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Zhao J.,State Key Laboratory Of Geodesy And Earths Dynamics | Zhao J.,Zhengzhou University | Gui Q.,Zhengzhou University
Boletim de Ciencias Geodesicas | Year: 2017

The weighed total least square (WTLS) estimate is very sensitive to the outliers in the partial EIV model. A new procedure for detecting outliers based on the data-snooping is presented in this paper. Firstly, a two-step iterated method of computing the WTLS estimates for the partial EIV model based on the standard LS theory is proposed. Secondly, the corresponding w-test statistics are constructed to detect outliers while the observations and coefficient matrix are contaminated with outliers, and a specific algorithm for detecting outliers is suggested. When the variance factor is unknown, it may be estimated by the least median squares (LMS) method. At last, the simulated data and real data about two-dimensional affine transformation are analyzed. The numerical results show that the new test procedure is able to judge that the outliers locate in x component, y component or both components in coordinates while the observations and coefficient matrix are contaminated with outliers. © 2017, Universidade Federal do Parana. All rights reserved.

Ding W.,University of Luxembourg | Ding W.,State Key Laboratory of Geodesy and Earths Dynamics | Teferle F.N.,University of Luxembourg | Kazmierski K.,Wrocław University of Environmental and Life Sciences | And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2017

It is anticipated that the performance of real-time (RT) GNSS meteorology can be further improved by incorporating observations from multiple Global Navigation Satellite System (GNSS), including GPS, GLONASS, Galileo, and BeiDou. In this paper, an operational RT system for extracting zenith troposphere delay (ZTD) using a modified version of the Precise Point Positioning With Integer and Zero-difference Ambiguity Resolution Demonstrator (PPP-WIZARD) was established. GNSS, including GPS, GLONASS, and Galileo, observation streams were processed using RT Precise Point Positioning (PPP) strategy based on RT satellite orbit/clock products from the Centre National d'Etudes Spatiales. An experiment covering 30 days was conducted, in which the observation streams of 20 globally distributed stations were processed. The initialization time and accuracy of the RT troposphere results using single-system and multisystem observations were evaluated. The effect of PPP ambiguity resolution was also evaluated. Results reveal that RT troposphere estimates based on single-system observations can both be applied in weather nowcasting, in which the GPS-only solution is better than the GLONASS-only solution. The performance can also be improved by PPP ambiguity resolution and utilizing GNSS observations. Specifically, we notice that ambiguity resolution is more effective in improving the accuracy of ZTD, whereas the initialization process can be better accelerated by GNSS observations. Combining all techniques, the RT troposphere results with an average accuracy of about 8 mm in ZTD can be achieved after an initialization process of approximately 8.5 min, which demonstrates superior results for applying GNSS observations and ambiguity resolution for RT meteorological applications. ©2017. American Geophysical Union. All Rights Reserved.

Chen P.,Xi'an University of Science and Technology | Chen P.,State Key Laboratory of Geodesy and Earths Dynamics | Chen J.,Wuhan University
Advances in Space Research | Year: 2014

We introduce a new global ionospheric modeling software - IonoGim, using ground-based GNSS data, the altimetry satellite and LEO (Low Earth Orbit) occultation data to establish the global ionospheric model. The software is programmed by C++ with fast computing speed and highly automatic degree, it is especially suitable for automatic ionosphere modeling. The global ionospheric model and DCBs obtained from IonoGim were compared with the CODE (Center for Orbit Determination in Europe) to verify its accuracy and reliability. The results show that IonoGim and CODE have good agreement with small difference, indicating that IonoGim owns high accuracy and reliability, and can be fully applicable for high-precision ionospheric research. In addition, through comparison between only using ground-based GNSS observations and multi-source data model, it can be demonstrated that the space-based ionospheric data effectively improve the model precision in marine areas where the ground-based GNSS tracking station lacks. © 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.

Chen P.,Xi'an University of Science and Technology | Chen P.,State Key Laboratory of Geodesy and Earths Dynamics | Yao Y.,Wuhan University
Advances in Space Research | Year: 2015

This paper investigates the characteristics of global plasmaspheric electron content (pTEC) using COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) occultation and GPS (Global Positioning System) data. The ionospheric electron content (iTEC) within 100-1000 km was obtained by fitting the COSMIC occultation electron density profiles, and the pTEC was obtained by subtracting the iTEC from CODE (Center for Orbit Determination in Europe) GIM (global ionosphere maps) TEC provided by University of Bern. This paper also investigates the characteristics of pTEC variations with local time, latitude and season. The results show that in 2011, the worldwide average of pTEC was 4.02 TECu, which is consistent with the findings of other studies. The pTEC shows significant diurnal variation characteristics, that is, pTEC is higher during daytime than during nighttime, but the percentage contribution of pTEC to GPS TEC is higher during nighttime than during daytime. The pTEC varies with the seasons, pTEC hemispheres symmetrically during spring and autumn, while pTEC in the summer hemisphere is higher than that in the winter hemisphere. Moreover, the percentage contribution of pTEC to GPS TEC (total electron content) is higher in winter hemisphere than in summer hemisphere. © 2015 COSPAR.

Chen P.,Xi'an University of Science and Technology | Chen P.,State Key Laboratory of Geodesy and Earths Dynamics | Yao W.,Xi'an University of Science and Technology | Zhu X.,Xi'an University of Science and Technology
Geophysical Journal International | Year: 2014

Considering the drawback of existing global weighted mean temperature model, this paper uses 2006-2012 NCEP reanalysis data to establish global empirical model for mapping zenith wet delays onto precipitable water-GTm_N, takes the influence of half-year periodicity of Tm into account when modelling and estimate the initial phase of each cycle. In order to evaluate the precision of GTm_N, we use three different Tm data sets from the NCEP during 2013, 650 radiosonde stations and COSMIC occultation in 2011 to test this model. The results show that GTm_N has higher precision in both ocean and continental area in every moment of every day. The accuracy of GTm_N is higher than Bevis formulas and GTm_II models. In addition, the actual surface temperature is not required in GTm_N model, and it will have wide application in GPS meteorology. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Xu K.-K.,Tongji University | Xu K.-K.,Henan Polytechnic University | Xu K.-K.,State Key Laboratory of Geodesy and Earths Dynamics | Wu J.-C.,Tongji University | Wu W.-W.,Tongji University
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

The aseismic slip or slow earthquakes is a very important component of the seismogenic process of faults. However, it is difficult to detect these small transient signals because of the low signal-to-noise ratio (SNR) in GNSS observation data. Based on the rich GNSS spatial-temporal data in active faults, a method of integrating processing of spatial-temporal noise and detection of transient aseismic slip signals is proposed. The transient signal and spatiotemporal correlated noise are expressed by the first-order Gaussian Markov process (FOGM). The SNR in the time domain is enhanced by Kalman filtering (KF). According to the high spatial coherence of fault deformation, the SNR in the space domain is enhanced by the principal component analysis (PCA). Combining spatiotemporal filtering of PCA with KF, the SNR of GNSS observation data is further improved. The result of simulations shows that the method can properly eliminate the effect of the linear trend, the year and half year cycle, further improve the space-time SNR of GNSS spatial-temporal data, and realize the detection of the transient aseismic slip signals even though the SNR is 1:1. Taking the slow slip event in Cascadia as an example, two aseismic slip events that happened in January 2007 and April 2008 were detected clearly. The interval of the two events was about 15 months and each event shows reverse displacements. The duration was about 18 days, and the displacement was about 8 mm, mainly distributed in the south edge of Cascadia subduction zone nearly in the range of 200 km. The slip characteristics were analyzed to be consistent with the relevant literature. Using the GNSS data in western Yunnan province from 2011 to 2013 provided by Crustal Movement Observation Network of China, the weak postseismic slip signals were detected. By principal component time response analysis, from March 2011 to June 2012, the displacements of NS and EW components exhibit obvious abnormal deviations, about 6 mm and 8 mm respectively. By space response analysis, the creep deformation is mainly distributed in the south section of the Lancangjiang fault, Red River fault and Xiaojiang fault. The spatial-temporal distribution corresponds to Burma MW7.2 earthquake on March 24, 2011. It is concluded that the fault activity in western Yunnan province is closely related to the Burma earthquake. Although it is difficult to improve the SNR of the single station GNSS observation data, using the spatial-temporal series of the whole GNSS network, according to the high spatial coherence of the fault deformation, based on KF combining with PCA, allows us to reduce the space-time irrelevant noise effectively and to reveal the temporal-spatial distribution characteristics of the transient aseismic slip. It would provide an important constraint and priori information for further fine inversion of fault parameters. ©, 2015, Science Press. All right reserved.

Jia H.G.,Southwest Jiaotong University | Jia H.G.,State Key Laboratory of Geodesy and Earths Dynamics | Liu L.Y.,Southwest Jiaotong University
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences - ISPRS Archives | Year: 2016

Natural causes and high-speed train load will result in the structural deformation of long-span bridges, which greatly influence the safety operation of high-speed railway. Hence it is necessary to conduct the deformation monitoring and regular status assessment for long-span bridges. However for some traditional surveying technique, e.g. control-point-based surveying techniques, a lot of human and material resources are needed to perform the long-term monitoring for the whole bridge. In this study we detected the long-term bridge deformation time-series by persistent scatterer interferometric synthetic aperture radar (PSInSAR) technique using the high-resolution SAR images and external digital elevation model. A test area in Nanjing city in China is chosen and TerraSAR-X images and Tandem-X for this area have been used. There is the Dashengguan bridge in high speed railway in this area as study object to evaluate this method. Experiment results indicate that the proposed method can effectively extract the long-term deformation of long-span high-speed railway bridge with higher accuracy.

Jia H.,Southwest Jiaotong University | Jia H.,State Key Laboratory Of Geodesy And Earths Dynamics | Liu L.,Southwest Jiaotong University
Journal of Modern Transportation | Year: 2016

This article focuses on reviewing the technologies of persistent scatterer interferometry (PSI), which has been often used to monitor the deformation of Earth surface. Three critical steps in the implementation of PSI were introduced, i.e., (1) detection of persistent scatterer (PS), (2) construction of PS network, and (3) PSI modeling and solution. Finally, the main problems and outlooks on the PSI technique are discussed and given. © 2016, The Author(s).

Fu G.,Prediction Institute | Fu G.,State Key Laboratory of Geodesy and Earths Dynamics | Fu G.,Chinese Academy of Sciences | Gao S.,Prediction Institute | And 4 more authors.
Journal of Geophysical Research: Solid Earth | Year: 2014

A dense relative gravity and Global Positioning System observation network with 302 stations was measured in the western Sichuan Basin (SB) to study gravity and isostasy. Bouguer Gravity Anomalies are negative in the study area, and change gradually from about -110 mGal (10- 5m s- 2) in the southeast to -220 mGal in the northwest. The new data reveal that the Moho beneath the western SB changes gradually from 39.5 km in the southeast to 43.7 km in the northwest and is inclined slightly to the northwest beneath the Chengdu Plain. The isostatic crustal thickness calculated by Airy isostatic theory varies between 39.5 and 42.0 km. The Longquan Shan (LQS) marks a clear boundary in the state of isostastic compensation in the study area. The Moho depth is almost identical to the Airy isostatic crustal thickness east of the LQS, where the crust is in isostatic balance. However, on the Chengdu Plain west of the LQS, differences between the Moho depth and Airy isostatic crustal thickness became larger from east to west, where the crust is out of isostatic balance. This indicates that the load of the Longmen Shan (LMS) on the west part of the crust of SB is mainly borne by the crust beneath the Chengdu Plain, and does little influence the crust east of the LQS. As a result we deduce that the LQS fault zone is a deeply rooted high angle fault zone that was broken by the load of the LMS. ©2014. American Geophysical Union. All Rights Reserved.

Li X.-L.,CAS Wuhan Institute of Geodesy and Geophysics | Li X.-L.,State Key Laboratory of Geodesy and Earths Dynamics | Mao W.-J.,CAS Wuhan Institute of Geodesy and Geophysics | Mao W.-J.,State Key Laboratory of Geodesy and Earths Dynamics
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2016

Abstract Conventional migration methods based on the elastic wave equation assume that the boundary is a free surface, where the normal and shear stresses are all zero. This assumption is not consistent with many kinds of seismic data, such as VSP (Vertical Seismic Profile) and OBC (Ocean Bottom Cable). In this paper, we analyze the stress boundary conditions for three kinds of models,including free-space, ocean-bottom and free-surface models. Under the assumption of up-going propagation, the relationships between the stress boundary condition and displacement boundary condition in the three models are established. Based on these relationships we derive the multimode and multicomponent Gaussian beam's continuation and migration equations accurately. The complete decomposition of wave modes is implemented automatically during the migration. Since the conventional cross-correlation image condition is not suitable for vector wave field imaging, we use cross-correlation of divergence and curl of vector wave fields. By setting the positive rotation direction of PS converted waves we solve the polarity reversal problem in a 3D space. Synthetic data from 2D and 3D models are used to validate the feasibility of the approach we propose. © 2016, Science Press. All right reserved.

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