基于Sentinel数据的组合极化反演土壤表层水分研究

土壤水分在农业生产发展中扮演着重要的角色,准确、实时地获取大范围的土壤水分对现代化农业建设有重要的意义。本文提出以Sentinel-1(0.453VV+0.547VH)的组合极化模式结合Sentinel-2和Landsat-8影像计算的归一化植被指数(NDVI)和归一化水指数(NDWI)进行大兴区的土壤水分反演研究。表明:(1)以Sentinel-1组合极化(0.453VV+0.547VH)为基础的反演土壤水分的方式可以实现对该地区土壤水分的高精度反演。(2)NDVI在通过水云模型反演土壤水分过程中,去除植被影响的效果要优于NDWI。(3)Sentinel-1组合极化(0.453VV+0.547VH)与NDVI结合反演土壤水分的相关性较高(r=0.886),优于单极化与NDVI结合反演土壤水分的相关性(rVV=0.798,rVH=0.743)。研究结论对于利用Sentinel-1双极化组合反演土壤水分有重要参考价值。

极化特征组合在ALOS PALSAR数据地物分类中的应用

极化SAR图像分类是目前遥感领域研究热点之一,它为地物信息获取和地物分类提供了新方法。文中对四川省彭州石化地区利用ALOS PALSAR全极化数据进行支持向量机(SVM)分类。试验中首先获得极化总功率,然后对数据进行Cloude-Pottier极化分解,再基于相干矩阵的特征值,提取特征参数香农熵和雷达植被指数。组合这些极化特征对影像进行SVM的分类,并与基于Freeman-Durden极化分解的SVM分类和Wishart监督分类进行比较。试验结果表明:本文采用的极化特征组合信息之间得到相互补充,分类结果效果较好,Kappa系数为97.14%,相对另两种方法的Kappa系数分别提高了5.26%和27.20%。

内蒙古自治区河套灌区冻结期土壤盐分的多极化雷达响应分析

土壤盐渍化严重影响河套灌区的农业生态和社会经济的发展,了解土壤盐渍化现状已成为亟待解决的问题。传统测量方法已无法满足人们对大面积土壤盐渍化分布的需求,相比之下,遥感能够快速获取盐渍地的宏观分布及变化情况。遥感作为一种新的技术手段应运而生,由于可见光、红外遥感存在一定局限性,具有全天候、穿透性强等优点的雷达遥感成为研究热点。以内蒙古自治区河套灌区磴口县为研究区,结合Radarsat-2四极化雷达遥感数据,对冻结期土壤的盐渍化进行响应分析。结果表明,极化组合(HV^2+HH^2)/(HV^2-HH^2)对不同盐渍土有较强的响应性与分离性,利用该极化组合建立回归模型,进而对研究区进行反演分析。经实测数据检验,该方法可在一定程度上满足盐渍化监测的需要,优于传统盐渍土分类方法。

基于后向散射模型的多极化SAR影像建筑物高度提取

以Radarsat-2为例,提出了一种利用多极化SAR影像并结合后向散射模型提取建筑物高度的方法。以北京城区为实验区,首先,分析了SAR影像中建筑物二次散射所对应的亮线连通区域,并统计出该区域对雷达后向散射截面的贡献量;然后,基于平行六面体假设,将建筑物主长度及其与雷达方位向的夹角定量化,并给出计算不同极化散射矢量的方法;最后,利用几何光学-物理光学(geometrical optics-physical optics,GO-PO)模型一阶近似解的后向散射模型估计建筑物高度,并通过比较多个局部训练区提取结果,探讨不同极化信息的提取效果并给出最优极化组合。实验结果表明,通过极化特征组合比仅利用单极化信息提取建筑物高度的精度更高,81.43%建筑物误差小于5 m,均方根误差4.45 m,与ASTER GDEM相关系数为0.909 5,提取结果可靠。

内蒙古河套灌区融解期土壤盐分多极化雷达响应分析

土壤盐渍化严重制约了河套灌区农业经济的发展,传统的点位测量方法已经无法满足人们对大面积土壤盐渍化分布认知的需求。遥感技术能快速获取盐渍地宏观分布及变化情况,而可见光、红外遥感存在一定的局限性,具有全天候、穿透性强的雷达遥感成为研究的焦点。以内蒙古河套灌区五原县为研究区,结合Radarsat-2四极化雷达遥感数据对融解期土壤的盐渍化进行响应分析。研究结果发现极化组合(VH^2+HH^2)/(VH^2-HH^2)对不同盐渍土有较强的响应性与分离性,以极化组合为参量建立回归模型y=0.552 3x-0.645 9,模型最终达到良好的相关性(R^2=0.768 1),利用回归模型对试验区不同程度盐渍化土壤分类分析,结合10个土壤样本点进行精度验证,结果多数土壤样本点的相对误差<10%,精度优于传统盐渍土分类方法。

基于极化雷达的裸露地表土壤水分反演研究

为准确、快速提取大范围裸露地表土壤水分空间分布,以河套平原巴彦淖尔市杭锦后旗陕坝镇灌区土壤水分四极化精细模式雷达监测为例,研究基于RADARSAT-2数据土壤水分提取的技术与方法,选择AIEM模型作为研究区裸露地表土壤水分反演模型的基础,建立适合河套灌区裸露地表土壤水分微波散射的经验模型。应用经验模型对河套灌区地表水分进行反演研究并与实测数据进行相关性分析。结果表明:极化组合VV-VH的相关程度高达0.931 1,经验模型能够满足土壤水分监测的需要,优于传统土壤水分分类方法,促进了极化微波遥感在土壤水分监测中的开拓应用。

内蒙古河套灌区土壤盐分多源多指数估算模型

【目的】探究河套灌区乌拉特灌域土壤盐分遥感反演的最优方法。【方法】针对单一数据源、单一指数、单一算法对土壤盐分反演精度不高的问题,分别以光谱指数、极化组合指数为建模因子,利用偏最小二乘回归(PLSR)、自适应增强回归(AdaBoost)、随机森林回归(RF)3种算法构建土壤盐分反演模型,筛选出最优的土壤盐分反演模型,并监测了2019—2021年10月乌拉特灌域土壤盐分的时空分布。【结果】对于PLSR和AdaBoost模型,光谱指数的预测效果优于极化组合指数,对于RF模型,极化组合指数的预测效果优于光谱指数。PLSR模型在反演10 cm深度处的土壤盐分时,光谱指数的反演效果最优,决定系数为0.70;AdaBoost模型在反演2cm深度处的土壤盐分时,光谱指数反演效果最优,决定系数为0.74;RF模型在反演2cm深度处的土壤盐分时,极化组合指数的反演效果最优,决定系数为0.64。乌拉特灌域土壤盐渍化程度较重的区域主要位于灌域东南部,而西北部和中部盐渍化程度较轻。【结论】应用AdaBoost算法并结合改进的光谱指数有望提升河套灌区乌拉特灌域表层土壤盐分的反演精度。

Influence of the Electric Field on the Properties of the Bound Magnetopolaron in GaAs Semiconductor Quantum Wells

The influence of the electric field on the properties of the bound magnetopolaron in an infinite-depth GaAs semiconductor quantum well is investigated using the linear-combination operator and the unitary transformation method. The relationships between the polaron＇s ground state energy and the Coulomb bound potential, electric field, magnetic field, and well-width are derived and discussed. Our numerical results show that the absolute value of the polaron＇s ground state energy increases as the electric field and the Coulomb bound potential increase, and decreases as the well-width and the magnetic field strength increase. When the well-width is small,the quantum size effect is significant.

Effects of Hg and Ga on microstructures and electrochemical corrosion behaviors of Mg anode alloys

The effects of Hg and Ga on the electrochemical corrosion behaviors of the Mg-2%Hg, Mg-2%Ga and Mg-2%Hg-2%Ga (mass fraction) alloys were investigated by measurements of polarization curves, galvanostatic tests and measurements of electrochemical impedance spectroscopy. Scanning electron microscopy, X-ray diffractometry and energy dispersive spectrometry were employed to characterize the microstructures and the corroded surface of the above alloys. The results demonstrate that the microstructure of the Mg-2%Ga alloy is solid solution and the Mg-2%Hg and Mg-2%Hg-2%Ga alloys have white second-phases at the grain boundaries. The Mg-2%Ga alloy has the worst electrochemical activity and the best corrosion resistance, showing a mean potential of -1.48 V and a corrosion current density of 0.15 mA/cm2. The Mg-2%Hg-2%Ga alloy has the best electrochemical activity and the worst corrosion resistance, showing a mean potential of -1.848 V and a corrosion current density of 2.136 mA/cm2. The activation mechanism of the Mg-Hg-Ga alloy is dissolution-deposition of the Hg and Ga atoms.

Experimental quantum teleportation of a two-qubit composite system

Quantum teleportation, a way to transfer the state of a quantum system from one location to another, is central to quantum communication and plays an important role in a number of quantum computation protocols. Although significant experimental advances have been made in teleportation of single qubits （photons and ions）, large scale applications require the transfer of composite systems containing two or more qubits, which has remained a real experimental challenge.

海水环境中组合电位极化对铁氧化菌腐蚀的影响

采用电化学测试、扫描电镜、激光共聚焦显微镜、Raman光谱等手段研究了-850 mV (vs. SCE,下同)转-1050 mV和-1050 mV转-850 m V组合电位阴极极化对X65钢在含铁氧化菌(IOB)的海水中腐蚀的影响。结果表明:两种组合电位极化都对IOB腐蚀有一定抑制作用;极化与开路电位下X65钢腐蚀产物种类差别不大,含量有区别。-1050 mV极化可以抑制IOB附着但不能完全去除已形成的生物膜,这是-1050 mV转-850 m V极化保护效果优于-850 mV转-1050 m V极化的原因。

Corrosion influence on surface appearance and microstructure of compo cast ZA27/SiC_p composites in sodium chloride solution

The influence of corrosion on the surface appearance and microstructure of particulate ZA27/SiCp composites was examined after 30 d immersion in a sodium chloride solution with the access of atmospheric oxygen. The composites with different contents of SiC micro-particles were synthesized via compo casting. Microstructural studies by means of optical microscopy （OM） and scanning electron microscopy （SEM） showed that corrosion occurred in the composite matrices, preferentially in regions of the η phase, rich in zinc. The corrosion processes did not affect the silicon carbide particles incorporated in the matrix alloy. According to the results of electrochemical polarization measurements, an increase in the content of SiC particles in the composite matrice has led to the lower corrosion resistance in the composites.

Self-Organizing Evolution of Anodized Oxide Films on Ti-25Nb-3Mo-2Sn-3Zr Alloy and Hydrophilicity

In the present work,hierarchical nanostructured titanium dioxide(TiO2) films were fabricated on Ti-25Nb-3Mo-2Sn-3Zr(TLM) alloy for biomedical applications via one-step anodization process in ethylene glycolbased electrolyte containing 0.5wt% NH4F.The nanostructured TiO2 films exhibited three distinct types depending on the anodization time:top irregular nanopores(INP)/beneath regular nanopores(RNP),top INP/middle regular nanotubes(RNT)/bottom RNP and top RNT with underlying RNP.The evolution of the nanostructured TiO2 films with anodization time demonstrated that self-organizing nanopores formed at the very beginning and individual nanotubes originated from underlying nanopore dissolution.Furthermore,a modified two-stage self-organizing mechanism was introduced to illustrate the growth of the nanostructured TiO2 films.Compared with TLM titanium alloy matrix,the TiO2 films with special nano-structure hold better hydrophilicity and higher specific surface area,which lays the foundation for their biomedical applications.

雷达植被指数与香农熵在GF-3影像分类中的应用

针对当前雷达影像分类过程中极化特征组合可提高分类精度这一问题,该文探讨了极化特征组合在高分三号(GF-3)数据地物分类中的应用,以北京市昌平地区GF-3全极化合成孔径雷达(SAR)数据为例,首先对数据进行最优极化分解选择,选取Cloude分解数据为最优数据;然后基于相干矩阵的特征值,提取特征参数雷达植被指数(RVI)与香农熵(SE);最后组合这些极化特征对影像进行决策树分类,并与传统支持向量机(SVM)分类方法的精度进行比较。结果表明:本文采用的RVI与SE极化特征组合的决策树分类方法,较传统SVM分类方法的精度,有一定的提高,尤其是对旱地与有林地、城镇建筑用地与工业用地的区分,效果更佳。