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Vegetation Products Derived from Fengyun-3D Medium Resolution Spectral Imager-Ⅱ

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Journal of Meteorological Research 2020年第4期34卷 775-785页

作者： Xiuzhen han Jun yang Shihao TANG yang han National Satellite Meteorological Center China Meteorological AdministrationBeijing 100081

The surface vegetation condition has been operationally monitored from space for many years by the Advanced Very High Resolution Radiometer(AVHRR) and the Moderate Resolution Imaging Spectroradiometer(MODIS) instruments. As these instruments are close to the end of their design life, the surface vegetation products are required by many users from the new satellite missions. The MEdium Resolution Spectral Imager-Ⅱ(MERSI-Ⅱ) onboard the Fengyun(FY) satellite(FY-3 series;FY-3 D) is used to retrieve surface vegetation parameters. First, MERSI-Ⅱ solar channel measurements at the red and near-infrared(NIR) bands at the top of atmosphere(TOA) are corrected to the surface reflectances at the top of canopy(TOC) by removing the contributions of scattering and absorption of molecules and aerosols. The normalized difference vegetation index(NDVI) at both the TOA and TOC is then produced by using the same algorithms as the MODIS and AVHRR. The MERSI-Ⅱ enhanced VI(EVI) at the TOC is also developed. The MODIS technique of compositing the NDVI at various timescales is applied to MERSI-Ⅱ to generate the gridded products at different resolutions. The MERSI-Ⅱ VI products are consistent with the MODIS data without systematic biases. Compared to the current MERSI-Ⅱ EVI generated from the ground operational system, the MERSI-Ⅱ EVI from this study has a much better agreement with MODIS after atmospheric correction.

关键词： MEdium Resolution Spectral Imager-Ⅱ(MERSI-Ⅱ) Fengyun(FY)satellite vegetation index(VI) atmospheric correction

ON THE DIFFUSION PHENOMENON OF QUASILINEAR HYPERBOLIC WAVES

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Chinese Annals of Mathematics,Series B 2000年第1期21卷 63-70页

作者： yang han ALBERT MILANI Department of Applied Mathematics South West Jiaotong University610031 ChengduChina Department of Mathematics University of Wisconsin—M ilwaukeeMilwaukeeWisconsin 53201USA

The authors consider the asymptotic behavior of solutions of the quasilinear hyperbolic equation with linear damping u_(tt)+u_(t)-div(a(u)u)=0,and show that,at least when n≥3,they tend,as t-+∞,to those of the nonlinear parabolic equation v_t-div(a(v)v)=0,in the sense that the norm||u(.,t)-v(.,t)||_(L∞(R^n))of the difference u-v decays faster than that of either u or *** provides another example of the diffusion phenomenon of nonlinear hyperbolic waves,first observed by Hsiao,*** Liu Taiping(see[1,2]).

关键词： Asymptotic behavior of solutions Quasilinear hyperbolic and parabolic equations Diffusion phenomenon

Fengyun-3D MERSI True Color Imagery Developed for Environmental Applications

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Journal of Meteorological Research 2019年第5期33卷 914-924页

作者： Xiuzhen han Feng WANG yang han National Satellite Meteorological Center China Meteorological AdministrationBeijing 100081 Beijing Piesat Information Technology Co.Ltd. Beijing 100195 Nanjing University of Information Science&Technology Nanjing 210044

Many techniques were developed for creating true color images from satellite solar reflective bands, and the so-derived images have been widely used for environmental monitoring. For the newly launched Fengyun-3 D(FY-3 D)satellite, the same capability is required for its Medium Resolution Spectrum Imager-II(MERSI-II). In processing the MERSI-II true color image, a more comprehensive processing technique is developed, including the atmospheric correction, nonlinear enhancement, and image splicing. The effect of atmospheric molecular scattering on the total reflectance is corrected by using a parameterized radiative transfer model. A nonlinear stretching of the solar band reflectance is applied for increasing the image contrast. The discontinuity in composing images from multiple orbits and different granules is eliminated through the distance weighted pixel blending(DWPB) method. Through these processing steps, the MERSI-II true color imagery can vividly detect many natural events such as sand and dust storms, snow, algal bloom, fire, and typhoon. Through a comprehensive analysis of the true color imagery, the specific natural disaster events and their magnitudes can be quantified much easily, compared to using the individual channel data.

关键词： Medium Resolution Spectrum Imager(MERSI) Fengyun satellite true color imagery

Remote Sensing of Tropical Cyclone Thermal Structure from Satellite Microwave Sounding Instruments:Impacts of Optimal Channel Selection on Retrievals

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Journal of Meteorological Research 2018年第5期32卷 804-818页

作者： yang han Fuzhong WENG Nanjing University of Information Science&Technology Nanjing 210044 State Key Laboratory of Severe Weather Chinese Academy of Meteorological SciencesBeijing 100081

Accurate information on atmospheric temperature of tropical cyclones （TCs） is important for monitoring and pre- diction of their developments and evolution. For hurricanes, temperature anomaly in the upper troposphere can be de-rived from Advanced Microwave Sounding Unit （AMSU） and Advanced Technology Microwave Sounder （ATMS） through either regression-based or variational retrieval algorithms. This study investigates the dependency of TC warm core structure on emission and scattering processes in the forward operator used for radiance computations in temperature retrievals. In particular, the precipitation scattering at ATMS high-frequency channels can significantly change the retrieval outcomes. The simulation results in this study reveal that the brightness temperatures at 183 GHz could be depressed by 30-50 K under cloud ice water path of 1.5 mm, and thus, the temperature structure in hur-ricane atmosphere could be distorted if the ice cloud scattering was inaccurately characterized in the retrieval system. It is found that for Hurricanes Irma, Maria, and Harvey that occurred in 2017, their warm core anomalies retrieved from ATMS temperature sounding channels 4 15 were more reasonable and realistic, compared with the retrievals from all other channel combinations and earlier hurricane simulation results.

关键词： Advanced Technology Microwave Sounder (ATMS) Microwave Retrieval Testbed (MRT) Warm core hurricane Irma Maria Harvey

Global Existence and Blow-up for Semilinear Wave Equations with Variable Coefficients

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Chinese Annals of Mathematics,Series B 2018年第4期39卷 643-664页

作者： Qian LEI han yang School of Mathematics Southwest Jiaotong University Chengdu 610031 China School of Transportation and Logistics Southwest Jiaotong University Chengdu 610031 China

The authors consider the critical exponent problem for the variable coefficients wave equation with a space dependent potential and source term. For sufficiently small data with compact support, if the power of nonlinearity is larger than the expected exponent, it is proved that there exists a global solution. Furthermore, the precise decay estimates for the energy, L^2 and L^(p+1) norms of solutions are also established. In addition, the blow-up of the solutions is proved for arbitrary initial data with compact support when the power of nonlinearity is less than some constant.

关键词： Semilinear wave equations Global existence Energy decay L^2 and L^p+1 estimates Blow up

Model Implementation and Analysis of a True Three-dimensional Display System

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Computer Systems Science & Engineering 2021年第12期39卷 403-414页

作者： Ye Tian yang yang han yang Ze Ji Changchun University of Science and Technology Changchun130022China Tsinghua University Beijing100084China Academy of Military Sciences Beijing100166China Cardiff University CardiffCF243AAUK

To model a true three-dimensional(3D)display system,we introduced the method of voxel molding to obtain the stereoscopic imaging space of the *** the distribution of each voxel,we proposed a four-dimensional(4D)Givone–Roessor(GR)model for state-space representation—that is,we established a local state-space model with the 3D position and one-dimensional time coordi-nates to describe the ***,we extended the original elementary operation approach to a 4D condition and proposed the implementation steps of the realiza-tion matrix of the 4D GR ***,we described the working process of a true 3D display system,analyzed its real-time performance,introduced the fixed-point quantization model to simplify the system matrix,and derived the conditions for the global asymptotic stability of the system after ***,we provided an example to prove the true 3D display system’s feasibility by *** GR-model-representation method and its implementation steps proposed in this paper simplified the system’s mathematical expression and facilitated the microcon-troller software ***-time and stability analyses can be used widely to analyze and design true 3D display systems.

关键词： True 3D display system method of voxel molding(MVM) Givone-Roessor(GR)model asymptotic stability Bounded-Input Bounded-Output(BIBO)stability real-time display

Effect of Plastic Anisotropy on the Formability of Aluminum 6016-T4 Sheet Material

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Chinese Journal of Mechanical Engineering 2017年第3期30卷 625-631页

作者： Young-Suk KIM Seung-han yang kyungpook national university Daegu 41566Republic of Korea

Sheet metal formed of lightweight materials such as aluminum sheeting has received great attention related to the reduction of vehicle emissions. This paper evaluates the anisotropic yield locus using Kuwabara＇s biaxial tensile tester and stretches formability using Hecker＇s hemispheri- cal punch stretching test for aluminum 6016-T4 sheet material. The anisotropic yield locus of the A16016-T4 sheet measured is fitted well by the modified Drucker yield func- tion. Moreover the best fitting to the experimental stress- strain curve from the tensile test was obtained by taking an appropriate hardening model. Analytical study to predict the stretch formability by using Hora＇s Modified Maximum Force Criterion （MMFC） was performed. The predicted forming limit curves （FLC） based on various yield functions were compared with the experiments and discussed.

关键词： Anisotropic yield function AluminumA16016-T4 Biaxial tensile test Forming limit curve

Solving viscoelastic problems with cyclic symmetry via a precise algorithm and EFGM

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Acta Mechanica Sinica 2006年第2期22卷 170-176页

作者： Zhi han Haitian yang Ling Liu State Key Lab of Structural Analysis of Industrial Equipment Department of Engineering Mechanics Dalian University of Technology Dalian 116024 China

The paper combines a self-adaptive precise algorithm in the time domain with Meshless Element Free Galerkin Method （EFGM） for solving viscoelastic problems with rotationally periodic symmetry. By expanding variables at a discretized time interval, the variations of variables can be described more precisely, and iteration is not required for non-linear cases. A space-time domain coupled problem with initial and boundary values can be converted into a series of linear recursive boundary value problems, which are solved by a group theory based on EFGM. It has been proved that the coefficient matrix of the global EFG equation for a rotationally periodic system is block-circulant so long as a kind of symmetry-adapted reference coordinate system is adopted, and then a partitioning algorithm for facilitating parallel processing was proposed via a completely orthogonal group transformation. Therefore instead of solving the original system, only a series of independent small sub-problems need to be solved, leading to computational convenience and a higher computing efficiency. Numerical examples are given to illustrate the full advantages of the proposed algorithm.

关键词： EFGM Cyclic symmetry Precise algorithm Viscoelastic problem

Retrieval of Oceanic Total Precipitable Water Vapor and Cloud Liquid Water from Fengyun-3D Microwave Sounding Instruments

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Journal of Meteorological Research 2021年第2期35卷 371-383页

作者： yang han Jun yang Hao HU Peiming DONG State Key Laboratory of Severe Weather Chinese Academy of Meteorological SciencesChina Meteorological AdministrationBeijing 100081 National Satellite Meteorological Center China Meteorological AdministrationBeijing 100081

Fengyun-3 D(FY-3 D) satellite is the latest polar-orbiting meteorological satellite launched by China and carries 10 instruments onboard. Its microwave temperature sounder(MWTS) and microwave humidity sounder(MWHS) can acquire a total of 28 channels of brightness temperatures, providing rich information for profiling atmospheric temperature and moisture. However, due to a lack of two important frequencies at 23.8 and 31.4 GHz, it is difficult to retrieve the total precipitable water vapor(TPW) and cloud liquid water path(CLW) from FY-3 D microwave sounder data as commonly done for other microwave sounding instruments. Using the channel similarity between Suomi National Polar-orbiting Partnership(NPP) advanced technology microwave sounder(ATMS) and FY-3 D microwave sounding instruments, a machine learning(ML) technique is used to generate the two missing low-frequency channels of MWTS and MWHS. Then, a new dataset named as combined microwave sounder(CMWS) is obtained,which has the same channel setting as ATMS but the spatial resolution is consistent with MWTS. A statistical inversion method is adopted to retrieve TPW and CLW over oceans from the FY-3 D CMWS. The intercomparison between different satellites shows that the inversion products of FY-3 D CMWS and Suomi NPP ATMS have good consistency in magnitude and distribution. The correlation coefficients of retrieved TPW and CLW between CMWS and ATMS can reach 0.95 and 0.85, respectively.

关键词： precipitable water vapor cloud liquid water Fengyun-3D(FY-3D) microwave machine learning(ML)