This study investigated the nonlinear changes in the vertical motion of 411 GNSS reference stations situated in mainland China and assessed the influence of the environmental load on their vertical displacement. The researchers evaluated the effect of environmental load by calculating the change in annual cycle amplitude before and after its removal, focusing on its impact across regions with distinct foundation types. The results demonstrate that removing the environmental load led to a considerable reduction of approximately 50.25% in the annual cycle amplitude of vertical motion for GNSS reference stations in mainland China. This reduction in amplitude improved the positioning accuracy of the stations, with the highest WRMS reduction being 2.72 mm and an average reduction of 1.03 mm. The most significant impact was observed in the southwestern, northern, and northwestern regions, where the amplitude experienced a notable decrease. Conversely, the southeastern region exhibited a corresponding increase in amplitude. This article innovatively explored the effects of environmental loads on diverse foundation types. When categorizing GNSS reference stations based on their foundation type, namely, bedrock, 18 m soil layer, and 4–8 m soil layer stations, this study found that removing the environmental load resulted in reductions in annual cycle amplitudes of 49.37%, 59.61%, and 46.48%, respectively. These findings indicate that 18 m soil layer stations were more susceptible to environmental load-induced vertical motion. In conclusion, the impact of the environmental load was crucial when analyzing the vertical motion of GNSS reference stations in mainland China, as it was essential for establishing a high-precision coordinate reference framework and studying the tectonic structure of the region.

Synthetic aperture radar interferometry (InSAR) measurement technology is a new remote sensing technology that can effectively monitor slight land deformation. Compared with traditional monitoring technology, InSAR technology has the advantages of wide coverage, all-weather and low cost, providing a technical means of high-resolution, high-precision and low-cost for hidden geological hazard identification and deformation monitoring along pipelines. For purpose of this paper, considering the complex terrains of research area, SBAS-InSAR technology was adopted for deformation information extraction. This technology performs better in identifying fast deformation by controlling temporal and perpendicular baseline thresholds, which is able to prevent temporal de-coherence caused by fast deformation. In this paper, we performed deformation time-series comprehensive processing and analysis on gas pipeline based on Sentinel-1 image data through short baseline data processing, obtained deformation results in terms of time series by calculating linear deformation rate and nonlinear deformation phase based on residual phase separation nonlinear deformation phase and atmospheric effect phase, and then conduct parameter calculation, linear deformation rate calibration, accumulative deformation quantity calculation, etc. Finally, we extracted pipeline deformation quantities from 2020 to 2022. The result showed that, the land deformation rate of the ascending track data during this period ranges from -43 mm/year to 25 mm/year, and that of the descending track data from -66 mm/year to 33 mm/year. The results show that the area along the gas pipeline is in stable condition on the whole, deformation mainly occurred along a section in the northwest of Haidian District, and a large quantity of deformation occurred since January of 2020 until December of 2021, with the maximum deformation quantity of -70mm, This result provided a reliable reference for safety monitoring and repair & maintenance of the gas pipeline.Further more, The possible causes of the deformations mainly include surface subsidence, groundwater mining and such factors. Precautionary measures need to be enhanced for the area at potential risk of surface subsidence, to get rid of the threat of sudden geological disasters and resulting losses particularly in extreme weather conditions. At the same time, terrains and geographical realities should be considered to further determine whether there exists any hidden geological hazard like unstable slope, surface subsidence or landslide and decide the potential risk the pipeline is faced in combination with actual conditions.

The thermoelastic deformation of GNSS monuments and foundations is a significant contributor to the vertical nonlinear variations observed in the GNSS coordinate time series. A rigorous thermoelastic effect model, which takes into account the diversity of monument depths and foundation types of the reference stations, was proposed in this paper to quantify the influence of thermal expansion on the vertical displacement using 409 GNSS reference stations in Mainland China. The periodic characteristics of the GNSS vertical time series, GREL time series, and thermal expansion effect show a higher consistency between the GREL time series and the thermal expansion effects. The annual amplitude of thermal expansion for GNSS reference stations across Mainland China ranges from 0.2 mm to 1.9 mm, increasing with latitude, with a characteristic distribution of lower values in the south and higher in the north. After applying thermal expansion corrections, 79.2% of the reference stations across Mainland China exhibit a decreasing trend in amplitude, with an average reduction of 0.4 mm. Regional variability in the correction effects is significant: the largest corrections occur in Central China, followed by Northwest China and East China, while corrections in Southwest China, South China, and North China are comparatively smaller, and the corrections in Northeast China are negative. The thermal expansion correction demonstrates similar effectiveness across different types of foundational reference stations. A reduction in amplitude was observed in 78.5% of bedrock monument stations and 80.2% of soil monument stations, with a difference of 1.7% between the two. The average reduction in amplitude variation for different types was the same at 0.4 mm, indicating a comparable effect. Notably, the correction effect varies significantly based on the burial depth of the GNSS monuments, with the largest correction observed for the 5.5 m soil monument stations, followed by 2 m bedrock monument stations, 18 m soil monument stations, and 7.5 m soil monument stations. The correction effect for 8.5 m soil monument stations is negative.

Significant spatial heterogeneity of tropospheric water vapor over the Tibetan Plateau, particularly along the vertical dimension, presents a major challenge to traditional tropospheric wet delay models used in GNSS applications across large height ranges. To address this issue, we developed a refined Tibetan zenith wet delay (ZWD) model based on pressure-level ERA5 reanalysis data with a spatial resolution of 0.25°, providing ZWD estimates at arbitrary times and heights. The model adopts an improved vertical correction in which ZWD vertical profiles are represented by a cubic polynomial height-correction function. The polynomial coefficients are estimated at each ERA5 grid node using ERA5-derived ZWD profiles and are further parameterized using harmonics up to the semidiurnal term to characterize temporal variability. ZWD at user locations is obtained through bilinear interpolation of the four surrounding grid nodes, ensuring continuous spatial and vertical coverage over Tibet. Validation using ERA5- and radiosonde-derived ZWDs shows that the TZ model achieves lower bias and reduced root-mean-square error (RMSE) than the widely used GPT3 model at both surface and elevated layers. These results indicate stable performance of the model across the full altitude range. The proposed model can be readily integrated into GNSS positioning frameworks. In precise point positioning (PPP), it may be introduced as a virtual observation of ZWD, with the model RMSE used to define the initial measurement-noise covariance. As the model provides a priori information rather than true observations, a time-varying down-weighting strategy is applied so that the ZWD estimation progressively relies on actual GNSS observations. In network real-time kinematic (NRTK) applications with large height differences, model-derived ZWD combined with mapping functions can be used to mitigate height-dependent double-differenced tropospheric delay residuals. This improves positioning accuracy, especially in the vertical component.

Railway reference stations are characterized by long span, strip distribution, cross-regional service, weak graphical structure, and requiring high monitoring precision. In view of this, the traditional modeling approaches for reference uniformity have become no longer quite applicable. Currently, coordinates reference maintenance is conducted separately in each area, so that there exist differences among various reference stations in respect of data processing software, mathematical physical model, solution strategy, adjustment method, and revision cycle. This causes systematic deviation in satellite navigation and positioning service reference between different areas. To ensure the uniformity and timeliness of high-precision location-based service reference of national railways, this study is intended to simulate cross-region, strip, isoheight-shape and Y-shape layout modes based on the actual situation of railway observation network, and implement selection of reference station control points, networking solution scheme design and result analysis considering the reference uniformity solution requirements of different layout modes to propose an inclusive coordinates reference uniformity solution scheme applicable for various strip layout modes and provide a practicable reference for the coordinates reference uniformity solution of reference stations of railways and shipping lanes. This is significant to the coordinates uniformity and regular updating maintenance of high-precision service datum network of railways.