Geodesy and Geodynamics最新文献

Combining GPS and BDS technology to monitor the deformation of long-span railway bridges with stricter deformation control requirements is of significance to the safety and control of the bridge and the safety of railway traffic. Previous studies have ignored the influence of coloured noise in the deformation time series. This is not conducive to accurate deformation analysis of long-span railway bridges. Therefore, GPS, BDS and GPS/BDS monitoring data of Ganjiang Bridge located in Ganzhou city, Jiangxi Province, China are adopted in this paper to filter the coloured noise in the deformation time series by principal component analysis (PCA), and the influence of coloured noise on the deformation analysis results of railway bridge is analysed. The experimental results show that the diurnal temperature difference causes the mid-span and the tower of the railway cable-stayed bridge to deform with a period of about one day in the vertical and longitudinal directions, respectively. Ignoring colored noise will make the uncertainty of the deformation parameter estimation overly optimistic. PCA can significantly reduce the coloured noise, and thus reduce the uncertainty of deformation parameter estimation by about 73%. Moreover, the average difference between the daily periodic motion amplitudes of the monitoring points obtained by using GPS and BDS deformation time series is 1.65 mm. The use of GPS/BDS deformation time series is not only helpful to reduce the influence of coloured noise, but also can reduce the difference between amplitude analysis results obtained from GPS and BDS deformation time series.

The research aims to study recent Antarctic plate kinematics based on Global Navigation Satellite System (GNSS) data. The research covers 60 continuous GNSS stations located on the Antarctic plate during 1994–2021. We determine the components of horizontal displacement vectors of these GNSS stations and construct the schematic map of their distribution. The results indicate that the direction of velocity vectors of horizontal displacements has a rotational nature in clockwise order. The analysis of deformation processes shows that a gradual decrease in the horizontal strain rates, maximum shear strain and area strain is taking place from west to east, in the direction of West Antarctica – the Transantarctic Mountains – East Antarctica. The absolute rotation pole of the Antarctic plate in the ITRF2014/IGS14 reference frame has been determined, and the obtained values are in good agreement with recent plate models.

Research on strain anomalies and large earthquakes based on temporal and spatial crustal activities has been rapidly growing due to data availability, especially in Japan and Indonesia. However, many research works used local-scale case studies that focused on a specific earthquake characteristic using knowledge-driven techniques, such as crustal deformation analysis. In this study, a data-driven-based analysis is used to detect anomalies using displacement rates and deformation pattern features extracted from daily global navigation satellite system (GNSS) data using a machine learning algorithm. The GNSS data with 188 and 1181 continuously operating reference stations from Indonesia and Japan, respectively, are used to identify the anomaly of recent major earthquakes in the last two decades. Feature displacement rates and deformation patterns are processed in several window times with 2560 experiment scenarios to produce the best detection using tree-based algorithms. Tree-based algorithms with a single estimator (decision tree), ensemble bagging (bagging, random forest and Extra Trees), and ensemble boosting (AdaBoost, gradient boosting, LGBM, and XGB) are applied in the study. The experiment test using real-time scenario GNSSdailydatareveals high F1-scores and accuracy for anomaly detection using slope windowing 365 and 730 days of 91-day displacement rates and then 7-day deformation pattern features in tree-based algorithms. The results show the potential for medium-term anomaly detection using GNSS data without the need for multiple vulnerability assessments.

Studying the dynamic changes in the coastline of the northeastern Caspian Sea is significant since the level of the Caspian is unstable, and the coastline change can cause enormous damage to the ecology, economy, and population of the coastal part of Kazakhstan. In this work, we use remote sensing and Geographic Information System (GIS) technologies to study the changes in the coastline of the northeastern Caspian Sea and predict the extent of flooding with increasing water levels. The proposed methodology for creating dynamic maps can be used to monitor the coastline and forecast the extent of flooding in the area. As a result of this work, the main factors affecting changes in the coastline were identified. After analyzing the water level data from 1988 to 2019, it was revealed that the rise in water level was observed from 1980 to 1995. The maximum sea level rise was recorded at −26.04 m. After that, the sea level began to fall, and between 1996 and 2009, there were no significant changes; the water level fluctuated with an average of −27.18 m. Then, a map of the water level dynamics in the Caspian Sea from 1988 to 2019 was compiled. According to the dynamics map, water level rise and significant coastal retreat were revealed, especially in the northern part of the Caspian Sea and the northern and southern parts of Sora Kaydak. The method for predicting the estimated flooding area was described. As a result, based on a single map, the flooding area of the northeast coast was predicted. A comparative analysis of Landsat and SRTM data is presented.

An earthquake called the M_W7.2 “El Mayor Cucapah” earthquake on April 4, 2010 has been analyzed for seismic precursor. The changes in the lineament system concerning its pattern and time intervals were analyzed during the earthquake preparation period and occurrence using the automated lineament detection method. The Landsat 5 TM images were processed using LESSA and ADALGEO software obtaining similar results. The statistical analysis revealed the stress accumulation due to plate interaction during earthquake formation. The study shows that the number of extracted lineaments changes rapidly about 23 months before the earthquake, and the systems return to the initial stage after 23 months. Most lineaments coincide with the extension of the San Andreas Fault as NW direction is the dominant trend. Thus, it can be concluded that the featural changes within the Rose diagram corresponding to the different strokes direction along with oriented elongation lines as disclosed in the present study using satellite images could be identified as a mid-term and/or short-term precursors of the earthquake. However, even though the dynamism of the El Mayor Cucapah earthquake is found in the extracted lineaments, it is possible to isolate more significant earthquakes even if new ones appear near the zone. Moreover, using two algorithms for lineament detection allows for the tectonics to corroborate the obtained lineaments and dynamism.

The study of inter-system bias (ISB) is important for multi-system fusion and the performance of different signal compatibility. In this paper, the stability of ISB at the BDS3/BDS2 receiver end is calculated and analyzed for different time spans (DOY 060∼090 in 2021) from a total of 31 MGEX and iGMAS stations. We adopted two estimation strategies, random walk and constant approach, using the precision products of orbit and clock bias provided by WUM, the influence of which on ISB was also analyzed. Our results showed that the ISB value varied little within a day, and the mean of daily ISB standard deviation was only 0.037 m when the observation condition was good. The signal reception was continuous, indicating a high ISB stability for one day. If extending the time series to one month, however, the ISB standard deviation calculated by constant approach, in which a constant ISB is estimated on a daily basis was about 0.1 m, and the results of adjacent days were not continuous, with no apparent pattern. Concerning the random walk approach, the obtained ISB time series also had a jump, and the conclusion was the same as that of the constant strategy. Besides, receiver types showed a strong regularity in ISB numerical situation, and the distribution of ISB values corresponding to the same receiver type was relatively close. Therefore, we conclude that the ISB parameters remain stable in the short term (one day) and less stable in the long-term period. It is recommended that the ISB term should be set as a constant estimate every day in BDS3/BDS2 solutions, regardless of receiver type consistency.

Temperature and pressure play key roles in Global Navigation Satellite System (GNSS) precipitable water vapor (PWV) retrieval. The National Aeronautics and Space Administration (NASA) and European Center for Medium-Range Weather Forecasts (ECMWF) have released their latest reanalysis product: the modern-era retrospective analysis for research and applications, version 2 (MERRA-2) and the fifth-generation ECMWF reanalysis (ERA5), respectively. Based on the reanalysis data, we evaluate and analyze the accuracy of the surface temperature and pressure products in China using the the measured temperature and pressure data from 609 ground meteorological stations in 2017 as reference values. Then the accuracy of the two datasets and their performances in estimating GNSS PWV are analyzed. The PWV derived from the pressure and temperature products of ERA5 and MERRA-2 has high accuracy. The annual average biases of pressure and temperature for ERA5 are −0.07 hPa and 0.45 K, with the root mean square error (RMSE) of 0.95 hPa and 2.04 K, respectively. The annual average biases of pressure and temperature for MERRA-2 are −0.01 hPa and 0.38 K, with the RMSE of 1.08 hPa and 2.66 K, respectively. The accuracy of ERA5 is slightly higher than that of MERRA-2. The two reanalysis data show negative biases in most regions of China, with the highest to lowest accuracy in the following order: the south, north, northwest, and Tibet Plateau. Comparing the GNSS PWV calculated using MERRA-2 (GNSS MERRA-2 PWV) and ERA5 (GNSS ERA5 PWV) with the radiosonde-derived PWV from 48 co-located GNSS stations and the measured PWV of the co-location radiosonde stations, it is found that the accuracy of GNSS ERA5 PWV is better than that of GNSS MERRA-2 PWV. These results show the different applicability of surface temperature and pressure products from MERRA-2 and ERA5 data, indicating that both have important applications in meteorological research and GNSS water vapor monitoring in China.

The use of geodetic observation data for seismic fault parameters inversion is the research hotspot of geodetic inversion, and it is also the focus of studying the mechanism of earthquake occurrence. Seismic fault parameters inversion has nonlinear characteristics, and the gradient-based optimizer (GBO) has the characteristics of fast convergence speed and falling into local optimum hardly. This paper applies GBO algorithm to simulated earthquakes and real LuShan earthquakes in the nonlinear inversion of the Okada model to obtain the source parameters. The simulated earthquake experiment results show that the algorithm is stable, and the seismic source parameters obtained by GBO are slightly closer to the true value than the multi peak particle swarm optimization (MPSO). In the 2013 LuShan earthquake experiment, the root mean square error between the deformation after forwarding of fault parameters obtained by the introduced GBO algorithm and the surface observation deformation was 3.703 mm, slightly better than 3.708 mm calculated by the MPSO. Moreover, the inversion result of GBO algorithm is better than MPSO algorithm in stability. The above results show that the introduced GBO algorithm has a certain practical application value in seismic fault source parameters inversion.

This study assesses the changes in land use/land cover (LULC) and land surface temperature (LST) to identify their impacts from 2000 to 2020 along the coast of Kanyakumari district, India using remote sensing techniques. Landsat images are used to estimate the LULC changes and the MODIS data for LST. The Maximum Likelihood Classification (MLC) method is used, and the LULC is classified into six categories: Agriculture Land, Barren Land, Salt Pan, Sandy Beach, Settlement, and Waterbody. Within the two decades of the present change detection study, upheave in the Settlement area of 49.89% is noticed, and the Agriculture Land is exploited by 20.09%. Salt Pan emits a high LST of 31.57 °C, and the Waterbodies are noticed with a low LST of 28.9 °C. However, the overall rate of LST decreased by 0.56 °C during this period. This study will help policymakers make appropriate planning and management to overcome the impact of LULC and LST in the forthcoming years.

Since 2008 a network of five sea-level monitoring stations was progressively installed in French Polynesia. The stations are autonomous and data, collected at a sampling rate of 1 or 2 min, are not only recorded locally, but also transferred in real time by a radio-link to the NOAA through the GOES satellite. The new ET34-ANA-V80 version of ETERNA, initially developed for Earth Tides analysis, is now able to analyze ocean tides records. Through a two-step validation scheme, we took advantage of the flexibility of this new version, operated in conjunction with the preprocessing facilities of the Tsoft software, to recover corrected data series able to model sea-level variations after elimination of the ocean tides signal. We performed the tidal analysis of the tide gauge data with the highest possible selectivity (optimal wave grouping) and a maximum of additional terms (shallow water constituents). Our goal was to provide corrected data series and modelled ocean tides signal to compute tide-free sea-level variations as well as tidal prediction models with centimeter precision. We also present in this study the characteristics of the ocean tides in French Polynesia and preliminary results concerning the non-tidal variations of the sea level concerning the tide gauge setting.