Geodesy and Geodynamics最新文献

Islands and the mainland are separated by seas, and the distances between them might be so long that the height on the mainland cannot be exactly translated to the islands, resulting in different height systems on the mainland and the islands. In this study, we used astrogeodetic deflections of the vertical and ellipsoidal heights of points on the mainland and island near their coastlines to implement height connection across sea areas. First, the modeled gravity and modeled astrogeodetic vertical deflections of segmentation points along connecting routes over the sea between the mainland and the island were determined by Earth Gravity Model (EGM), and the ellipsoidal heights of segmentation points were determined by the satellite altimetry data sets. Second, we used a linear interpolation model to increase the precision of the vertical deflections of segmentation points. Third, we computed the geopotential difference of points between the mainland and the island using a method derived from geopotential theory and the astronomical leveling principle. Finally, we estimated the normal height of the point on the island using the geopotential-difference iterative computation approach. Using observed data of normal heights, ellipsoidal heights, and astrogeodetic vertical deflections referring to height sites in Qingdao, Shandong Province, we conducted a numerical experiment involving the normal height connection across sea regions. We determined the data of the ellipsoidal heights and gravity of segmentation points along the connecting route across the water in the numerical experiment using DTU10. The distance of the height connection across the sea was approximately 10.5 km. According to China's official leveling specifications, the experimental results met the criterion of third-class leveling precision.

This paper investigates the correlation between tidal stress and earthquakes for periods ranging from hours to months in the limited zone of the Palu region (Central Sulawesi, Indonesia). Through Schuster and binomial tests, we examined the relation between the seismicity (time density of seismic events) and tidal potential arising from the Moon and Sun, using all tidal components simultaneously and focusing on the estimation of specific terms. The results show significant correlations between the seismicity and tidal potential for S₂ (0.5 d) and O₁ (1.075 d) tidal components in the case of solely isolated earthquake events, particularly for shallow earthquakes. Meanwhile, there is a strong relationship between aftershocks and tidal components larger than the M_f period (13.661 d). Finally, the analysis of the temporal variation of the earthquake-tide relation reveals an optimal correlation for about six years before the 2018 great Palu earthquake. The correlation becomes insignificant afterwards.

The gravity and magnetic data can be adopted to interpret the internal structure of the Earth. To improve the calculation efficiency during the inversion process and the accuracy and reliability of the reconstructed physical property models, the triple strategy is adopted in this paper to develop a fast cross-gradient joint inversion for gravity and magnetic data. The cross-gradient constraint contains solving the gradients of the physical property models and performing the cross-product calculation of their gradients. The sparse matrices are first obtained by calculating the gradients of the physical property models derived from the first-order finite difference. Then, the triple method is applied to optimize the storages and the calculations related to the gradients of the physical property models. Therefore, the storage compression amount of the calculations related to the gradients of the physical property models and the cross-gradient constraint are reduced to one-fold of the number of grid cells at least, and the compression ratio increases with the increase of the number of grid cells. The test results from the synthetic data and field data prove that the structural coupling is achieved by using the fast cross-gradient joint inversion method to effectively reduce the multiplicity of solutions and improve the computing efficiency.

High-precision polar motion (PM) prediction is of important significance in astronomy, geodesy, aviation, hydrographic mapping, interstellar navigation, and so on. SSA can effectively extract the trend and period terms of PM,in the process of achieving high-precision medium- and long-term polar motion prediction, it is necessary to solve the end effect problem and overfitting problem of SSA forecasting method; therefore, ARMA was applied to decreasethe end effect, and a suitable combination of reconstructed components was determined to avoid the high variance reaction of SSA overfitting. Based on the decomposition and reconstruction of the PM by SSA, the reconstructed components are determined to participate in the SSA iterative fitting model according to the variance contribution rate. The combination of the reconstructed components representing the polar motion period term and the trend term is determined according to the correlation analysis of the selected reconstructed components. After the above work, the principal component prediction sequence is obtained by fitting the period term and the trend term to convergence, respectively, and then, the SSA end effect is modified, and the residual term is predicted based on ARMA. The test results show that he prediction accuracy of SSA + ARMA at the front of the X and Y directions are improved by 96.90% and 97.53% compared with those of SSA, respectively, and the forecast accuracy of 365 days are improved by 37.93% and 19.53% in the X and Y directions compared with those of Bulletin A, respectively.

To estimate the parameters of the mixed additive and multiplicative (MAM) random error model using the weighted least squares iterative algorithm that requires derivation of the complex weight array, we introduce a derivative-free cat swarm optimization for parameter estimation. We embed the Powell method, which uses conjugate direction acceleration and does not need to derive the objective function, into the original cat swarm optimization to accelerate its convergence speed and search accuracy. We use the ordinary least squares, weighted least squares, original cat swarm optimization, particle swarm algorithm and improved cat swarm optimization to estimate the parameters of the straight-line fitting MAM model with lower nonlinearity and the DEM MAM model with higher nonlinearity, respectively. The experimental results show that the improved cat swarm optimization has faster convergence speed, higher search accuracy, and better stability than the original cat swarm optimization and the particle swarm algorithm. At the same time, the improved cat swarm optimization can obtain results consistent with the weighted least squares method based on the objective function only while avoiding multiple complex weight array derivations. The method in this paper provides a new idea for theoretical research on parameter estimation of MAM error models.

Mount Semeru, an active volcano in East Java, Indonesia, erupted on December 4, 2021, following extreme rainfall that caused an avalanche of hot pyroclastic flows and lava. The tropospheric conditions and dominant particle components in the atmosphere can be monitored using Global Navigation Satellite System (GNSS) technology and remote sensing satellites. GNSS signal propagation delay in Precise Point Positioning (PPP) processing can be used to determine Zenith Tropospheric Delay (ZTD) and Precipitable Water Vapor (PWV) variables so that atmospheric conditions can be generated. In addition, by using remote sensing satellite data, it is possible to obtain rainfall data with high temporal resolution as well as the dominant particle and gas content values during eruptions. During the eruption period, the high value of PWV was dominated by the high intensity of precipitation during the rainy season. High rainfall before the eruption caused activity inside the mountain to increase, which occurred in avalanche type eruption. Apart from that, the atmosphere around Semeru was also dominated by SO₂ content, which spreaded for tens of kilometers. SO₂ content began to be detected significantly by remote sensing sensors on December 7, 2021. In this study, deformation and atmospheric monitoring were also carried out using low-cost GNSS at the Semeru Monitoring Station on September 9–15, 2022. The results of the ZTD and ZWD values show the dominance of the wet component, which is directly proportional to rainfall activity in this period.

Singular spectrum analysis is widely used in geodetic time series analysis. However, when extracting time-varying periodic signals from a large number of Global Navigation Satellite System (GNSS) time series, the selection of appropriate embedding window size and principal components makes this method cumbersome and inefficient. To improve the efficiency and accuracy of singular spectrum analysis, this paper proposes an adaptive singular spectrum analysis method by combining spectrum analysis with a new trace matrix. The running time and correlation analysis indicate that the proposed method can adaptively set the embedding window size to extract the time-varying periodic signals from GNSS time series, and the extraction efficiency of a single time series is six times that of singular spectrum analysis. The method is also accurate and more suitable for time-varying periodic signal analysis of global GNSS sites.

Different from other normal modes of the Earth's free oscillation that depend on all the six components (M_rr, M_tt, M_pp, M_rt, M_rp, and M_tp) of the centroid moment tensor, the amplitudes of the radial modes depend on the M_rr component (e.g., scalar moment (M₀), dip (δ), and slip (λ)) and hypocenter depth of the focal mechanism, and hence can be easily used to constrain these parameters of the focal mechanism. In this study, we use the superconducting gravimeter (SG) records after the 2011 Tohoku earthquake to analyze the radial modes ₀S₀ and ₁S₀. Based on the solutions of the focal mechanism provided by the GCMT and USGS, we can obtain the theoretical amplitudes of these two radial modes. Comparing the theoretical amplitudes with the observation amplitudes, it is found that there are obvious differences between the former and the latter, which means that the GCMT and USGS focal mechanisms cannot well represent the real focal mechanism of the 2011 event. Taking the GCMT solution as a reference and changing the depth and the three parameters of the M_rr moment, the scalar moment (M₀) and the dip (δ) have significant influences, but the effects of the slip (λ) and the depth are minor. After comparisons, we provide a new constraint (M₀ = 5.8 ± 0.09 × 10²² N·m, δ = 10.1 ± 0.08°, λ = 88°, and depth = 20 km) for the focal mechanism of the 2011 event. In addition, we further determine the center frequency (1.631567 ± 2.6e^-6 mHz) and quality factor (2046.4± 50.1) of the ₁S₀ mode.

Almost all European countries use at least two horizontal reference systems, which allow them to minimize all risks when changing the coordinate system. The first system is used for the needs of the national survey in general, and also for technical applications in engineering surveys. A brief description of this system can be written by the formula: Geocentric Ellipsoid (GRS80) + Projection (UTM). More than half of the European countries for the second national systems use the GRS80 geocentric ellipsoid together with a projection other than UTM, some of them continue to use the projection of the old coordinate systems. The rest of the countries, excluding Ukraine, adapted the existing national coordinate systems to modern requirements, removing deformations from them concerning the ETRS89. A small number of European countries have implemented the GRS80 geocentric ellipsoid together with the UTM projection for cadastral surveys and topographic maps with a scale of 1:5000 and larger. Only one country, Ukraine, chose a variant for the new coordinate system (UCS2000), which is briefly written by the formula: Old Not Geocentric Ellipsoid + New Projection. The analysis of modern coordinate systems of Europe made it possible to formulate two variants of the future coordinate system of Ukraine based on a geocentric ellipsoid. It is shown that the transition to a geocentric ellipsoid will change the coordinates and heights of the points, but practically will not change the distance between the points and the area of the parcels.

Alterations made to the natural ground surface and the anthropogenic activity elevate the surface and air temperature in the urban areas compared with the surrounding rural areas, known as urban heat island effect. Thermal remote sensors measure the radiation emitted by ground objects, which can be used to estimate the land surface temperature and are beneficial for studying urban heat island effects. The present study investigates the spatial and temporal variations in the effects of urban heat island over Tiruchirappalli city in India during the summer and winter seasons. The study also identifies hot spots and cold spots within the study area. In this study, a significant land surface temperature difference was observed between the urban and rural areas, predominantly at night, indicating the presence of urban heat island at night. These diurnal land surface temperature fluctuations are also detected seasonally, with a relatively higher temperature intensity during the summer. The trend line analysis shows that the mean land surface temperature of the study area is increasing at a rate of 0.166 K/decade with p less than 0.01. By using the spatial autocorrelation method with the urban heat island index as the key parameter, hot spots with a 99 percent confidence level and a 95 percent confidence level were found within the urban area. A hot spot with 95 and 90 percent confidence level was identified outside the urban area. This spike in temperature for a particular region in the rural area is due to industry and the associated built-up area. The study also identified cold spots with a 90 percent confidence level within the rural area. However, cold spots with a 95 and 99 percent confidence level were not identified within the study area.