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

Gravity data is always saved and used in grid format, which is also demanded for frequency domain computation as fast fourier transformation. Therefore, gridding method becomes the first and very important step of gravity data processing. Some gridding methods, such as Shepard and Kriging, were introduced into this step and improved the gridding precision. But when it comes to the case of sparse data, the gridding precision were sharply reduced. Moreover, the regular grid densification method was rarely studied. To meet the demands of regular grid densification, the fractal interpolating curve surface theory was introduced and applied in this paper. The computing formulae was deduced in detail. An experiment was carried out and result showed that, compared to the RBF method, the FIC method was better on the precision but worse on the error extremum. It means the FIC method showed bad behavior in data smoothing. Based on the Bouguer anomaly, a "remove-restore" method was applied to solve this problem. Result showed that not only was the precision improved by BAFIC method, but also was the error extremum reduced to a great extent, which made the result more reliable and applicable. The vertical scale parameter which plays a great role in BAFIC method was chosen after times of experiments in this paper, which could be optimized by better and precise methods. © 2016, Wuhan University All right reserved.

Yang Y.X.,National Key Laboratory of Geo Information Engineering | Li J.L.,Zhengzhou University | Wang A.B.,Beijing Satellite Navigation Center | Xu J.Y.,Zhengzhou University | And 4 more authors.
Science China Earth Sciences | Year: 2014

BeiDou regional navigation satellite system (BDS) also called BeiDou-2 has been in full operation since December 27, 2012. It consists of 14 satellites, including 5 satellites in Geostationary Orbit (GEO), 5 satellites in Inclined Geosynchronous Orbit (IGSO), and 4 satellites in Medium Earth Orbit (MEO). In this paper, its basic navigation and positioning performance are evaluated preliminarily by the real data collected in Beijing, including satellite visibility, Position Dilution of Precision (PDOP) value, the precision of code and carrier phase measurements, the accuracy of single point positioning and differential positioning and ambiguity resolution (AR) performance, which are also compared with those of GPS. It is shown that the precision of BDS code and carrier phase measurements are about 33 cm and 2 mm, respectively, which are comparable to those of GPS, and the accuracy of BDS single point positioning has satisfied the design requirement. The real-time kinematic positioning is also feasible by BDS alone in the opening condition, since its fixed rate and reliability of single-epoch dual-frequency AR is comparable to those of GPS. The accuracy of BDS carrier phase differential positioning is better than 1 cm for a very short baseline of 4.2 m and 3 cm for a short baseline of 8.2 km, which is on the same level with that of GPS. For the combined BDS and GPS, the fixed rate and reliability of single-epoch AR and the positioning accuracy are improved significantly. The accuracy of BDS/GPS carrier phase differential positioning is about 35 and 20 % better than that of GPS for two short baseline tests in this study. The accuracy of BDS code differential positioning is better than 2.5 m. However it is worse than that of GPS, which may result from large code multipath errors of BDS GEO satellite measurements. © 2013, Science China Press and Springer-Verlag Berlin Heidelberg.

Wei Z.,Xian Research Institute of Surveying and Mapping | Wei Z.,National Key Laboratory of Geo Information Engineering
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2012

This paper is devoted to treating the permanent tide in geodesy. First the numerical expression of the permanent tide potential is derived, then formal expressions of three kinds of tidal values and transformations among them for six types of geodetic observables frequently encountered are given, and finally the characteristic and usage of the three tidal systems in geodesy are discussed.

Yang Y.,National Key Laboratory of Geo Information Engineering | Yang Y.,Xian Institute of Surveying and Mapping
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2012

Uncertainty always exists in satellite navigation process and results, which includes random errors, systematic errors, outliers and colored noises etc. There are many different measures for evaluating the quality of the navigation results, such as precision, accuracy, reliability and uncertainty, and so on. In practice, the accuracy, precision and error itself are often confused by the users, so are the uncertainty and the uncertainty measures. Especially, the accuracy is often followed several times standard deviation or error percentage. For example, the user range accuracy (URA) index is often followed standard deviation. In this paper, the user range error (URE) is redefined based on the uncertainty concept. Then the URE and URA are distinguished and their relationship is obtained. The uncertainty is distinguished from the uncertainty measure. The often used reliability concept in geodetic adjustment is introduced and described. At last, several notes on the concept of error, precision, accuracy, URE and URA are given.

Li J.,Zhengzhou University | Yang Y.,National Key Laboratory of Geo Information Engineering | Xu J.,Zhengzhou University | He H.,Beijing Satellite Navigation Center | Guo H.,Beijing Satellite Navigation Center
GPS Solutions | Year: 2013

The regional constellation of BeiDou navigation satellite system (BDS) has been officially in operation since December 27, 2012, and real-time kinematic positioning using BDS and GPS multi-frequency observations is feasible. A heavy computational problem arises when resolving ambiguities in the case of multi-system with multi-frequency observations. A multi-carrier fast partial ambiguity resolution strategy is developed with the property that the extra-wide-lane and wide-lane ambiguities in the multi-frequency case can be resolved reliably in advance. Consequently, the technique resolves ambiguities sequentially instead of the usual batch ambiguity resolution (AR) mode so as to improve the computational efficiency of AR significantly. The strategy is demonstrated with real BDS/GPS dual- and triple-frequency observations. The results have shown that the probability of correct AR by the proposed method is comparable to that of the batch AR. Experimentally, the new method is about 2.5 times as fast as the batch AR in the dual-frequency case, 3 times in the mixed dual- and triple-frequency case and 3.5 times in the triple-frequency case. © 2013, Springer-Verlag Berlin Heidelberg.

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