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2023 Vol. 48, No. 3

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Column on “GNSS Environmental Detection and Remote Sensing Technology”
Theory and Discussion
Technical Report and Application

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2023, 48(3)

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Column on “GNSS Environmental Detection and Remote Sensing Technology”

2023, 48(3): 1-1.

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A review of the application of GNSS reflected signal on land surface remote sensing

YANG Dongkai, LI Jie

2023, 48(3): 3-11, 32. doi: 10.12265/j.gnss.2023035

[Abstract](620) [FullText HTML] (228) [PDF 2886KB](122)

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Global Navigation Satellite System (GNSS) has been developed for more than half a century, and it can not only provide users with navigation, positioning and timing services, but also be used for remote sensing of the Earth, and its applications are beyond imagination. Based on the application of GNSS-R, this paper systematically introduces the basic concepts and signal characteristics of GNSS-R, focuses on the land surface remote sensing applications, and analyzes the possible future development directions, which can provide an important reference for the application of GNSS-R.

Research progress and prospects of GNSS-IR interpretation of surface environmental parameters

ZHOU Xin, ZHANG Shuangcheng, ZHANG Qin, LIU Qi, MA Zhongmin, LIU Ning

2023, 48(3): 12-23. doi: 10.12265/j.gnss.2023061

[Abstract](740) [FullText HTML] (173) [PDF 3796KB](92)

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The Global Navigation Satellite System (GNSS) has the characteristics of all-weather, near real-time, and high accuracy, and can continuously transmit L-band signals, which are widely used for positioning, navigation, and timing (PNT). As the research and application of GNSS continue to grow, the Global Positioning System Interferometric Reflectometry (GNSS-IR) technology provides a new means of surface parameter detection. After the GNSS radio navigation signal is reflected by different surface media (such as soil, snow, water surface, etc.), the reflected GNSS multipath signals carry the characteristic information of the reflecting surface, and the physical parameters of the surface reflecting surface can be effectively obtained through the analysis of parameters such as amplitude, phase, and frequency in GNSS reflecting signals. GNSS-IR, as a current research hotspot in the field of GNSS and remote sensing, has made some research progresses and achievements. This paper introduces in detail the principle and method of GNSS-IR and the progress of the application of this technology in soil moisture, vegetation, snow and water level. Based on this, problems and development directions in GNSS-IR research are presented.

Ground moving target imaging method study using GNSS-based passive bistatic radar

TANG Tao, WANG Pengbo, CHEN Jie, ZHOU Xinkai, ZENG Hongcheng

2023, 48(3): 24-32. doi: 10.12265/j.gnss.2023042

[Abstract](386) [FullText HTML] (95) [PDF 4727KB](72)

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Passive bistatic radar based on Global Navigation Satellite System (GNSS) is a potential space-based radar system, which has the advantages of low power consumption and good concealment. Due to the low signal power density, it is necessary to increase the target signal-to-noise ratio through long-time integration. However, target motion will cause range migration and Doppler spread, and the traditional pulse doppler radar processing method is no longer applicable. Aiming at this problem, this paper proposes a moving target imaging method based on Radon Fourier transform (RFT). Firstly, by adding the Doppler rate compensation factor to the traditional RFT method, the three-dimensional parameters of the moving target are jointly searched and estimated. And then through parameters compensation to complete the target imaging in the range Doppler domain. This method not only considers the influence of Doppler phase modulation, but also realizes rapid deployment in the range frequency domain, which can achieve a better imaging effect than traditional methods. The performance of the proposed method is verified based on the actual experiment using GPS satellite as the illuminator of opportunity.

Ionospheric modeling and accuracy evaluation of multi-system GNSS in high-latitude region

XIAO Yong

2023, 48(3): 33-38. doi: 10.12265/j.gnss.2023025

[Abstract](409) [FullText HTML] (108) [PDF 2864KB](71)

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Ionospheric delay is one of the main error sources that affect the positioning and navigation accuracy. The accurate establishment of ionospheric model is significant for high-precision navigation and positioning. Aiming at the research of multi-GNSS ionospheric modeling in high-latitude region, the multi-GNSS ionospheric modeling method is first given, and then the ionospheric modeling is carried out by using the observation datasets of 11 MGEX stations distributed uniformly in high-latitude region. The modeling accuracy of GPS system and multi-GNSS systems is compared and analyzed under the ionospheric polynomial model and spherical harmonic model. The results show that the difference between the differential code bias (DCB) estimates of each system calculated by the two ionospheric models is small, and the deviation of most of the satellite DCB estimates is less than 0.5 ns. For both two ionospheric models, the coefficient estimation accuracy under multi-GNSS systems is better than that under single GPS system, as well as the VTEC residual is smaller than that under single GPS system. The modeling accuracy of the ionospheric harmonic model is 3.09 TECU for single system and 1.80 TECU for multi-GNSS systems, with an improvement of 41.7%.

Lower atmospheric duct monitoring based on ground-based GNSS occultation signal

WANG Hongguang, ZHANG Lijun, WANG Qiannan, HAN Jie

2023, 48(3): 39-43. doi: 10.12265/j.gnss.2023046

[Abstract](318) [FullText HTML] (77) [PDF 2628KB](63)

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The atmospheric duct has a significant impact on the propagation of ultra-short and the above radio waves. In order to solve the problem of real-time acquisition of the parameters of the marine atmospheric duct, it is proposed to extract the environmental information of the marine atmospheric duct from the received signals of the ground-based GNSS satellite occultation process. The parabolic equation method is used to realize the forward model for predicting the received power of ground-based GNSS occultation signals from ducting parameters. Through combining the forward model, the parameterized atmospheric duct model and the objective function with genetic algorithm, the inversion algorithm of ducting parameters based on the received power of GNSS occultation signal is realized. The influence of standard refraction, surface duct and elevated duct on GNSS occultation signal received near the ground is simulated. Through experiments, the measured occultation signals of Beidou, GLONASS and GPS under different refraction environments are obtained, and the measured GNSS occultation signals are used to retrieve the low-altitude atmospheric duct. The results show that the adopted method can effectively monitor and retrieve the low-altitude atmospheric duct, which has the characteristics of passive remote sensing.

Land subsidence monitoring in coal mining collapse area of Urumqi

FENG Jian, YANG Zaozao, XU Ying, CHEN Hao

2023, 48(3): 44-51. doi: 10.12265/j.gnss.2023020

[Abstract](354) [FullText HTML] (84) [PDF 12730KB](44)

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The Jurassic coal-bearing layers in Urumqi intersect the major metropolitan region in a near east-west direction, with the geological features of many coal-bearing seams and massive and virtually vertical single coal seams. For decades, coal resource mining has harmed Urumqi’s urban environment, and the ensuing subsidence zones endanger the productivity and lives of the surrounding population, as well as severely limiting the city’s development of the cities and the development and usage of land resources. The main data source in this paper is Sentinel-1A data from the Liudaowan coal mine and Reed Huliang coal mine, which straddle Shuimoegou and Midong districts in Urumqi, and SBAS-InSAR technique is used to monitor the surface subsidence phenomena of historical abandoned coal mines, existing mined coal mines, and surrounding residential areas in the study area from June 2018 to the end of June 2022. The SBAS-InSAR technology is used to process SAR data, obtain surface time series deformation results in the study area, and generate annual average rate and cumulative deformation variables after geocoding, and it is discovered that the extent of subsidence funnels in several mining areas expanded and the cumulative subsidence in the center of the subsidence funnels exceeded −150 mm. The total sinking of GPS and SBAS findings is determined after comparison with the results of the GPS. The trend is stable, and the root mean square error is less than 2-3 mm.

Research on BeiDou full-band GNSS-R water level inversion

FU Pinggui, KUANG Cuilin, CHU Bin

2023, 48(3): 52-56, 92. doi: 10.12265/j.gnss.2023083

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China's BeiDou-3 (BDS-3) has abundant frequency band data, which makes the system promising for application in the field of Global Navigation Satellite System Reflectometry (GNSS-R). In this paper, we systematically carry out the study of BDS-R water level inversion, firstly, we compare the performance of two algorithms of spectral analysis and nonlinear fitting in water level inversion, and the results show that the overall accuracy of nonlinear fitting is better than that of spectral analysis; then, we introduce Savitzky-Golay filtering algorithm to denoise the inversion results for various errors, and the numerical values show that the difference between the results before and after denoising and the measured water level The average RMSE of the difference between the results before and after denoising and the measured water level is reduced by 7.4 cm, and the inversion accuracy of the full frequency band of BeiDou is comparable to that of GPS L5.

Research on moving target detection technology based on GNSS-R

ZHU Pengfei, ZHU Qinglin, DONG Xiang, SUN Mingchen

2023, 48(3): 57-61, 134. doi: 10.12265/j.gnss.2023078

[Abstract](531) [FullText HTML] (128) [PDF 3138KB](79)

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The mobile target detection technology based on GNSS-R is a new remote sensing detection method that uses the reflection signal of global satellite navigation signals to remotely detect the target area. From technical perspective, the GNSS-R mobile target detection technology is a passive bistatic radar. By analyzing the geometric configuration of GNSS signal propagation, the characteristics of the monitoring areal feature are analyzed to determine whether there is a moving target in the detection area. after experimental verification proveds that, when a moving object passes through the monitoring area, the system can accurately detect the moving target and calculate the target height and position information..

Refinement of BKlob model based on multi-source data

LIU Jialong, ZHU Yongxing, JIA Xiaolin, SONG Shuli, CHENG Na

2023, 48(3): 62-71. doi: 10.12265/j.gnss.2023092

[Abstract](225) [FullText HTML] (97) [PDF 3686KB](39)

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BDS-3 has launched global services, and the service area of the BDS Klobuchar (BDSklob) model has also expanded to a global scale. The global performance of the BDSklob model has also attracted great attention. In response to the low accuracy of the BDSklob model outside the service area and abnormal correction in polar regions during the BDS-2 period, this paper proposes a new BDSklob model refinement scheme-multi-source data refinement method-based on parameter refinement method, using empirical models IRI-Plas-2017, BDGIM model, and multi-source data from CODE’s GIM products. The results show that the refinement methods of various data sources have significantly improved the performance of the BDSklob model, especially in polar regions; BDSklob_ C (GIM product with CODE data source) has the highest processing accuracy; BDSklob_ B (data source is BDGIM) takes the second place in accuracy, but without the help of external data sources, refinement processing can be completed in the Beidou system; BDSklob_ the accuracy of I (data source is IRI model) is slightly poor, but based on the predictive ability of empirical models, it can meet the needs of real-time refinement processing.

Influence analysis of different weighted mean temperature models on precipitable water vapor

CHEN Xiangming, WANG Baobao, LI Ruoyu, LIN Leke, ZHU Qinglin

2023, 48(3): 72-76. doi: 10.12265/j.gnss.2023016

[Abstract](378) [FullText HTML] (106) [PDF 2049KB](48)

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The weighted mean temperature (WMT) is an important parameter to calculate precipitable water vapor in ground based GNSS meteorology. Four local linear statistical models of the WMT were derived from their historical radiosonde data in 2019. The comparison with other WMT models and the precipitable water vapor calculated by them show that Mao model and Mendes model have higher precision in the four cities, and it is necessary to establish local model for high-precision applications. The findings provide valuable reference for engineering fields concerned with the weighted mean temperature.

2023, 48(3): 2-2.

[Abstract](108) [FullText HTML] (74) [PDF 98KB](12)

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Theory and Discussion

Research on GNSS RTK positioning performance of smart phone based on extended antenna

YUAN Liangxiong, WANG Hao, SHEN Zhiheng

2023, 48(3): 77-84. doi: 10.12265/j.gnss.2023024

[Abstract](385) [FullText HTML] (95) [PDF 4802KB](58)

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The observation data quality of Mi8 smartphone with external low cost spiral antenna is studied, and the analysis and evaluation are carried out from the aspects of carrier to noise ratio (SNR), pseudo-distance residual, phase residual, etc. The results show that the carrier to noise ratio of original Global Navigation System (GNSS) observation value of Mi8 smartphone with external antenna is about 10 dB-Hz higher than that of mobile phone with internal antenna. And the carrier to noise ratio level is almost the same as that of the measured receiver. Pseudo range residual within 5 m, phase accuracy within 3 m. Different from the mobile phone with internal antenna, the pseudo distance residual of the mobile phone with external antenna has strong correlation with height angle and carrier to noise ratio. On this basis, two kinds of weighting models based on height angle and carrier to noise ratio are given, and real-time dynamic (RTK) positioning performance tests are carried out in static and dynamic environments based on the extended antenna of Mi8 mobile phone. The experimental results show that the RTK positioning accuracy of Mi8 mobile phone with external antenna can reach centimeter level in both static and dynamic environments. Moreover, using a random model based on carrier to noise ratio weighting has higher positioning accuracy in dynamic scenarios compared to a random model with height angle weighting. Specifically, it has an accuracy improvement of about 16% and 50% in the horizontal and vertical directions, respectively.

GNSS/INS loose combined navigation based on factor graph optimization PPP

YANG Xianci, QIAO Shubo, XIAO Guorui, JIA Xiaoxue, PENG Huadong, LI Songwei

2023, 48(3): 85-92. doi: 10.12265/j.gnss.2023027

[Abstract](817) [FullText HTML] (322) [PDF 4285KB](118)

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Aiming at the problem of global navigation satellite system signal loss caused by building occlusion, multipath effect and insufficient satellite visibility, a precise point positioning (PPP) algorithm based on factor graph optimization is proposed for the integrated positioning of GNSS and INS. First, with reference to the classical PPP dual-frequency lonosphere-free model, the pseudo-range and carrier factors are constructed, and the nonlinear least-squares problem is solved according to the nonlinear optimization theory. Then, the optimized PPP location information is used as the GNSS PPP factor, and the refined pre-integration factor considering the rotation of the earth is constructed into the GNSS/INS loose combination factor graph frame, to realize the nonlinear optimization of integrated navigation information. The results of on-board real measurement show that the positioning accuracy of the proposed algorithm is 37.09%, 28.79% and 64.59% higher than that of the extended Kalman filter algorithm in the north, east, and down directions respectively for PPP; For GNSS/INS integrated navigation, the positioning accuracy of the algorithm is 49.08%, 41.22% and 71.86% higher than that of the extended Kalman filter algorithm in three directions.

Assessment of antenna array-aided RTK positioning with different cut-off elevation angles

WANG Chao, LIU Changjian, XIAO Guorui, SUN Shuang, MENG Xin

2023, 48(3): 93-101. doi: 10.12265/j.gnss.2023028

[Abstract](208) [FullText HTML] (102) [PDF 6480KB](37)

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To evaluate the positioning performance of antenna array-aided real time kinematic (RTK), the mathematical model of antenna array-aided RTK is compared with the mathematical model of RTK firstly, and then a set of static measurement is processed with antenna array-aided RTK and RTK at different cut-off elevation angles. It is demonstrated that the strength of RTK is enhanced by increasing the redundancy of the double-difference observation equation from antenna array, which can improve the success rate of ambiguity resolution and positioning accuracy. Based on the combination of GPS and BDS, the antenna array-aided RTK achieves 93.6% ambiguity resolution success rate at a large cut-off elevation angle of 50°. Moreover, the horizontal accuracy of the fixed solution is better than 1 cm and the height accuracy is better than 2 cm, which can fulfill the demand of high-precision positioning and improve the applicability of RTK in urban canyon environment.

An improved VIO front-end method based on inertial prior correction of image grayscale

XU Jinle, PAN Shuguo, GAO Wang, LIU Hong, WANG Xiang

2023, 48(3): 102-109. doi: 10.12265/j.gnss.2023067

[Abstract](264) [FullText HTML] (120) [PDF 3950KB](39)

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Aiming at the problems of camera image sequences with excessive or weak illumination and significant changes in illumination intensity due to different lighting scenarios in a closed environment, a visual-inertial odometer (VIO) system based on inertial prior prediction to enhance images was proposed to solve the problem of features tracking loss due to extreme lighting conditions. This image enhancement algorithm performs grayscale gamma correction on the current image by predicting the pixel positions of feature points using inertia and associating the grayscale relationships between the corresponding feature point neighborhoods in the front and rear images. Experimental verification with TUM dataset shows that the proposed algorithm has an average improvement of 17.7% in positioning accuracy compared to VINS-Mono. Experiments in real indoor and outdoor environments also show better performance compared to VINS-Mono.

Multipath interference detection method for vector receivers based on joint multi-channel SQM metrics

JIA Qiongqiong, ZHU Chuansheng

2023, 48(3): 110-119. doi: 10.12265/j.gnss.2023037

[Abstract](303) [FullText HTML] (125) [PDF 4630KB](47)

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Vector receivers provide better performance in complex environments than traditional scalar receivers by sharing information between tracking channels to assist each other. However, multipath interference can severely limit the performance of vector receivers in complex environments such as urban canyons, and the effects of multipath can be eliminated if it is detected and dealt with in a timely manner. This paper researches multipath detection based on signal quality monitoring (SQM) from the perspective of the mechanism of multipath effects on vector receivers. Firstly, this paper proposes a multipath detection method for vector receivers with joint multi-channel SQM metrics, based on the analysis of existing SQM metrics for scalar receiver signals, combined with the characteristics of vector receiver channel coupling. Finally, this paper verifis through simulation experiments that the proposed method can effectively detect multipath with amplitude ratio less than 0.5 and the relative code delay in the range of 0.3–0.6 chips.

Technical Report and Application

Development of a real-time deformation monitoring system with integrated GNSS and accelerometer

WANG Peiyuan, TU Rui, HAN Junqiang, ZUO Hang, TAO Linlin, FANG Jing

2023, 48(3): 120-126. doi: 10.12265/j.gnss.2023012

[Abstract](386) [FullText HTML] (208) [PDF 3467KB](66)

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This paper designs an STM32 microcontroller based Global Navigation Satellite System (GNSS) and accelerometer data acquisition device that enables real-time deformation monitoring applications. The STM32F103ZET6 is used as the main control chip, and also the GNSS board and accelerometer are used to acquire data, and the data are transmitted to the server through the 4G module. The data are read from the server and the Kalman filter algorithm is used to fuse GNSS data with accelerometer data so that real-time deformation monitoring can be achieved and verified by static experiments. The results show that the baseline drift of the accelerometer can be automatically corrected and the standard deviation of displacement (STD) is better than 1.114 cm in all three directions after fusion; the STD of velocity is better than 0.072 cm/s; and the STD of acceleration is better than 0.485 cm/s² after correction of baseline drift.

Flight tracking and monitoring system based on BDS

MAO Xinsheng, XU Huan, PAN Luping

2023, 48(3): 127-134. doi: 10.12265/j.gnss.2023095

[Abstract](269) [FullText HTML] (89) [PDF 4035KB](33)

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In order to solve the problem of global seamless tracking and monitoring of aircraft, a flight tracking and monitoring system based on positioning and communication function provided by Beidou Navigation Satellite System (BDS) is designed. A newly developed airborne BDS equipment with positioning and communication functions integrated is installed on aircraft by retrofit. The installed BDS equipment calculates the BDS position of the aircraft and acquires important aircraft parameters like flight number, on-board fuel quantity, etc. BDS position and the acquired aircraft parameters, which are packed according to a pre-designed protocol, are sent to user ground system periodically. The whole system, including positioning source, communication link and the receiving system on the ground, is fully independently self-controllable. Flight tests are conducted after retrofit, and test results show that the rate of successful communication meet expectation. Besides, BDS and GPS data collected from flight tests are exported and compared. Flight track generated by BDS and GPS show good consistency through comparison. The designed system has been delivered to airline users for daily use.