Table of Content

20 January 2022, Volume 51 Issue 1

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Review

On geospatial information science in the era of IoE

LI Deren, XU Xiaodi, SHAO Zhenfeng

2022, 51(1):  1-8.  doi:10.11947/j.AGCS.2022.20210564

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With the development of new technologies such as 5G/6G, cloud computing, internet of things and artificial intelligence, we have entered a new era of Internet of Everything(IoE). Five characteristics of geospatial information technology in the era of IoE discussed in this paper as followed:the development of satellite positioning technology has changed from GNSS and ground measurements to PNT system with wider service coverage; remote sensing technology has moved from isolated satellite observation to space-air-ground wireless sensor network; geographic information service moves from map database to true 3D realistic scene and digital twin; 3S integration develops from mobile measurement to intelligent robot service; research scope of geospatial information science changes from earth observation to internet of thing monitoring and perception of human activities in order to reveal the relationship between human and environment. On this basis, this paper further analyzes the challenges in the new era, and puts forward three major scientific issues to be solved:How can geographic information products meet the needs of people and robots at the same time? What are the mechanism and bottleneck of remote sensing image interpretation? How to use spatiotemporal big data to mine the relationship between man and nature and realize the leap from spatial perception to spatial cognition? Geospatial information science must and can make greater contributions to the digital earth and intelligent society in the era of IoE!

Geodesy and Navigation

OD/SINS adaptive integrated navigation method with non-holonomic constraints

LIU Wanke, NONG Qi, TAO Xianlu, ZHU Feng, HU Jie

2022, 51(1):  9-17.  doi:10.11947/j.AGCS.2022.20210122

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In the ground vehicle integrated navigation GNSS/OD/SINS, the global navigation satellite system (GNSS) signal is susceptible to environmental interference or even interruption. The non-holonomic constraint (NHC) is applied to the odometer (OD)/strap-down inertial navigation system (SINS) combination, which can effectively suppress the error divergence of the integrated navigation system during the GNSS signal interruption. Usually, NHC's noise setting is based on a fixed empirical value. However, the trajectory of the vehicle is complex and changeable during actual movement, and its motion state cannot fully satisfy the NHC premises and assumptions. The noise given by experience cannot accurately reflect the actual vehicle motion. Therefore, this paper analyzes the relationship between NHC noise and vehicle motion state, and constructs a NHC noise adaptive method based on vehicle motion state. Validation of the real-world experiments of the selected scene shows that the result of the noise-adaptive NHC/OD/SINS combined navigation is compared with the fixed-noise NHC/OD/SINS combination, when the GNSS signal is interrupted for 110 s and the vehicle turns continuously, the maximum horizontal position error is reduced by 68.4%; when the GNSS signal is interrupted for 74 seconds and the vehicle is traveling in a straight line, the maximum horizontal position error is reduced by 87.3%; the error divergence of the integrated navigation system during the GNSS interruption can be better suppressed.

High-precision indoor positioning based on robust LM visual inertial odometer and pseudosatellite

YANG Gaochao, WANG Qing, YU Baoguo, LIU Pengfei, LI Shuang

2022, 51(1):  18-30.  doi:10.11947/j.AGCS.2022.20200251

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Visual inertial odometer (VIO) and pseudo-satellite have been widely used in positioning indoors, but in practical applications, both approaches have their own limitations. The visual odometer depends on the actual positioning environments. Gross errors occur in environments with obvious changes in depth of field and uneven illumination, and errors will inevitably accumulate over time. However, relatively high-precision pose measurements can be obtained between adjacent frames. Due to the influence of indoor multipath, the accuracy and reliability of pseudolite indoor positioning are difficult to guarantee. To increase the reliability and stability of indoor positioning, based on the robust LM nonlinear optimization theory, this study mainly investigate indoor high-precision positioning technology approach of integrating high-precision pose measurements of VIO between adjacent frame and pseudolite. The algorithm can not only resist gross errors, but also reduce the influence of unreasonable weight settings among different sensors. Finally, the high-precision dynamic capture equipment built in the indoor environment is used to verify the proposed method. The experimental results show that the method can eliminate the cumulative error of the visual inertial odometer without relying on the loopback, and effectively improve the indoor positioning accuracy and reliability. Compared with the VIO, the positioning accuracy is improved by 59.0% and 77.5% respectively after using the improved LM algorithm for scenes 1 and 2.

A layered constant gradient acoustic ray tracing underwater positioning algorithm considering round-trip acoustic path

YAN Fengchi, WANG Zhenjie, ZHAO Shuang, NIE Zhixi, SUN Zhen, LI Weijia

2022, 51(1):  31-40.  doi:10.11947/j.AGCS.2022.20210234

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The acoustic ray tracing algorithm is typically adopted for high precision underwater positioning. However, the traditional acoustic ray tracing method is usually based on the one-way acoustic propagation path without the consideration of the displacement of shipborne transducer during the process of acoustic signal propagation. Therefore, the systematic deviation will be introduced in the positioning for seafloor transponder, which will limit the positioning accuracy of seafloor points. To solve this problem, a layered constant gradient acoustic ray tracing underwater positioning algorithm considering round-trip acoustic path is proposed in this paper. Combined with the actual propagation path of underwater acoustic signal, the round-trip acoustic path underwater positioning model is established according to the position of the transducer at the time of acoustic signal emission and reception, and the layered constant gradient acoustic ray tracing algorithm is applied to solve the foresaid problem. Experiments were carried out on the two observation patterns of circular tracing line and cross lines. The results show that the proposed method can effectively improve the underwater positioning accuracy on the premise of ensuring the calculation efficiency.

Rigorous modification model of upward continuation and its applications on the downward continuation of gravity anomaly

HUANG Motao, DENG Kailiang, WU Taiqi, OUYANG Yongzhong, CHEN Xin, LIU Min, WANG Xu

2022, 51(1):  41-52.  doi:10.11947/j.AGCS.2022.20200547

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The global integral model of upward continuation for gravity anomaly is often used in the data quality assessment for airborne gravity measurement and the iterative solution of downward continuation. In order to eliminate the singularity of the integral kernel function, we have to make a remove-restore transformation to the integral model based on an equation of integral identity. And at the same time, the global integral domain has to be divided into two parts of near and far zones. During this processing, the deviation of identical formula caused by the transformation of integral domain from global to local integration is often ignored in the traditional modified method, which leads to unnecessary model errors and ultimately affects the reliability of upward continuation solution, and even affects the stability of iterative solution of downward continuation. In response to this problem, some analysis and research have been made on the integral model modification of upward continuation and its application of downward continuation for gravity anomaly in this paper. Based on the measured data situation and the applied condition of the integral identity, a set of step-by-step modified formulas of the upward continuation integral model are derived, and a correction formula is proposed to compensate the omission of the traditional modified model. Finally, the rigorous modified model is applied to the iterative solution of downward continuation for gravity anomaly. The ultra-high-degree geopotential model EGM2008 is used as a standard potential field to carry out a set of numerical calculation test, and the calculated accuracy of step-by-step modified models of the upward continuation and the applied effect in the iterative solution of downward continuation for gravity anomaly are estimated and evaluated separately. It proves the necessity and effectiveness of adopting the rigorous modified model.

An analytical method for bathymetry inversion using vertical gravity gradient anomaly

XU Huan, YU Jinhai, AN Bang, WAN Xiaoyun

2022, 51(1):  53-62.  doi:10.11947/j.AGCS.2022.20200578

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At present, the main principle of the seafloor topography inversion method is to fit the most appropriate linear relationship between topography and gravity or gravity gradient. However, different topography will have different linear relationships. In order to overcome the constraint of uncertainty, this paper firstly derives the expression of vertical gravity gradient generated by cubic prism. Then, by gridding the research sea area, a functional relationship between vertical gravity gradient (VGG) and sea depth is established, i.e. the observation equations of sea depth. On the basis of which, it is that the observation equations have strong anti-error interference properties through simulation calculation. Because the observation equations are affected by the seamounts outside the study area (divided into boundary effects and far area effects), it is necessary to propose corresponding mathematical methods to deal with these effects. This paper proposes to expand the research sea area to obtain an expanded area, and then study the observation equations on the expanded sea. At this time, in order to avoid the singularity of the observation equations, a regularization method is introduced to solve the expanded observation equations and cut out the sea depth in the study area. Simulation experiments show that after using the regularization method, the root-mean-square error of the inverted sea depth is only 0.48 m. Finally, this paper inverts an actual seafloor topography of the South China Sea, and the results are compared with the 289 ship sounding data. The root-mean-square error of the inversion results can reach 109 m.

Pre-seismic anomalies and co-seismic gravity changes of 2011 Tohoku-Oki earthquake (M_w 9.0) detected by superconducting gravity data

DONG Jie, ZHANG Zeyu, WEN Hanjiang, SUN Wenke

2022, 51(1):  63-70.  doi:10.11947/j.AGCS.2022.20210014

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High-precision superconducting gravity data had been widely used in the study of geodynamics. The detection of the pre-seismic anomalies and co-seismic gravity changes caused by a huge earthquake is helpful to the study of focal mechanism and early warning. Meanwhile, the co-seismic observations can be used in the inversion of fault slip model. We study the gravity changes caused by the Tohoku-Oki earthquake (M_w 9.0) using the second sampling data in March 2011 of 7 Superconducting Stations in Japan, China and Europe. We obtained the corrected gravity changes by the preprocessing of tide, air-pressure and drift correction, et al. Comparing the 2861 M_b ≥ 4 earthquakes near the Japan island at the same period and analyzing the filtered gravity changes, we can exclude the influence of non-main earthquakes and find the obvious pre-seismic anomalies at frequencies 0.12 Hz ≤ f ≤ 0.18 Hz. The pre-seismic anomalies occurred 89 h before the earthquake for all the stations. The maximum amplitude of pre-seismic anomalies reaches 28×10^-8 m/s² at Medicina. Moreover, the theoretical co-seismic gravity changes simulated by the spherical dislocation theory and the CMT solution, are very close to the observed values of superconducting gravimeters. The absolute values of co-seismic gravity changes are inversely proportional to the epicenter distances.The observations at near-field are closer to the theoretical calculations than that at far-field, and the former can be used as the constraints for fault inversion.

Non-ergodic approximation method for intersections of airborne gravity survey network

QU Jinhong, JIANG Zuoxi, ZHOU Xihua, LUO Feng, LI Fang

2022, 51(1):  71-79.  doi:10.11947/j.AGCS.2022.20210037

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The gravity difference at the intersections of the airborne gravity survey network is an important basis for objectively evaluating the measurement quality of the survey lines, and it is alsoan important way to adjust the level difference of the gravity field between the survey lines. With the enlargement and irregularity of the survey network, it is very important to search the intersections accurately and quickly. Existing methods all traverse one by one after narrowing the range of intersections, which cannot guarantee that all intersections can be searched quickly and accurately. The non-ergodic approximation method proposed in this paper is to perform iterative approximation through a combination of fast approximation and fine-tuning approximation, avoiding one-by-one traversal and directly approaching the intersections quickly. Experimental results show that this method is not only suitable for continuous and uniform conventional networks, but also suitable for irregular and unconventional networks. The search speed is 3~4 orders of magnitude higher than the existing methods, and it is also far superior than the famous Canadian commercial geophysical software of Oasis Montaj.

Adaptive Kalman filter method with colored noise for fiber optic gyroscope random drift

JIN Kaidi, CHAI Hongzhou, SU Chuhan, XIANG Minzhi

2022, 51(1):  80-86.  doi:10.11947/j.AGCS.2022.20200614

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Random noise reduces the accuracy of output seriously as an important part of fiber optic gyroscope (FOG) error. Accurate modeling and compensation of random noise is an effective way to improve the accuracy of FOG. To solve the problem that FOG random noise is complicated and to accurately analyze difficultly, and the colored noise in the ARIMA model is modeled as the state equation by using the state expansion method, the Harvey algorithm is reconstruct to whiten colored noise. At the same time, considering the uncertainty of priori noise and the coupling between states and noise caused by online update of ARIMA model, variational Bayesian adaptive filter (VBAKF) is used to correct the state and measurement noise. Experiments show that the Harvey method reduces the random noise sequence variance by 40% compared with the traditional filtering modeling method. The Harvey method combined with VBAKF reduces the sequence variance by 54%; VBAKF can better estimate the measurement noise than the dynamic Allan variance. Method in this paper can effectively suppress the effects of colored noise and random model inaccuracy in the random noise Kalman filter, and improve the accuracy of random error compensation.

Real time recognition method of weak signal in space debris laser ranging

MA Tianming, ZHAO Chunmei, HE Zhengbin, ZHANG Haoyue

2022, 51(1):  87-94.  doi:10.11947/j.AGCS.2022.20200527

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In view of the high false detection rate of traditional secondary filtering algorithm in real-time recognition of weak signal from space debris laser ranging, based on the characteristics of the time correlation of echo signal from space debris laser ranging, a method combining primary filtering and linear fitting is proposed, by which the search cost and recognition accuracy of real-time identification of weak signal is considered and the real-time identification of weak signal from space debris laser ranging is realized. The algorithm was verified using the actual data of space debris laser ranging, and the results showed that the weak signal of space debris can be quickly and accurately extracted by the real-time recognition algorithm for weak signal of laser ranging proposed in this paper, and the false detection rate was decreased from 5.72% to 0.12%, the rate of missed inspection was decreased from 0.77% to 0.34%, which is of great significance to improve the success rate of space debris detection.

Cartography and Geoinformation

Semantic similarity measurement for building polygon aggregation in multi-scale map space

GAO Xiaorong, YAN Haowen, LU Xiaomin

2022, 51(1):  95-103.  doi:10.11947/j.AGCS.2022.20210074

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Map generalization is a process of spatial similarity transformation in multi-scale map spaces. Cartographers generalize under the guidance of the similarity principle; at the same time, map readers form mental maps and reconstruct the real world from maps containing similarity. Thus, it is of great significance to study and measure the similarity relations with respect to the scale reduces in multi-scale map spaces. However, due to the poor computability of similarity and the purpose of its computation is to reveal deeper information, there are few achievements on similarity relations especially semantic relations in multi-scale map spaces. To solve this problem, semantic similarities in city block aggregation (from approximately 1:1750 to 1:14 000) under the constraint of semantic functional units are computed, and the method for measuring the semantic similarity is the matching-distance model based on ontology and set theory. By the experiment of different city block generalization, the semantic similarity values at key scales were obtained and the results were analyzed and evaluated. The experimental results have shown that the building aggregation under the constraint of semantic functional units is in accordance with map readers' cognitive needs. The method described in this paper is helpful for map to play a better role as a carrier of information transmission.

Hierarchical evolution model and coding calculation of three-dimensional Hilbert curve

WU Yuhao, CAO Xuefeng, YU Anzhu, SUN Wanzhong

2022, 51(1):  104-114.  doi:10.11947/j.AGCS.2022.20200241

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The coding calculation of grid cells is the core of the discrete global grid system, which supports efficient calculation of indexing and analysis. Hilbert curve has the characteristics of high clustering and strong continuity, and is an important tool for global discrete grid coding. The lattice element coding using Hilbert curve realizes the coordinate equivalent dimensionality reduction expression, but the research on the basic theoretical problems of grid coding still not complete. In this paper, the hierarchical evolution relationship of the three-dimensional Hilbert curve in the octree three-dimensional grid is used as a breakthrough. The state matrix and the evolution matrix are used to construct a hierarchical evolution model, and then the calculation methods of Cartesian coordinates to Hilbert codes and adjacent grid Hilbert codes are designed respectively. Compared with the existing algorithms, the algorithm in this paper is based on a hierarchical evolution model, which avoids cumbersome iteration steps and conversion steps, and the algorithm flow is simple and straightforward. The experimental results show that the calculation efficiency of Cartesian coordinates to Hilbert codes in this paper is "7%~23%" higher than that of the iterative algorithm, and the calculation efficiency of neighbor grid elements Hilbert codes is 4.0~4.5 times higher than that of the conversion algorithm.

Image Processing and Reconstruction

A hybrid SfM method based on partition optimization

XU Biao, DONG Youqiang, ZHANG Li, SUN Yushan, LIU Yuxuan, ZHA Bing, HAN Xiaoxia

2022, 51(1):  115-126.  doi:10.11947/j.AGCS.2021.20210105

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Aiming at solving the problem of sparse 3D reconstruction of large-scale unordered images, this paper proposes a robust, efficient, and easy-to-parallel hybrid SfM method based on partition optimization. Firstly, the SIFT algorithm is used for image matching, and image partitioning is completed using image correlation scores calculated from the matching results without other auxiliary information such as GPS/INS. Secondly, an improved incremental SfM method is applied to achieve rapid reconstruction in each partition, and a number of standards are introduced to automatically eliminate the unreliable partitions and re-divide the images in these partitions into other partitions to achieve dynamic adjustment. Finally, a robust and high-precision partition fusion algorithm is proposed to realize accurate fusion of camera parameters, image posture, and 3D information of the scene. The experimental results of multiple challenging data sets of different scales, different image types, and different scenes show that our proposed hybrid SfM method has good robustness to different data sets and dramatically improves efficiency while maintaining high precision,which especially suitable for large-scale image sets.

A RFM adjustment method for satellite remote sensing image with Fourier compensation

YU Junpeng, WU Weidong, SUN Jiaming, MAN Yiyun, SHEN Gang

2022, 51(1):  127-134.  doi:10.11947/j.AGCS.2021.20200429

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The geometric distortion of satellite optical remote sensing images is an important factor that restricts its positioning accuracy. It is difficult to completely eliminate the complex distortion of the image using the common system error compensation model. Based on the rational function model adjustment scheme, and according to the approximation characteristics of the Fourier series, this paper proposes to replace the general polynomial with a binary Fourier polynomial as the system error compensation term to adapt to any form of distortion that meets the continuous condition. Simulation and actual data adjustment test results show that the new method can effectively compensate the image positioning system errors caused by the inaccurate internal and external orientation elements of the image and different magnitudes of distortion. Given enough ground control points, the positioning accuracy of the RFM adjustment using the third-order Fourier compensation term is significantly better than that of the traditional method using general polynomial compensation terms. The positioning accuracy of the plane and elevation after the adjustment of the SPOT-5 different track stereo image can reach 3.34 m and 2.48 m, the plane and elevation positioning accuracy of QuickBird co-track stereo image pair adjustment reached 0.77 m and 0.54 m, both reaching the sub-pixel accuracy level. The binary Fourier polynomial can be used as a general image system error compensation model, which can be further applied to the distortion correction process of aerial and close-range images.

Multi-path RSU network method for high-resolution remote sensing image building extraction

ZHANG Yuxin, YAN Qingsong, DENG Fei

2022, 51(1):  135-144.  doi:10.11947/j.AGCS.2021.20200508

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Inaccurate boundaries and holes are two major problems when extracting buildings from high-resolution remote sensing images by a convolution network. To solve these problems, we proposed the MPRSU-Net (multi-path residual U-block network), which is based on the RSU (residual U-block). The RSU is able to fuse local features and multi-scale features, with the help of the encoder-decoder structure and the residual connection. However, a single RSU is not enough to gather enough information, MPRSU-Net parallels RSU blocks of different scales by the multi-path structure and exchanges information among these blocks to further enhance the feature aggregation efficiency. Experimental results showed that the MPRSU-Net achieved 95.65%,88.63% precision, and 91.17%,79.31% IoU on 0.3 m resolution WHU and Inria building datasets, which showed the effectiveness of the proposed method. In addition, compared with the U² Net, MPRSU-Net is much lighter in computation and reduces the amount of model parameters by 68.63%, demonstrating that the method has some application value.

River waterbody extraction from SAR images based on speckle reduction and multi-resolution topological analysis

YANG Yun, LI Yu, ZHAO Quanhua

2022, 51(1):  145-158.  doi:10.11947/j.AGCS.2022.20190395

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Aiming at the discontinuity of river waterbody extraction from high-resolution SAR images caused by speckle noise and building occlusion, a river waterbody extraction method combining adaptive speckle reduction and multi-resolution topological analysis is proposed. Firstly, the Beta metric is introduced into the speckle reduction anisotropic diffusion to achieve adaptive speckle filtering of SAR images. Secondly, the local threshold segmentation and connected region identification are used to quickly extract river waterbody segments from the denoised image. Then, a Gaussian pyramid is constructed with the smallest circumscribed convex polygon of the river waterbody segments as the object, and multi-resolution topological analysis is performed to obtain the information of river discontinuities. Finally, the regional growth strategy is used to distinguish the discontinuities layer by layer to realize the automatic connection of adjacent river waterbody segments. The proposed method is verified by TerraSAR-X and GF-3 high-score SAR images. The results show that the proposed method can effectively extract complete river waterbody. The effectiveness and robustness of the proposed method are verified by the qualitative and quantitative evaluation of multiple SAR images.