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Linear spectral unmixing algorithm for modelling suspendedsediment concentration of ash oods, upper Tekeze River, Ethiopia 预览
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作者 Hagos GGebreslassie Assefa MMelesse +1 位作者 Kevin Bishop Azage GGebremariam 《国际泥沙研究:英文版》 SCIE 2020年第1期79-90,共12页
Flash floods are the highest sediment transporting agent,but are inaccessible for in-situ sampling and have rarely been analyzed by remote sensing technology.Laboratory and field experiments were done to develop linea... Flash floods are the highest sediment transporting agent,but are inaccessible for in-situ sampling and have rarely been analyzed by remote sensing technology.Laboratory and field experiments were done to develop linear spectral unmixing(LSU)remote sensing model and evaluate its performance in simulating the suspended sediment concentration(SSC)in flash floods.The models were developed from continuous monitoring in the laboratory and the onsite spectral signature of river bed sediment deposits and flash floods in the Tekeze River and in its tributary,the Tsirare River.The Pearson correlation coefficient was used to determine the variability of correlations between reflectance and SSCs.The coefficient of determination(R2)and root mean square of error(RMSE)were used to evaluate the performance of the generated models.The results found that the Pearson correlation coefficient between SSCs and reflectance varied based on the level of the SSCs,geological colors,and grain sizes.The performance of the LSU model and empirical remote sensing approaches were computed to be R2?0.92,and RMSE-±0.76 g/l in the Tsirare River and R2-0.91,and RMSE-±0.73 g/l in the Tekeze River and R2?0.81,RMSE-±2.65 g/l in the Tsirare river and R2?0.76,RMSE-±10.87 g/l in the Tekeze River,respectively.Hence,the LSU approach of remote sensing was found to be relatively accurate in monitoring and modeling the variability of SSCs that could be applied to the upper Tekeze River basin. 展开更多
关键词 Empirical remote sensing Flash floods Linear spectral unmixing Suspended sediment concentration Tekeze River
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Sharp upper bounds for the adjacency and the signless Laplacian spectral radius of graphs 预览
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作者 WU Xian-zhang LIU Jian-ping 《高校应用数学学报:英文版(B辑)》 SCIE CSCD 2019年第1期100-112,共13页
Let G be a simple graph with n vertices and m edges.In this paper,we present some new upper bounds for the adjacency and the signless Laplacian spectral radius of graphs in which every pair of adjacent vertices has at... Let G be a simple graph with n vertices and m edges.In this paper,we present some new upper bounds for the adjacency and the signless Laplacian spectral radius of graphs in which every pair of adjacent vertices has at least one common adjacent vertex.Our results improve some known upper bounds.The main tool we use here is the Lagrange identity. 展开更多
关键词 graph SPECTRAL RADIUS signless LAPLACIAN SPECTRAL RADIUS upper bound
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Removing Moisture Effect on Soil Reflectance Properties: A Case Study of Clay Content Prediction
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作者 Yaron OGEN Shira FAIGENBAUM-GOLOVIN +3 位作者 Amihai GRANOT Yoel SHKOLNISKY Naftaly GOLDSHLEGER Eyal BEN-DOR 《土壤圈:英文版》 SCIE CAS CSCD 2019年第4期421-431,共11页
Visible, near-infrared and shortwave-infrared(VNIR-SWIR) spectroscopy is an efficient approach for predicting soil properties because it reduces the time and cost of analyses. However, its advantages are hampered by t... Visible, near-infrared and shortwave-infrared(VNIR-SWIR) spectroscopy is an efficient approach for predicting soil properties because it reduces the time and cost of analyses. However, its advantages are hampered by the presence of soil moisture, which masks the major spectral absorptions of the soil and distorts the overall spectral shape. Hence, developing a procedure that skips the drying process for soil properties assessment directly from wet soil samples could save invaluable time. The goal of this study was twofold:proposing two approaches, partial least squares(PLS) and nearest neighbor spectral correction(NNSC), for dry spectral prediction and utilizing those spectra to demonstrate the ability to predict soil clay content. For these purposes, we measured 830 samples taken from eight common soil types in Israel that were sampled at 66 different locations. The dry spectrum accuracy was measured using the spectral angle mapper(SAM) and the average sum of deviations squared(ASDS), which resulted in low prediction errors of less than 8% and 14%, respectively. Later, our hypothesis was tested using the predicted dry soil spectra to predict the clay content, which resulted in R^2 of 0.69 and 0.58 in the PLS and NNSC methods, respectively. Finally, our results were compared to those obtained by external parameter orthogonalization(EPO) and direct standardization(DS). This study demonstrates the ability to evaluate the dry spectral fingerprint of a wet soil sample, which can be utilized in various pedological aspects such as soil monitoring, soil classification,and soil properties assessment. 展开更多
关键词 dry SPECTRAL FINGERPRINT nearest NEIGHBOR SPECTRAL correction partial least SQUARES reflectance spectra SOIL MOISTURE SOIL property spectroscopy wet SOIL
A trigonometric series expansion method for the Orr-Sommerfeld equation 预览
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作者 Ying TAN Weidong SU 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第6期877-888,共12页
A trigonometric series expansion method and two similar modified methods for the Orr-Sommerfeld equation are presented. These methods use the trigonometric series expansion with an auxiliary function added to the high... A trigonometric series expansion method and two similar modified methods for the Orr-Sommerfeld equation are presented. These methods use the trigonometric series expansion with an auxiliary function added to the highest order derivative of the unknown function and generate the lower order derivatives through successive integra- tions. The proposed methods are easy to implement because of the simplicity of the chosen basis functions. By solving the plane Poiseuille flow (PPF), plane Couette flow (PCF), and Blasius boundary layer flow with several homogeneous boundary conditions, it is shown that these methods yield results with the same accuracy as that given by the conventional Chebyshev collocation method but with better robustness, and that ob- tained by the finite difference method but with fewer modal number. 展开更多
关键词 Orr-Sommerfeld EQUATION SPECTRAL method trigonometric function PARALLEL SHEAR flow hydrodynamical stability EIGENVALUE PROBLEM
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Constant envelope FrFT OFDM: spectral and energy efficiency analysis 预览
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作者 DIDA Mussa Ally HUAN Hao +2 位作者 TAO Ran WANG Teng URYNBASSAROVA Didar 《系统工程与电子技术:英文版》 SCIE EI CSCD 2019年第3期467-473,共7页
Constant envelope with a fractional Fourier transformorthogonal frequency division multiplexing(CE-FrFT-OFDM)is a special case of a constant envelope OFDM(CE-OFDM),both being energy efficient wireless communication te... Constant envelope with a fractional Fourier transformorthogonal frequency division multiplexing(CE-FrFT-OFDM)is a special case of a constant envelope OFDM(CE-OFDM),both being energy efficient wireless communication techniques with a 0 dB peak to average power ratio(PAPR).However,with the proper selection of fractional order,the first technique has a high bit error rate(BER)performance in the frequency-time selective channels.This paper performs further analysis of CE-FrFT-OFDM by examining its spectral efficiency(SE)and energy efficiency(EE)and compare to the famous OFDM and FrFT-OFDM techniques.Analytical and comprehensive simulations conducted show that,the CE-FrFT-OFDM has five times the EE of OFDM and FrFT-OFDM systems with a slightly less SE.Increasing CE-FrFT-OFDM’s transmission power by increasing its amplitude to 1.7 increases its SE to match that of the OFDM and FrFT-OFDM systems while slightly reducing its EE by 20%to be four times that of OFDM and FrFTOFDM systems.OFDM and FrFT-OFDM’s amplitude fluctuations cause rapid changing output back-off(OBO)power requirements and further reduce power amplifier(PA)efficiency while CE-FrFTOFDM stable operational linear range makes it a better candidate and outperforms the other techniques when their OBO exceeds 1.7.Higher EE and low BER in time-frequency selective channel are attracting features for CE-FrFT-OFDM deployment in mobile devices. 展开更多
关键词 FRACTIONAL Fourier transform (FrFT) constant ENVELOPE SPECTRAL EFFICIENCY (SE) energy EFFICIENCY (EE) high power AMPLIFIER
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Detection of short-term urban land use changes by combining SAR time series images and spectral angle mapping
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作者 Zhuokun PAN Yueming HU Guangxing WANG 《地球科学前沿:英文版》 CSCD 2019年第3期495-509,共15页
Rapid urban sprawl and re-construction of old towns have been leading to great changes of land use in cities of China. To witness short-term urban land use changes, rapid or real time remote sensing images and effecti... Rapid urban sprawl and re-construction of old towns have been leading to great changes of land use in cities of China. To witness short-term urban land use changes, rapid or real time remote sensing images and effective detection methods are required. With the availability of short repeat cycle, relatively high spatial resolution, and weather-independent Synthetic Aperture Radar (SAR) remotely sensed data, detection of short-term urban land use changes becomes possible. This paper adopts newly released Sentinel-1 SAR data for urban change detection in Tianhe District of Guangzhou City in Southern China, where dramatic urban redevelopment practices have been taking place in past years. An integrative method that combines the SAR time series data and a spectral angle mapping (SAM) was developed and applied to detect the short-term land use changes. Linear trend transformations of the SAR time series data were first conducted to reveal patterns of substantial changes. Spectral mixture analysis was then conducted to extract temporal endmembers to reflect the land development patterns based on the SAR backscattering intensities over time. Moreover, SAM was applied to extract the information of significant increase and decrease patterns. The results of validation and method comparison showed a significant capability of both the proposed method and the SAR time series images for detecting the short-term urban land use changes. The method received an overall accuracy of 78%, being more accurate than that using a bi-temporal image change detection method. The results revealed land use conversions due to the removal of old buildings and their replacement by new construction. This implies that SAR time series data reflects the spatiotemporal evolution of urban constructed areas within a short time period and this study provided the potential for detecting changes that requires continuously short-term capability, and could be potential in other landscapes. 展开更多
关键词 Sentinel-1 SAR time series IMAGES urban land use change DETECTION TEMPORAL ENDMEMBER spectral angle mapping
Rogue waves during Typhoon Trami in the East China Sea 预览
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作者 JIANG Xingjie GUAN Changlong WANG Daolong 《海洋湖沼学报(英文)》 SCIE CAS CSCD 2019年第6期1817-1836,共20页
As concluded from physical theory and laboratory experiment,it is widely accepted that nonlinearities of sea state play an important role in the formation of rogue waves;however,the sea states and corresponding nonlin... As concluded from physical theory and laboratory experiment,it is widely accepted that nonlinearities of sea state play an important role in the formation of rogue waves;however,the sea states and corresponding nonlinearities of real-world rogue wave events remain poorly understood.Three rogue waves were recorded by a directional buoy located in the East China Sea during Typhoon Trami in August 2013.This study used the WAVEWATCHⅢmodel to simulate the sea state conditions pertaining to when and where those rogue waves were observed,based on which a comprehensive and full-scale analysis was performed.From the perspectives of wind and wave fields,wave system tracking,High-Order Spectral method simulation,and some characteristic sea state parameters,we concluded that the rogue waves occurred in sea states dominated by second-order nonlinearities.Moreover,third-order modulational instabilities were suppressed in these events because of the developed or fully developed sea state determined by the typhoon wave system.The method adopted in this study can provide comprehensive and full-scale analysis of rogue waves in the real world.The case studied in this paper is not considered unique,and rules could be found and confirmed in relation to other typhoon sea states through the application of our proposed method. 展开更多
关键词 rogue WAVE WAVE system TRACKING HIGH-ORDER SPECTRAL method NONLINEAR effect
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Collaboration Filtering Recommendation Algorithm Based on the Latent Factor Model and Improved Spectral Clustering 预览
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作者 Xiaolan Xie Mengnan Qiu 《国际计算机前沿大会会议论文集》 2019年第1期98-100,共3页
Due to the development of E-Commerce, collaboration filtering (CF) recommendation algorithm becomes popular in recent years. It has some limitations such as cold start, data sparseness and low operation efficiency. In... Due to the development of E-Commerce, collaboration filtering (CF) recommendation algorithm becomes popular in recent years. It has some limitations such as cold start, data sparseness and low operation efficiency. In this paper, a CF recommendation algorithm is propose based on the latent factor model and improved spectral clustering (CFRALFMISC) to improve the forecasting precision. The latent factor model was firstly adopted to predict the missing score. Then, the cluster validity index was used to determine the number of clusters. Finally, the spectral clustering was improved by using the FCM algorithm to replace the K-means in the spectral clustering. The simulation results show that CFRALFMISC can effectively improve the recommendation precision compared with other algorithms. 展开更多
关键词 COLLABORATION FILTERING RECOMMENDATION algorithm LATENT Factor Model Cluster validity index SPECTRAL CLUSTERING
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Site dependent and spatially varying response spectra 预览
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作者 Hakima Djilali Berkane Zamila Harichane +1 位作者 Erkan Celebi Sidi Mohammed Elachachi 《地震工程与工程振动:英文版》 SCIE EI CSCD 2019年第3期497-509,共13页
The goal of this study is to provide a stochastic method to investigate the eff ects of the randomness of soil properties due to their natural spatial variability on the response spectra spatial variation at sites wit... The goal of this study is to provide a stochastic method to investigate the eff ects of the randomness of soil properties due to their natural spatial variability on the response spectra spatial variation at sites with varying conditions. For this purpose, Monte Carlo Simulations are used to include the variability of both incident ground motion and soil parameters in the response spectra by mean of an appropriate coherency loss function and a site-dependent transfer function, respectively. The approach is built on the assumption of vertical propagation of SH type waves in soil strata with uncertain parameters. The response spectra are obtained by numerical integration of the governing equation of a single-degree-of-freedom (SDOF) system under non-stationary site-dependent and spatially varying ground motion accelerations simulated with non-uniform spectral densities and coherency loss functions. Numerical examples showed that randomness of soil properties signifi cantly aff ects the amplitudes of the response spectra, indicating that as the heterogeneity induced by the randomness of the parameters of the medium increases, the spectral ordinates attenuate. 展开更多
关键词 response SPECTRA RANDOMNESS SPECTRAL density MONTE Carlo
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Concentration and Characterization of Colored Dissolved Organic Matter in the Surface Microlayer and Subsurface Water of the Yellow Sea and the East China Sea 预览
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作者 ZHANG Jing ZHAO Junjie +1 位作者 YANG Guipeng LIU Weifeng 《中国海洋大学学报:英文版》 SCIE CAS CSCD 2019年第2期383-393,共11页
The distribution and chemical properties of colored dissolved organic matter(CDOM)in the Yellow Sea and the East China Sea during December 2011-January 2012 were investigated.The input of freshwater and biological act... The distribution and chemical properties of colored dissolved organic matter(CDOM)in the Yellow Sea and the East China Sea during December 2011-January 2012 were investigated.The input of freshwater and biological activities had an evident influence on the CDOM levels(characterized by the light absorption coefficient at the wavelength of 355 nm a355)in the study area.The spatial distribution of CDOM levels displayed a gradually decreasing trend from the coastal waters(0.37m^-1)to the open sea(0.18m^-1).The spectral slope ratio(the slope ratio SR defined as S275-295:S350-400)during the cruise was correlated with salinity,and exhibited a large variation from inshore(average of 2.515)to offshore sites(average of 5.327)compared with the distribution of a355.The values of SR were related to CDOM molecular weight(MW).The a355,SR,and chlorophyll a in 37 samples collected from the surface microlayer were significantly correlated with those in the corresponding subsurface water samples,implying a strong exchange action between the microlayer and bulk water.The a355 and SR of CDOM exhibited significant microlayer enrichment,with mean enrichment factors(EFs)of 1.72 and 1.62,respectively. 展开更多
关键词 COLORED dissolved organic matter(CDOM) absorption coefficient SPECTRAL SLOPE ratio YELLOW SEA East China SEA
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The INTERNODES Method for Non-conforming Discretizations of PDEs 预览
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作者 Paola Gervasio Alfio Quarteroni 《应用数学与计算数学学报(英文)》 2019年第3期361-401,共41页
INTERNODES is a general purpose method to deal with non-conforming discretizations of partial differential equations on 2D and 3D regions partitioned into two or several disjoint subdomains. It exploits two intergrid ... INTERNODES is a general purpose method to deal with non-conforming discretizations of partial differential equations on 2D and 3D regions partitioned into two or several disjoint subdomains. It exploits two intergrid interpolation operators, one for transfering the Dirichlet trace across the interfaces, and the other for the Neumann trace. In this paper, in every subdomain the original problem is discretized by either the finite element method (FEM) or the spectral element method (SEM or hp-FEM), using a priori non-matching grids and piecewise polynomials of different degrees. Other discretization methods, however, can be used. INTERNODES can also be applied to heterogeneous or multiphysics problems, that is, problems that feature different differential operators inside adjacent subdomains. For instance, in this paper we apply the INTERNODES method to a Stokes- Darcy coupled problem that models the filtration of fluids in porous media. Our results highlight the flexibility of the method as well as its optimal rate of convergence with respect to the grid size and the polynomial degree. 展开更多
关键词 Domain decomposition Non-conforming approximation Non-conforming grids Interpolation FINITE ELEMENT METHOD hp-finite ELEMENT METHOD Spectral ELEMENT METHOD
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光谱技术在自动水质监测中的应用研究 预览
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作者 孟梅 《广东化工》 CAS 2019年第10期169-169,151共2页
光谱技术是重要的水质检测技术之一,对自动水质监测的应用有重要意义。从技术应用的角度,综述了光谱技术在自动水质监测中的应用现状。为更好实现其在自动水质监测中应用,应加强光谱对污染物的响应特点,不同光谱技术的协同使用和新光谱... 光谱技术是重要的水质检测技术之一,对自动水质监测的应用有重要意义。从技术应用的角度,综述了光谱技术在自动水质监测中的应用现状。为更好实现其在自动水质监测中应用,应加强光谱对污染物的响应特点,不同光谱技术的协同使用和新光谱技术的研发等方面的研究。 展开更多
关键词 光谱 自动监测 水质
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C1-Conforming Quadrilateral Spectral Element Method for Fourth-Order Equations 预览
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作者 Huiyuan Li Weikun Shan Zhimin Zhang 《应用数学与计算数学学报(英文)》 2019年第3期403-434,共32页
This paper is devoted to Professor Benyu Guo's open question on the C1-conforming quadrilateral spectral element method for fourth-order equations which has been endeavored for years. Starting with generalized Jac... This paper is devoted to Professor Benyu Guo's open question on the C1-conforming quadrilateral spectral element method for fourth-order equations which has been endeavored for years. Starting with generalized Jacobi polynomials on the reference square, we construct the C1-conforming basis functions using the bilinear mapping from the reference square onto each quadrilateral element which fall into three categories-interior modes, edge modes, and vertex modes. In contrast to the triangular element, compulsively compensatory requirements on the global C1-continuity should be imposed for edge and vertex mode basis functions such that their normal derivatives on each common edge are reduced from rational functions to polynomials, which depend on only parameters of the common edge. It is amazing that the C1-conforming basis functions on each quadrilateral element contain polynomials in primitive variables, the completeness is then guaranteed and further confirmed by the numerical results on the Petrov-Galerkin spectral method for the non-homogeneous boundary value problem of fourth-order equations on an arbitrary quadrilateral. Finally, a C1-conforming quadrilateral spectral element method is proposed for the biharmonic eigenvalue problem, and numerical experiments demonstrate the effectiveness and efficiency of our spectral element method. 展开更多
关键词 QUADRILATERAL spectral element method FOURTH-ORDER equations Mapped POLYNOMIALS C1-conforming basis POLYNOMIAL inclusion COMPLETENESS
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Exponential Stabilization of Euler-Bernoulli Beam with Input Time-Delay in the Boundary Control 预览
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作者 Jilong Wu Yingfeng Shang 《哈尔滨工业大学学报:英文版》 EI CAS 2019年第3期20-25,共6页
The boundary control problem of a cantilever Euler-Bernoulli beam with input time delay is considered.In order to exponentially stabilize the system, a feedback controller is adopted.And we study the well-posedness an... The boundary control problem of a cantilever Euler-Bernoulli beam with input time delay is considered.In order to exponentially stabilize the system, a feedback controller is adopted.And we study the well-posedness and exponential stability of the closed-loop system.The approach used in this paper is done by several steps.Firstly, the well-posedness of this system is proved by semi-group theory.Secondly, the asymptotical expression of eigenvalue is investigated by spectral analysis.Thirdly, the exponential stability of the system is studied by multiplier technology.Finally, numerical simulations on the dynamical behavior of the system are given to support the results obtained. 展开更多
关键词 FEEDBACK control time delay LYAPUNOV function EXPONENTIAL stability SPECTRAL analysis
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基于纹理和光谱信息的奈曼旗防风遥感解译
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作者 贾俊英 曹瑞 +3 位作者 张小波 史婷婷 杨敏 李旻辉 《中国中药杂志》 CAS CSCD 北大核心 2019年第19期4111-4115,共5页
中药材种植面积是制定中药材生产、扶贫等政策和确定药材贸易数量的重要依据,精确掌握中药材种植的分布、面积和产量等信息是中药种植结构调整的基础。奈曼旗现为内蒙古通辽市最大的蒙中药材种植地,及时有效地获取奈曼旗的蒙中药材种植... 中药材种植面积是制定中药材生产、扶贫等政策和确定药材贸易数量的重要依据,精确掌握中药材种植的分布、面积和产量等信息是中药种植结构调整的基础。奈曼旗现为内蒙古通辽市最大的蒙中药材种植地,及时有效地获取奈曼旗的蒙中药材种植面积对后续产业发展具有重要意义。该研究选取奈曼旗大面积种植的药用植物防风为例,以融合的2 m分辨率的资源三号(ZY-3)遥感影像作为数据源,基于地面调查的数据,选取各典型地物的样本数据,得出不同地物的光谱特征曲线,获取防风光谱信息;采用基于概率统计的滤波纹理分析方法,选取5种不同纹理滤波下的纹理图像显示结果进行比较分析,最终确定基于信息熵的防风纹理特征。应用遥感影像的纹理和光谱信息提取解译奈曼旗防风的分布范围及种植面积。结果表明:防风主要分布在奈曼旗的东北地区和中南部地区,种植面积达5 336亩(1亩≈667 m~2)。野外实地验证数据与遥感解译结果吻合程度很高,差异性较小。说明采用光谱信息和纹理信息结合的方法可以实现防风的判别,解译结果可为县域制定中药材产业扶贫行动和农业产区经济发展规划提供参考。 展开更多
关键词 防风 遥感技术 种植面积 光谱 纹理
Directional Analysis of Urban Expansion Based on Sub-pixel and Regional Scale: A Case Study of Main Districts in Guangzhou, China 预览
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作者 ZHAO Yi ZHONG Kaiwen +2 位作者 XU Jianhui SUN Caige WANG Yunpeng 《中国地理科学:英文版》 SCIE CSCD 2019年第4期652-666,共15页
Multi-scale data have had a wide-ranging level of performance in the area of urban change monitoring. Herein we investigate the correlation between the impervious surface fraction(ISF) and the Defense Meteorological S... Multi-scale data have had a wide-ranging level of performance in the area of urban change monitoring. Herein we investigate the correlation between the impervious surface fraction(ISF) and the Defense Meteorological Satellite Program/Operational Linescan System(DMSP/OLS) nighttime stable light(NTL) data with respect to the urban expansion in the main districts of Guangzhou. Landsat 5 Thematic Mapper and Landsat 8 Operational Land Image(OLI) data from 1988 to 2015 were used to extract the ISF using the linear spectral mixture analysis model and normal difference build-up index at the sub-pixel scale. DMSP/OLS NTL data from 1992 to 2013 were calibrated to illustrate the urban nighttime light conditions at the regional scale. Urban expansion directions were identified by statistics and kernel density analysis for the ISF study area at the sub-pixel scale. In addition, the correlation between the ISF and DMSP/OLS NTL data were illustrated by linear regression analysis. Furthermore, Profile Graph in ArcGIS was employed to illustrate the urban expansion from the differences in correlation in different directions. The conclusions are as follows: 1) The impervious surface(IS)in the study area has expanded to the northeast and the east, starting with the old urban zones, and the high-density IS area has increased by321.14 km~2. 2) The linear regression analysis reveals a positive correlation between the ISF and the DMSP/OLS NTL data. The multi-scale data changes are consistent with the actual urban planning of Guangzhou. 3) The DMSP/OLS NTL data overestimate the urban extent because of its saturation and blooming effects, causing its correlation with ISF to decrease. The pattern of urban expansion influences the saturation and blooming effects of the DMSP/OLS NTL data. 展开更多
关键词 impervious surface FRACTION linear spectral mixture ANALYSIS NIGHTTIME light kernel density profile graph
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FM-to-AM conversion in angular filtering based on transmitted volume Bragg gratings
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作者 Fan Gao Baoxing Xiong +1 位作者 Xiang Zhang Xiao Yuan 《高功率激光科学与工程:英文版》 CSCD 2019年第2期97-103,共7页
FM-to-AM conversion for angular filtering based on transmitted volume Bragg gratings(TBGs)is discussed.Simulation results show that a narrower spectral selectivity of TBGs led to stronger FM-to-AM conversion.Good angu... FM-to-AM conversion for angular filtering based on transmitted volume Bragg gratings(TBGs)is discussed.Simulation results show that a narrower spectral selectivity of TBGs led to stronger FM-to-AM conversion.Good angular selectivity and a wide bandwidth for the TBGs can be obtained by controlling the grating period and thickness.FM-to-AM conversion can be effectively suppressed and the distortion criterion for the filtered beam reduces to less than 5%.FMto-AM conversion of TBGs is demonstrated in the’Shenguang’ facility,and the results are in good agreement with the simulation. 展开更多
关键词 FM-to-AM CONVERSION spectral SELECTIVITY volume BRAGG GRATING
Hyper-spectral characteristics of rolled-leaf desert vegetation in the Hexi Corridor,China 预览
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作者 WEI Huaidong YANG Xuemei +4 位作者 ZHANG Bo DING Feng ZHANG Weixing LIU Shizeng CHEN Fang 《干旱区科学:英文版》 SCIE CSCD 2019年第3期332-344,共13页
Desert plants survive harsh environment using a variety of drought-resistant structural modifications and physio-ecological systems.Rolled-leaf plants roll up their leaves during periods of drought,making it difficult... Desert plants survive harsh environment using a variety of drought-resistant structural modifications and physio-ecological systems.Rolled-leaf plants roll up their leaves during periods of drought,making it difficult to distinguish between the external structures of various types of plants,it is therefore necessary to carry out spectral characteristics analysis for species identification of these rolled-leaf plants.Based on hyper-spectral data measured in the field,we analyzed the spectral characteristics of seven types of typical temperate zone rolled-leaf desert plants in the Hexi Corridor,China using a variety of mathematical transformation methods.The results show that:(1)during the vigorous growth period in July and August,the locations of the red valleys,green peaks,and three-edge parameters,namely,the red edge,the blue edge,and the yellow edge of well-developed rolled-leaf desert plants are essentially consistent with those of the majority of terrestrial vegetation types;(2)the absorption regions of liquid water,i.e.,1400-1500 and 1600-1700 nm,are the optimal bands for distinguishing various types of rolled-leaf desert plants;(3)in the leaf reflectance regions of 700-1250 nm,which is controlled by cellular structure,it is difficult to select the characteristic bands for differentiation rolled-leaf desert vegetation;and(4)after processing the spectral reflectance curves using a first-order differential,the envelope removal method,and the normalized differential ratio,we identify the other characteristic bands and parameters that can be used for identifying various types of temperate zone rolled-leaf desert plants,i.e.,the 510-560,650-700 and 1330-1380 nm regions,and the red edge amplitude.In general,the mathematical transformation methods in the study are effective tools to capture useful spectral information for species identification of rolled-leaf plants in the Hexi Corridor. 展开更多
关键词 rolled-leaf desert VEGETATION spectral CHARACTERISTICS mathematical transformation VEGETATION identification Hexi CORRIDOR
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EFFICIENT AND ACCURATE NUMERICAL METHODS FOR LONG-WAVE SHORT-WAVE INTERACTION EQUATIONS IN THE SEMICLASSICAL LIMIT REGIME
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作者 Tingchun Wang Xiaofei Zhao +1 位作者 Mao Peng Peng Wang 《计算数学:英文版》 SCIE CSCD 2019年第5期645-665,共21页
This paper focuses on performance of several efficient and accurate numerical methods for the long-wave short-wave interaction equations in the semiclassical limit regime. The key features of the proposed methods are ... This paper focuses on performance of several efficient and accurate numerical methods for the long-wave short-wave interaction equations in the semiclassical limit regime. The key features of the proposed methods are based on:(i) the utilization of the first-order or second-order time-splitting method to the nonlinear wave interaction equations;(ii) the ap-plication of Fourier pseudo-spectral method or compact finite difference approximation to the linear subproblem and the spatial derivatives;(iii) the adoption of the exact integration of the nonlinear subproblems and the ordinary differential equations in the phase space. The numerical methods under study are efficient, unconditionally stable and higher-order accurate, they are proved to preserve two invariants including the position density in L^1. Numerical results are reported for case studies with different types of initial data, these results verify the conservation laws in the discrete sense, show the dependence of the numerical solution on the time-step, mesh-size and dispersion parameter ε, and demonstrate the behavior of nonlinear dispersive waves in the semi-classical limit regime. 展开更多
关键词 LONG-WAVE short-wave INTERACTION EQUATIONS SEMICLASSICAL limit TIME-SPLITTING METHOD Spectral METHOD Compact finite difference METHOD Conservative properties
Hypergraphs with Spectral Radius at Most r√(2+√5)
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作者 Shoudong MAN Linyuan LU 《数学研究及应用:英文版》 CSCD 2019年第2期111-131,共21页
In this paper,we consider the r-uniform hypergraphs H with spectral radius at most r√(2+√5).We show that H must have a quipus-structure,which is similar to the graphs with spectral radius at most 2/3√2[Woo-Neumaier... In this paper,we consider the r-uniform hypergraphs H with spectral radius at most r√(2+√5).We show that H must have a quipus-structure,which is similar to the graphs with spectral radius at most 2/3√2[Woo-Neumaier,Graphs Combin.2007]. 展开更多
关键词 r-uniform HYPERGRAPHS SPECTRAL RADIUS α-normal
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