Journal of Surveying and Mapping, Vol. 53, No. 2, 2024

The content of this article comes from the Journal of Surveying and Mapping, Issue 2, 2024 (drawing review number: GS Jing (2024) No. 0297)

Separable nonlinear least squares calculation method and its application in LiDAR waveform decomposition

Wang Ke

School of Civil Engineering and Civil Engineering, Shandong University of Technology, Zibo 255000, China

Funds: National Natural Science Foundation of China (42074009); Natural Science Foundation of Shandong Province (ZR2020MD043)

About author:WANG Ke (1990—), female, graduated from Shandong University of Science and Technology in June 2021 with a Ph.D. degree in engineering (Supervisor: Prof. Guolin Liu), and her research direction is the theory and application of modern measurement data processing. E-mail: [email protected]

WANG Ke. Separable Nonlinear Least Squares Calculation Method and Its Application in LiDAR Waveform Decomposition[J]. Journal of Surveying and Mapping,2024,53(2):391-391. DOI: 10.11947/j.AGCS.2024.20220697

WANG Ke. Research on computing methods of separable non-linear least squares and application in LiDAR waveform decomposition[J]. Acta Geodaetica et Cartographica Sinica, 2024, 53(2): 391-391. DOI: 10.11947/j.AGCS.2024.20220697

Read more: http://xb.chinasmp.com/article/2024/1001-1595/20240217.htm

As the most basic nonlinear optimization method, nonlinear least squares is widely used in the parameter estimation of nonlinear function models in the field of surveying and mapping. The Gaussian characteristic parameters of the LiDAR full-waveform echo signal are usually solved without considering the structural characteristics that the model can be decomposed into multiple Gaussian functions, but all the parameters to be solved are regarded as nonlinear parameters, and the Taylor series expansion formula is used to linearize the nonlinear model, and then the LM (Levenberg-Marquardt) algorithm is used to solve the problem, which has high requirements for the initial values of the parameters. According to the source of the actual problem, if the function model can be represented as a linear combination of nonlinear functions, it is called a separable non-linear least squares (SNLLS) problem, and the most common method to solve such problems is the variable projection (VP) algorithm. However, the complexity of the calculation of the derivative of the variable projection operator in the separable nonlinear least squares objective function based on the traditional VP algorithm will reduce the efficiency of solving the separable nonlinear least squares problem, and the pathology of the nonlinear function matrix will also lead to the inaccurate solution results. Therefore, on the basis of analyzing the principle of the VP algorithm, this paper improves the objective function calculation method of the traditional VP algorithm, combines the nonlinear parameter optimization method, conducts in-depth research on the linear parameter and nonlinear parameter estimation method after parameter separation, and applies and verifies the separable nonlinear least squares calculation method around the solution of the characteristic parameters of the Gaussian function component in LiDAR waveform decomposition. The main research content of the paper includes the following aspects.

(1) The method of parameter separation and parameter non-separation for separable nonlinear least squares problem is systematically analyzed. Focusing on the special structure of the separable nonlinear least squares problem, combined with the nonlinear model and the parameter adjustment problem, based on the analysis of the principle of the VP algorithm, the derivative calculation formula of the projection operator of the objective function variable is derived. Through theoretical analysis and experiments of airborne LiDAR waveform decomposition, it is proved that the results of the separable nonlinear least squares method based on the VP algorithm are consistent with the nonlinear least squares method with non-parameter separation, and the parameter separation method based on the VP algorithm has the advantages of less iterations, low dependence on the initial value of the parameters, and can reduce the degree of pathology of the original problem.

(2) An improved VP algorithm based on singular value decomposition (SVD) and finite difference method is proposed. The finite difference method is used to approximate instead of the numerical calculation of Jacobian matrices, which avoids the partial derivative calculation of pseudo-inverse matrices, solves the complex problem of traditional variable projection algorithms, and effectively improves the computational efficiency of separable nonlinear least squares problems. Combined with the matrix factorization method, the nonlinear function matrix is decomposed by SVD in the optimization process, which simplifies the calculation of the objective function and ensures the stability of the pseudo-inverse matrix solution, and the improved variable projection algorithm not only combines the special structural characteristics of separable nonlinear least squares, simplifies the calculation of the matrix, but also improves the calculation efficiency and numerical stability in the iteration process of separable nonlinear parameters. The algorithm is verified by simulating the Gaussian function test and the ICESat-1 spaceborne LiDAR waveform decomposition test.

(3) For the solution of separable least squares nonlinear parameters, an LM algorithm based on trust-region (TR) criterion and a particle swarm optimization (PSO) algorithm based on parameter constraints are proposed. Based on the analysis of the basic principles of the LM algorithm, the LM algorithm based on the trust domain criterion adjusts the damping parameters in the iterative process based on the idea of TR criterion, and realizes the fast convergence of separable nonlinear parameters to the optimal solution along the effective search direction. Based on the traditional particle swarm optimization algorithm, the PSO algorithm is based on the fast search speed of the artificial intelligence algorithm combined with nonlinear parameter optimization, and the parameter range of particle initialization is narrowed by increasing the interval constraint of the parameters, and the global convergence of separable nonlinear parameters is improved. The feasibility of the LM algorithm based on TR criterion and the particle swarm optimization algorithm based on parameter constraints to solve the separable nonlinear parameters are verified by the numerical examples of the trigonometric function model and the estimation of the nonlinear characteristic parameters of the spaceborne LiDAR waveform Gaussian function.

(4) For the solution of separable least squares linear parameters, an improved spectral correction iterative algorithm based on U-curve is proposed. In order not to change the equivalence relationship of the equations, based on the spectral correction iterative algorithm, the method of determining the ridge parameters by the L curve is used to determine the spectral correction parameters, which improves the degree of sickness of the nonlinear function matrix and ensures the stability of the normal equation solving, and verifies the effectiveness of the method in dealing with the pathological conditions of linear parameters through the fractional model example test and the estimation test of the characteristic parameters of the GF-7 spaceborne LiDAR waveform.

(5) The application of the separable nonlinear least squares method in LiDAR waveform decomposition is expanded. In view of the structural characteristics of the echo signal model, which can be decomposed into multiple Gaussian function models, the VP algorithm is used to separate the linear parameters (amplitude) from the nonlinear parameters (crest position and width) in the waveform decomposition, and the nonlinear characteristic parameters of the Gaussian function components are solved by the LM algorithm based on the TR criterion. The effectiveness of the method is verified by goodness of fit, root mean square error and maximum deviation, and the application of separable nonlinear least squares calculation method in the field of surveying and mapping is expanded.

Research on key technologies for joint processing of BDS-2/BDS-3 satellite observation data

Hu Chao

Anhui University of Science and Technology, Huainan 232001, Anhui, China

Funds: National Key R&D Program of China (2020YFA0713502); Natural Science Foundation of Anhui Province(2108085QD173); National Natural Science Foundation of China (41874039); Natural Science Research Project of Anhui Universities(KJ2020A0310)

About author:HU Chao (1990—), male, associate professor, graduated from China University of Mining and Technology in July 2020 with a doctorate degree in engineering (Supervisors: Academician Yang Yuanxi and Professor Wang Qianxin), and his research direction is satellite geodesy. E-mail: [email protected]

HU Chao. Research on Key Technologies of BDS-2/BDS-3 Satellite Observation Data Joint Processing[J]. Journal of Surveying and Mapping,2024,53(2):392-392. DOI: 10.11947/j.AGCS.2024.20220698

HU Chao. An investigation of key technologies related to combining BDS-2 and BDS-3 observations in data processing[J]. Acta Geodaetica et Cartographica Sinica, 2024, 53(2): 392-392. DOI: 10.11947/j.AGCS.2024.20220698

Read more: http://xb.chinasmp.com/article/2024/1001-1595/20240218.htm

As the core of global navigation and location services, high-quality satellite observation data and high-precision orbit clock errors play a vital role in the service capability of the entire system. In this paper, the key technologies such as spatial configuration, fast and high-precision processing, orbital clock aberration refinement and observation data deviation in the joint processing of BDS-2/BDS-3 satellite observation data were discussed and systematically studied.

(1) In view of the accuracy and timeliness of fast and ultra-fast orbit products in the analysis center and the uneven distribution of tracking stations around the world, a tracking station optimization strategy based on Geometric Attenuation Factor (GDOP) of Accuracy of Orbit Determination Observation Equation was proposed. Based on the criterion of the minimum GDOP value of the observation equation, the global location of the smallest tracking stations was screened through global grid division, and the optimal distribution of global tracking stations was determined gradually and cumulatively. Experiments show that 90% of the accuracy of the overall orbital parameters of all stations can be obtained by filtering the list of stations, and the timeliness is improved by about 50%.

(2) In order to further improve the screening efficiency of ground tracking stations, an optimal site solution strategy based on global grid scaling and genetic algorithm was proposed. An OEDOP that takes into account the accuracy of parameters such as track and ERP is defined. It realizes the rapid determination of the multi-system global station distribution based on the attributes and parameter accuracy of the comprehensive tracking station. Based on the set 5%, 10%, 15% and 20% OEDOP thresholds, the parameter processing efficiency is increased by 1.96, 3.32, 5.27 and 6.17 times under the premise that the accuracy of orbit and pole shift measurement is lost by 0.33~9.92 cm and 5.77~41.53 uas, respectively.

(3) In view of the phenomenon of the later accuracy reduction of ultrafast orbit observation, an orbit refinement model based on the accuracy attenuation factor (DOP) of orbit determination parameters was proposed. Based on the Akaike information criterion, the DOP value prediction model was constructed and optimized, and the orbit state parameter correction function with the DOP value as the independent variable was established, which realized the improvement of the accuracy of the ultra-fast observation orbit in the later stage. The influence of the arc length and function model of satellite-to-ground observation data on the orbit correction effect is discussed. The experimental results show that the orbit correction strategy proposed in this paper can improve the accuracy of ultra-fast orbit observation by 12.35%~22.02% at 3 h.

(4) In order to solve the problem of low accuracy of Beidou ultra-fast prediction clock error products, a clock preprocessing strategy combining the frequency data of the clock error sequence and the Baarda algorithm was proposed, and the noise reduction processing of the clock sequence was realized based on the Tikhonov regularization algorithm, which improved the accuracy of BDS-2 and BDS-3 clock error prediction by 1.0%~15.2% and 23.2%~31.9%, respectively. The correlation coefficients between BDS-2/BDS-3 satellites were extracted, and the stochastic model of prediction clock error was refined. The PLS+BPNN algorithm is used to realize the model residual extraction and forecasting. The clock error prediction results show that the improved model can improve the 18-hour prediction accuracy of BDS-2 and BDS-3 satellites by 30.7%~47.3% and 49.9%~59.3%, respectively. In this paper, the BDS-2/BDS-3 ultrafast orbit determination strategy based on clock error constraint is studied, and the optimal observed arc length merging method for the initial state of the predicted orbit is constructed.

(5) The estimation, analysis and modeling of the system deviation parameters (ISB) in the BDS-2/BDS-3 satellite joint precision orbit determination were studied. A joint orbit determination system deviation estimation model based on singular value decomposition was proposed. The short-term prediction model of systematic deviation time series is constructed, and the orbit determination strategy of introducing systematic deviation constraints in ultra-fast precision orbit determination is realized, which weakens the deviation between BDS-2/BDS-3 satellite-to-ground observation data. By establishing a short-term forecast model for ISB time series and introducing the forecast value into the ultra-fast orbit determination as a constraint, the accuracy of the 18-hour overlapping arc of BDS-2 and BDS-3 orbits can be improved by -0.4~1.0 cm and 0.8~4.1 cm, respectively.

(6) A one-step modeling strategy of pseudorange bias and multipath delay based on LS+AR model for BDS-2/BDS-3 satellite joint processing is proposed. Considering the BDS-2/BDS-3 inter-satellite correlation and noise reduction algorithm, the modeling ability of Beidou pseudorange deviation and multipath delay is effectively improved. The single-frequency PPP test shows that the improved strategy can improve the positioning accuracy of B1I frequencies E, N and U by 2.9%~31.6%, 3.3%~21.4% and 0.2%~69.2%, respectively, and increase the B3I frequencies E, N and U directions by 2.8%~14.3%, 0~20.9% and 1.5%~15.3%, respectively.

Study on the movement law and regional control of rock strata in deep mining of huge thick and weakly cemented overburden rock

Zhang Guojian1,2,3

1. School of Surveying, Mapping and Geoinformation, Shandong Jianzhu University, Jinan 250101, Shandong, China;

2. School of Environment and Geomatics, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China;

3. Shandong Energy Group Technology Research Institute, Jinan 250101, Shandong, China

Funds: National Natural Science Foundation of China (51974292); National Natural Science Foundation of China (52204097)

About author:ZHANG Guojian (1989—), male, graduated from China University of Mining and Technology in June 2020 with a Ph.D. degree in engineering (Supervisor: Prof. Guo Guangli), and his research interests are deformation monitoring and subsidence control. E-mail: [email protected]

ZHANG Guojian. Study on the movement law and regional control of rock strata mined in deep mining of huge thick and weakly cemented overburden rock[J]. Journal of Surveying and Mapping,2024,53(2):393-393. DOI: 10.11947/j.AGCS.2024.20220704

ZHANG Guojian. Study on the strata movement rule and regional control of deep mining with the super-thick and weak cementation overburden[J]. Acta Geodaetica et Cartographica Sinica, 2024, 53(2): 393-393. DOI: 10.11947/j.AGCS.2024.20220704

Read more: http://xb.chinasmp.com/article/2024/1001-1595/20240219.htm

In this paper, the physical and mechanical properties and microstructure characteristics of weakly cemented sandstone were studied through experiments, and the differences in rock mechanical properties, overburden structure characteristics and surface movement and deformation laws in the eastern and western deep mining areas were compared and analyzed, and the influencing factors leading to the small surface subsidence of the deep mining of the huge thick and weakly cemented overburden were clarified. Then, by means of mechanical analysis, numerical simulation and physical simulation, the surface movement and deformation law of deep mining of huge thick and weakly cemented overburden rock, the movement and failure characteristics of overlying rock formation, and the regional rock formation movement control method of deep mining of huge thick and weakly cemented overburden was proposed, and the specific results are as follows.

(1) There are obvious differences in the surface movement and deformation law of coal mining in the deep mining areas of the east and west, and the essential reason is that the lithology of the huge thick and weakly cemented sandstone is weak, but the overall stiffness of the rock layer is large. (1) Although the uniaxial compressive strength of the Cretaceous Zhidan Group sandstone is between 10~20 MPa, the lithology is weak. The internal voids of the rock are large, and the fractures and joints are almost not developed; The cementation is calcareous and insoluble in water, and the mechanical properties of the cementation are similar to those of rock particles. The thickness of the rock layer is large, and the folds and faults are not developed, which makes the overall stiffness of the sandstone of the Zhidan Group larger. (2) The uniaxial compressive strength of the sandstone of the Zhiluo Formation is between 20~40 MPa, and the lithology is moderately hard. The rocks are relatively dense, and there are fewer fractures and cavities. Although the cement is a clay mineral, it is not easily soluble in water; The thickness of the rock layer is large, and the folds and faults are not developed, which makes the overall stiffness of the sandstone of the Zhiluo Formation larger.

(2) Factors such as mining space, structural characteristics of overburden and horizontal tectonic stress have significant effects on the surface movement and deformation law of deep mining of huge thick and weakly cemented overburden rock: when D1/H0≥3 and D3/H0≥3, the ground expression is fully mined; The changes in the relative spatial distance and relative order of the main critical layer structure and the subcritical layer structure in the overburden structure have obvious differences in the influence on the surface movement and deformation law, the change of the relative spatial distance of the main critical layer structure and the subcritical layer structure has little impact on the surface subsidence coefficient, horizontal movement coefficient and main influence angle tangent, and the change of the relative order of the main critical layer structure and subcritical layer structure has a greater impact on the surface subsidence coefficient, but has little impact on the horizontal movement coefficient and the main influence angle tangent. When the horizontal structural stress reaches twice the vertical stress, the surface subsidence coefficient decreases to a maximum of 0.49, a decrease of 61.3%, a maximum increase of 1110 m, an increase of 205.6%, and a maximum increase of 1710 m, an increase of 247.8%.

(3) The displacement parallax method based on proportional series correction was used to monitor the similar material models, and the measurement accuracy was about 0.47 mm. This paper proposes the idea of superimposed similar material simulation for deep mining and the method of joint monitoring of monocular close-range photogrammetry, which overcomes the limitations of conventional similar material simulation to study the movement of rock formations in deep mining, and provides ideas and technical support for the study of the dynamic development process of regional deformation under the combined influence of multiple working faces in deep mining mining areas, and even the joint mining influence of multiple mining areas.

(4) The failure mode of the hugely thick and weakly cemented overburden rock is a "beam-arch shell" failure, and the failure boundary is an arch fracture, which gradually changes from a complete "arch shell" failure to a "semi-arch shell" failure with the continuous expansion of the mining range. With the increase of the thickness of the single layer, the failure mode of the thick layer of weakly cemented sandstone changes from the "arch shell" type to the "arch shell-beam-arch shell" type failure. Before the "archshell-beam" failure of the huge thick and weakly cemented sandstone, its movement process showed an obvious time correlation, and then the temporal correlation of the movement process disappeared, showing the characteristics of mining and sinking. Due to the "arch-shell-beam-arch shell" failure mode of the Juhou Zhidan Group sandstone, the mining surface of the deep multi-working face of the Juhou weakly cemented overburden rock is subsided.

(5) Combined with the theory of key layers, the theory of rock beams and the theoretical model of granular media of random media, this paper reveals the mechanism of the influence of thick-layered weakly cemented sandstone and horizontal tectonic stress on the movement law of the deep-mined rock strata of the huge-thick and weakly cemented overburden, which provides a theoretical basis for the rational explanation of the obvious small surface subsidence and the wide influence range of the deep mining of the heavily thickened and weakly cemented overburden in the deep mine. Combined with the rock beam theory and the pressure arch theory, the failure mode of the huge thick and weakly cemented overburden was analyzed, the tensile stress and shear stress equations at any point on any section of the rock beam were derived, and the balance equations of bending moment, shear force and axial force of any section of the arch trace were established.

(6) A method for controlling surface subsidence and reducing energy accumulation in the deep coal partial backfill mining of huge thick and weakly cemented overburden based on the main key layer is proposed. By studying the influencing factors and response rules of surface subsidence control and energy accumulation reduction effect of deep coal partial backfill mining based on the main key layer, it is considered that the influence degree of each influencing factor on the movement control effect of the partially filled mining rock layer based on the main key layer is as follows: the width of the collapsed working face> the filling rate> the width of the coal pillar in the section> the width of the filling face. The degree of influence on the energy accumulation of partial backfill mining based on the main critical layer is as follows: the width of the coal pillar in the section> the filling rate> the width of the collapsed working face > the filling working face. By analyzing the stress distribution characteristics of the composite backfill and the overlying rock layer of the backfill face based on the partial backfill mining of the main critical layer, it is pointed out that the control mechanism of the partial backfill mining based on the main critical layer is the synergistic effect between the composite backfill and the structure of the main critical layer.

Research on key technologies for monitoring underground illegal mining in mining areas based on InSAR/GIS

Xia Yuanping

School of Surveying and Mapping Engineering, East China University of Technology, Nanchang, Jiangxi 330013

Funds: National Natural Science Foundation of China (42174055; 41962018）

About author:XIA Yuanping (1982—), male, graduated from China University of Mining and Technology in December 2020 with a Ph.D. degree in engineering (Supervisor: Prof. Wang Yunjia), and his research direction is land environment and disaster monitoring. E-mail: [email protected]

Xia Yuanping. Research on Key Technologies for Monitoring Underground Illegal Mining in Mining Areas Based on InSAR/GIS[J]. Journal of Surveying and Mapping,2024,53(2):394-394. DOI: 10.11947/j.AGCS.2024.20220707

XIA Yuanping. Research on the key technologies of InSAR/GIS monitoring for illegal underground mining in coal mining area[J]. Acta Geodaetica et Cartographica Sinica, 2024, 53(2): 394-394. DOI: 10.11947/j.AGCS.2024.20220707

Read more: http://xb.chinasmp.com/article/2024/1001-1595/20240220.htm

Illegal underground mining is a persistent problem in many mining areas. Due to the difficulty in identifying underground illegal mining incidents, although the relevant departments have taken certain preventive measures, they are still repeatedly prohibited, which seriously affects the normal mining order of the mine and is easy to form a hidden danger of safety accidents. Therefore, in order to determine the underground mining area without people entering the underground or underground measurement space, and then make it possible to identify illegal mining, this paper starts from solving the three key technical problems of surface deformation information acquisition, the correlation between surface deformation information and underground mining location, and the identification of legal and illegal mining, and comprehensively uses the theoretical achievements of space earth observation technology, GIS, mining subsidence and other technologies to solve the problem of InSAR obtaining surface deformation information within the mining area. Taking the surface subsidence caused by underground coal mining as the research object, on the basis of revealing the correlation mechanism between surface deformation information and underground mining face, a GIS spatio-temporal data model that can integrate multi-source data and reflect the geological space and distribution characteristics in the process of multi-level spatio-temporal change is constructed, a screening model of underground legal mining and illegal mining is established, and InSAR and GIS technology are integrated to realize the rapid and efficient monitoring of underground illegal mining in mining areas.

(1) This paper summarizes the current research and development status of using InSAR technology for surface deformation monitoring in mining areas, and analyzes the main error sources of InSAR deformation detection and its main influencing factors in the monitoring of illegal mining in mining areas.

(2) In view of the geological phenomena and dynamic processes induced by underground mining, combined with the actual needs of underground illegal mining monitoring, a GIS data model supporting the dynamic expression of geological spatiotemporal processes was constructed, and the detailed structure and spatiotemporal database table structure of various types of mining subsidence were described. On this basis, a method of integrating InSAR and GIS technology for the identification of underground illegal mining is proposed, and the architecture of the illegal mining identification platform is built to provide a platform guarantee for the identification and monitoring of different types of illegal mining events.

(3) In view of the unlicensed underground mining events that cause large-scale surface deformation, an algorithm model for quickly and accurately delineating the surface mining subsidence area from the differential interferogram with a large distribution range is constructed according to the unique spatial, geometric and deformation characteristics of the surface subsidence area caused by underground mining. On this basis, the identification of illegal mining incidents from the delineated mining subsidence area was realized, and the identification results of underground illegal mining were basically consistent with the actual situation through data comparison and field investigation, and had a good identification effect.

(4) In view of the unlicensed mining incident that causes a small amount of surface deformation and is hidden under the house, the subsidence information of the corresponding PS point set of surface buildings (residential areas) is extracted by combining PS-InSAR technology and high-resolution optical remote sensing, and the deformation and spatiotemporal characteristics of the extracted building subsidence information are analyzed, and a method is proposed to quickly and accurately detect suspected illegal mining points from the subsidence information of buildings with large coverage. Based on the case study of Worldview-2 and PALSAR data in Shandi Village in the suburbs of Yangquan City, the illegal coal mining points in the village were successfully detected, and the detection results were highly consistent with the existing monitoring data, which has certain engineering applicability and practical application value.

(5) Combined with the InSAR surface deformation monitoring technology and the mining subsidence prediction method, the spatiotemporal relationship model of surface subsidence and underground mining face is established through the principle of mining subsidence, and a location inversion method of underground goaf for transboundary mining identification is proposed. Both the simulated and measured data show that the proposed method has high engineering application value because it does not rely on the complex nonlinear model and the average relative error of the inverted goaf location is smaller, both compared with similar algorithms based on complex nonlinear models and algorithms that ignore the coal seam dip angle.

Three-dimensional water vapor tomography method fusing GNSS and RS data and its application

Zhang Wenyuan

School of Environment and Geomatics, China University of Mining and Technology, Xuzhou, Jiangsu, 221116

Funds: National Natural Science Foundation of China (42271460; 42361134583；U22A20569）； Fundamental Research Funds for the Central Universities(2024QN11077)

About author:ZHANG Wenyuan (1996—), male, graduated from China University of Mining and Technology in December 2022 with a Ph.D. degree in engineering (Supervisors: Academician Yang Yuanxi, Professor Zhang Shubi), and his research direction is GNSS and RS water vapor inversion and application. E-mail: [email protected]

ZHANG Wenyuan. Three-dimensional Water Vapor Tomography Method Integrating GNSS and RS Data and Its Application[J]. Journal of Surveying and Mapping,2024,53(2):395-395. DOI: 10.11947/j.AGCS.2024.20220710

ZHANG Wenyuan. Study on the three-dimensional water vapor tomography method combining GNSS and RS data and its applications[J]. Acta Geodaetica et Cartographica Sinica, 2024, 53(2): 395-395. DOI: 10.11947/j.AGCS.2024.20220710

Read more: http://xb.chinasmp.com/article/2024/1001-1595/20240221.htm

In recent years, extreme weather events have occurred frequently around the world, and extreme weather such as typhoons and heavy rainfall have triggered meteorological disasters such as urban waterlogging, flash floods and geological landslides, which have had a serious impact on the ecological environment, economic society and the safety of people's lives and property. At present, GNSS water vapor tomography has achieved vigorous development as a promising means of high spatiotemporal atmospheric water vapor detection. Based on the three-dimensional water vapor tomography technology, this paper focuses on the key problems of geometric defects of tomography observation in the GNSS water vapor tomography model, comprehensively uses the new generation of GNSS technology and RS technology, systematically constructs the theory and method of three-dimensional water vapor tomography that integrates GNSS and RS data, and proposes a new technology of GNSS-RS water vapor tomography. Furthermore, with the help of deep learning technology, a rainfall prediction model based on three-dimensional tomography water vapor field is preliminarily established, which is expected to promote the expansion of GNSS/RS technology in meteorological monitoring and early warning. This paper starts from the perspectives of model optimization, algorithm improvement, and product application, and the main research contents and results are as follows.

(1) Taking the fusion of GNSS and RS water vapor products as the starting point, a GNSS water vapor tomography optimization algorithm with RS PWV constraints is constructed, and the feasibility of integrating RS PWV data into the water vapor tomography model is discussed, and the parameterization idea of RS PWV signal is given. The experimental results based on the Xuzhou area show that the optimization algorithm can appropriately improve the accuracy of the chromatography results, but due to the lack of RS PWV constraints in the voxel base analysis model, the improvement effect of the chromatography results is not significant.

(2) In order to solve the problem that the constraints of RS PWV cannot give full play to its observation advantages, a new idea of constructing RS SWV observations is proposed, and an approximate cone-shaped RS water vapor signal is formed, and a water vapor tomography method based on GNSS/RS SWV joint observation is developed. The experimental results based on spatially complementary GNSS/RS combined signals show that the proposed method can fully improve the number of observations and voxel blocks of the 3D tomography model, and show a good ability to reconstruct the 3D water vapor field.

(3) Considering the characteristics of RS water vapor products with high high resolution, combined with the modeling advantages of the node base analysis model, the node parameterization process of RS PWV/SWV is given, and the GNSS/RS joint water vapor tomography algorithm based on node parameterization is constructed. Compared with the node base analysis algorithm based on GNSS data, the node base algorithm based on GNSS and RS PWV and the node base algorithm based on GNSS and RS SWV can invert 3D water vapor tomography products with higher precision.

(4) In order to solve the problem of obvious temporal resolution difference between RS water vapor products and GNSS data, an optimized water vapor tomography method fusing GNSS and RS-like virtual signals was proposed. In this method, a cone-like RS-like virtual signal with the same temporal resolution as the GNSS signal is innovatively constructed with reference to the approximate conical RS SWV signal. Tomography experiments based on the dense GNSS station network in Hong Kong and the sparse GNSS station network in Xuzhou show that the proposed optimization method significantly improves the spatiotemporal stability of the observation structure of the 3D tomography model, and achieves the effect of inverting all-weather and high-precision 3D water vapor tomography products.

(5) Focusing on the shortcomings of the algebraic reconstruction algorithm in the solution of water vapor tomography equations, an adaptive algebraic reconstruction algorithm based on dynamic error allocation criterion and height angle weighting of three-dimensional water vapor tomography was proposed. Based on the vertical non-uniform distribution characteristics of atmospheric water vapor, a dynamic error distribution criterion considering the change of water vapor density is proposed, and then the height angle weighting model is introduced to rationalize the weighting of the observations, and the experimental results in Xuzhou area verify the significant advantages of the adaptive algorithm compared with the ordinary algorithm in reconstructing the three-dimensional water vapor field.

(6) Due to the lack of rainfall forecasting tools based on 3D water vapor tomography products, a short-term rainfall prediction method based on 3D water vapor field and deep learning was proposed. In this method, the correlation between vertical water vapor observations and three-dimensional water vapor density field and rainfall evolution was preliminarily discussed, and the ANN rainfall forecasting model based on vertical water vapor information and CNN rainfall forecasting model based on water vapor images were constructed, respectively.

Research and application of key technologies of high-precision pseudo-satellite systems

Fan Cao Ming

Department of Electronic Engineering, Tsinghua University, Beijing 100084

Funds:National Natural Science Foundation of China (42274018)

About author:FAN Caoming (1992—), male, graduated from Shandong University in December 2022 with a Ph.D. degree in engineering (Supervisor: Prof. Xing Jianping), and his research direction is high-precision global/regional positioning. E-mail: [email protected]

FAN Caoming. Research and application of key technologies of high-precision pseudo-satellite systems[J]. Journal of Surveying and Mapping,2024,53(2):396-396. DOI: 10.11947/j.AGCS.2024.20230001

FAN Caoming. Research and application of key technologies for high accuracy pseudolite system[J]. Acta Geodaetica et Cartographica Sinica, 2024, 53(2): 396-396. DOI: 10.11947/j.AGCS.2024.20230001

Read more: http://xb.chinasmp.com/article/2024/1001-1595/20240222.htm

With the advent of the intelligent era, people have put forward higher and higher requirements for positioning, navigation and timing (PNT) performance, such as accuracy, completeness, continuity, robustness, etc. Although the global navigation satellite system (GNSS) has a global, all-weather PNT function, the GNSS signal is very weak when it reaches the ground, and it faces three major problems: occlusion, deception and interference, and cannot be used normally in complex environments such as physical occlusion and electromagnetic interference. Pseudolite systems (PLS) can be used as an effective complement, backup and enhancement scheme in the event of GNSS failure or performance degradation. Therefore, PLS has very important research significance and value.

This paper conducts in-depth research on the improvement of PLS independent positioning performance and its enhancement of GNSS, and the main work and contributions are as follows.

(1) An on-site absolute calibration method for antenna phase center is proposed. In this method, the phase center calibration of the receiving antenna and the transmitting antenna is carried out by using the pseudo-satellite self-transceiver all-in-one machine. In order to eliminate the influence of hardware delay changes, a method for monitoring hardware delay changes is proposed. Taking advantage of the different characteristics of multipath at different stations, calibration is carried out at multiple stations, so that the multipath error is randomized and the influence of multipath error calibration results is weakened. The experimental results show that the accuracy of the antenna phase center calibrated by this method can reach the millimeter level, which lays a solid foundation for the realization of high-precision positioning and ambiguity fixation of PLS.

(2) Thanks to the accurate calibration of the antenna phase center, it is possible to restore the whole circumference of the carrier phase ambiguity. However, the initial phase bias (TPB) of the transmitter terminal of PLS is still an important factor hindering the fixation of PLS ambiguity, and a method for online calibration of TPB is proposed, and the characteristics of TPB are analyzed. Experiments have shown that the TPB hardly changes over time without a system restart. Therefore, PLS does not need to advertise TPB frequently. After obtaining the TPB advertised by PLS, the user receiver can use it to correct the carrier phase measurement, which can achieve fixed ambiguity in the whole circle, so as to accelerate the convergence and improve the positioning accuracy.

(3) PLS can not only be used for independent positioning, but also can be used to enhance GNSS. The long convergence time of GNSS precise point positioning (PPP) hinders the widespread application of GNSS PPP. However, the pseudolite (PL) satellite is close to the user, and the user's receiver can produce rapid geometric changes when the user's receiver moves, which reduces the correlation between parameters, which is conducive to the rapid convergence of parameters. Taking advantage of PLS, this paper enhances GNSS PPP by using a compact combination model of single-frequency PLS original observation measurement and dual-frequency GNSS original observation measurement. The results show that the convergence time is shortened from about 900 s to about 4 s after PLS enhancement, which is about 99.5%. Over the 900 s data duration, the average GNSS ambiguity fixation rate reaches about 90% after PLS enhancement. In addition, PLS-enhanced GNSS PPP showed better positioning accuracy compared to single-GNSS PPP. Even in the case of a short period of strengthening, the contribution of PLS is still noticeable. For example, if the PLS can provide an additional enhancement of about 8 s after position convergence, GNSS PPP will be able to independently provide continuous high-precision positioning information. However, a longer enhancement time is beneficial for improving the fixation rate of GNSS ambiguity. All in all, the GNSS PPP positioning accuracy, convergence speed and ambiguity fixation rate have been significantly improved after PLS enhancement.

(4) Considering the limited PLS coverage, i.e., the limited enhancement time, it is crucial to converge the GNSS PPP parameters (especially the GNSS ambiguity parameters) in the limited enhancement time. Therefore, the potential of PLS should be exploited as much as possible, and the benefits brought by PLS should be effectively utilized. In this paper, the contribution of PLS to GNSS PPP convergence under different combination models is analyzed, and a dual-filter tightly coupled (DF-TC) model is proposed, which can make more reliable use of PLS fixed solution information. When the number of PLs is sufficient and the enhancement time is long enough, there is no significant difference in the positioning effect of different combination models, but when the number of PLs is insufficient to support PLS positioning alone, the semi-tight combination model will fail. In addition, in the case of short-term enhancement, the dual-filter compact combination model shows the best enhancement performance, which can significantly reduce the enhancement time required for GNSS, which means that the required coverage of PLS can be smaller, and it is more flexible and convenient to use.

Research on the key algorithm of long-time Sentinel-1InSAR deformation monitoring

Ma Zhangfeng

Singapore Earth Observation Centre, Nanyang Technological University, Singapore 639798

Funds: National Natural Science Foundation of China (42274038)

About author:MA Zhangfeng (1995—), male, graduated from Hohai University in December 2022 with a Ph.D. degree in engineering (Supervisor: Prof. Huang Teng), and his research direction is imaging geodesy. E-mail: [email protected]

马张烽. 长时序Sentinel-1InSAR形变监测关键算法研究[J]. 测绘学报，2024，53(2)：397-397. DOI: 10.11947/j.AGCS.2024.20230002

MA Zhangfeng. Research on key algorithms for long-time-series deformation monitoring by Sentinel-1 InSAR[J]. Acta Geodaetica et Cartographica Sinica, 2024, 53(2): 397-397. DOI: 10.11947/j.AGCS.2024.20230002

Read more: http://xb.chinasmp.com/article/2024/1001-1595/20240223.htm

As an emerging space geodetic technology, interferometric synthetic aperture radar (InSAR) can obtain surface deformation information in all weather, large area, continuous, high-precision and high-spatial resolution, which effectively improves the observation accuracy, expands the observation range and shortens the observation period compared with traditional geodesy. This technology has broad prospects in exploring the genesis and mechanism of earthquakes, volcanic eruptions, and land-sea elevations. Based on the background of the large amount of data that needs to be dealt with in the current InSAR data processing process, a long-time InSAR processing process based on Sentinel-1 binary satellite is proposed, and the main research contents are as follows.

(1) A Sentinel-1 TOPS (terrain observation with progressive scans) wide-format data registration method was proposed. This method solves the problem of insufficient registration accuracy under the condition of fast decoherence by introducing the phase sequential estimator into the registration workflow, and the sequential registration method supports the need to reprocess the registered data without repeating the registration data when introducing new images into the dataset, and compresses the registered data, saving about 90% of the process file storage space.

(2) A new Sentinel-1 timing sub-band overlap region interferometry technique is proposed. MethodBy introducing the phase optimization estimator of the overlap region, the phase signal-to-noise ratio of the overlap region is improved, and a correction method for the interferometry orbit error of the overlapping region of the sub-zone considering the plate motion is proposed, and the millimeter-level azimuth temporal deformation of the Chaman fault is obtained, revealing that the Chaman fault accommodates about 27% of the relative motion of the Indo-Eurasian plate.

(3) A new three-dimensional phase unwrapping method for single-vision InSAR data is proposed. In this method, the all-pair shortest path (APSP) algorithm of graph theory is introduced into the spatial dimension unwrapping instead of the conventional Delaunay network to maximize the time coherence of the entanglement network, so as to approximate the phase continuity assumption in the two-dimensional spatial domain. In the one-dimensional time domain, the unwrapping error correction is regarded as a sparse signal recovery problem, and the integer linear programming method in the field of compressive sensing is introduced to improve the accuracy of unwrapping error correction. Compared with the traditional unwrapping method, this method can reduce the unwrapping error by about 29%.

(4) A new method for phase unwrapping error correction for multi-view InSAR data is proposed. In this method, the decorrelation phase correction and integer linear programming are combined to improve the accuracy of the dewrapping error correction, and the influence of the deentling error on the shallow creep model of strike-slip faults is further discussed. The results show that the new error correction method is about 61% more accurate than the traditional StaMPS (stanford method for persistent scatterers) 3D unwrapping method. The uncertainty of the creep model deduced from the unwrapping error corrected InSAR data is lower than that of the unwrapped error-corrected model.

(5) By in-depth summarizing the research contents of (1)-(4), this paper proposes a new processing framework, which can not only obtain the radar line-of-sight deformation, but also obtain the azimuth deformation results of the overlapping region of the sub-band. In this paper, the effectiveness of the proposed workflow is verified in three representative geomorphological process areas. Compared with the conventional processing process, the computing efficiency is improved by about 65% and the storage space is reduced by about 21.8%.

An automatic synthesis method of map point group targets considering weight information

禄小敏1,2

1. School of Geomatics, Surveying, Mapping and Geoinformatics, Lanzhou Jiaotong University, Lanzhou 730070, China;

2. National and Local Joint Engineering Research Center for Application of Geographic National Conditions Monitoring Technology, Lanzhou 730070, Gansu, China

Funds: National Natural Science Foundation of China (41930101; 42161066）

About author:LU Xiaomin (1982—), female, graduated from Lanzhou Jiaotong University in June 2019 with a Ph.D. degree in engineering (Supervisor: Prof. Yan Haowen), and her research direction is cartography synthesis. E-mail: [email protected]

LU Xiaomin. Automatic Synthesis Method of Map Point Group Targets Considering Weight Information[J]. Journal of Surveying and Mapping,2024,53(2):398-398. DOI: 10.11947/j.AGCS.2024.20230010

LU Xiaomin. Point cluster generalization approaches taking into account the weights of the points[J]. Acta Geodaetica et Cartographica Sinica, 2024, 53(2): 398-398. DOI: 10.11947/j.AGCS.2024.20230010

: http://xb.chinasmp.com/article/2024/1001-1595/20240224.htm On a small-scale map, many features are distributed in clusters of points. When the scale of the map is further reduced, the dot symbols will be stacked and covered by each other. In order to maintain the clarity, hierarchical characteristics and aesthetics of the map, it is necessary to synthesize the point group, that is, extract a certain number of relatively important points from the original point group and delete the relative secondary points. The weight of the points reflects the importance of a single point in the overall point group, which is very important in the design of the point group synthesis algorithm. According to the consideration of the weight information in the process of point group synthesis, the existing point group synthesis algorithms can be divided into two categories: the first type of algorithm does not take into account the weight information in the process of point group synthesis, and the second type of algorithm takes into account the weight information in the process of point group synthesis, but there are still some problems such as subjective point group weight setting, lack of current reference value of the comprehensive results, and failure to take into account the constraints and influence of road network in point group synthesis. In order to make up for the above shortcomings, this paper systematically studies the point group synthesis method considering the weight information with the help of relevant data acquisition technology and theories and tools such as pulse-coupled neural network, network-weighted Voronoi graph, Delaunay triangulation, etc., on the basis of scientific analysis and calculation of the weight information of the point group. The main contents of the paper are as follows. (1) In order to make the weight information reflect the importance of points in the point group as comprehensively and truly as possible, and better guide the synthesis of point groups, the algorithm combined with the attribute characteristics of the point group, studied the weight influencing factors of different types of points, and calculated the weight of the point group on this basis. (2) The weights are calculated according to the influence range of the point group and the number of affected people, and the point group synthesis is realized on this basis. For geospatial facilities with rich semantic information, the relevant data acquisition and processing technology is used to realize the calculation and expression of the influence range and affected population of the point group, and a high-current trend point group synthesis algorithm considering the actual influence range and affected population is proposed. (3) The constraint effect of the road network associated with the point group is introduced into the process of influencing range construction, and the weighted Voronoi diagram of the network is used to calculate the weight of the point group and realize the synthesis of the point group. For the facility group whose influence range cannot be determined, the constraints of the road network are introduced, and a network-weighted Voronoi graph construction method based on pulse-coupled neural network is proposed, and on this basis, a point group synthesis algorithm considering the constraints of the road network is realized. Based on the concurrency and automatic wave generation principle of pulse-coupled neural network, the construction of network-weighted Voronoi graph is realized on the basis of improved pulse-coupled neural network, which provides a technical reference for further research in the fields of point group synthesis and spatial analysis and optimization. Based on the network-weighted Voronoi graph, the construction of the Voronoi polygon of the point group network was realized by using the constrained Delaunay triangulation and dynamic threshold peeling method. The area of the Voronoi polygon of the network and the total length of the road sections inside the polygon are used as the basis for the measurement of the weight of the point group, and a comprehensive algorithm considering the level of the point group, the road attribute and the constraint effect of the road network on the point group is realized. (4) For point groups (such as trees, telephone poles, and control points) whose importance cannot be distinguished or cannot be determined, the algorithm chooses to maintain their geometric structure and topological characteristics to the greatest extent. Delaunay triangulation and dynamic threshold peeling method are used to extract the outer contour points of the point group, and on this basis, the Douglas-Peucker algorithm and the Voronoi diagram of the inner points under the constraint of the outer contour are used to realize the trade-off between the outer contour points and the inner points, respectively, which solves the problem of insufficient consideration of topological information caused by the independent simplification of the contour points and the inner points while inheriting the advantages of the existing algorithms in maintaining the outer contour and the internal density of the point group. Finally, the applicability and effectiveness of the proposed method were tested. The analysis shows that the proposed method effectively transmits all kinds of information of the original point group on the basis of taking into account the weight information of the point group as much as possible, which makes up for the shortcomings of the existing algorithms and solves the comprehensive problem of various types of point groups in geographical space.

First trial: Zhang Lin review: Song Qifan

Final Judge: Jin Jun

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