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Time filter

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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. Source


Huang G.,Changan University | Yang Y.,China National Administration of GNSS and Applications | Yang Y.,State Key Laboratory of Geographic Information Engineering | Liu C.,Changan 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. Source


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. Source


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. Source


Huang G.,Changan University | Yang Y.,Xian Research Institute of Surveying and Mapping | Yang Y.,State Key Laboratory of Geographic Information Engineering | Zhang Q.,Changan University | Tu R.,Changan 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. Source

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