We investigate the crustal stress field in Inner Mongolia using 728 focal mechanism solutions and 14 460 P-wave polarity data derived from 2 793 earthquakes based on three different strategies. The Inner Mongolia area is divided into 1°×1° grids, and three methods are applied: a composite focal mechanism solution method based on first-motion polarity data, a Bayesian right trihedra method(BRTM) based on focal mechanisms, and a weighted fusion method of polarity and focal mechanism data. The results from polarity-based and focal mechanism-based methods show good consistency. The abundance of polarity data, compared to limited focal mechanism data, enables stress inversion in a wider spatial extent. After weighted fusion of polarity-based results with focal mechanism data, the BRTM successfully obtains stress results at 125 grid points, expanding the coverage and reducing uncertainties. The study reveals significant spatial variations in the stress field across Inner Mongolia area. The eastern regions are dominated by shear and extension, with shearing concentrated along the Daxinganling and extension characterizing the basins on both sides. Localized compression is observed near Chifeng and Tongliao in the southeast. The northern margin of Ordos block exhibits extension characteristics, while the Alxa block displays shear features. The orientations of maximum principal stress exhibit considerable differences, while the minimum principal stress directions remain relatively uniform.

Based on 963 records of intensity meters and 410 records of strong motion seismographs of 37 earthquakes of M_L3.2 to 5.9 in Beijing-Tianjin-Hebei and its surrounding areas from 2019 to 2022, we use the P_d method to establish 36 magnitude estimation models between P_d amplitude within 2 to 7 seconds after P-wave arrival time of vertical waveform and magnitude. By fitting the standard deviation, the optimal filtering frequency bands of intensity meters and strong motion seismographs are determined to be 1 to 3 Hz and 0.5 to 3 Hz respectively. Meanwhile, we establish the magnitude estimation model of intensity meters and strong motion seismographs within 3 seconds after P-wave arrival time using P_d method. The parameter fitting results show that fitting slope and correlation coefficient are high, the standard deviation is small, and the overall reliability is high. The results of reverse and new data verification indicate that the magnitude deviation of P_d method is mainly within ±0.5, which shows that the two models established in this paper are reasonable and can be well applied in Beijing-Tianjin-Hebei region.

Based on the catalogue data from Fujian digital seismic network, a total of 3 720 earthquakes that occurred in Fujian from 2010 to 2023 are selected to study the local magnitude (M_L) deviations. The magnitude residual method is used to obtain a new calibration function (R₃(Δ)), station correction values (S_j) and medium propagation direction correction values (S_θ) which are applicable to Fujian, enhancing the accuracy of local magnitude measurement. The results indicate that standard deviation of magnitude deviations decreases from 0.29 to 0.19 after correction. In order to improve the accuracy of earthquake warning magnitude measurement, we apply the first station's magnitude, resulting in the standard deviation of magnitude deviations decreases from 0.31 to 0.25. It is evident that the new calibration function, station correction values and medium propagation direction correction values exhibit strong practicality in Fujian.

We use T-shaped, linear, regular pentagonal, and spiral arrays at the same site for micromotion detection comparison experiments to analyze the effects of cross-correlation time window length, geometry of observation array, and their spreading on the quality of frequency-Bessel (F-J) dispersion energy imaging. The results indicate that, for the same observation time, increasing the cross-correlation time window length can effectively distinguish the fundamental and higher-mode dispersion curves, but it will reduce the number of superposition segments, resulting in lower dispersion spectrum resolution.The F-J method does not have special requirements for the arrangement of observation array and is suitable for random and linear distributions. When the array aperture is the same, the quality and resolution of dispersion imaging for an observation array with a greater number of array spacing combinations will be higher. The F-J method has certain requirements for the deployment range of observation array. For example, when the deployment range is too small, the quality of dispersion imaging using the F-J method is poor and it is unable to separate higher-mode dispersion curves.

The dynamic evolution characteristics of regional gravity field at different time scales before the Wushi M_S7.1 earthquake are obtained by using the mobile gravity observation data of southern Tianshan area from 2020 to 2023, and the approximate field source depth corresponding to each order wavelet gravity detail is obtained by power spectrum analysis method. The results show that: 1)Before the Wushi M_S7.1 earthquake, the gravity changes in Wuqia-Bachu and Aksu areas show an obvious four-quadrant distribution, and the epicenter is located at the edge of four quadrants and near the zero line. 2)The wavelet transform results of gravity field in southern Tianshan area from 2020 to 2023 show that before the Wushi M_S7.1 earthquake, the gravity changes in Wuqia-Bachu area shows obvious four-quadrant distribution, and the epicenter is located at the edge of four quadrants and near the zero line.

We use the precise clock offset data released by IGS to analyze the key performance indicators of six GPS-Ⅲ satellite clocks that have been launched and operated in orbit, including frequency accuracy, frequency drift rate, and frequency stability, and compare them with the previous GPS clocks. The results show that rubidium clocks carried by GPS-Ⅲ are generally stable in operation and have good data quality, which is related to the improvement of anti-interference ability. There is no significant change or difference in time frequency performance, which is basically consistent with the previous generation Block ⅡF rubidium clocks. The frequency stability of GPS-Ⅲ rubidium clocks are better, which helps to improve the accuracy of PNT services. The research can provide reference and guidance for the upgrading and transformation of other GNSS system satellites.

The solar pressure perturbation, as the largest non-conservative force experienced by in-orbit navigation satellites, is an important error source for precise orbit determination. Currently, most solar radiation pressure models are established for global positioning system(GPS) satellites, and there is relatively little adaptability analysis of solar radiation pressure models for precise orbit determination accuracy of Beidou-3(BDS-3) satellites. We use observation data from the multi-GNSS experiment(MGEX) to conduct orbit determination experiments based on five solar radiation pressure models, including ECOM1-9, ECOM1-7, ECOM1-5, ECOM2, ECOMC. The results show that the applicability of solar radiation pressure model varies for satellites developed by different manufacturers. For satellites developed by China Academy of Space Technology(CAST), the ECOMC model exhibits optimal applicability in radial, tangential, and normal directions. For satellites developed by Shanghai Engineering Center for Microsatellites(SECM), the radial, tangential, and normal directions have the best accuracy for ECOM1-5, ECOMC, and ECOMC models, respectively. For 3D entirety, the ECOMC model is recommended for orbit determination of both CAST and SECM satellites. From the 24-hour prediction results, for CAST type satellites, the accuracy of ECOM1-9, ECOM1-7, ECOM1-5, ECOM2, and ECOMC models is 23.3 cm, 20.6 cm, 17.2 cm, 21.8 cm, and 10.4 cm, respectively. For SECM type satellites, the accuracy is 25.7 cm, 19.1 cm, 15.9 cm, 12.9 cm, and 11.9 cm, respectively.

We propose an adaptive stochastic model for low-cost receiver precise point positioning(PPP) in complex environments. The model improves PPP performance by adaptively adjusting the weight ratio of pseudorange observations and carrier phase observations of all GNSS satellites in a single epoch. We take the Hexinxingtong UM982 low-cost GNSS receiver to conduct PPP tests in three complex environments, including tree shade, high buildings and glass walls. The static PPP results show that the positioning accuracy of adaptive stochastic model is improved by 24%, 45% and 50% in three complex environments, respectively, and the convergence time is shortened by 49%, 27% and 24%, respectively, compared with the traditional empirical weighted stochastic model. The kinematic PPP results show that the positioning accuracy of adaptive stochastic model is improved by 35% in complex environment.

To reduce the positioning errors of global navigation satellite system(GNSS) in complex environments, we propose a method that combines high-precision points with distance intersection to accurately estimate the coordinates of an undetermined point. The observation equation is constructed as a nonlinear Gauss-Helmert model. To address the nonlinearity within this model, we introduce a back-propagation(BP) neural network for auxiliary processing. Compared with the traditional linearization methods, the BP neural network can effectively fit complex nonlinear functional relationships. The simulation experiments and actual measurement results show that this method can significantly reduce the impact of complex environments on positioning accuracy, and improve the positioning accuracy in E, N and U directions by 78.1%, 72.8%, and 79.2%, respectively.

The elevation datum is an important component of the surveying and mapping datum, providing data support for maior national proiects, Addressing the issue of accurately monitoring elevation datum affected by factors such as surface deformation, we present a study to analyze surface deformation based on time-series InSAR data and leveling time-series data. The study conducts periodic re measurement of elevation datum in deformation area, achieving dynamic monitoring primarily through updating elevation datum, point usability analysis, and point subsidence analysis. Taking Shandong province as an example, we carry out an experiment, The results show that the method proposed in this paper can effectively reduce monitoring costs and difficulties, yield reliable results, significantly enhance the supportability and service quality of surveying and mapping datum, and provide a new dynamic monitoring approach for regional elevation datum.