Current Articles
2021, Volume 46, Issue 9
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2021,
46(9):
1265-1272.
doi: 10.13203/j.whugis20210241
Abstract:
We make an in-depth analysis of the concept of resilient PNT (positioning, navigation, and timing) system put forward by the United States and China, and point out their differences.Especially in view of the main requirements of the future national comprehensive PNT system, the concept of resilience is expounded that the resilient index of the PNT system can be divided into three categories: external force interference characteristic, internal technical characteristic and performance effect characteristic.At the same time, considering the differences of different levels of PNT system design, PNT flexibility is divided into three levels: user-level resilience, system-level resilience and system-level resilience.Based on the above work, it tries to help promote the theoretical research in the field of PNT system in China.
We make an in-depth analysis of the concept of resilient PNT (positioning, navigation, and timing) system put forward by the United States and China, and point out their differences.Especially in view of the main requirements of the future national comprehensive PNT system, the concept of resilience is expounded that the resilient index of the PNT system can be divided into three categories: external force interference characteristic, internal technical characteristic and performance effect characteristic.At the same time, considering the differences of different levels of PNT system design, PNT flexibility is divided into three levels: user-level resilience, system-level resilience and system-level resilience.Based on the above work, it tries to help promote the theoretical research in the field of PNT system in China.
2021,
46(9):
1273-1283, 1297.
doi: 10.13203/j.whugis20200312
Abstract:
Objectives Partial errors-in-variables(PEIV) model is a more general form of errors in variables(EIV) model. It has been widely used in the data processing of global navigation satellite system(GNSS), coordinate conversion, deformation monitoring and data fitting in the past ten years. Methods First, the development history of PEIV model is reviewed. Then, five core problems of PEIV model are summarized and analyzed, including parameter estimation algorithm, precision estimation, random model estimation, expansion algorithm and data processing application. Finally, the applications of PEIV model are outlined. Results We point out three questions for further research, including how to process big data by PEIV parameter estimation method, how to correct the bias of weighted total least squares(WTLS) adjustment by sampling method, and how to derive the formula of higher order parameter estimation covariance matrix are. Conclusions This review paper aims to further promote the development of surveying and mapping data processing and provide readers with suggestions and references.
2021,
46(9):
1284-1290.
doi: 10.13203/j.whugis20200243
Abstract:
Objectives The universal errors-in-variables(EIV) model extends the EIV model to the most general form, and the weighted total least squares(WTLS) algorithm is proposed to take into account the random errors in observation vector, observation vector coefficient matrix and parameter coefficient matrix. Methods In this paper, the universal EIV function model is expanded and the secondorder term is included into the constant term of the model. Thus, the universal EIV model is represented as Gauss-Helmert model in linear form, and the linearized total least squares(LTLS) algorithm and approximate precision estimation formula of the universal EIV model are derived. Results The estimation results of LTLS algorithm are consistent with that of WTLS algorithm of universal EIV model, which verifies the correctness and feasibility of the proposed algorithm. Conclusions When the model contains a large number of estimators, the LTLS algorithm of the universal EIV model significantly improves the computational efficiency and converges faster.
2021,
46(9):
1291-1297.
doi: 10.13203/j.whugis20190196
Abstract:
Objectives The inequality constrained partial errors-in-variables(ICPEIV) model is mainly solved by linear approximation method and nonlinear programming algorithms. The linear approximation method is computationally inefficient and the nonlinear programming algorithms are complicated because they are based on optimization theory. The nonlinear programming algorithms are impracticable to apply in surveying fields because the connections between nonlinear programming methods and classical adjustment have not been established. Methods Under the total least squares(TLS) criterion, the inequality constrained TLS problem is transformed into the quadratic programming according to the Kuhn-Tucker condition. Then an improved Jacobian iteration approach is proposed to solve the quadratic programming. Results The proposed method does not require the linearization process and has the same form with the classical least squares which is easy to code. Conclusions The numerical examples show that the proposed method is efficient in computation and concise in form and it is a beneficial extension of classical least squares theory.
2021,
46(9):
1298-1308.
doi: 10.13203/j.whugis20200182
Abstract:
Objectives For global navigation satellite system(GNSS), the ranging performance of observation would influence the system service capability. Methods Parabolic antenna with large-diameter could greatly reduce the impact of the ground equipment and the environment on signal acquisition. Based on data from parabolic antenna, observation characteristics and ranging performance of BeiDou-3 global satellite navigation system(BDS-3) are analyzed. Results The results show that, regarding the pseudorange deviation on BeiDou-3 satellite, no systematic deviation of the same magnitude, compared with BeiDou-2, is found on the signal of B1 I, B3 I, B1 C, B2 a, and B2 b. There are fluctuations on some signals. However, the correlation with elevation angle is not strong, and the average magnitude of all satellite fluctuations is 0.1 m. This paper analyzes the multipath variation and noise level of carrier observation for BeiDou-3 satellite of each signal using triple-frequency combinations. The fluctuations of carrier phase triple combination are of the millimeter level, and those fluctuations do not closely correlate with the elevation or time. The root mean square of the triple-frequency carrier combination from parabolic antenna is mostly less than 0.6 mm. Conclusions The results indicate that no systematic bias occurs in code and phase observation of BDS-3, and the system has a good ranging performance.
2021,
46(9):
1309-1317.
doi: 10.13203/j.whugis20190353
Abstract:
Objectives The global navigation satellite system(GNSS) coordinate time series can be used to analyze the motion of GNSS station, and the colored noise in coordinate time series affects the estimation accuracy of the motion parameters. Therefore, in order to improve the reliability of the motion analysis, it is necessary to take effective measures to eliminate the colored noise. Methods This paper proposes a method to eliminate colored noise by combining wavelet packet transform and information entropy theory. First, the simulation time series containing flicker noise is estimated to verify the estimation accuracy of the flicker noise. Then, discrete wavelet transform and wavelet packet transform are respectively carried out on the residual series of the simulation time series, and the flicker noise is eliminated by using information entropy.On this basis, the denoising effects of these two methods are compared. Finally, the coordinate time series at KMIN station is used as the measured data to further verify the denoising effect of wavelet packet coefficient information entropy. Results The experimental results show that the power spectrum and the time series of colored noise eliminated by using wavelet packet coefficient information entropy are in good agreement with the original colored noise. Conclusions The proposed method can effectively eliminate colored noise in the residual series and only retain white noise.
2021,
46(9):
1318-1327.
doi: 10.13203/j.whugis20190387
Abstract:
Objectives Global navigation satellite system(GNSS) tomography, characterized by reconstructing the three-dimensional distribution of the atmospheric water vapor, has proved its capacity for studying the extreme weather events. The ill-conditioned problem resulting from the GNSS acquisition geometry is the critical issue of the GNSS tomography system. Algebraic reconstruction techniques, with the advantages of simple iteration and fast convergence, has been widely applied to the tropospheric tomography. However, the error allocation principle based on the intersection length of GNSS rays with each ray-voxel affects the accuracy of tomographic results. An improved adaptive algebraic reconstruction techniques are proposed to address this problem. Methods In view of the unreasonable error allocation in the traditional algorithm, we suggest a new error allocation principle based on the variation of water vapor density(WVD) in voxels for the adaptive algorithms, in which the product of the intersection length and WVD is considered as a new principle to redistribute the difference between the GNSS slant water vapor(SWV)and the reconstructed SWV. Besides, the weight matrix model of elevation angles is introduced to the improved algorithm to optimize the tomographic results. Results The new algorithms are tested by measured data from Xuzhou continuously operating reference stations(CORS) network and radiosonde during July2016. Experimental results reveal that the WVD derived from the adaptive algorithms performs better than that of the general algorithms in root mean squared error(RMSE), standard deviation(STD) and mean absolute error(MAE), and the RMSE is decreased by 25.91%, 15.81%, and 24.64% for adaptive algebraic reconstruction technique(AART), adaptive multiplicative algebraic reconstruction technique(AMART)and adaptive simultaneous iterative reconstruction technique(ASIRT) respectively. Under the conditions of light rain, moderate rain and heavy rain, the adaptive algorithms retrieve better water vapor profile than the traditional ones. Conclusions Overall, the water vapor profile derived from the adaptive algorithms agrees with the radiosonde distribution better than the traditional algorithms, which reveals the advantage of the proposed method on optimizing the tomography solutions.
2021,
46(9):
1328-1335.
doi: 10.13203/j.whugis20190192
Abstract:
Objectives In order to make the best use of seafloor topographic information contained in gravity data and improve the quality of seafloor topographic inversion results based on gravity data, the South China Sea is selected as the experimental sea area. Methods The effects of different order seafloor in frequency domain are discussed in detail when recovering the gravity anomaly and vertical gravity gradient anomaly in different seafloor topographic environments. Results The results of numerical analysis and experiment show that the results of one-time seafloor topographic play a major role in the contribution of gravity information. With the increase of the order of seafloor topography, the amplitude of gravity information decreases continuously. The high order gravity anomaly/vertical gravity gradient anomaly varies obviously in the sea area where the seafloor topography fluctuates sharply and its amplitude is larger, while gravity information varies slightly in the flat sea area. The vertical gravity gradient anomaly is more sensitive to high frequency part of seafloor topography than gravity anomaly. Conclusions In the process of inversion of seafloor topography based on gravity data, if the input data source is gravity anomaly, it is suggested that the second term of seafloor topography should be taken into account. If the input data source is vertical gravity gradient anomaly, it is suggested that the third term or the fourth term of seafloor topography should be taken into account so as to make full use of the information contained in gravity data.
2021,
46(9):
1336-1344.
doi: 10.13203/j.whugis20200595
Abstract:
Objectives In order to calculate the high precision gravity gradient in level 1b (L1b) data processing of gravity field and steady-state ocean circulation explorer(GOCE)satellite, it is necessary to accurately measure the satellite attitude angular velocity. In the coordinate system transformation of the attitude data of astrology, the low precision angular velocity components of a single astrology instrument will transmit the noise to other angular velocity components, which will affect the calculation accuracy of the whole gravity gradient. Methods In this paper, based on the noise characteristics of the astrological instrument, the weighted matrix of the noise distribution on each axis of the astrological instrument is constructed, and the optimal attitude quaternion is solved jointly for the attitude quaternion of two or more astrological instruments, so as to provide accurate attitude control for subsequent angular velocity recovery. Results Compared with the single astro-meter calculation method, the accuracy of the optimal attitude angular velocity components wy and wz obtained by the combination of multiple astro-meters can reach about 1 order of magnitude higher within 10-100 mHz, and the noise level is up to 10-6 rad/s, which can effectively suppress the noise propagation caused by the low precision angular velocity components in coordinate system transformation. Conclusions The results show that the satellite attitude angular velocity calculated by the combination of multiple astrological instruments can be significantly improved in the whole power spectral density, the power spectral density of gravity gradient trace values calculated by the combined method of multiple astrologers is also significantly improved compared with the single astrologer method.
2021,
46(9):
1345-1353.
doi: 10.13203/j.whugis20210328
Abstract:
Objectives In video-based multiple object tracking, the object detection and re-identification have a strong correlation. The existing methods generally train the object detection and re-identification networks separately, which makes the tracking speed fail to meet the real-time requirements. In this paper, we integrate the detection and re-identification into one network to accelerate the tracking process, and also solve the problems of identity switching and failure tracking. Methods This paper develops a pedestrian motion model and obtains the optimal state estimation of pedestrians using center point detection. The person re-identification model with deep layer features uses the Mahalanobis distance and cosine distance to enhance the ability of person identification. And the Hungary algorithm is used for data online association, where the state estimation results become more accurate using Kalman filtering, and the unrelated lost objects are predicted by motion. Results Experiments are conducted on MOT15, MOT16 and MOT17 datasets using the proposed algorithm and other multi-pedestrian tracking algorithms, and the multiple object tracking accuracy of tracking results using our proposed algorithm is 63.5, 72.4 and 70.9, respectively, and the identity F1-measure is optimal, with the real-time rate. Conclusions The proposed algorithm can accelerate the tracking speed by network parameter sharing, and improve the recognition accuracy by person re-identification training.
2021,
46(9):
1354-1361.
doi: 10.13203/j.whugis20210323
Abstract:
Objectives The spatial layout of vectorized complex architectural drawings is widely used in 5G base station construction, smart homes, and AR/VR(augmented reality/virtual reality). Methods To solve the difficulty of identifying the spatial layout of drawings caused by various irregular drawing elements, a high?performance fusion recognition method combining raster image and vector representation is proposed. First, the rasterized representation of architectural plan drawings is used to extract the main development direction, and several enclosed spaces are constructed. Then, the vectorized representation of architectural plan drawings is used and according to the directional and adjacency characteristics of space recognition, the half?wall structure is innovatively proposed to calculate geometric position and topological relationship. The wall layout can be rebuilt as a whole with high precision according to the principle of space duality. Finally, the proposed method and the traditional methods are analyzed on the vector building plan data set of various wall layouts. Results The experimental results show that the proposed fusion dual recognition algorithm is usable and effective for various types of building models. Conclusions It has higher robustness and is less interfered by specific architectural drawing types.
2021,
46(9):
1362-1369,1385.
doi: 10.13203/j.whugis20210308
Abstract:
Objectives Traversability analysis is one of the necessary parts for rovers on extraterrestrial surface to explore unknown environment. Methods In this paper, we propose a data-driven method for traversability analysis for rovers on extraterrestrial surface. Based on the inputting multi-dimensional terrain information, the proposed method models traversability analysis as a semantic segmentation problem, which can explicitly compute a traversability map of this circumstances for a specific rover. Meanwhile, we provide an algorithm for generating training dataset for the rover. We first run the rover in the field to collect directed traversability results at certain positions, and then fulfill the undirected traversability map with these results by converting this problem into a global optimization problem, since undirected traversability map is more intuitive and straightforward for path planning. We can get the dataset for a specific rover by linking this map with the data of environment. In order to get the data more efficiently, we design an algorithm to generate virtual extraterrestrial terrains randomly and to simulate the running of a specific rover. Results We generate a set of visible multi-dimensional terrain information and perform traversing test in virtual environment, which is used for generating traversibility labels in the optimization method. Based on the terrain information and labels, we train a U-Net-like network for predicting labels according to the given multi-dimensional information, and the network performs well on test dataset with the accuracy of 93.8% on average. Conclusions The proposed data⁃driven method for traversability analysis is effective in virtual environment.
2021,
46(9):
1370-1377.
doi: 10.13203/j.whugis20200507
Abstract:
Objectives The spatial delimitation of urban area is the foundation for monitoring the urbanization level and determining city scale from the perspective of geographical space. Methods Based on the requirements of urban area defined in Document No. 51 of the State Council, this paper clarifies the connotations of urban area with further understandings and proposes a process for delimiting urban area in geographical space by connecting map polygons of governmental residents and neighborhood committee, which can reduce the subjectivity and fuzziness in the spatialization of process of urban area. Results This paper develops the main idea and spatial delimitation about urban area and takes Wuhan as an example to illustrate the details about spatial delimitation of urban areas. Conclusions This paper mainly discusses how to unify urban delineation under the current technical conditions, and does not mention how to use other auxiliary data, such as the application of multi-source big data in urban delineation, because of the unbalanced development of big data infrastructure in different cities. But it does not mean that the application of population big data and urban big data is not important. On the contrary, the application of big data in the work of urban areadelimitation is the next research focus and the future development trend.
2021,
46(9):
1378-1385.
doi: 10.13203/j.whugis20190274
Abstract:
Objectives It is usually necessary to eliminate non-combat targets for conducting marine combat situation analysis. Because non-combat targets have little impacts on situational analysis and the retained combat-correlated targets have high reference value. Most of the existing behavior mining methods, which are based on the idea of clustering, are complicated and ineffective in cleaning of non-combat targets. Methods Therefore, this paper defines multi-dimension record similarity(MDRS) and proposes a real-time cleaning method for marine non-combat targets(MNCT-RTCM). The proposed method realizes the real-time cleaning of non-combat targets by similar duplicate record detection of multi-dimensional track data. Results The experiments are carried out on simulated military scenarios, and the results are evaluated and analyzed by calculating the recall rate and the precision rate. Conclusions The results show that the MNCT-RTCM method can effectively detect non-combat targets and achieve real-time cleaning of noncombat targets in the marine combat environment.
2021,
46(9):
1386-1394.
doi: 10.13203/j.whugis20190204
Abstract:
Objectives Morphology of polar sea ice changes continuously under the influences of external driving forces, e.g., wind, flow and waves. Observations and change regularity analysis on morphology of polar sea ice not only is helpful for the optimization of sea ice thermodynamics numerical simulation and the inversion of sea ice thickness based on roughness parameters, but also provide distinct importance for understanding the response of polar sea ice morphology to climate change. Methods Based on the undulations profiles of sea ice bottom in Northwestern Weddell Sea measured by the helicopter-borne electromagneticinduction bird(EM-bird) system during the winter of 2006, this paper establishes a nonlinear statistical optimal model with the cutoff draft as the identified variable to separate the ridge keels and local undulations on sea ice bottom. Then, the keel morphology parameters and correlation between the keel draft and frequency are statistically analyzed. Finally, a new parameter T is hatched to assess the correlation between the ridge sail height and keel draft. Results The results suggest that the optimal cutoff draft is 3.8 m and the keel spacing is the main factor affecting the ridging intensity. Despite marked sea ice deformation in different regions in Northwestern Weddell Sea, morphology changes of the keel are not evident. There is a good log correlation between draft and frequency of the keel, which vividly describes morphology and distribution of the keel. The newly hatched parameter T has a significant linear correlation with keel depth(r=0.93). Conclusions The newly proposed modeling method can separate the keel from sea ice bottom undulations more accurately, which provides a new theoretical reference for morphological correlation analysis between surface and bottom of sea ice, and the inversion of sea ice thickness and bottom draft from its surface height.
2021,
46(9):
1395-1403.
doi: 10.13203/j.whugis20200402
Abstract:
Objectives The airborne laser bathymetry system transmitted laser pulse through the complex channel which consisted of atmosphere, air-sea interface and water channel. The signal power decreased exponential with the increment of the water depth, and the pulse waveform was stretched and distorted at the same time. These two types of transmission characteristics would limit the maximum detection depth and the measurement accuracy of depth, respectively. Methods The purpose of the proposed algorithm is to improve the measurement accuracy of laser bathymetry system on the premise of ensuring the maximum detection depth performance. First, the water quality and Monte Carlo simulation method are used to study the different depth of echo signal characteristics. It reveals the propagation properties of laser signal and establishes a new parameter design method for laser bathymetry system, which can meet the requirment of international airborne laser depth bathymetry system. Then, the waveform distortion of echo signals at different depths are simulated under the specific system parameters. The adaptive matching filter algorithm is designed to improve the measurement precision. Results The simulation results revealed that the designed system parameters and the adaptive matched filtering algorithm can achieve the performance with the maximum detection depth of 50 m with measurement accuracy of 166 mm in the daytime and with the maximum detection depth of 70 m with measurement accuracy of 172 mm at night for laser bathymetry system. Conclusions The results show that the adaptive matched filtering algorithm can improve the measurement accuracy and serve the marine surveying and mapping of China.
2021,
46(9):
1404-1411.
doi: 10.13203/j.whugis20190258
Abstract:
Objectives According to the spatial attitude characteristics of the indoor walls, a point cloud vector tracking algorithm for automatically drawing the indoor plan was proposed. Methods Firstly, the indoor wall point cloud with a certain thickness was intercepted and projected onto the horizontal plane, and square grids were established on the projection plane. The plane points after projection were segmented and managed, and the point cloud in every grid was clustered by the eight neighborhood algorithm. Then the grid center of gravity method was used to generate sparse points, which were tracked and sorted according to the distance between points in the neighborhood and the angle of connection vector. The vector sequence of tracking direction was established, and the point cloud segmentation of different walls was completed combined with mutation of angle between adjacent values in the vector sequence. Finally, the least squares algorithm was used to fit the line of the same wall point cloud, and the intersection point of the adjacent wall line was obtained. Results The plane projection line segment of the house wall and its spatial connection relationship were established. The wall projection line segment was output in sequence. The drawing of the house plan was completed and the DXF format data exchange file was exported. Conclusions The proposed algorithm was verified by the analysis of indoor scanning data of a residential building. The results show that the proposed algorithm can accurately and quickly analyzed and processed the indoor laser scanning point cloud, and completed the drawing of interior plan.
2021,
46(9):
1412-1422.
doi: 10.13203/j.whugis20200031
Abstract:
Objectives With the development of urbanization, the urban heat island has attracted a lot attention because of its adverse effects on health of residents and urban sustainability. Local climate zone(LCZ)provides a novel framework of land-cover classification for the study of urban heat island. In this research, we investigated the impact of urban morphology on the seasonal variations of land surface temperature(LST) in different LCZs in Shenzhen, which is a core city of Guangdong-Hong Kong-Macao Greater Bay Area and a pilot demonstration zone with Chinese characteristics. Methods Multi-view high-resolution remote sensing images were employed to map the LCZs in the neighborhood scale. Additionally, the Pearson partial correlation and stepwise regression models were applied to analyze the influence of urban morphology on the seasonal characteristics of LST in different LCZs. Results LST varies greatly among seasons in the different LCZs. In addition, urban morphology plays important roles in the variations of LST among LCZs. And the two-dimensional metrics correlate more strongly with LST than the three-dimensional metrics in the LCZ1-LCZ3. The effects of the three-dimensional metrics in the LCZ4-LCZ6 and LCZ8 are more pronounced than that in the LCZ1-LCZ3. Conclusions Urban morphological variables of LCZs in different seasons have different effects on the surface temperature. Compared with the three-dimensional metrics, the two-dimensional metrics have a stronger correlation with the surface temperature. Moreover, the influence of three-dimensional metrics is enhanced in non-compact construction.
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