Journal of University of Chinese Academy of Sciences

XIAO Jun, SHI Guangtian

2023, 40 (5): 577-595. DOI: 10.7523/j.ucas.2022.038

With the development of 3D data acquisition technology, point cloud wins the favor of researchers for it's simple but effective representation and it is widely used in the fields of remote sensing, scene reconstruction, 3D modeling, etc. Considering that the data acquisition process is easily disturbed by many factors such as equipment, environment and material, raw point cloud is often corrupted with noise and so it is of great significance to explore robust and efficient denoising algorithms. This paper firstly investigates the relevant research works of point cloud denoising and divides them into traditional algorithms based on the optimization idea and denoising algorithms based on the deep learning idea according to the implementation principles. Secondly, the research progress of each kind of algorithm is discussed and a detailed analysis of representative algorithms is presented. Thirdly, the data sets, the evaluation metrics and experimental results are summarized with an in-depth comparison. Finally, the problems and possible development directions and trends of point cloud denoising are prospected.

Temporal and spatial variation of diurnal asymmetric warming and its drivers in China

HE Chang, DENG Jianming, CHEN Shuang

2023, 40 (5): 596-604. DOI: 10.7523/j.ucas.2022.042

Abstract ( 686 ) PDF (0KB) ( 0 )

Recently, a major feature of global warming is asymmetrical temperature increase during day and night, i.e., the rate of warming at night is greater than that during the day. However, effects of asymmetrical warming have not yet attracted widespread attention. In this study, by collecting historical observation data of 838 meteorological stations in China, and using methods such as trend estimation, the characteristics of the temporal and spatial variation of diurnal temperature range (DTR) and the long-term trends of DTR from 1952 to 2018 were analyzed. The results indicated that:spatially, the regions with the highest average annual DTR in the country were distributed in the northwest and southwest, followed by the northeast and north China, and the areas with lowest DTR located in central, eastern, and southern China. The average monthly DTR in the year was generally multimodal. Among four seasons, DTR in spring and autumn was higher than in summer. From 1952 to 2018, the annual average DTR decreased significantly (τ=-0.396; p<0.01). Long-term changes in DTR were positively correlated with evaporation, sunshine hours, latitude and altitude, and negatively correlated with wind speed, precipitation, relative humidity, station pressure, total cloudiness, and longitude.

Assessment of aquatic ecology status of Li Canal and its protection strategies

ZHANG Qimou, LIN Siqun, GAO Ya, GAO Junfeng

2023, 40 (5): 605-613. DOI: 10.7523/j.ucas.2022.009

Abstract ( 313 ) PDF (0KB) ( 0 )

The status of river ecology plays an important role in maintaining biodiversity and sustainable development. An accurate assessment of the aquatic ecology status of rivers in the context of the regional natural environment can provide a scientific basis for protecting river ecology. The aquatic ecology status of the Li Canal during 2017-2020 was evaluated according to the local standard for ecological river and lake status of Jiangsu Province. The aquatic ecology status of the Li Canal is "Good", with an improving trend during the study period. The indicators rated as "Good" and "Excellent" are mainly those in the aspects of water security, aquatic organism and aquatic habitat. Five of the eight indicators reach "Excellent", and two are rated as "Good". For the indicators in aquatic space aspect, the management (protection) boundary delineation rate is 100%. Public Satisfaction has been improved from "Moderate" in 2017-2018 to "Excellent" in 2019-2020. The shoreline use management index rating is "Satisfactory", with no significant improvement in the overall governance index. Our assessment results imply that it is necessary to strengthen water quality protection, to rationalize the development and utilization of the shoreline, to improve the institutional mechanism for river management and to strengthen the construction of law enforcement teams in the Li Canal.

Tectonic evolution and mineralization of Carlin-type gold deposits in Youjiang basin

FENG Hongye, JU Yiwen, ZHU Hongjian, YU Kun, QIAO Peng, JU Liting, XIAO Lei

2023, 40 (5): 614-636. DOI: 10.7523/j.ucas.2021.0084

Abstract ( 629 ) PDF (0KB) ( 0 )

Youjiang basin (Nanpanjiang basin) experienced a complex tectonic evolution of Paleozoic prototype basin-superimposed basin, and finally, it appears as a residual basin. According to the tectonic setting, sedimentary series and magmatic rocks, the evolution of Youjiang basin after Caledonian movement can be divided into six stages:intracontinental extensional basin (early rift valley) evolution stage (D²₁-D¹₂), oceanic extensional basin (rift ocean basin) evolution stage (D₂-T₁), ocean basin extinction and foreland flexure basin evolution stage (T²₁-T¹₃), fold orogeny and post collisional extension stage (T¹₃-J₁), NW trending compression orogeny stage (J₂-K²₁), and local extension stage (K³₁-E). There are a large number of Carlin-type gold deposits in the basin, and most ore bodies occur in thrust-fold belts. The Carlin-type gold deposit has multi-stage metallogenic characteristics, large-scale mineralization mainly began in the compressive background and continued to the post orogenic extension stage, and there are two concentrated metallogenic periods. The first stage was formed in the evolution stage of foreland flexure basin related to collision orogeny to post collisional extension (235-193 Ma, Carlin-type gold deposit in the central and southern part of the basin). The mineralization in this stage was controlled by metamorphic hydrothermal fluids or hydrothermal fluids relate to magmatic melting which induced by the superposition of collision orogeny of the Yangtze Block and the Indochina Block and the subduction of the Paleo-Pacific plate to the Eurasian continent. The second stage was formed in the stage of NW trending compression orogeny to local extension (148-103 Ma, Carlin-type gold deposit in the whole Youjiang basin). The mineralization in this stage was mainly affected by the magmatic hydrothermal activities during the superposition and transformation of the pre-existing structures by the NW trending compression orogeny. Magmatic or metamorphic hydrothermal activities under extensional background before the Early Triassic has the effect of initial enrichment, and it has the effect of superimposed and reformation post mineralization after the Early Cretaceous. The ore-forming fluid of Carlin-type gold deposit has the characteristics of mixed sources. It is mainly metamorphic hydrothermal solution in the central and southern part of the basin, and mostly mixed source hydrothermal solution in the central part of the basin. While, the ore-forming fluid is mainly magmatic hydrothermal solution in the northern part of Youjiang basin. Through comparative analysis, it is considered that the ages obtained by different dating methods can represent the metallogenic age to a certain extent. And the combined application of multiple methods should be used to limit the metallogenic age of Carlin-type gold deposits.

SAR image change detection algorithm based on hierarchical fuzzy clustering and wavelet convolution neural network

ZHANG Meng, PAN Zhigang

2023, 40 (5): 637-646. DOI: 10.7523/j.ucas.2022.013

Abstract ( 517 ) PDF (0KB) ( 0 )

Traditional synthetic aperture radar (SAR) image change detection methods have some problems, such as big impact by speckle noise, difficult to use deep information of the image, and low detection accuracy. To solve above problems, this paper presents an SAR amplitude image change detection algorithm based on convolution neural network and fuzzy clustering. Firstly, a hierarchical FLICM algorithm based on Gabor texture is used to pre-classify the difference images, and reliable training samples are automatically selected based on the pre-classification results without manual labeling. Then, a multiscale channel attention mechanism is introduced, and a MSCA_WCNN is used to complete the second classification, and the result of change detection is obtained. This algorithm extracts the different scale features of SAR images while suppressing the irrelevant feature channels to effectively utilize the image features. The wavelet convolution neural network achieves the denoising function while preserving the useful information of the image and enhances the robustness of the algorithm. The comparison experiments using real spaceborne SAR image data show that the algorithm has high detection accuracy and the effectiveness of the algorithm is verified.

Real-time imaging algorithm for ship ISAR based on parameter estimation and sub-aperture selection

SU Baihuaning, LIU Chang, WANG Chao

2023, 40 (5): 647-657. DOI: 10.7523/j.ucas.2022.016

Abstract ( 362 ) PDF (0KB) ( 0 )

Airborne inverse synthetic aperture radar (ISAR) imaging is a key technology for microwave imaging and classification of dynamic ships in long-range, all-day, all-weather conditions. Long-time accumulation can bring better signal-to-noise ratio and signal-to-noise ratio of ISAR images, but unknown motions such as ship's sway can significantly affect the long-time focusing effect. In response, this paper proposes a real-time processing method for ship imaging that combines ship motion parameter estimation and sub-aperture search. Based on the translation compensation, the rotational motion parameters of the ship are estimated based on the variation curves of the ship's Doppler spread, centerline slope and scattering point time-frequency curves, the optimal imaging aperture is extracted in real time, and the polar coordinate formatting and rotation compensation are combined with the parameter estimation to obtain clear images of the ship. The results show that compared with traditional imaging methods, this method can effectively improve the effect of long-period focus processing and acquire high-resolution ISAR ship images in real time.

Polarimetric SAR image terrain classification based on superpixel and LightGBM

WANG Yize, SUN Jili, YAN Chengjie, ZHANG Zheng

2023, 40 (5): 658-669. DOI: 10.7523/j.ucas.2022.023

Abstract ( 406 ) PDF (0KB) ( 0 )

Speckle noise of polarimetric synthetic aperture radar(SAR) image reduces the accuracy of terrain classification. Combine multiple features of polarimetric SAR image to do classification, and the large dimension of input features consumes too much time. To handle the above problems, we propose a classification algorithm based on superpixel and LightGBM. With polarimetric features and texture features, the algorithm is good at classification. LightGBM is used to deal with large dimension of input features, which can obtain the pixel-based first-level classification result efficiently. SLIC is used to generate the superpixel-based polarimetric SAR image, and the superpixel-based two-level classification result is obtained by voting pixel by pixel in each superpixel, which solves the influence of speckle noise. Experimental results, using the measured polarimetric SAR data, show that the overall classification accuracy is more than 97%, and it has a low time-consuming.

An adaptive limiting method in LEO satellite multi-beam system based on neural network

LIU Zijian, JIANG Quanjiang, LIU Huijie

2023, 40 (5): 670-676. DOI: 10.7523/j.ucas.2022.012

Abstract ( 302 ) PDF (0KB) ( 0 )

Aiming at the problem that the peak-to-average ratio is too high when the LEO satellite multi-beam system communicates with multiple target directional angles, a method for suppressing the peak-to-average ratio based on a deep neural network is proposed. This method can adaptively select the optimal threshold of the limiting method based on the input layer parameters such as the target direction angle position of the multi-beam communication system, the SNR of the receiving end, and the error range of the BER. The signal synthesized on the element is subjected to amplitude limiting operation, which reduces the peak-to-average ratio of the LEO satellite multi-beam system while ensuring the BER of the system. Finally, it is verified by simulation that this method can significantly improve the peak-to-average ratio within the error range of the BER compared with the traditional fixed-threshold limiting method.

Optimal design of the vacuum interlock and monitor systems for BSRF soft X-ray endstation

LI Jialiang, LIU Shuhu, SHANG Congjian, WANG Fei

2023, 40 (5): 677-686. DOI: 10.7523/j.ucas.2021.0069

Abstract ( 567 ) PDF (0KB) ( 0 )

Beijing synchrotron radiation facility (BSRF) 4B7B soft X-ray endstation is an ultra-high vacuum system, which is connected to the upstream beamline through an electromagnetic plug-in valve. Scientific research users are prone to misoperation when changing samples in experiment. When valve is not closed, vacuum system is vented and equipment is damaged. In order to avoid vacuum accidents, this article proposes to optimize the original manual protection measures and design vacuum safety interlock protection systems. Vacuum gauge, pneumatic angle valve, and electromagnetic flapper valve are interlocked and controlled by electrical components, aiming to improve the convenience and reliability of user's operation on the basis of ensuring the vacuum safety of endstation when user changes samples. The safety interlocking protection system control cabinet was confirmed to meet the expected design requirements after many commissioning inspections and trial runs after landing, and was formally applied in soft X-ray calibration experiment, effectively ensuring the safety and reliability of equipment during user operation. In addition, application prospect of the safety interlock protection system in beamline of high energy photon source (HEPS) in the future is discussed in this article, and engineering design experience is provided for construction of vacuum interlocking protection system of HEPS beamline.

Multi-channel voice activity detection in low signal-to-noise ratio environment

XIAO Si, GONG Jie, LI Baoqing

2023, 40 (5): 687-693. DOI: 10.7523/j.ucas.2022.011

Abstract ( 358 ) PDF (0KB) ( 0 )

Traditional voice activity detection algorithm only uses the time-frequency information, hence the detection accuracy will reduce rapidly in the low signal-to-noise environment, especially when the noise is non-stationary. Multi-channel speech signal has rich spatial information, which helps to improve the accuracy of detection as a supplement to time-frequency information. In this paper, on the basis of multi-channel spatial feature research, we propose a new multi-channel voice activity detection algorithm, by leveraging the maximum eigenvalue of the multi-channel covariance matrix (covariance matrix maximum eigenvalue, CMME) of the received array signals. First, we extract the CMME of the array signal as the feature of detection frame by frame, to track the speech signal. Then the double threshold method is adopted to determine whether the current frame is a speech frame. The results show that, compared with Mel energy ratio and the improved energy zero-entropy algorithm, the proposed algorithm has higher detection accuracy in VCTK and laboratory corpus, and thus is more robust in the low signal-to-noise ratio and non-stationary noise environment.

Vector approximate message passing soft frequency domain equalization for probabilistic constellation shaping

WU Xisheng, WU Yanbo, ZHU Min, LI Dong, CHU Runcong

2023, 40 (5): 694-700. DOI: 10.7523/j.ucas.2022.010

Abstract ( 302 ) PDF (0KB) ( 0 )

The convergence characteristic of the vector approximate message passing soft frequency-domain equalization algorithm is improved by the energy spreading transform at the transmitter. The output of the equalizer can be considered as free of inter-symbol interference. The relation between the output of the equalizer and the transmitted symbols can be modeled by an additive white Gaussian noise channel. Over the bandwidth-constrained additive white Gaussian noise channel, the uniform distribution modulation format has a gap to the Shannon limit. The gap can be closed by probabilistic constellation shaping. The a priori information of unequal probability symbols is used to improve the structure of the equalizer and enhance the performance at the receiver. Theoretical analysis and simulation results show that the proposed algorithm can substantially improve the convergence speed as well as the equalization performance over classical Proakis B and Proakis C multipath channels. There is about 0.5 dB performance gain compared with the uniform distribution signal.

Design of object detection and weak position location system base on coaxial dual-rotor drone

FENG Hangtao, ZENG Shaofeng, ZHANG Lu, YANG Xu, LIU Zhiyong

2023, 40 (5): 701-709. DOI: 10.7523/j.ucas.2022.017

Abstract ( 541 ) PDF (0KB) ( 0 )

Unmanned aerial vehicles (UAV) controlled by autonomous control algorithms often have greater advantages than manned aircraft in the execution of directional strikes and other dangerous tasks. When performing blasting tasks, the robustness of the UAV detection algorithm in different scenarios is often not guaranteed, which greatly affects the UAV's positioning of the target, thus reducing the success rate of the mission. In order to solve the above problems, the crossdomain-based object detection algorithm is used to improve the robustness of the UAV detection algorithm in different scenarios, and the online GPS clustering algorithm is used to improve the robustness of object positioning. At the same time, in view of the impact of the object blasting position on the blasting result, the system uses an algorithm for locating weak parts to improve the accuracy and success rate of blasting.

Multipath routing protocol for MANET based on flooding limiting

WANG Xiaoxiang, WANG Mingliang, XU Huihui, QIN Ronghua

2023, 40 (5): 710-719. DOI: 10.7523/j.ucas.2022.004

Abstract ( 480 ) PDF (0KB) ( 0 )

Mobile ad hoc network (MANET) is widely used in emergency rescue scenarios because of its dynamic network reconfiguration. However, the dynamic topology of MANET causes routes to be easily broken and route reconstruction will occupy more network resources. To solve this problem, this paper proposed a new multipath routing protocol FLMP based on flooding limiting and multiple measurement functions. It uses the flooding limiting mechanism based on node mobility, combines local and global optimal ideas to construct routs, and uses multiple route measurement functions to select the optimal main route and backup route for data transmission. The simulation results show that the FLMP routing protocol can effectively reduce the number of routing breaks, ensure reliable data transmission, and significantly reduce overhead.

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