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Ye S.,Wuhan University | Zhao L.,Wuhan University | Chen D.,Wuhan University | Pan X.,Tianjin Institute of Geotechnical Investigation & Surveying | And 2 more authors.
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2016

In real-time deformation monitoring applications, ambiguity cannot be quickly and reliably resolved under poor conditions using dual-frequency observations. In this paper, we analyze the single epoch ambiguity resolution success rate of GPS and BDS system under different calculating models. A new method based on triple-frequency BDS observations is proposed to fix the original ambiguity based on the TCAR (three-carrier ambiguity resolution. Sidereal day filtering based on observing domain reduces multipath errors in wide-lane observations under conditions where the original ambiguity cannot be fixed reliably. Real data is used to test the method, results show that the success rate and accuracy are improved in comparision to the dual-frequency models. A success rate of 100% was achieved using the wide-lane ambiguity resolution, and the RMS values for the wide-lane fixed solution reached 7 mm after filtering. © 2016, Research and Development Office of Wuhan University. All right reserved.


Zhang F.,Fujian Surveying and Mapping Institute | Xu C.,Minjiang University
Journal of Geomatics | Year: 2011

Phase windup in GPS precise point positioning can not be eliminate or mitigate easily, so it is important to deal them with accurate correction models, or set residuals of them as unknown parameters. The phase windup error and it's correction models are discussed detailed. Numerical result shows the accuracy of PPP using the correction model.


Luo W.,Fujian Surveying and Mapping Institute | Luo W.,Indiana University | Zhang H.,Indiana University | Zhang H.,University of Louisville
Proceedings - 2015 IEEE International Conference on Big Data, IEEE Big Data 2015 | Year: 2015

In this study we analyzed a series of LiDAR point clouds acquired over Taijiang district (part of Fujian province, China). The objective was to detect and extract water surface area from individual LiDAR point cloud, in a parallel means. To this end, interactive visualization of fine-grained data, global cluster algorithms, and statistical investigation were applied. We first rasterized point clouds into a series of matrices; then a density based algorithm (DBSCAN) allowed us to isolate the single cluster features which represented the water surfaces. Base on the clustered features, our framework created polygons for further quantitative assessments. The computations for the cluster analyses and their parallelized versions were carried out using R free software for statistical computing and graphics. © 2015 IEEE.


Ai N.,Beijing Forestry University | Wei T.,Beijing Forestry University | Zhu Q.,Beijing Forestry University | Zhao X.K.,Beijing Forestry University | And 2 more authors.
Physical Geography | Year: 2016

The semiarid loess area in north Shaanxi Province is one of the most serious areas of water erosion in China. The Chinese government initiated the project “Grain-for-Green” for soil erosion control in 1999, with significant effect. Vegetation, rainfall, soil, and topography are the most dominant natural factors affecting soil erosion; therefore, the aim of this research was to investigate the effects of these four factors on runoff and soil loss at the runoff-plot scale over five years and use the Gray relational analysis methods to compare the impacts of these factors. Five runoff-measuring sites were established in five different vegetation types. The results show that the relative impacts of the four factors on runoff were: rainfall > soil > topography > vegetation, and the relative impacts of the factors on sediment yield were soil > runoff > rainfall > topography > vegetation. We also analyzed the weights of these four factors on runoff and sediment yield during the wettest year alone. For that year, the relative weights of the factors on runoff were topography > rainfall > soil > vegetation, and the relative weights of the factors on sediment yield were runoff > soil > rainfall > topography > vegetation. © 2016 Taylor & Francis


Liu Y.,Wuhan University | Ye S.,Wuhan University | Jiang P.,Wuhan University | Chen H.,Design Science | And 2 more authors.
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2015

More linear combinations with longer wave-length and smaller noise can be formed with triple frequencies, which will accelerate ambiguity resolution. The TCAR and CIR methods are most representative, based on the no-geometry model but these approaches neglect information between satellites. In this paper, a geometry-based step by step ambiguity resolution method is presented, extra wide-lane ambiguities, two wide-lane ambiguities and narrow-lane ambiguities of two ionospheric-free combinations are fixed sequentially. An experiment with real BeiDou observation data demonstrated that for baselines within 10 km, nearly all the ambiguities can be fixed at a single epoch. ©, 2015, Wuhan University. All right reserved.

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