Feed aggregator

Author(s): Yakun Dong, Kamran Sadiq, Otmar Scherzer, and John C. Schotland

We present a method to reconstruct the dielectric susceptibility (scattering potential) of an inhomogeneous scattering medium, based on the solution to the inverse scattering problem with internal sources. We consider a scalar model of light propagation in the medium. We employ the theory of reprodu…

[Phys. Rev. E 110, 065302] Published Wed Dec 11, 2024

An Erratum to this paper has been published: https://doi.org/10.1134/S1064226924550023

An Erratum to this paper has been published: https://doi.org/10.1134/S106422692456002X

An Erratum to this paper has been published: https://doi.org/10.1134/S1064226924570014

An Erratum to this paper has been published: https://doi.org/10.1134/S1064226924560018

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

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.

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.

Author(s): E. V. Parkevich, K. V. Shpakov, I. S. Baidin, A. A. Rodionov, A. I. Khirianova, Ya. K. Bolotov, and V. A. Ryabov

Comprehensive measurements of the x-ray emissions in the peripheral direction of extended high-voltage discharges in 55-cm open air gaps are performed at voltages up to 1 MV. The data on the spatial, temporal, and spectral characteristics of x rays are obtained. We demonstrate that the emission of p…

[Phys. Rev. E 110, 065204] Published Mon Dec 09, 2024

Author(s): Qiang Yi et al.

In this research, ∼0.14-micron-thick aluminum tamped by plastic is heated up to ∼110eV by the x-ray pulse from the Z-pinch-driven dynamic Hohlraum on an 8-MA machine in China. After an ∼6−ns heating stage, higher-energy xrays from an ∼2−ns- long backlight pulse pass through the hot aluminum. The tra…

[Phys. Rev. E 110, 065205] Published Mon Dec 09, 2024

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%.

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).

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.

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.

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.

Author(s): V. Yu. Bychenkov, A. V. Brantov, M. G. Lobok, and A. S. Kuratov

Femtosecond laser pulse propagation in a relativistic self-trapping (RST) regime in a near-critical density plasma makes it possible to maximize the total charge of the accelerating electrons and laser-to-electrons conversion rate, that can be used to provide a large amount of the terahertz range co…

[Phys. Rev. E 110, 065203] Published Thu Dec 05, 2024

Author(s): Qizheng Sun, Xiaojing Liu, Xiang Chai, Hui He, Lianjie Wang, Bin Zhang, and Tengfei Zhang

We propose an upwind hybrid discontinuous Galerkin (HDG) method for the first-order hyperbolic linear Boltzmann transport equation, featuring a flexible expansion suitable for multiscale scenarios. Within the HDG scheme, primal variables and numerical traces are introduced within and along faces of …

[Phys. Rev. E 110, 065301] Published Thu Dec 05, 2024

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.

Author(s): O. E. Vais, M. G. Lobok, and V. Yu. Bychenkov

Propagation of ultrarelativistically intense laser pulses in a self-trapping mode in a near critical density plasma makes it possible to produce electron bunches of extreme parameters appropriate for different state of the art applications. Based on three-dimensional particle-in-cell (PIC) simulatio…

[Phys. Rev. E 110, 065202] Published Wed Dec 04, 2024