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2021 Vol. 46, No. 6

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2021, 46(6): 1-2.

[Abstract](420) [FullText HTML] (188) [PDF 1939KB](49)

Abstract:

Research progress of GNSS atmosphere-ocean remote sensing technology

AN Hao, YAN Wei, DU Xiaoyong, BIAN Shuangshuang

2021, 46(6): 1-10. doi: 10.12265/j.gnss.2021101303

[Abstract](600) [FullText HTML] (483) [PDF 2364KB](117)

Abstract:
The atmosphere-ocean remote sensing technology of fully mining Global Navigation Satellite Systems (GNSS) signal resources has always been a research hotspot. With the construction and development of GNSS, a series of novel technologies and methods to obtain the parameters of atmospheric and oceanic environment by GNSS delayed signals, reflected signals, occultation signals and polarimetric signals have appeared successively. In this paper, the principles of GNSS delay (GNSS-D), GNSS reflectometry (GNSS-R), GNSS radio-occultation (GNSS-RO) and GNSS Polarimetric radio-occultation (GNSS-PRO) technologies are respectively summarized on the basis of reviewing the general situation of GNSS atmosphere-ocean remote sensing technology. The progress of their research are also illustrated comprehensively and systematically, especially the mechanism, advantages and status of emerging GNSS-PRO technology. Finally, the development prospect of this field is discussed. The breakthrough and development of related technologies will play an increasingly important role in the earth science fields such as meteorology, hydrology, ocean, land and space environment.

Analysis of the effect of gravity field models on precise orbit determination of Swarm satellites

FANG Wenhao, KONG Qiaoli, LI Changsong, ZHANG Dezhi, ZHANG Linggang, WANG Tianfa

2021, 46(6): 11-15. doi: 10.12265/j.gnss.2021083102

[Abstract](303) [FullText HTML] (143) [PDF 2513KB](23)

Abstract:
In order to obtain the precise orbits of the Swarm satellite, the satellite-borne GPS data and reduced-dynamic orbit determination method are adopted, and the pseudo-stochastic pulse parameters are introduced into the equation. The influence of GOCO06s Earth gravity field model with different degree on the accuracies of the solved orbits for Swarm satellite are analyzed in detail, and the orbit accuracies of Swarm satellite are investigated and compared using PGM2000a, EIGEN-2, EGM2008 and GECO gravity field models with 100 degree. The results show that when the degree of GOCO06s gravity field model increase between 30 and 100, the orbit accuracies of Swarm-A, Swarm-B and Swarm-C satellite in radial, tangential and normal directions will be higher and higher. However, when the degree is higher than 100, the orbit determination accuracy is basically stable, and the orbit determination accuracy is better than 3 cm in all directions. In addition, the EGM2008, GECO and EGM2008 GOCO06s models with 100 degree are used to determine the orbit of three Swarm satellites. The orbit accuracy of the solutions is equivalent and higher than that of other gravity field models of the same degree.

BDS/GPS/LEO precise point positioning based on fourier series fitting LEO orbit error

LI Xiangjun, YE Xiaozhou, LIU Wenxiang, WANG Feixue

2021, 46(6): 16-24. doi: 10.12265/j.gnss.2021071901

[Abstract](571) [FullText HTML] (134) [PDF 3933KB](54)

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In view of the problems that most of the low earth orbit (LEO) constellation designs are in the preliminary demonstration stage, the LEO orbit cannot be accurately obtained, and the orbit error is difficult to express accurately, BDS /GPS/LEO precise point positioning (PPP) based on Fourier series fitting LEO orbit error is proposed. Since the orbit error presents a quasi-periodic sinusoidal characteristic, the Fourier series is used to fit the LEO orbit error, and the LEO observation data and ephemeris products are generated by simulation. Finally, the influence of LEO orbit error on the accuracy and convergence time of BDS/GPS/LEO PPP is analyzed. The simulation results show that the BDS/GPS/LEO PPP error increases gradually with the increase of the LEO orbit error, but it is not significantly related to the station latitude and the LEO constellation configuration. And in order to ensure the convergence time of BDS/GPS/LEO PPP in the global area shorter than that of BDS/GPS PPP, the root mean square (RMS) of the LEO orbit error should be less than 5 cm, 11 cm, 12 cm in the 6×10,12×10,18×10 LEO constellation configuration respectively.

Study on surface deformation of Longyangxia hydropower station reservoir area based on BDS and InSAR

ZHANG Yongying, ZHANG Shengpeng, GONGBAO Zhaxi, LI Shuiping, LI Yagang, SHENG Tianchen

2021, 46(6): 25-29. doi: 10.12265/j.gnss.2021040802

[Abstract](383) [FullText HTML] (154) [PDF 2479KB](39)

Abstract:
At present, BeiDou Navigation Satellite System (BDS), continuously operation reference sations (CORS) and synthetic aperture radar interferometry (InSAR) are developing rapidly and have a bright future. However, the focus of using the above technology to monitor the deformation of the reservoir area is artificial buildings, which does not verify the availability of BDS or integrate the advantages of CORS technology. In view of this problems, combined with the advantages of BDS and CORS with high temporal resolution and InSAR high spatial resolution, a suitable combined monitoring scheme is explored in Longyangxia reservoir area. The results show that: there is a large area of surface deformation area in Longyangxia reservoir area during the study period, with the maximum subsidence rate of 52.48 mm/a and the maximum uplift rate of 43.60 mm/a. The accuracy of BDS real-time dynamic difference monitoring results is 7.1 mm, and the accuracy of InSAR monitoring results is 4.4 mm, which meet the precision of deformation monitoring It is feasible to use InSAR to screen large area deformation area and combine CORS with BDS for real-time dynamic difference monitoring of key areas.sults is 4.4 mm, which meet the precision of deformation monitoring It is feasible to use InSAR to screen large area deformation area and combine CORS with BDS for real-time dynamic difference monitoring of key areas.

Analysis of anti-spoofing performance of GNSS nulling anti-jamming antenna

REN Binbin, NI Shaojie, CHEN Feiqiang, WU Jian, GAO Lichao

2021, 46(6): 30-36. doi: 10.12265/j.gnss.2021070601

[Abstract](611) [FullText HTML] (169) [PDF 2781KB](62)

Abstract:
In order to analyze the anti-spoofing performance of the nulling anti-jamming antenna for Global Navigation Satellite Systems (GNSS) in the spoofing interference scenario, the theoretical formula for the power of authentic and spoofing signal is derived which are processed by the nulling antenna using power inversion algorithm with limited snapshots. The influence of the power of the spoofing signal arriving at the antenna array interface on the output power of the authentic and spoofing signal is analyzed in detail. And the spoofing suppression ratio is used to measure the anti-spoofing performance of the adaptive nulling antenna using power inversion algorithm. The analysis shows that even if the power of the spoofing signal is below the noise level, the adaptive nulling anti-jamming receiver using power inversion algorithm can still suppress the spoofing. And when the spoofing signal-to-noise ratio is high, the suppression effect is more obvious. Finally, the conclusion is verified by simulation and hardware platform test.

Analysis on the development of core positioning parameters of GPS navigation message

CHANG Zhiqiao, XIN Jie, SHI Xin, HUANG Shuanglin, SHAO Jiani

2021, 46(6): 37-43. doi: 10.12265/j.gnss.2021070501

[Abstract](522) [FullText HTML] (192) [PDF 2232KB](44)

Abstract:
This paper summarizes the development process of GPS spatial signal interface control file, and compares the message structure and broadcast mode of three existing navigation message types. The development characteristics and improvement effects of ephemeris parameters, clock error parameters and integrity parameters are analyzed in detail. The analysis results show that the new GPS navigation message provides high accuracy of broadcast ephemeris and clock error products by increasing the core positioning parameters and reducing the quantization unit. After adding two parameters, the average root mean square (RMS) value of the ephemeris fitting position error is reduced from 0.137 m to 0.025 m. In order to adapt to the high-precision ephemeris fitting model, the distance quantization unit is also reduced to millimetre. By reducing the quantization unit of satellite clock error parameters, the RMS predicted 1 h clock error is reduced from 0.097 m to 0.042 m.

Improved weighted centroid indoor positioning algorithm for 5G base stations

YAN Zichun, WANG Xiaopeng, WANG Bohui, CHAI Hailong

2021, 46(6): 44-48. doi: 10.12265/j.gnss.2021071201

[Abstract](471) [FullText HTML] (150) [PDF 2700KB](57)

Abstract:
In response to the problem that in existing base station indoor localization algorithm the selection of localization base stations and the unreasonable setting of weights may lead to low localization accuracy, this paper proposes an improved weighted centroid indoor localization algorithm based on received signal strength indicator (RSSI) in the 5G environment. The algorithm obtains the distance from five known base stations to the point to be located by RSSI ranging, and then makes a circle with the known base station location as the centre. For the intersecting pentagonal area, any three vertices are taken to form a triangle. The triangle's centroid coordinates are calculated by setting the appropriate weights according to the type of base station and the distance to the point to be located, and then a maximum likelihood estimation is made based on the ten triangle's centroid coordinates to obtain the final location point. The simulation results show that the indoor localization accuracy of this algorithm is significantly improved when compared with the normal and weighted centroid algorithms in both sparse and dense base station environments.

Study on a tight integrated navigation and positioning algorithm of GNSS/visual observation

FENG Yi, TU Rui, HAN Junqiang, ZHANG Yin, LI Fangxin, HONG Ju, ZHANG Shixuan

2021, 46(6): 49-54. doi: 10.12265/j.gnss.2021081001

[Abstract](639) [FullText HTML] (166) [PDF 2742KB](51)

Abstract:
The Global Navigation Satellite System (GNSS) signals are susceptible to occlusion or electromagnetic interference in weak GNSS environments, which may seriously affect the reliability, continuity and accuracy of navigation and positioning. To solve this problem, this paper studies a tightly integrated navigation and positioning method with GNSS and visual combined observations. Firstly, with the image data collected by the camera, the ORB-SLAM2 open source platform is used to obtain the visual position result increment, and then combined with the GNSS pseudo-range observation data using Kalman filter for combined positioning solution. Validation is conducted with measured GNSS pseudo-range observation data and image data, the test results show that the algorithm can not only effectively improve the continuity and accuracy of navigation and positioning in weak GNSS environment, but also maintain continuous navigation when the number of satellites is less than four.

Analysis of the influence of time-domain anti-interference on correlation peaks under channel characteristics

LI Xianghao, CHEN Feiqiang, LU Zukun, LIU Zhe, HAN Chunyang, OU Gang

2021, 46(6): 55-62. doi: 10.12265/j.gnss.2021012902

[Abstract](278) [FullText HTML] (111) [PDF 3694KB](23)

Abstract:
Due to the non-ideal characteristics of analog components such as antennas and RF front-ends, ranging errors will occur in the Global Navigation Satellite System (GNSS) receiver. At present, the deviation of the ranging value caused by the traditional anti-jamming algorithm has become the main obstacle to the improvement of the accuracy of high-precision ranging receiver. In this paper, theoretical derivation proves that when the channel characteristics are ideal, the correlation function will still be asymmetric due to the time-varying characteristics of the anti-jamming filter coefficients under iteration and the uncertainty of the interference auto correlation value. When the channel characteristics are not ideal, the traditional time-domain anti-jamming algorithm based on a single antenna will further deteriorate the originally asymmetrical correlation peak distortion. It is proved that under the non-ideal channel characteristics, the asymmetric correlation peak distortion caused by the time-domain anti-interference filter is further deteriorated due to the superposition effect of the correlation functions of each delay.

Precision test and analysis of MERRA-2 vapor products in Qinghai-tibet plateau

JIANG Zhicheng, CAO Haidi, SHI Chenyang, CHAI Xiang, ZHANG Zhenwei

2021, 46(6): 63-67. doi: 10.12265/j.gnss.2021072201

[Abstract](419) [FullText HTML] (254) [PDF 2416KB](40)

Abstract:
MERRA-2 is the latest atmospheric reanalysis data, and the grid water vapor products provided by it have high temporal and spatial resolution, but there is still no literature to evaluate the applicability of MERRA-2 water vapor products in Qinghai-Tibet Plateau. It is urgent to carry out the applicability analysis of MERRA-2 water vapor products in this region. In this paper, the water vapor vertical profile function of Qinghai-Tibet Plateau is established by using MERRA-2 grid water vapor data and lattice dot height data, and the water vapor value of lattice dot is calculated to nearby sounding station or the Global Navigation Satellite System (GNSS) station by using water vapor vertical profile function, and then the bilinear interpolation method is used to calculate the water vapor interpolation in horizontal direction. Finally, the accuracy analysis is carried out. The results show that the daily average deviation between stations in the plateau area is mostly within 2 mm, and the monthly average deviation is less than 1 mm. While the accuracy of MERRA-2 water vapor products is higher in the middle and north of the plateau and lower in the south.

Noise analysis and velocity field correction of Inner Mongolia CMONOC coordinate time series

LI Xin, YAO Dexin

2021, 46(6): 68-73. doi: 10.12265/j.gnss.2021070801

[Abstract](341) [FullText HTML] (99) [PDF 2516KB](13)

Abstract:
This paper use the Global Navigation Satellite System (GNSS) data product service platform of China earthquake administration to obtain the observation data of 15 continuous terrestrial network stations in the Inner Mongolia from 2010-06 to 2021-06, and use GAMIT/GLOBK software and HRCTOR software to calculate the coordinate time series after removing the singular values. Finally, Bayesian information criterion (BIC) numerical analysis is combined with to determine the optimal noise model: the optimal model of Inner Mongolia coordinate time series in the east (E) direction is white noise+flicker noise (WN+FN), and the optimal noise model in the north (N) and zenith (U) directions is white noise+power law noise (WN+PL). The optimal noise model is used to correct the velocity field. Under the ITRF14 framework, the average moving speed of the land network in Inner Mongolia is 30.653 mm/a, and the moving direction is 26°57′51″SEE; The average moving speed in the vertical direction is 0.792 mm/ a.

Research on GPS elevation fitting method for linear engineering

YUAN Xiaoyan, SHI Chenyang, CHAI Xiang, CAO Haidi

2021, 46(6): 74-77. doi: 10.12265/j.gnss.2021053103

[Abstract](405) [FullText HTML] (159) [PDF 2957KB](27)

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Aiming at the characteristics that mathematical models are only applicable to specific terrain and neural network models are easy to fall into local optimal solution, an optimal weighting algorithm is proposed. Two mathematical models and two neural network models are used to fit the GPS elevation of linear engineering respectively, and a single algorithm with good fitting effect of each model is combined into an optimal weighting algorithm. The results show that the polynomial fitting algorithm is superior to the multifaceted function method, and the genetic simulated annealing algorithm optimized BP neural network algorithm (GSA-BP) is better than other algorithms, which is the best single algorithm. The precision of the weighted algorithm is 17.7% and 10.0% higher than that of the single member algorithm, respectively, and can basically meet the requirements of the fourth grade leveling, which is feasible in GPS elevation fitting of linear engineering.

Design and implementation of indoor 2D positioning system based on RSSI joint algorithm

ZHANG Liangcheng, GU Liuwan, LI Xiaoming, MU Xiaomin, YANG Tao, TANG Jie

2021, 46(6): 78-83. doi: 10.12265/j.gnss.2021072901

[Abstract](502) [FullText HTML] (270) [PDF 3074KB](29)

Abstract:
Previous location fingerprint matching algorithm have some problems of low positioning accuracy caused by huge calculating. This study proposed a joint algorithm based on received signal strength indication (RSSI). The joint algorithm integrate K nearest neighbor position fingerprint matching and triangulation auxiliary. Firstly, the positioning coordinates was obtained and modified by triangulation and then position fingerprint matching was conducted. This can improve the positioning accuracy. A software integrating location fingerprint collection and online positioning was developed using Android Studio in Java language and tested on the test site. The results show that the RSSI-based algorithm can resch positioning accuracy between 1 and 3 meters in 2D plane, which is higher than the single algorithm.

Generalized ridge estimation method for morbid weighted total least squares

WENG Ye, SHAO Desheng

2021, 46(6): 84-89. doi: 10.12265/j.gnss.2021061601

[Abstract](339) [FullText HTML] (156) [PDF 2170KB](26)

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For the variable error (EIV) model in the weighted case, the generalized ridge estimation method is used to deal with the morbid problem of the total least squares adjustment. Combined with optimization criterion and covariance propagation rate, the correction formula of unknown parameters is derived. Accordsing to the principle of minimizing mean square error of parameter estimation, the iterative solution of ridge parameter in generalized ridge estimation is given by solving partial derivative, and the meaning and function of generalized ridge parameter are discussed. The weighted least squares estimation, total least squares estimation, the weighted least squares ridge estimation, total least squares ridge estimation, generalized ridge estimation of the weighted least squares and generalized ridge estimation of total least squares are compared and analyzed by examples. The advantages and disadvantages of generalized ridge estimation of weighted total least squares are described.

A fast spaceborne GNSS-R sea surface wind speed retrieval method based on observation correction

TAN Chengdan, LUO Ruidan, LI Yafeng, YUAN Chao, YANG Guang, TIAN Xiangwei

2021, 46(6): 90-97. doi: 10.12265/j.gnss.2021071402

[Abstract](589) [FullText HTML] (111) [PDF 3021KB](31)

Abstract:
The fast-delivery inversion (FDI) algorithm is a typical spaceborne Global Navigation Satellite system Reflectometry (GNSS-R) sea surface wind speed inversion method, which has the characteristics of low computational complexity and fast processing. However, the retrieval observation extraction accuracy in FDI algorithm is low, which leads to low wind speed retrieval accuracy. In view of this, an improved FDI algorithm based on observation correction is proposed to realize the fast and high-precision retrieval of sea surface wind speed. In this method, firstly, the auxiliary measurement information is used to correct the observation to reduce the influence of interference factors, then the sea surface wind speed value is extracted from the ASCAT satellite wind speed data based on the statistical analysis method, and finally the geophysical model function (GMF) relationship between the sea surface wind speed and the corrected observation is established to realize the retrieval of sea surface wind speed. Compared with the traditional FDI algorithm, the wind speed retrieval bias of this method is smaller, and the root-mean-square error (RMSE) is reduced by 29%.

Adaptive detection method pedestrian step frequency in multi scenes

GUO Cheng, WU Fei, ZHU Hai

2021, 46(6): 98-106. doi: 10.12265/j.gnss.2021062101

[Abstract](391) [FullText HTML] (287) [PDF 4006KB](42)

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Aiming at the problems of over counting and wrong counting in step frequency detection, which affect the indoor positioning accuracy of pedestrian dead reckoning (PDR), an adaptive step frequency detection algorithm is proposed. Because there is a large amount of interference noise in the data directly collected by the built-in acceleration sensor of smart phone, a combined filtering denoising method is proposed.The acceleration data is denoised by preprocessing filter combination of exponential hull moving average, Kalman filter (KF) and low-pass filter. Then, in different scenes, such as upstairs and downstairs, horizontal ground and unlimited walking speed, the number of peak-valley values is obtained after the peak-valley value de differentiation, adaptive dynamic threshold and peak-valley value pairing detection algorithm, so as to achieve accurate step counting in multi scenes and multi gait. The experimental results show that, compared with the peak detection method and dynamic threshold algorithm, the proposed method can effectively eliminate the false steps and adapt to the upstairs and downstairs scenes, and the average accuracy of the experiment in the comprehensive scene reaches 99.44%.

BeiDou space-time blockchain

LIU Guangming, XIE Guojun, SHA Feng, CHENG Wei

2021, 46(6): 107-111. doi: 10.12265/j.gnss.2021071202

[Abstract](559) [FullText HTML] (172) [PDF 2233KB](75)

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It is briefly introduced the proof-of-work consensus algorithm of blockchain technology. It is pointed out that the ambiguity of space-time will cause consensus divergence, and lead to reduced efficiency and waste of computing power. It is proposed to transmit common-channel signaling through BeiDou Navigation Satellite System (BDS) short message service, which can construct a scale-free network and avoid the asynchronous network ecology. It is also made a more in-depth discussion on the application of blockchain, and pointed out that all distributed behaviors can apply blockchain technology to solve the trust problem. Discussed that when blockchain technology is used in the real world, it should ensure the credibility of the ledger, the credibility of the physical and the credibility of space-time at the same time. It is proposed that the role of BeiDou is not only convenient and reliable to collect space-time tags, but also has the deeper meaning that the BeiDou positioning, navigation and timing (PNT) service has space-time credibility, including: service ubiquity, benchmark uniformity, space-time self-consistency, causal inevitability and consensus synchronization. Finally, the specific application of the BeiDou space-time blockchain is classified and introduced, including: full-chain supervision of processes, efficient resource sharing, and task crowd-creation collaboration.

Evaluation of GNSS satellite timing performance under far sea and far region mobile platform

ZHU Enhui, WANG Zhiping, LI Guojun

2021, 46(6): 112-117. doi: 10.12265/j.gnss.2021080401

[Abstract](305) [FullText HTML] (125) [PDF 2263KB](24)

Abstract:
Compared with the satellite timing performance under terrestrial stationary condition, it is more susceptible to the effects of visible satellite and space electromagnetic environment under the condition of mobile platform in the far sea and far region. This paper use high-performance cesium atomic clock as the reference external frequency standard for satellite receivers to perform timing tests at test points in the East Siberian sea, the northernmost test point, the Arctic Ocean return point, the Bering Sea test point, and the Japan Sea test point. Based on the number of satellites and frequency accuracy, the dynamic Global Navigation Satellite System (GNSS) multi-system timing performance of distant sea is analyzed. The test results can be used as an important basis for the timing performance evaluation of important waterways in the northern hemisphere and test areas in the polar seas. The test results show that the average number of visible satellites of the GNSS system at all test points is maintained at more than 10, the one-way time difference jitter is maintained within ±20 ns, and the output frequency accuracy can reach the magnitude of 10^-13.

Iversion of normalized difference vegetation index based on GPS-IR

XIAO Xingxing, LYU Weicai, ZHONG Chen, CAO Jinjin, LI Yanjie, ZHANG Can

2021, 46(6): 118-124. doi: 10.12265/j.gnss.2021060901

[Abstract](351) [FullText HTML] (106) [PDF 2757KB](36)

Abstract:
In view of the fact that GPS receiver is sensitive to the water content of surrounding vegetation when receiving L-band signal, the normalized difference vegetation index (NDVI) of the station is retrieved by using the change of GPS reflected signal. In this paper, the normalized microwave reflection index (NMRI) calculated from the continuous observation data of two GPS reference stations in recent five years is used to construct a univariate linear model for NDVI inversion. The correlation coefficients R of the inversion results are 0.626 53 and 0.625 73 respectively, and the root mean square error root mean square error (RMSE) are 0.051 29 and 0.055 08 respectively. The correlation coefficients of the inversion results are increased by 2% and 6% respectively by using BP neural network model, which indicates that the regional NDVI inversion results of GPS-interferometric reflectometry (GPS-IR) have high reliability. This study provides a theoretical support for obtaining accurate position, real-time continuous and high-resolution NDVI.

Analysis of strain field considering the influence of colored noise in Qinghai area

ZHANG Xing, WEI Guanjun

2021, 46(6): 125-130. doi: 10.12265/j.gnss.2021061101

[Abstract](365) [FullText HTML] (81) [PDF 2999KB](20)

Abstract:
Based on the 10-years coordinate time series data of crustal movement observation network of 14 china (CMONOC) continuous stations in Qinghai, the optimal noise model of each continuous station was determined by using Bayesian information criterion (BIC), and then the modified horizontal velocity field was obtained. On this basis, the global rotation and linear strain model was established to analyze the strain characteristics in Qinghai. The results show that the noise characteristics of CMONOC continuous station in Qinghai are different in different directions. The optimal noise models in east (E), north (N) and up (U) directions are “white noise + power law noise (WN+PL)”, “white noise + Gaussian Markov noise (WN+GGM)” and “white noise + flicker noise (WN+FN)” respectively. After considering the influence of colored noise (CN), the average horizontal motion velocity of CMONOC continuous station in Qinghai based on the framework of ITRF2014 is 39.61 mm/a and the motion direction is 88°57'58"NEE. The northeastern and southwestern parts of the Qinghai region with relatively strong tectonic activities are characterized by compressive strain and tensile strain, respectively. From northeast to southwest, the compression strain gradually decreases and the tensile strain gradually increases, which is generally manifested as the compression strain.