To improve the positioning accuracy of mobile intelligent terminals, we analyze the observation data of multiple satellite systems collected by Xiaomi Mi8 and Huawei Mate20 smartphones, estimate the parameters of signal-to-noise ratio model based on pseudorange residuals of different satellite systems, and finally carry out the static pseudorange single-point positioning experiment. The results show that the pseudorange accuracy of BDS and GPS observed on mobile phones is close to each other and is higher than that of GLONASS. The correlation between pseudorange residual and SNR is stronger compared to elevation angle. In the parameter estimation of SNR model, the fitting effect of Xiaomi Mi8 is better than that of Huawei Mate20. The fitting effect of BDS is worse than that of other satellite systems, and the horizontal positioning and elevation positioning accuracy of SNR model after parameter fitting are 2.37 meter and 8.38 meter, respectively, which is about 10% higher than that of elevation model.

Whether the initial search space is set reasonably or not directly affects the reliability and search efficiency of ambiguity resolution. In view of the constellation characteristics of BDS system, it is necessary to analyze the correlation between ellipsoid volume and the number of candidate points, and the effect of data redundancy for BDS2 and BDS3 under different satellite numbers and frequencies. For the drawback that objective function method is prone to produce too many candidate vectors when determining the ambiguity search space, we propose an optimized search space determination method, and verify the effectiveness of improved method through experiments. The results show that the improved search space determination method significantly reduces the number of actual ambiguity candidate vectors, with average improvement up to 35.02%, and ensures that the number of candidate vectors contained in 94% space satisfies the requirements. The improved search space method improves search efficiency by nearly 33% on average after applying it to different search methods, which is conducive to separating the redundant candidate vectors in initial search space, thus improving the ambiguity search efficiency.

Low-cost real-time kinematic (RTK) receivers exhibit weaker resistance to multipath effects, leading to a significant decline in single point positioning (SPP) performance in remote ocean environment. We comprehensively analyze the impact of carrier phase smoothing multipath reduction algorithm on the performance of low-cost RTK receivers in remote ocean environment. The results show that the multipath effects on RTK receivers in remote ocean environment are 2~3 times greater than that in land environment, with the strongest resistance observed at E5 frequency. The effectiveness of smoothing multipath reduction is related to pseudorange multipath effects. After using smoothing multipath reduction algorithm, the SPP accuracy of RTK receivers improves by 62% in remote ocean environment and 24% in land environment. The SPP accuracy of GPS/Galileo/BDS-3 multi-systems is superior to 1 meter, meeting the precision requirements for fine ocean operations.

We propose a numerical iterative search-based method to determine the optimal settings of random process parameters for pseudo-ambiguity by controlling orbit determination strategies and other variables. The GPS data from doy 92 to 101 in 2021 of GRACE-C and SWARM-A LEO satellites are used, along with CNT and MADOCA real-time precise ephemeris products to simulate real-time precise orbit determination(RTPOD). We conduct optimization experiments of random process parameters for pseudo-ambiguity. The results indicate that under the optimal parameter settings, the RTPOD three-dimensional position errors of the two LEO satellites range from approximately 4.62 to 7.56 cm. Compared to traditional floating-point ambiguity solution, the RTPOD accuracy with CNT and MADOCA products exhibit an average improvement of about 39.15% and 29.61%, respectively.

Due to the differences in ranging accuracy and stability of satellite laser ranging(SLR) stations, different weighting must be assigned to stations with different performance in precision orbit determination. We apply the fuzzy C-means(FCM) cluster weighting to precise orbit determination of LAGEOS-2 and compare its impact on orbit accuracy with the original station weighting. The results show that: 1) Compared to the original station weighting, FCM weighting better reflects the performance of each SLR station, improves orbit accuracy and increases observation quantity. 2) Among the four quality analysis centers of ILRS, under the original station weighting, the quality reports of JCET exhibit slightly superior orbit accuracy compared to other centers. When using FCM weighting, the results obtained from quality reports of all four analysis centers yield similar orbit accuracy level, ranging between 4.83 and 4.86 cm.

The basic data for polar motion parameter prediction usually applies the final solution product published by the international earth rotation and reference systems service, which has a data resolution of 1 day. In this paper, we use the radial basis function to interpolate polar motion observations, and obtain polar motion products with a resolution of 6 hours. We test 500 sets of prediction experiments based on LS+AR model. The experimental results show that compared with the prediction results without interpolation, the prediction accuracy of proposed method in the polar motion X and Y directions improves by 22.4% and 38.4% in the ultra-short-term forecast of 1-7 days.

We optimize the back propagation neural network(BPNN) by using particle swarm optimization(PSO), and establish an optimized GPT3 model(MGPT3). We use the zenith tropospheric delay(ZTD) data of 30 IGS stations in Europe for 366 days in 2020 as an example to compare the accuracy of MGPT3, UNB3m and GPT3 models in predicting ZTD. The results show that the RMSE of MGPT3 model is 18.49 mm, which improves the accuracy by 55.0% and 47.7% compared to UNB3m and GPT3 models, respectively.

We conduct PPP experiments using 80 global MGEX stations in September 2021, and compare the results with ZTD product released by the international GNSS service (IGS) as a reference. The results reveal significant advantages in ZTD accuracy of multi-system joint estimation. The average RMSE accuracy of GPS+BDS dual-system is approximately 0.6 mm higher than that of single GPS system, while the GPS+BDS+GLONASS+Galileo four-system exhibits a further improvement of about 0.9 mm than dual-system. The ZTD estimation accuracy of GPS under single-system condition is higher than that of BDS. In terms of spatial distribution, the improvement of ZTD estimation accuracy is more significant with increasing latitude. The four-system PPP ZTD accuracy is better than 5 mm when latitude exceeds 50°. Moreover, elevation increase of observation stations can improve ZTD estimation accuracy while latitude remains unchanged. The ZTD estimation accuracy is significantly improved under ambiguity resolution. The average absolute error (MAE) and root mean square error (RMSE) of ZTD estimated by single GPS system are 7.6 mm and 8.4 mm, respectively, which are about 11% and 12% higher than floating-point solutions. The average convergence time is reduced by 20 minutes.

The ill-posed problem results in a large variance in parameter estimation. It is difficult to conduct a precision comparison of regularization and truncated singular value decomposition(TSVD) methods when the true values of parameters are unknown. To address this problem, we propose a mean square error relative comparative method. Firstly, we determine the relative deviation of regularization estimation and TSVD estimation relative to least squares estimation, avoiding the dependency of deviation calculation on the true values. Secondly, we utilize the relative deviation and relative standard deviation to determine the relative decreases of root mean square errors, and the optimal solution is determined by comparing the magnitude of relative decreases. Finally, we verify the feasibility and effectiveness of root mean square error relative comparative method through two sets of experiments.

We detect and identify large-scale geohazards in Nyalam to Zhangmu section of China-Nepal highway based on StaMPS-SBAS InSAR method using 130 ascending and descending orbit images of Sentinel-1A satellite from 2017-04 to 2019-06, combined with GACOS atmospheric correction. The results show that there are 54 hidden danger points in the study area, forming multiple landslide groups, with a maximum deformation rate of 114 mm/a for ascending orbit and 122 mm/a for descending orbit. According to precipitation data, there are 35 hidden danger points where deformation is related to precipitation, and the seasonal characteristics of deformation are obvious. The research results can help to understand trends and causes of surface deformation in this section, enrich the historical records of geohazard points, and provide reference for continuous monitoring of geohazard in the region.

We process 69 Sentinel-1A satellite images using SBAS-InSAR from July 2018 to August 2019, and obtain surface deformation in Shuicheng district, Liupanshui city as dynamic evaluation factors to address the lack of dynamic feature data in traditional landslide susceptibility studies. The results show that, by fusing ten static evaluation factors and InSAR deformation feature data as dynamic evaluation factors, in a weighted information model coupled with analytic hierarchy process(AHP) and information volume method, the model performance improves approximately 13.3% compared to using only static feature data. The area under the ROC curves is 0.756 02 and 0.888 68, respectively. To assess zoning accuracy, we overlay historical disaster sites on two types of zoning maps. Compared to scenarios without the inclusion of deformation features, the introduction of deformation features corrected approximately 12.44% of misclassified areas, significantly enhancing zoning reliability.

We use remote sensing data from the C-band Sentinel-1 and L-band ALOS-2 satellites, which cover the Menyuan area, and apply differential interferometry(D-InSAR), pixel offset tracking(POT), and multi-aperture InSAR(MAI) techniques to obtain the coseismic surface deformation fields of the 2022 Menyuan, Qinghai M_W6.6 earthquake in line-of-sight and azimuth directions. By combining the surface stress-strain model with the variance component estimation(SM-VCE) method, we deduce the three-dimensional coseismic displacement. Furthermore, we use both nonlinear and linear approaches to invert the geometric parameters, such as dip angle and strike, as well as the distribution characteristics of coseismic slip. The results reveal that the earthquake was a left-lateral strike-slip event, with the fault extending northwest-southeast from the epicenter. The maximum horizontal displacement reached 1.58 m, and the predominant sliding occurred within a depth range of 0 to 8 km underground, with a maximum slip of 3.54 m. Based on the inversion results, the moment magnitude of earthquake is estimated to be M_W6.67.

In order to accurately estimate the GNSS velocity field in Jiangxi province and its adjacent area, we select the coordinate time series of 133 GNSS stations in the study area from the crustal movement observation network of China(CMONOC), and deeply study the influence of environmental loading changes on noise models. We calculate the nonlinear change caused by environmental loading, use the maximum likelihood criterion and Bayesian information criterion to determine the optimal noise model of each coordinate time series before and after loading correction, and estimate the velocity uncertainty. The combination of flicker noise and white noise is the main noise model of 133 GNSS stations in Jiangxi and its adjacent area. The noise characteristics of coordinate time series can be directly affected by environmental loading correction. Moreover, the velocity uncertainty of E, N and U directions decrease by 23%, 22% and 21%, respectively, after adding the environmental loading correction. The results show that environmental loading correction is helpful to accurately determine the optimal noise model of GNSS stations in Jiangxi and its adjacent area, and improve the accuracy and reliability of velocity field estimation. It is suggested to consider the influence of environmental loading when calculating GNSS velocity field.

Gravity matching navigation precision is affected by the selection of gravity adaptive region. To effectively select the optimal adaptive area, we use the single feature criterion of information entropy and the multi feature criterion of multi-attribute decision making to evaluate the adaptability of gravity base map. Firstly, we select  gravity standard deviation, correlation coefficient, roughness and gradient, gravity feature abundance and mean cumulative gradient parameters. Secondly, we screen the adaptive and non-adaptive regions in the same sea area using single/multi feature criteria, and verify gravity matching navigation by terrain contour matching(TERCOM) algorithm. Finally, we compare and analyze the matching navigation accuracy of the two methods. The results show that the mismatch rate of single feature criterion in the adaptive/non-adaptive regions is 30% and 20%, respectively. There is no obvious mismatch of multi feature criterion in the adaptive area, and the error is several hundred meters, while there are many mismatches in the non-adaptive area. The results indicate that multi feature analysis criterion can accurately and effectively evaluate the adaptability of gravity matching region compared with single feature analysis criterion.

Using seismic data of Jianghan-Dongting basin and its surrounding areas from historical records to 2021 to analyze the spatiotemporal distribution characteristics of earthquakes, we obtain the relationship between deep tectonics and earthquakes by using the hypoDD algorithm to relocate 788 earthquakes, and analyze the characteristics of tectonic stress field by using the P-wave first motion method to calculate the focal mechanism solutions of M_L≥2.8 earthquakes. The results show that earthquakes are distributed unevenly in space, the seismicity of basin boundary is stronger than that inside basin, and there is an obvious periodic rule of alternating quiet and active in time. The relocated earthquakes are distributed in clusters in NW and NE directions in Ningxiang, Shimen, Yuanan-Dangyang, Nanzhang- Jingmen, and Ezhou-Huangshi, and the seismogenesis of this five regions are closely related to fault tectonic activity. The type of focal mechanism solution is mainly thrust fault, the dominant orientation of P-axis is nearly EW, and its plunge angle is almost horizontal, the orientation of T-axis is mainly SN and NE, and its plunge angle is large. The horizontal collision between the Indian ocean plate and the Eurasian plate result in the formation of a nearly EW tension stress field in the Tibetan plateau, which pushes the basin eastward. In addition, the Philippine sea plate subducts northwestward and the Pacific plate subducts westward, resulting in the formation of a nearly EW compression stress field in the basin, which make the regional fault structure prone to vertical differential movement, and then led to the gestation and occurrence of earthquakes in the Jianghan-Dongting basin and its surrounding areas.

We use the data of 24 stations in the reservoir head area collected by Three Gorges reservoir induced earthquake monitoring system from 2016 to 2018, and use PALM method to analyze microseismic detection and positioning in Three Gorges reservoir area. A total of 12 814 seismic events are detected, which is about 4 times the number of seismic events in Three Gorges seismic network directory during the same period. The complete magnitude decreased from M_L0.8 to M_L0.3, proving that the PALM method is an effective way to improve the detection ability of seismic network. Based on the construction of a more comprehensive microseismic catalog, we delineate the spatial distribution characteristics of seismic activity in Three Gorges reservoir area. The results show that the focal depth in Badong area is relatively shallow, mostly within 5 km, mainly related to non-structural factors such as karst, coal mine collapse, and shallow unloading. The focal depth in Zigui area is relatively deep, mostly within 5 to 15 km, mainly related to the Jiuwanxi and Xiannüshan faults in the reservoir area.

We reveal the physical characteristics of metal zero-length spring for marine gravimeter, describe the technology of developing metal zero-length spring based on Fe-Ni constant elastic alloy, and systematically summarize the key development process and difficulties. We develop a series of metal zero-length springs for marine gravimeters with excellent performance and good zero-length state.

According to IEC 60751 and ASTM E644-11 international standards, we study the thermal hysteresis of quartz crystal type, platinum resistance type and thermistor type seismic water temperature observation instruments in the temperature ranges of 0 ℃ to 100 ℃, 0 ℃ to 70 ℃ and 0 ℃ to 50 ℃, and define the heat leakage effect of local immersion calibration. Further, we analyze the contribution of both to measurement uncertainty, and identify the instrument drift characteristics. The results show that the thermal hysteresis of thermometer reduces with the decrease of measuring point temperature, and the maximum value is 0.025 5 ℃(platinum resistance type, 50 ℃ measuring point). At the same temperature point, the thermal hysteresis of quartz crystal type thermometer is less than that of platinum resistance and thermistor types. When the local immersion method is used for calibration, the immersion depth of temperature sensing element should not be less than 30 cm, and the maximum heat leakage effect is about 0.01 ℃(100 ℃ measuring point). The thermal hysteresis component contributes the most to measurement uncertainty of platinum resistance thermometer(about 60.7%), and quartz crystal thermometer shows the best measurement accuracy. The measurement results of instrument drift for different sensor types are close, with a range of only 0.000 3 ℃/24 h. In the future, the instrument stability can be improved, and the heat leakage effect can be reduced, by replacing the temperature sensing element, optimizing the design, upgrading the process, using a large depth constant temperature bath, heat preservation device and modifying formula.