveals that the velocity results obtained via the RMCA are more robust than those obtained via the traditional least squares algorithm and the SS scheme and are more continuous than those obtained via RANSAC. The RMCA is evidently well designed and efficient, demonstrating significant application value.

Abstract

The Europa Imaging System (EIS) consists of a Narrow-Angle Camera (NAC) and a Wide-Angle Camera (WAC) that are designed to work together to address high-priority science objectives regarding Europa’s geology, composition, and the nature of its ice shell. EIS accommodates variable geometry and illumination during rapid, low-altitude flybys with both framing and pushbroom imaging capability using rapid-readout, 8-megapixel (4k × 2k) detectors. Color observations are acquired using pushbroom imaging with up to six broadband filters. The data processing units (DPUs) perform digital time delay integration (TDI) to enhance signal-to-noise ratios and use readout strategies to measure and correct spacecraft jitter. The NAC has a 2.3° × 1.2° field of view (FOV) with a 10-μrad instantaneous FOV (IFOV), thus achieving 0.5-m pixel scale over a swath that is 2 km wide and several km long from a range of 50 km. The NAC is mounted on a 2-axis gimbal, ±30° cross- and along-track, that enables independent targeting and near-global (≥90%) mapping of Europa at ≤100-m pixel scale (to date, only ∼15% of Europa has been imaged at ≤900 m/pixel), as well as stereo imaging from as close as 50-km altitude to generate digital terrain models (DTMs) with ≤4-m ground sample distance (GSD) and ≤0.5-m vertical precision. The NAC will also perform observations at long range to search for potential erupting plumes, achieving 10-km pixel scale at a distance of one million kilometers. The WAC has a 48° × 24° FOV with a 218-μrad IFOV, achieving 11-m pixel scale at the center of a 44-km-wide swath from a range of 50 km, and generating DTMs with 32-m GSD and ≤4-m vertical precision. The WAC is designed to acquire three-line pushbroom stereo and color swaths along flyby ground-tracks.

Abstract

The T-15MD tokamak is equipped with a gyrotron setup, which currently includes one gyrotron with an operating outlet frequency of 82.6 GHz and a power of 1 MW. The length of the waveguide path from the gyrotron to the tokamak is 37 m. A significant result obtained earlier has been the measurement of HF‑radiation power using a small calorimetry load (0.95 MW at a pulse duration of 125 ms). The results of the first joint tests of a gyrotron and a waveguide path for a dummy load in a long pulse operation from a “V-iktoriya” high-voltage power supply are presented. The pulse duration of 9.4 s is achieved. The estimated microwave radiation power is 0.85 MW.

Abstract

The influence of the toroidal magnetic field ripples on the spatial structure and frequency of the geodesic acoustic mode (GAM) in tokamak plasma has been investigated. It is shown that the toroidal asymmetry of the magnetic configuration leads to coupling of oscillations of the GAM electric potential with toroidal and poloidal inhomogeneous perturbations of the plasma pressure. For tokamaks with a large aspect ratio, the GAM dispersion law is derived, taking the non-uniformity of the ripple in the tokamak cross-section into account. Increasing the number of coils \(n\) of the toroidal field reduces the effect of ripple as \( {\sim} {\text{1/}}{{n}^{2}}\) . The applicability of the standard theory to finding the frequency and spatial structure of GAM in large tokamaks is shown.

Abstract

The possibility of using the method of dual-wavelength digital holographic interferometry to assess the wear of protective elements of the Globus-M2 spherical tokamak after working plasma discharges is demonstrated. At this stage of the work, the protective elements were removed from the tokamak discharge chamber and used as samples in the holographic setup. A diagram of a holographic interferometer for recording primary holographic images is presented, in which control of the radiation wavelength recording and monitoring systems is carried out through a hardware and software complex in real time. The results of measurements of the shape of tokamak elements are presented. It is shown that when the difference in wavelengths changes, the sensitivity of the measurement method changes, and in the proposed configuration of the optical scheme it is possible to determine the minimum value of the shape change at a level of 10–30 μm. At the same time, the error in determining the phase difference, by which the surface profile is assessed, in the digital method can reach about 2π/40.

Abstract

We investigated the correlation between density perturbations (bursts), having stochastic or intermittent character and magnetic fluctuations detected by Mirnov coils. To achieve this, we designed and constructed a novel Mixed-Probe system in the IR-T1 tokamak. Our experimental approach involved two steps: first with Resonant Helical magnetic Fields (RHF) and then without RHF. The conditional averaged analysis of the probe ion saturation current ( \({{\tilde {I}}_{{{\text{sat}}}}}\) ) revealed that stochastic density bursts or intermittencies were more likely to exist during the time interval between t = 10 and 12 ms. Before applying RHF, the intermittencies exhibited a strong cross-correlation with magnetic fluctuations. The predominant frequencies observed are below 7 kHz. Interestingly, after applying RHF, the peaks in the frequency of the \({{\tilde {I}}_{{{\text{sat}}}}}\) signal disappeared, and there was no predominant peak in the FFT of \({{\tilde {I}}_{{{\text{sat}}}}}\) . We further analyzed the radial and poloidal velocities of bursts and magnetic fluctuations using diagnostic data. The results suggested that magnetic fluctuations induced oscillations in the background plasma, affecting the radial motion of the density perturbations. Notably, the poloidal velocity of the magnetic field perturbations exceeded that of the bursts, allowing it to shear the poloidal plasma flux and generate the density bursts. The differing velocities confirmed their coupling for a specific time, followed by decoupling. Overall, in the IR-T1 tokamak, applying RHF reduced the cross-correlation between magnetic fluctuations and stochastic density bursts.

Abstract

The analysis of possible divertor working regimes and edge plasma parameters for TRT tokamak project is performed basing on modeling. It is shown that for the separatrix power of 18 MW corresponding to approximately twice higher full input power the low divertor integral heat flux 5 MW/m2 can be provided for the separatrix plasma density lower than 7 × 1019 m–3 and the effective charge Zeff lower than 2. These parameters are realistic for this device. In case of bigger separatrix power the working regime is possible with higher divertor heat load still within the technological limits of the machine. Modeling also shows positive effect of the increase of the distance between the separatrix and the vacuum vessel structures and better performance of the corner divertor configuration comparing to the “ITER-like” one.

Abstract

It is demonstrated experimentally that the thermophoretic force acting upon microparticles in the thermal field in complex plasma can be used for effective control of a cloud of charged microparticles formed in an electrostatic trap in the positive-column stratum of a glow discharge. Variation in the thermal-field temperature gradient is found to cause changes in the cloud location in plasma volume, its shape and size, along with suppression of oscillations of microparticles in the directions transverse with respect to this gradient. Microparticles of larger size experience stronger thermal action, and damping of microparticle oscillations occurs in conjunction with changes in the cloud spatial position. Obtained experimental results are consistent with theoretical concepts of the phenomena under consideration.

Abstract

The results of a study of the interaction of a powerful flow of hydrogen plasma with a supersonic gas jet in front of a tungsten target are presented. Nitrogen or neon injected in front of the target surface provides a reliable method of shielding tungsten from direct exposure to hydrogen plasma. It has been experimentally shown that the resulting plasma of the gas jet is a powerful source of short-wave line radiation. Energy density absorbed by a tungsten target ≈25 J/cm2 is half the energy absorbed by tungsten during pulsed action of a hydrogen plasma flow without a gas jet ≈50 J/cm2. The maximum temperature achieved by the tungsten surface is ≈3700 K with the use of a gas jet and ≈5800 K without a gas jet. The presence of a gas jet-screen in front of the tungsten leads to the localization of evaporated tungsten near the target at distances of up to 1 cm from the surface.

Abstract

A phenomenological gasdynamic model of the compression of the gas Z-pinch neck through whose ends the plasma flows out at a high velocity was considered. Calculations showed that in this process, conditions are created under which the relaxation of the ion plasma component is delayed compared to the macroscopic compression dynamics. Therefore, the description of the Z-pinches at their maximum compression stage has to account for the ion kinetics. This approach can explain the mechanism of the ion acceleration to high energies as well as the high intensity of the neutron radiation at the final stage of the neck compression.

Abstract

In a number of experiments, the surfaces of condensed matter, for example, the electrodes of pulsed power facilities, are exposed to powerful pulsed X-ray radiation with an energy flux density of ~1 TW/cm2. The source of this radiation can be, for example, Z-pinches formed by current compression of multi-wire liners. Under the effect of this radiation, evaporation and plasma formation processes can occur on the surface of the electrodes. This paper provides a theoretical examination of these processes. In the case where the plasma layer thickness is small compared to the characteristic dimensions of the electrodes, plasma formation can be described by one-dimensional equations of magnetohydrodynamics taking radiation transfer into account. One-dimensional calculations performed for the experimental conditions at the Angara-5-1 facility (energy flux density coming from the pinch, ~0.2 TW/cm2, radiation exposure time ~15 ns, electrode material Fe), have shown that the characteristic plasma temperature in this case is ~40 eV, density ~3 mg/cm3, and its expansion speed is ~60 km/s. It is interesting that the magnetic fields in these experiments, which are relatively small (~0.8 MG) and are incapable to lead to plasma formation, restrain the expansion of the plasma with their pressure and affect its characteristic values and expansion speed. The speed obtained in the calculation is somewhat less than that measured experimentally using an X-ray electron-optical converter (~90 km/s), that may be due to not one dimensional turbulent plasma expansion or due to experimental errors.