全球定位系统

2019 Vol. 44, No. 4

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Study on joint time-keeping of hydrogen masers and cesium clocks based on frequency drift calibration

LIU Yang, PENG Jing, GONG Hang, HU Yini, OU Gang

2019, 44(4): 1-7. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.001

[Abstract](421) [PDF 686KB](140)

Abstract:
In the case of hydrogen masers and cesium clocks joint time-keeping without an external tracing link, to solve the problem that the weighted average algorithm can’t give full play to the long-term stability of the cesium clocks due to the small weight assigned to the cesium clocks by the occasions that focus on shortterm stability, a two-stage Kalman filter algorithm to generate local atomic timescale is proposed in this paper. The first-stage Kalman filter uses the cesium clock to calculate the frequency drift of the hydrogen masers and calibrates the frequency drift of the hydrogen masers. The second-stage Kalman filter uses a single-state variable model to generate the local atomic time which is based on the data of cesium clocks and hydrogen masers whose drift has been calibrated. The experimental results show that the longterm stability of the local atomic timescale can be improved on the premise of maintaining short-term stability: the improvement of 10-day-stability is in 10^-15 and the improvement of month-stability is in 10^-14. It is shown that the long-term stability of the local atomic timescale generated by the proposed algorithm is better.

Research on improvement method of positioning accuracy of area array image

LENG Bo, WANG Feng, YOU Hongjian, HU Yuxin

2019, 44(4): 8-15. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.002

[Abstract](297) [PDF 874KB](100)

Abstract:
To improve the imaging positioning accuracy of the area array camera, the airborne area array image of the northern part of Songyuan City, Jilin Province is taken as the experimental object to analyze the error and calibration of the imaging process. The imaging location of airborne area array camera has large offset errors caused by three attitude angle errors of the outer orientation elements and small distortion errors caused by internal orientation elements, such as camera lens distortion. Aiming at the above problems, the rigorous geometric positioning model is firstly used to obtain the preliminary positioning results of the area array image. Then, the resection and polynomial additional parameter models are used to solve the error caused by the internal and external orientation elements, and the more accurate positioning results are obtained. Finally, the experimental verification is carried out. The test results show that after the error calibration of the internal and external azimuth elements, the accuracy can be controlled within 5 m, and the accuracy can be improved by 94.37％. The treatment effect is remarkable. By studying the error generated by the internal and external orientation elements in the calibration area array imaging process, the positioning accuracy of the area array camera is improved, which has certain value and scientific reference for the application and promotion of area array camera imaging.

Performance analysis of IMU fine alignment based on wavelet de-noising

ZHANG Xuanxuan, YANG Cheng

2019, 44(4): 16-24. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.003

[Abstract](326) [PDF 789KB](96)

Abstract:
Precision alignment performance is an essential condition to ensure the accuracy of inertial navigation. This paper summarizes the research status of precision alignment at home and abroad, and finds that precision alignment is usually achieved by Kalman filter and linear error equation of small misalignment angle of inertial sensor. Based on this, Kalman filter and wavelet analysis are used in this paper. The precision alignment performance of three kinds of inertial sensors with different performances is analyzed. It is found that the high precision inertial sensors have better alignment accuracy, while the low precision sensors have lower alignment accuracy due to noise deviation and non-linear reasons, even the situation of filter divergence.

True digital orthophoto image generation method based on 3D model of UAV real

CHENG Libo, DUAN Ping, LI Jia, YAO Yongxiang, LI Chen, WANG Yunchuan

2019, 44(4): 25-32. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.004

[Abstract](456) [PDF 1036KB](61)

Abstract:
Digital Orthophoto Map (DOM) uses digital differential rectification method to eliminate projection error caused by tilted camera and topographic relief, but it can produce double projection phenomenon. True digital orthophoto map (TDOM) can effectively solve the double projection phenomenon of DOM. A method for making TDOM based on the real three-dimensional(3D) model of the Unmanned Aerial Vehicle(UAV) image is proposed. First, the aerial photogrammetry image acquired by UAV mounting five-lens camera and 3D model of real scene is generated. Then the top contour boundary line of the building is collected and its 3D volume model is constructed. Finally, TDOM is generated by occlusion detection and compensation based on 3D model of building top contour boundary line. The UAV image of Yunnan Normal University in Chenggong as experimental data is used as experimental data to verify the proposed method, and the experiments show that the method can be used to generate high quality TDOM.

Unsupervised classification of high spatial remote sensing image combining L0 smoothing and superpixel

YANG Zenan, HUANG Liang, WANG Xiaoxuan, FANG Liuyang, SONG Jing

2019, 44(4): 33-39. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.005

[Abstract](322) [PDF 920KB](78)

Abstract:
Aiming at the problem that the unsupervised classification method is easy to form “salt and pepper” noise and generate many errors and missed points in the classification of high spatial remote sensing images, an unsupervised classification method of high spatial remote sensing image based on L0 smoothing and superpixel is proposed. Firstly, a L0 algorithm is instituted to smooth the high space remote sensing image and reduce a range of image noises and redundant information. Then, a superpixel method of SLIC (Simple Linear Iterative Clustering) is used for that further inhibiting the salt and pepper phenomenon while reducing the processing complexity, and the initial clustering map is obtained. Finally, the K-means unsupervised classification method is established to receive the final classification result image. Furthermore, three high spatial remote sensing images are selected as experimental data to verify the method proposed in this paper. The experimental results show that the proposed method can achieve accurate classification of features, and the overall accuracy is 72.46％, 77.55％ and 78.44％ respectively. The Kappa coefficients are 0.788, 0.779 and 0.779 respectively. The proposed method can effectively solve the phenomenon of “salt and pepper” in the classification, improve the classification accuracy and have certain reference value for high spatial remote sensing image classification.

Application of wavelet and Fourier transform in time series analysis

CAI Fu, SUN Fuping, DAI Hailiang, ZHU Xinhui, ZHANG Longlong

2019, 44(4): 40-46. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.006

[Abstract](455) [PDF 771KB](109)

Abstract:
Exactly decomposing the feature information of time series is the precondition to nonlinear variation analysis. According to the characteristics of Fourier and wavelet transform, two methods are integrated and applied to analyze time series in time domain and frequency domain, and comprehensive algorithm of wavelet and Fourier transform is presented. Firstly, the wavelet function DB4 is used to decompose the coordinate time series into five layers to get the high frequency and low frequency parts. Then, the time domain waveforms of each harmonic and the possible sudden change information and intervals are obtained. Finally, the exact frequency and amplitude of each harmonic are obtained on the basis of fast Fourier transform. The results show that the low-frequency analysis can intuitively obtain the “annual term” and “two-year cycle term”, while the high-frequency analysis is consistent with the extraction of short-term cycles such as “semiannual term” and “one-season term”. So the method based on wavelet transform and Fourier transform has many advantages compared with Fourier transform and wavelet transform alone, it can effectively extract the feature information of station time series, and has a big research value.

Study on anti-jamming and signal enhancement algorithms for satellite navigation

WANG Fujun, DING Xiaoyan, XIE Weihua, XU Hanqing

2019, 44(4): 47-52. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.007

[Abstract](512) [PDF 699KB](159)

Abstract:
Aiming at the problem that power inversion (PI) anti-jamming algorithm can only suppress jamming but can not enhance navigation signal, a cascade spatial anti-jamming algorithm is proposed. Firstly, the parallel power inversion algorithm based on orthogonal subspace projection is used to eliminate the strong interference, and then blind beamforming based on cyclostationarity is used to enhance the navigation signal and further improve SINR. Finally, the effectiveness of this method is verified by simulation.

A mathematical model of pseudo-range single point positioning and its programming

GUO Ping, ZHOU Shi, DUAN Taisheng, LI Xueshi, WANG Kaosheng

2019, 44(4): 53-60. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.008

[Abstract](595) [PDF 923KB](128)

Abstract:
In this paper, the mathematical model of pseudo-range single-point positioning is analyzed in detail, and detailed steps and error equations are listed, including coordinate transformation and some important technical details involved. The spatial rectangular coordinates XYZ of single-point positioning of each epoch of the station and coordinates calculated by synthesizing metadata of each epoch are calculated by programming. Using the original data obtained from some engineering surveys and converted into RINEX format, the coordinates of the surveying station are calculated by using the pseudo-range observation value of GPS satellite and navigation N file. The coordinates are compared and analyzed with the approximate coordinates calculated by the program of the receiver. The results show that the coordinates are about meter-level, while the accuracy of singlepoint positioning is meter-level. It is proved that the mathematical model is feasible and easy to be realized by programming.

Research on periodic analysis and noise reduction method of elevation coordinate timing of CORS based on wavelet transform

WEI Guanjun, CHEN Chen, HUANG Yiyu, WEI Haolin

2019, 44(4): 61-67. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.009

[Abstract](342) [PDF 731KB](94)

Abstract:
Taking the elevation coordinate time series data of six CORS stations in Hong Kong CORS network as the research object, wavelet multi-resolution analysis is used to detect the periodic variation and nonlinear motion trend in the coordinate time series from the time-frequency angle. The threshold method performs noise reduction processing on the coordinate timing, and compares the noise reduction effects according to different noise reduction quality evaluation indexes. The results show that there are very obvious characteristics of annual cycle and semi-annual periodic variation in the elevation coordinate timing. The wavelet noise reduction can effectively eliminate or reduce the noise information in the original time series, and obtain the coordinate time series closer to the theoretical analysis.

A new differential loran navigation system

DING Changchun, CHEN Jiayi, LIU Rui

2019, 44(4): 68-76. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.010

[Abstract](414) [PDF 1061KB](114)

Abstract:
As the compass for the advance of modern society, the navigation system has penetrated into daily life, science and technology culture, national economy, military tasks and other fields, and is an essential infrastructure for the normal operation of modern society.As a typical representative of land-based longwave navigation system, Loran navigation system is an important part of the global navigation system. Due to its relatively low navigation accuracy, its role in the global navigation system is declining.In recent years, the improvement of accuracy of long-wave navigation system is mainly achieved by setting up difference stations, but this method has high cost and low update rate of correction data.To solve this problem, a new differential Loran navigation system is proposed in this paper, and the key technologies are briefly introduced, analyzed, simulated and tested.

Preliminary study on the correlation between GNSS ZTD and soil water content based on wavelet transform

WANG Xuan, LOU Zesheng

2019, 44(4): 77-81. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.011

[Abstract](244) [PDF 541KB](85)

Abstract:
Based on the data of GNSS ZTD of NMEL station of the CMONOC from November 2018 to January 2019 and the soil water content data of the Lightning River Basin Soil Moisture Detection Test Area of the Institute of Remote Sensing and Digital Earth of the Chinese Academy of Sciences, the correlation analysis between GNSS ZTD and soil water content on the monthly time scale are carried out by means of wavelet transform. The results show that GNSS ZTD is correlated with soil water content in monthly time scale, the correlation between GNSS ZTD and soil water content is significantly higher after wavelet decomposition, and the correlation between GNSS ZTD and soil water content is higher. The correlation between GNSS ZTD and soil water content is abnormal in short time, such as precipitation.

Positioning performance analysis of a low-cost μ-blox single-frequency multi-GNSS receiver

LONG Chiyu, WEN Qiang

2019, 44(4): 82-88. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.012

[Abstract](416) [PDF 907KB](150)

Abstract:
In recent years, high precision positioning of low-cost miniaturized GNSS receiver has been a hot topic on account of the big surge of high precision positioning in mass market. In this paper, we analyse the quality of GNSS observations and evaluate the positioning performance of a new low-cost, single frequency, multi-GNSS receiver μ-blox M8P in different scenarios with different processing strategies, providing reference for high precision positioning of low-cost GNSS receiver. The experimental results show that the carrier to noise ratio of GNSS observations of μ-blox is lower than that of geodetic receiver and the pseudorange and carrier phase noise are higher. In static mode the low-cost GNSS receiver can achieve a high performance with a precision of centimeter level from short baseline relative positioning. In dynamic urban vehicle test the low-cost GNSS receiver can provide a precision of sub-meter to meter level with short baseline relative positioning. In a signal-constrained environment, the GPS／GLONASS combined positioning can provide more stable results.

Research on real-time monitoring method of water vapor ionosphere and platform construction based on Chongqing CORS

LIU Xingwei, XU Chaoqian, WU Han, PU Dexiang, GAO Xiang

2019, 44(4): 89-95. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.013

[Abstract](332) [PDF 717KB](75)

Abstract:
The method of atmospheric precipitable water vapor based on PPP and the 3D ionospheric tomography method based on pixel base are studied. Combined with Chongqing CORS and IGS real-time service product (RTS), a regional water vapor ionospheric monitoring platform is constructed. The platform can provide high spatial and temporal resolution water vapor 2D, ionospheric 2D and 3D products in real time, and now web is released online. The platform extends the service field of CORS in Chongqing, which is of great significance for monitoring short-term abrupt weather phenomena and studying fine morphological changes of the ionosphere.

Application of generalized extension interpolation method in BDS precise clock correction

HUA Xirui, LI Zhongqin, LI Zhenchang, KOU Ruixiong

2019, 44(4): 96-101. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.014

[Abstract](282) [PDF 637KB](97)

Abstract:
In high-precision satellite data processing, satellite clock correction data interpolation is an important task, and its accuracy directly influences satellite positioning accuracy. Traditional interpolation and fitting methods have certain limitations. In this paper, the generalized continuation interpolation method is applied to the clock difference data processing of BeiDou satellite. By interpolating the clock difference data with 5 min epoch interval into 30 s, and then comparing with the precision clock difference data of 30 s, the interpolation accuracy is evaluated.Discussing the relationship between the values of r, s , and tparameters and the interpolation precision. optimal parameter combination is obtained, and the interpolation result of the traditional Lagrange interpolation method is compared under the combination of the parameters. The results show that the generalized extension interpolation method satisfies the processing of the Beidou satellite clock data, and the accuracy meets the requirements and slightly higher than the Lagrange interpolation method.

Study on the improved method of GPS elevation linear fitting for a construction section of South-to-North water diversion project

MENG Junzhen, MA Kaifeng, HUANG Guiping, ZHAO Jiwei, YANG Weisen

2019, 44(4): 102-106. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.015

[Abstract](315) [PDF 575KB](109)

Abstract:
Based on the requirement that GPS geodetic height cannot be directly applied to engineering and needs to be converted to normal height, aiming at the characteristics of GPS control alignment in a bid section of South-to-North Water Transfer Project, the application of orthogonal function, cubic spline and Akima curve fitting and corresponding improved methods to GPS elevation fitting is emphatically studied. The results show that the accuracy of the three improved methods can be improved when the point selection is suitable for the linear fitting region. Among them, the accuracy of the fitting results by the improved Akima curve fitting method is improved nearly three times, and total mean square error of elevation difference reaches 6.07 mm, which shows the obvious superiority of the improved Akima curve fitting method for this selection scheme.

Application of PPP technology in non-datum or multi-datum survey area

FENG Jianghai, LIU Shaoyin, HAO Hengqiang, WANG Kai

2019, 44(4): 107-112. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.016

[Abstract](359) [PDF 661KB](112)

Abstract:
When setting up the first-level control network without reference or multi-reference measurement area, the joint measurement of control points will consume a lot of energy, and the cumulative error is large. The precise singlepoint positioning (PPP) technology can effectively solve the problem. Based on a large number of IGS station data and measured data calculated by GrafNav software PPP, it is concluded that the plane error of PPP solution is less than 1 cm and the elevation error is less than 10 cm. At the same time, when the measurement period exceeds 4 hours, the variation of PPP solution error is small, and the longer the period, the better the stability of the solution accuracy. However, when the datum transformation is performed in the multireference measurement area, the epoch transformation has a great influence on the Y direction, and the accuracy of the reference transformation is greatly affected by the displacement variation value of the station.

Accuracy analysis of standard single point positioning of BDS-3

LI Guoliang, QIAN Yuyang

2019, 44(4): 113-118. doi: DOI:10.13442/j.gnss.1008-9268.2019.04.017

[Abstract](449) [PDF 450KB](185)

Abstract:
According to the construction situation and development strategy of BeiDou Satellite Navigation System, the construction of Beidou Satellite Navigation System in China has entered the third stage. Based on the data of IGS continuous tracking station, this paper firstly analyses the data quality of BDS-3 signal, then analyses the positioning accuracy of BDS-3 quasi-single point, and compares it with the positioning accuracy of BDS-2 standard single point. The results show that the data quality of BDS-3 is better in the observation area, and the positioning accuracy of BDS-3 single point is better. The positioning accuracy of the system is better than that of BDS-2.