Time filter

Source Type

Sun W.,61243 Troops | Wu X.,Zhengzhou University | Wang Q.,Zhengzhou University | Liu X.,Xian Research Institute of Surveying and Mapping | And 3 more authors.
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2016

Aiming to address the problem of variance component inconformity between signal and noise from multi-source gravity anomalies, the variance component estimate was introduced into the least square collocation (LSC) method, while the Tikhonov normalizing method was used to address the covariance matrix singularity problem. Experiments under different error conditions were carried out and compared. Results showed that, as compared to the LSC method, the proposed method reduced the systematic error of data fusion. It showed better behaviors both in fusion precision and reliability than standard LSC. © 2016, Research and Development Office of Wuhan University. All right reserved.


Zhang Q.,Zhengzhou University | Zhang Q.,State Key Laboratory of Geographic Information Engineering | Zhang Q.,Xian Research Institute of Surveying and Mapping | Sui L.,Zhengzhou University | And 5 more authors.
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2014

For the three types of GNSS system time offset monitoring approach, we analyze the basic principles and methods and made a comparison of their accuracy, reliability and implementation, and finding that the PPS-based method is more suitable for time offset monitoring. We present a detailed discussion and description, including hardware configuration, data collection and post processing content for the PPS-based method. In an experiment we use both GPS and GLONASS dual-mode receivers to generate the 1 PPS of GPS and GLONASS second pulse signals, and used the Stanford SR620 time interval counter for PPS precision measurement. We thereby obtained GPS and GLONASS system time offset measurement values, and adopted a FIR filter with a Hanning window to get the GPS and GLONASS system time offset average 317.1 ns, with a standard deviation of 5.01 ns. ©, 2014, Research and Development Office of Wuhan University. All right reserved.


Chen G.,Wuhan University | Chen G.,National Engineering Research Center for Geographic Information System | Zeng A.,Zhengzhou University | Zeng A.,State Key Laboratory of Geographic Information Engineering | And 4 more authors.
Solid Earth | Year: 2016

To establish the horizontal crustal movement velocity field of the Chinese mainland, a Hardy multi-quadric fitting model and collocation are usually used. However, the kernel function, nodes, and smoothing factor are difficult to determine in the Hardy function interpolation. Furthermore, the covariance function of the stochastic signal must be carefully constructed in the collocation model, which is not trivial. In this paper, a new combined estimation method for establishing the velocity field, based on collocation and multi-quadric equation interpolation, is presented. The crustal movement estimation simultaneously takes into consideration an Euler vector as the crustal movement trend and the local distortions as the stochastic signals, and a kernel function of the multi-quadric fitting model substitutes for the covariance function of collocation. The velocities of a set of 1070 reference stations were obtained from the Crustal Movement Observation Network of China, and the corresponding velocity field was established using the new combined estimation method. A total of 85 reference stations were used as checkpoints, and the precision in the north and east component was 1.25 and 0.80mmyr-1, respectively. The result obtained by the new method corresponds with the collocation method and multi-quadric interpolation without requiring the covariance equation for the signals. © Author(s) 2016.


Zhang Q.,PLA University of Science and Technology | Zhang Q.,State Key Laboratory of Geographic Information Engineering | Tan S.,73061 Troops | Song Y.,Surveying Team of Air Force
Journal of Geomatics | Year: 2016

The reasons for GNSS inter-system bias were introduced in this paper. The system bias estimation method based on PPP algorithm was described in detail and the impact factors for this algorithm were analyzed. In this paper we used the PPP algorithm to estimate the GPS-GLONASS system bias based on globally distributed dual-mode IGS observation data. The results show that standard deviation of each GPS-GLONASS system bias is between 0-3 ns, and the accuracy of the same-type receiver is similar. The results obtained by the proposed method are relevant to single receiver, but the self-consistent single receiver can be used for multi-mode navigation.


Huang G.,Chang'an University | Yang Y.,China National Administration of GNSS and Applications | Yang Y.,State Key Laboratory of Geographic Information Engineering | Liu C.,Chang'an University | And 2 more authors.
Lecture Notes in Electrical Engineering | Year: 2013

The standard GNSS combined PPP algorithm cannot be used satisfactorily in the real-time and high frequency precise positioning because of its low compute efficiency. A new algorithm based on the parameter equivalent reduction principle is proposed. First, the observations equation and the normal equation which belong to the single navigation system can be solved independently. Second, the normal equations of overlapping parameters between the different systems can be obtained by using parameter equivalent reduction principle. At last, the combined PPP resolutions can be computed easily by using the Least Squares method. The proposed algorithm can improve the calculating efficiency immensely. In addition, an adaptively combined method which can automatically adjusts the contributed weight of different GNSS systems is also proposed in this paper. The numerical examples using the data set of three IGS stations, show that the PPP precisions and efficiencies based on the proposed model have been improved significantly compared with those of standard model. This proposed principle can also be applied in the GNSS precise satellite clock determination and the indifference baseline network adjustment plus the GNSS time offset monitoring. © 2013 Springer-Verlag Berlin Heidelberg.


Zhang Q.,Zhengzhou University | Zhang Q.,State Key Laboratory of Geographic Information Engineering | Zhang Q.,Xian Research Institute of Surveying and Mapping | Sui L.,Zhengzhou University | And 4 more authors.
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2014

For in-orbit Beidou satellites, we make use of precise orbit for broadcast ephemeris SIS error analysis. We not only estimate SISURE, but also take correlation analysis and normality test. Through observational data of October 2012 we find that the average SISURE is 1.45 m; the R-T and T-N have low correlation, while among the other components are micro-correlation. We also find that nearly all the SIS error components do not fit the normal distribution, and large errors can be detected by kurtosis abnormal values, while systematic bias can be detected by skewness abnormal values.


Zhang Q.,Zhengzhou University | Zhang Q.,State Key Laboratory of Geographic Information Engineering | Sui L.,Zhengzhou University | Gan Y.,Zhengzhou University | And 2 more authors.
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2015

For in-orbit GPS satellites, we adopted the NGA precise ephemeris in WGS84 from NGA and ITRS from IGS, using the seven-parameter Bursa model combined with different satellite-borne atomic clock stabilities at the same time to transform the parameters between WGS84 and ITRS using the least squares criterion. We eliminated the trend term based on the time sequence of the transformation parameters and at last we used spectral analysis to explore its cyclical nature. We use NGA and IGS precise ephemeris, from January 1, 2009 to June 2012, a total of 1 306 d, collecting every coordinate transform parameter to analyze long-term evolution characteristics: three translational the parameters have the 345 d, 690 d and 345 d periodic terms, while three rotation parameters, with the 459 d, 172 d and 459 d cycle item scale parameter respectively, are found not to be not periodic terms. ©, 2015, Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University. All right reserved.


Zhang Q.,PLA University of Science and Technology | Zhang Q.,State Key Laboratory of Geographic Information Engineering | Wang Y.,PLA University of Science and Technology | Sun Y.,PLA University of Science and Technology | And 2 more authors.
Optik | Year: 2016

Little cracks in civil engineering structures may be the first indication of a serious defect. Crack monitoring of concrete is crucial for the integrity of civil engineering structures. In this paper, fiber Bragg grating (FBG) sensors were used for monitoring the crack of two CFRP concrete composite arches in MTS loading and unloading test. During the test, time series of strain data can be obtained by different FBG sensors. At the same time, initial cracking time is observed and recorded by the experimenters. After the test, a method based on Hilbert-Huang Transform (HHT) is used for determining the cracking time, which take the advantage of Empirical Mode Decomposition (EMD). The test results indicate that the HHT based method can be used to determined the cracking time when using different pasting method, even if the fix location of FBG sensors is not very accurate, and the 2nd IMF is better than other IMFs in crack monitoring, which is selected as a criterion in crack monitoring. © 2016 Elsevier GmbH. All rights reserved.


Huang G.,Chang'an University | Yang Y.,Xian Research Institute of Surveying and Mapping | Yang Y.,State Key Laboratory of Geographic Information Engineering | Zhang Q.,Chang'an University | Tu R.,Chang'an University
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2013

The characteristics of GPS Common View (GPS CV) and GPS Carrier Phase time transfer (GPS CP) methods are introduced, and a new continuous time and frequency transfer algorithm based on GPS single Different Carrier Phase observations is proposed. The new algorithm uses an ionosphere-free combination of single but different observations from the same satellite and the processing steps are also consistent with simple traditional GPS CP. But, the Bayesian estimation of prior information is proposed to smooth the day-boundaries of time transfer results. Simulation results, which compared to that of GPS CP method, show that the proposed new algorithm improves the precision and frequency stability of the time and frequency transfer results remarkably.

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