Journal of Geodesy最新文献

{"title":"Two methods for spherical harmonic analysis of area mean values over equiangular blocks based on exact spherical harmonic analysis of point values","authors":"Rong Sun, Zhicai Luo","doi":"10.1007/s00190-024-01900-y","DOIUrl":"https://doi.org/10.1007/s00190-024-01900-y","url":null,"abstract":"<p>Currently, the least-square estimation method is the mainstream method for recovering spherical harmonic coefficients from area mean values over equiangular blocks. Since the least-square estimation method involves matrix inversion, it requires great computation power when the maximum degree to be solved is large. In comparison, numerical quadrature methods are faster. Recent numerical quadrature methods designed for spherical harmonic analysis of area mean values over blocks delineated by equiangular and Gaussian grids are both fast and exact for band-limited data. However, for band-limited area mean values over an equiangular grid that has <span>(N)</span> blocks along the colatitude direction and <span>(2N)</span> blocks along the longitude direction, the maximum degree that can be recovered by using current exact numerical quadrature methods is no larger than <span>(N/2-1)</span>. In this study, by using Lagrange’s method for polynomial interpolation, recently proposed numerical quadrature methods that employ the recurrence relations for the integrals of the associated Legendre’s functions are modified into two new methods. By using these methods, the maximum degree of recovered spherical harmonic coefficients is <span>(N-1)</span>. The results show that these newly proposed methods are comparable in computation speed with the current numerical quadrature methods and are comparable in accuracy with the least-square estimation method for both band-limited and aliased data. Moreover, solving linear systems is not necessary for these two new methods. The error characteristics of these two new methods are quite different from those of methods that employ least-square methods. The spherical harmonic coefficients recovered using these new methods can effectively supplement those recovered using least-square methods.</p>","PeriodicalId":54822,"journal":{"name":"Journal of Geodesy","volume":"87 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142566170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On theoretical and practical analyses of BDS-3/Galileo/GPS all-in-view and PPP time transfer with the consideration of satellite clock biases","authors":"Dong Zhang, Fu Zheng, Meng Wang, Yuanhui Lin, Liangcheng Deng, Zhen Wang, Chuang Shi","doi":"10.1007/s00190-024-01904-8","DOIUrl":"https://doi.org/10.1007/s00190-024-01904-8","url":null,"abstract":"<p>Benefited from the advantage of high precision, wide area and low cost, the time transfer method based on precise point positioning (PPP) has become a popular technique for the remote clock comparisons. Although the time reference to which satellite clocks are referred can be eliminated by the difference between stations, the effect of satellite clock biases on the estimation of receiver clock offset is always ignored for PPP time transfer. Considering the PPP technique is extended from the all-in-view (AV) by the full use of precise carrier phase observables, a method to evaluate the effects of satellite clock biases on AV and PPP time transfer is proposed first. Then, the GPS, Galileo and BDS-3 time transfer results with different international GNSS Service (IGS) precise products are compared to verify the negative effects of satellite clock biases on AV and PPP time transfer. In our experiment, precise orbit and clock products provided by GFZ (German Research Centre for Geosciences), ESA (European Space Agency) and COD (Center for Orbit Determination in Europe) are used to obtain the clock comparison results of nine time links, including three short baselines, three medium baselines and three long baselines. The results show that the effects of satellite clock biases on AV and PPP time transfer are related to the magnitude of satellite clock biases and the baseline distance between stations. After removing the satellites with larger satellite clock biases, we assess the negative effects of satellite clock biases on AV and PPP time transfer for GPS, Galileo and BDS-3, respectively. By using GFZ, COD and ESA precise products for AV time transfer, the inconsistency of GPS and Galileo time transfer results caused by satellite clock biases is below 0.2 ns for long baseline. Due to the larger satellite clock biases for BDS-3, the inconsistency of BDS-3 AV time transfer results caused by satellite clock biases could reach 0.3 ns for medium baseline and even reach 0.9 ns for long baseline. For GPS and Galileo PPP time transfer, the inconsistency of time transfer results is below 0.05 ns for long baseline. However, the inconsistency of BDS-3 PPP time transfer results can only achieve 0.11 ns for medium baseline and 0.3 ns for long baseline. Thus, it is concluded that the satellite clock biases of BDS-3 precise satellite clock products need refining to improve the performance of BDS-3 PPP time transfer.</p>","PeriodicalId":54822,"journal":{"name":"Journal of Geodesy","volume":"4 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142519528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A new approach to improve the Earth's polar motion prediction: on the deconvolution and convolution methods","authors":"CanCan Xu, ChengLi Huang, YongHong Zhou, PengShuo Duan, QiQi Shi, XueQing Xu, LiZhen Lian, XinHao Liao","doi":"10.1007/s00190-024-01890-x","DOIUrl":"https://doi.org/10.1007/s00190-024-01890-x","url":null,"abstract":"<p>Combining the Liouville equations for polar motion (PM) with forecasted geophysical effective angular momentum (EAM) functions can significantly improve the accuracy of Earth's PM predictions. These predictions rely on deconvolution and convolution methods. Deconvolution derives the geodetic EAM function from the PM observations, while convolution uses both the geodetic and geophysical EAM functions to reproduce and predict the PM values. However, there are limitations in existing numerical realisations of deconvolution and convolution that must be addressed. These limitations include low-frequency biases, high-frequency errors, and edge errors, which can negatively impact the accuracy of PM prediction. To overcome these concerns, we develop the Convolution Least Squares (Conv-LS) scheme through a multi-perspective analysis in the frequency domain, PM domain, and EAM domain. By comparing representative approaches for reproducing three different PM series (IERS C01, IERS C04, and IGS) with varying sampling intervals (18.25 days, daily, and 6 h), we demonstrate that the Conv-LS scheme can effectively eliminate the usually present spurious signals and also integrate high-accuracy deconvolution algorithms to reduce reproduced errors further. Compared to the traditional approacsh (using a low-accuracy discrete PM equation for deconvolution and numerical integration for convolution), our new approach (utilising a high-accuracy deconvolution algorithm along with the Conv-LS scheme for convolution) reduces the standard deviations of the residuals' x-component by 31.0%, 60.1%, and 13.7% for C01, C04, and IGS PM series, respectively, while also reducing the y-component by 17.3%, 47.0%, and 14.0%, respectively. These results highlight the superiority of the Conv-LS scheme, leading us to recommend it for practical applications.</p>","PeriodicalId":54822,"journal":{"name":"Journal of Geodesy","volume":"34 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142489994","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An accurate and lightweight calculation for the high degree truncation coefficient via asymptotic expansion with applications to spectral gravity forward modeling","authors":"Linshan Zhong, Hongqing Li, Qiong Wu","doi":"10.1007/s00190-024-01895-6","DOIUrl":"https://doi.org/10.1007/s00190-024-01895-6","url":null,"abstract":"<p>The truncation coefficient is widely utilized in non-global coverage computations of geophysics and geodesy and is always altitude dependent. As the two commonly used calculation methods for truncation coefficients, i.e., the spectral form and the recursive formula, both suffer from decreasing precision caused by high-altitude, leading to slow convergence for the former and numerical instability recursion for the latter. The asymptotic expansion mathematically converges with increasing degree and can precisely compensate for the shortcomings of the two methods. This study introduces asymptotic expansion to accurately compute the truncation coefficient for the spectral gravity forward modeling to a high degree. The evaluation at the whole altitudes and whole integral radii indicates that the proposed method has the following advantages: (i) The calculation precision increases with increasing degree and is altitude independent; (ii) the accurate calculation can be supported by a double-precision format; and (iii) the calculation can be conducted nearly without extra time cost with increasing degree. Generally, asymptotic expansion is used to calculate the high degree truncation coefficients, while the truncation coefficients at low degrees can be calculated using spectral form or recursive formulas in multiprecision format as a supplement; and the available range of asymptotic expansion is provided in the appendix.</p>","PeriodicalId":54822,"journal":{"name":"Journal of Geodesy","volume":"64 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142405051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"IAG Newsletter","authors":"Gyula Tóth","doi":"10.1007/s00190-024-01901-x","DOIUrl":"https://doi.org/10.1007/s00190-024-01901-x","url":null,"abstract":"","PeriodicalId":54822,"journal":{"name":"Journal of Geodesy","volume":"7 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-10-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142385184","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Improved GPS tropospheric path delay estimation using variable random walk process noise","authors":"Zachary M. Young, Geoffrey Blewitt, Corné Kreemer","doi":"10.1007/s00190-024-01898-3","DOIUrl":"https://doi.org/10.1007/s00190-024-01898-3","url":null,"abstract":"<p>Accurate positioning using the Global Positioning System relies on accurate modeling of tropospheric delay. Estimated tropospheric delay must vary sufficiently to capture true variations; otherwise, systematic errors propagate into estimated positions, particularly the vertical. However, if the allowed delay variation is too large, the propagation of data noise into all parameters is amplified, reducing precision. Here we investigate the optimal choice of tropospheric constraints applied in the GipsyX software, which are specified by values of random walk process noise. We use the variability of 5-min estimated positions as a proxy for tropospheric error. Given that weighted mean 5-min positions closely replicate 24-h solutions, our ultimate goal is to improve 24-h positions and other daily products, such as precise orbit parameters. The commonly adopted default constraint for the zenith wet delay (ZWD) is 3 mm/√(hr) for 5-min data intervals. Using this constraint, we observe spurious wave-like patterns of 5-min vertical displacement estimates with amplitudes ~ 100 mm coincident with Winter Storm Ezekiel of November 27, 2019, across the central/eastern USA. Loosening the constraint suppresses the spurious waves and reduces 5-min vertical displacement variability while improving water vapor estimates. Further improvement can be achieved when optimizing constraints regionally, or for each station. Globally, results are typically optimized in the range of 6–12 mm/√(hr). Generally, we at least recommend loosening the constraint from the current default of 3 mm/√(hr) to 6 mm/√(hr) for ZWD every 300 s. Constraint values must be scaled by √(<i>x</i>/300) for alternative data intervals of <i>x</i> seconds.</p>","PeriodicalId":54822,"journal":{"name":"Journal of Geodesy","volume":"4 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142383861","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Satellite’s differential code bias conversion model between different IGS clock products using uncombined BDS-3 multi-frequency data","authors":"Jingzhu Zhao, Lei Fan, Shiwei Guo, Chuang Shi","doi":"10.1007/s00190-024-01899-2","DOIUrl":"https://doi.org/10.1007/s00190-024-01899-2","url":null,"abstract":"<p>Differential code bias (DCB) is widely used to achieve consistency between global navigation satellite system (GNSS) observations at different frequencies. Since a strong correlation exists between satellite DCBs at different frequencies and the satellite clock offset, the DCB products need to be aligned with the corresponding clock products. This paper proposes a satellite’s DCB conversion model between different clock products released by the International GNSS Service (IGS) via the uncombined method. First, a one-step uncombined approach with a simplified ionospheric processing model is proposed for multi-frequency DCB estimation. In the second step, a linear function model is applied to represent the relationship between the initial satellite clock bias and the DCB estimates at different frequencies. To test the proposed model, BeiDou global system (BDS-3) multi-frequency data collected from 60 multi-GNSS experiment stations and precise clock products released by four IGS analysis centers are used to estimate the DCB. The DCB estimates are compared to the DCB products released by the Chinese Academy of Sciences (CAS) and the Deutsches Zentrum für Luft-und Raumfahrt (DLR). The average root-mean-square (RMS) values of the differences between the DCB estimates and the two DCB products are 0.61 ns and 0.52 ns, which are significantly larger than the corresponding monthly standard deviations. This indicates that systematic bias exists between the DCB estimates and the two DCB products. Additionally, systematic biases are also observed in the DCB estimation when different clock products are used, with the maximum value reaching 4 ns. In order to study the propagation of parameter errors between the DCB estimates and the clock products, regression analysis is conducted to determine the linear model coefficients of the DCB conversion model. The results show that the model coefficients for the four frequency pairs C2I-C6I, C2I-C1X, C2I-C5X and C2I-C7Z are 0.394, 0.237, 0.238, and 0.238, respectively. Kinematic precision point positioning is conducted for model verification. During the first 6-h period, the average three-dimensional RMS of the positioning errors is 13.5 cm when the DCB estimates are corrected by the conversion model, which is improved by 32.5%, 14.6%, and 11.3% compared with the usage of the CAS and DLR products and those without model conversion, respectively.</p>","PeriodicalId":54822,"journal":{"name":"Journal of Geodesy","volume":"6 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142363136","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Contribution to the global VGOS network by potential sites in South America","authors":"María Eugenia Gómez, Laura Isabel Fernández, Hayo Hase","doi":"10.1007/s00190-024-01897-4","DOIUrl":"https://doi.org/10.1007/s00190-024-01897-4","url":null,"abstract":"<p>Very-long-baseline interferometry (VLBI) networks have historically lacked enough antennas to densify the southern hemisphere adequately. This situation not only impacts directly the realization of the Celestial Reference System but also the determination of the Earth Orientation Parameters (EOP). In the last years, a significant step in the modernization of the VLBI infrastructure has been taken with the VLBI Global Observing System (VGOS). However, the distribution of VGOS antennas is still far from being homogeneous. In this work, we used the software VieSched<span>++</span> for VLBI scheduling to simulate nine new VGOS arrays. These networks, which are more dense in the southern hemisphere and focus on South America, were planned considering existing geodetic sites where a VGOS antenna could be added and new sites where the installation is feasible. We compared the statistical performance of the proposed networks with that of a simulated standard VGOS network and the actual VGOS performance for the last 2 years. A more uniform station distribution does not seem to be associated with better repeatabilities for station coordinates, but the results for EOP and source coordinates improve as expected.</p>","PeriodicalId":54822,"journal":{"name":"Journal of Geodesy","volume":"202 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142330353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A robust approach to terrestrial relative gravity measurements and adjustment of gravity networks","authors":"Franco S. Sobrero, Kevin Ahlgren, Michael G. Bevis, Demián D. Gómez, Jacob Heck, Arturo Echalar, Dana J. Caccamise, Eric Kendrick, Paola Montenegro, Ariele Batistti, Lizeth Contreras Choque, Juan Carlos Catari, Roger Tinta Sallico, Hernan Guerra Trigo","doi":"10.1007/s00190-024-01891-w","DOIUrl":"https://doi.org/10.1007/s00190-024-01891-w","url":null,"abstract":"<p>Like many geophysical observations, relative gravity (RG) measurements are affected by random errors, systematic errors, and occasional blunders. When RG measurements are used to build large gravity networks in remote areas under adverse environmental or logistical conditions (such as extreme temperatures, heavy precipitation, rugged terrain, difficult or dangerous roads, and high altitudes), it is more likely for significant errors to occur and accumulate. Therefore, obtaining accurate gravity estimates at regional gravity networks largely depends on defensive data collection protocols and robust adjustment techniques. In this work, we present a measurement field protocol based on highly redundant observation patterns, and a two-step least squares adjustment scheme implemented as a MATLAB package. This software helps us identify blunders, mitigates the impact of random errors, and downweights or removes outlier observations. The methodology also guarantees that adjusted gravity values have well-constrained standard error estimates. We illustrate the capabilities of our approach through the case study of the Bolivian gravity network, where we determined the acceleration due to gravity at 2548 stations that spread over difficult and sometimes extreme environments, with a typical level of uncertainty of 0.10–0.15 mGal.</p>","PeriodicalId":54822,"journal":{"name":"Journal of Geodesy","volume":"30 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142313518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Bridging the gap between GRACE and GRACE Follow-On by combining high–low satellite-to-satellite tracking data and satellite laser ranging","authors":"Matthias Weigelt, Adrian Jäggi, Ulrich Meyer, Daniel Arnold, Torsten Mayer-Gürr, Felix Öhlinger, Krzysztof Sośnica, Sahar Ebadi, Steffen Schön, Holger Steffen","doi":"10.1007/s00190-024-01888-5","DOIUrl":"https://doi.org/10.1007/s00190-024-01888-5","url":null,"abstract":"<p>The satellite missions GRACE and GRACE Follow-On have undoubtedly been the most important sources to observe mass transport on global scales. Within the Combination Service for Time-Variable Gravity Fields (COST-G), gravity field solutions from various processing centers are being combined to improve the signal-to-noise ratio and further increase the spatial resolution. The time series of monthly gravity field solutions suffer from a data gap of about one year between the two missions GRACE and GRACE Follow-On among several smaller data gaps. We present an intermediate technique bridging the gap between the two missions allowing (1) for a continued and uninterrupted time series of mass observations and (2) to compare, cross-validate and link the two time series. We focus on the combination of high-low satellite-to-satellite tracking (HL-SST) of low-Earth orbiting satellites by GPS in combination with satellite laser ranging (SLR), where SLR contributes to the very low degrees and HL-SST is able to provide the higher spatial resolution at an lower overall precision compared to GRACE-like solutions. We present a complete series covering the period from 2003 to 2022 filling the gaps of GRACE and between the missions. The achieved spatial resolution is approximately 700 km at a monthly temporal resolutions throughout the time period of interest. For the purpose of demonstrating possible applications, we estimate the low degree glacial isostatic adjustment signal in Fennoscandia and North America. In both cases, the location, the signal strength and extend of the signal coincide well with GRACE/GRACE-FO solutions achieving 99.5% and 86.5% correlation, respectively.</p>","PeriodicalId":54822,"journal":{"name":"Journal of Geodesy","volume":"231 1","pages":""},"PeriodicalIF":4.4,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142174711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}