基于Sentinel-2A影像的玉米冠层叶绿素含量估算

农作物叶片中的叶绿素通过吸收光能参与光合作用产生化学能,及时、准确地估算叶绿素含量对于农作物长势、养分含量监测、品质评价和产量估算具有重要意义。Sentinel-2卫星的重访周期为5 d,空间分辨率为10 m,具有13个光谱波段,其中包括三个波宽仅为15 nm对叶绿素含量变化敏感的红边波段,是叶绿素含量估算的理想数据源。植被指数是基于农作物在不同波段的反射特性,通过不同波段组合方式刻画长势和叶绿素含量的差异,可用于大区域范围内的玉米冠层叶绿素含量快速、精确估算。以Sentinel-2A影像为数据源,开展基于多种植被指数的玉米冠层叶绿素含量估算方法研究。课题组于2016年8月6-11日在河北省保定市（115°29′-116°14′E,39°5′-39°35′N）进行玉米冠层叶绿素含量的实地测量,并在每个采样位置上采用中绘i80 智能RTK(real-time kinematic)测量系统进行定位。Sentinel-2A影像预处理工作包括几何校正、辐射定标和大气校正,其中大气校正使用Sen2Cor模型和SNAP模型。首先,基于预处理后的Sentinel-2A遥感影像,分别计算CI_green(green chlorophyll index), CI_red-edge(red-edge chlorophyll index), DVI(difference vegetation index), LCI(leaf chlorophyll index), MTCI(MERIS terrestrial chlorophyll index), NAVI(normalized area vegetation index), NDRE(normalized difference red-edge), NDVI(normalized difference vegetation index), RVI(ratio vegetation index), SIPI(structure insensitive pigment index)植被指数。然后,建立样方位置上实测叶绿素含量与各植被指数的统计关系,从而构建玉米冠层叶绿素含量估算模型,并以野外实测玉米冠层叶绿素含量为依据,对基于各植被指数的估算结果进行精度评价。最后,利用筛选出的最优叶绿素含量估算模型,估算研究区内的玉米冠层叶绿素含量。研究的目标为：（1）通过比较分析,构建合适的玉米冠层叶绿素含量估算模型,估算精度以决定系数R2、均方根误差RMSE以及相对误差RE作为评价指标;（2）确定最优波段组合方案：在红边波段中选择与可见光、近红外波段组合效果更优的波段组合方案;（3）确定参与植被指数计算的红边波段的最优数量。精度评价结果表明：（1）选用的植被指数与玉米冠层叶绿素含量呈多项式拟合关系,其中使用红边波段计算的植被指数的估算结果明显优于未使用红边波段的估算结果;红边波段引入后明显提高了可见光、近红外波段对叶绿素含量的拟合的精度,CI_{green(560, 705)}指数比CI_{green(560, 842)}的回归模型R2提高0.516,红边波段参与计算的DVI相对于RVI来说,估算结果更稳定。（2）对于不同的植被指数,参与运算的Sentinel-2A影像的两个红边波段,估算精度的提高程度不同。对于可见光波段参与计算的植被指数来说,在红边波段1（中心波长为705 nm）的估算精度较高,如LCI,CI_green,DVI和RVI等;对于近红外波段参与计算的植被指数来说,在红边波段2（中心波长为740 nm）的估算精度较高,如CI_red-edge,NDRE和NAVI等。（3）对于Sentinel-2A影像来说,两个红边波段共同参与叶绿素含量估算时能取得最高的的估算精度。选用的植被指数中,MTCI_{(665, 705, 740)}指数与玉米冠层叶绿素含量估算精度最高,回归模型拟合精度R2为0.803,模型验证R2为0.665,RMSE为3.185,相对误差RE为4.819%。MTCI_{(665, 705, 740)}指数计算中使用了两个红边波段,突出红边波段反射率差值变化,与玉米冠层叶绿素含量表现出很好的相关性。最后,利用优选出的基于MTCI指数的叶绿素含量估算模型,对研究区范围内的叶绿素含量进行估算并完成空间制图。     

Geometries,stabilities, and electronic properties analysis in In_nNi~((0,±1)) clusters: Molecular modeling and DFT calculations

Density functional theory(DFT) with the B3 LYP method and the SDD basis set is selected to investigate In_nNi,In_nNi~-, and In_nNi~+ (n = 1–14) clusters. For neutral and charged systems, several isomers and different multiplicities are studied with the aim to confirm the most stable structures. The structural evolution of neutral, cationic, and anionic In_nNi clusters, which favors the three-dimensional structures for n = 3–14. The main configurations of the In_nNi isomers are not affected by adding or removing an electron, the order of their stabilities is also nearly not affected. The obtained binding energy exhibits that the Ni-doped In_(13) cluster is the most stable species of all different sized clusters. The calculated fragmentation energy and the second-order energy difference as a function of the cluster size exhibit a pronounced even–odd alternation phenomenon. The electronic properties including energy gap(E_g), adiabatic electron affinity(AEA), vertical electron detachment energy(VDE), adiabatic ionization potential energy(AIP), and vertical ionization potential energy(VIP) are studied. The total magnetic moments show that the different magnetic moments depend on the number of the In atoms for charged In_nNi. Additionally, the natural population analysis of In_nNi~((0,±1)clusters is also discussed.     

干涉法测量低频表面波的衰减系数

对于频率为几十赫兹的低频衰减液体表面波,结合激光干涉法和激光扫描法,实验得到反衬度很高的调制干涉图样,理论上给出了干涉图样的条纹宽度,条纹分布范围与表面声波振幅之间的解析关系,实时测量了液体表面波的衰减系数.     

基于循环式径向剪切干涉法的波前重建算法研究

 提出一种基于循环式径向剪切干涉的波前重建算法。先将畸变波前经径向剪切干涉仪形成的空间相位调制干涉条纹图通过傅立叶变换处理获得对应的位相差分布，再直接采用迭代算法能精确重建原始波前，为ICF系统中复杂畸变波前的在线准确检测提供了可能，并给出了应用实例。     

金刚石紫外发光器件研究进展

蓝光或紫外激光在光电子学和光储存方面有广阔的应用，一直是国际上关注的前沿领域．而金刚石是最好的半导体紫外发光材料．特别是用于高温、高压、高功率、强辐射和强腐蚀环境中更能显示其优越性．目前人们已在实验上用同质外延、异质外延的方法制备了金刚石紫外发光二极管，观察到了较强的紫外光发射．人们尝试用金刚石与其他半导体材料结合的方法，成功地研制出了金刚石紫外发光二极管，开拓了该研究领域最新研究方向．文章对这些金刚石紫外发光器件研究的最新进展进行了评述．     

近满壳偶偶核闯入态及组态混合的微观分析

本文应用一种描述近满壳偶偶核的闯入态的微观理论,计算了对应于¹¹⁰Cd组态的低能谱及波函数.系统地考察了各种因素对闯入态形成的影响、产生组态混合的机制及强度.通过与唯象工作的比较,考察了微观s-d哈密顿量.     

近满壳偶偶核闯入态及组态混合的微观分析

本文应用一种描述近满壳偶偶核的闯入态的微观理论,计算了对应于~(110)Cd组态的低能谱及波函数。系统地考察了各种因素对闯入态形成的影响、产生组态混合的机制及强度。通过与唯象工作的比较,考察了微观s-d哈密顿量。     

A=130附近核谱结构相变的IBM-2描述

在以玻色子展开为基础的IBM微观方案框架下,本文研究了Ba、Sm同位素的低能核谱的相变,表明该方案能够对相变给出统一的描述.     

First-principles calculations of structure and elasticity of hydrous fayalite under high pressure

The structures,elasticities,sound velocities,and electronic properties of anhydrous and hydrous fayalite(Fe_2SiO_4and Fe_(1.75)H_(0.5)SiO_4)under high pressure have been investigated by means of the density functional theory within the generalized gradient approximation(GGA)with the on-site Coulomb energy being taken into account(GGA+U).The optimized results show that H atoms prefer to substitute Fe atoms in the Fe1 site.Compared with the anhydrous fayalite Fe_2SiO_4,the mass density,elastic moduli,and sound velocities of Fe_(1.75)H_(0.5)SiO_4 slightly decrease.According to our data,adding 2.3 wt%water into fayalite leads to reductions of compressional and shear wave velocities(VPand VS)by3.4%–7.5%and 0.3%–3.4%at pressures from 0 GPa to 25 GPa,respectively,which are basically in agreement with the2%–5%reductions of sound velocity obtained by the experimental measurement in the low velocity zones(LVZ).Based on the electronic structure,the valence and conduction bands are slightly broader for hydrous fayalite.However,hydrous fayalite keeps the insulation characteristics under the pressures up to 30 GPa,which indicates that hydration has little effect on its electronic structure.