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。     

Luminescence studies of o-hydroxy p-amino and p-dimethylamino methyl benzoate

Steady-state and time-resolved spectroscopic studies of two bisubstituted derivatives of methyl benzoate dissolved in methylcyclohexane (McH), tetrahydrofuran (THF), and ethanol (EtOH) have been performed at 293 and 77 K. The compounds under study are capable of showing multimode fluorescence emission at room temperature. The kind of emission, i.e., locally excited state emission Fl(LE), proton-transfer emission Fl(PT) and twisted intramolecular charge-transfer emission Fl(CT) dependent on the solvent. Low temperature measurements show that for those molecules a phosphorescence enhancement via a proton-transfer tunneling is observed. For the molecules under study compositeness of the emission process is explained on an energy scheme, which is based on experimentally determined and theoretically calculated data. Stated dynamic Stokes shift and phosphorescence red-edge effect indicates that both molecules form an inhomogeneous emitting system in solvents used. The experiments are supported with quantum chemical semiempirical calculations.     

Tryptophan exposure and accessibility in the chitooligosaccharide-specific phloem exudate lectin from pumpkin (Cucurbita maxima). A fluorescence study

The exposure and accessibility of the tryptophan residues in the chitooligosaccharide-specific pumpkin (Cucurbita maxima) phloem exudate lectin (PPL) have been investigated by fluorescence spectroscopy. The emission λ_max of native PPL, seen at 338 nm was red-shifted to 348 nm upon denaturation by 6 M Gdn.HCl in the presence of 10 mM β-mercaptoethanol, indicating near complete exposure of the tryptophan residues to the aqueous medium, whereas a blue-shift to 335 nm was observed in the presence of saturating concentrations of chitotriose, suggesting that ligand binding leads to a decrease in the solvent exposure of the tryptophan residues. The extent of quenching was maximum with the neutral molecule, acrylamide whereas the ionic species, iodide and Cs⁺ led to significantly lower quenching, which could be attributed to the presence of charged amino acid residues in close proximity to some of the tryptophan residues. The Stern–Volmer plot for acrylamide was linear for native PPL and upon ligand binding, but became upward curving upon denaturation, indicating that the quenching occurs via a combination of static and dynamic mechanisms. In time-resolved fluorescence experiments, the decay curves could be best fit to biexponential patterns, for native protein, in the presence of ligand and upon denaturation. In each case both lifetimes systematically decreased with increasing acrylamide concentrations, indicating that quenching occurs predominantly via a dynamic process.     

一种基于无人机高光谱数据的植被盖度估算新方法

从分析对植被覆盖度(FVC)敏感的光谱特性入手,使用Avafield-3光谱仪(测量范围300～2 500 nm),利用人工草坪控制植被覆盖度的方式研究混合光谱与植被覆盖度的关系,通过实验发现红边区间(680～760 nm)对植被覆盖度最为敏感,而红边区间光谱的一阶导数与植被覆盖度的相关性最高(>0.98),且有较强的稳定性,因此选择红边斜率k作为估算植被盖度的参数。参考混合光谱分解法反演植被覆盖度的经典模型--即以NDVI(normalized difference vegetation index)为参数的植被覆盖度反演模型,以红边斜率代替NDVI构建了2个反演植被覆盖度FVC的新的红边斜率模型,该模型是对经典模型的进一步改进。为验证模型精度,以研究区内无人机(UVA)的高光谱数据和研究区实际测量的植被覆盖度数据进行验证：对高光谱数据计算每个像元680～760 nm之间的斜率,利用PPI(pixel purity index)提取纯像元,计算纯植被像元光谱斜率的最大值和纯土壤像元光谱斜率最小值,利用新的红边斜率FVC模型求取植被覆盖度;实测数据采用照相方法,经过几何校正、监督分类后统计植被覆盖度,结果表明：通过实测数据与无人机高光谱数据获取的植被覆盖数据进行验证,新构建的基于红边斜率的两个植被覆盖度模型的精度(R2分别达0.893 3和0.892 7)都略高于以NDVI为参数的模型(R2分别达0.839 9和0.829 9)。提出使用红边斜率计算植被覆盖度的模型,具有较明确的生物物理意义,具有较高的应用潜力和推广价值。     

不同碱化程度土壤对其上覆植被冠层光谱特征的影响

通过实地光谱测量,研究了不同碱化程度土壤上向日葵在不同生育期冠层光谱反射率、红边参数及与对应的土壤碱化度和pH之间的关系。结果表明,不同碱化程度土壤上向日葵生育期冠层反射光谱具有绿色植物的光谱反射特征,随着向日葵生育期的推进,向日葵冠层光谱反射率逐渐增大,到开花期在809nm处形成一个高的反射峰。在近红外短波范围,向日葵光谱反射率随碱化程度的减轻而增大。用红边一阶微分光谱特征参数分析,向日葵冠层反射光谱红边位置在整个生育期处于702~720nm之间,并随着碱化程度的加重,红边位置和红边斜率呈"蓝移"现象;而在同一碱化程度水平上,随向日葵生育期的推进,红边位置和红边斜率均出现先"红移"后"蓝移"的现象。相关分析和回归分析显示,土壤碱化度、pH与红边位置均呈极显著正相关和二次多项式关系,R2值分别为0.745 6和0.615 3。     

机器学习法的干旱区典型农作物分类

当前,基于机器学习方法开展农作物分类研究,对于确保干旱区粮食安全和生态安全有着极为重要的现实意义。基于机器学习方法,采用时间序列Sentinel 2A遥感数据提取农作物分类信息,通过引入地块基元和红边特征,探讨了不同分类特征组合对机器学习分类精度的影响。结果表明：随机森林分类器可以有效集成光谱和植被指数等多维向量的优势,将其应用于干旱区典型农作物分类上的精度均在89%以上,分类组总体精度最高可达94.02%。地块基元点集支持下的分类特征提取方法能够提高机器学习效率和农作物分类精度,使光谱组及指数组的分类精度分别提高3.13%和4.07%,并能有效解决“椒盐”效应及耕地边缘廓线模糊等问题。红边光谱和红边指数的引入分别使随机森林分类器总体精度提高2.39 %和1.63%,并使春、冬小麦的识别能力显著提高,表明红边特征能够帮助分类器更敏感地捕捉不同作物特有的生长特性及物候差异。该研究结果可为机器学习方法及Sentinel 2A卫星在干旱区农业遥感的应用提供参考。     

Red-Edge Excitation Study of Nonexponential Fluorescence Decay of Indole in Solution and in a Protein

Proteins are known to be heterogeneous systems with a hierarchy of internal motions. However, those properties are often ignored when the complex fluorescence decay of tryptophan residues is compared to model studies with indole derivatives in solution. Here two simple models are presented, which illustrate different aspects of protein organization: (1) Trp zwitterion in buffer exemplifies ground-state heterogeneity and (2) indole in water/glycerol mixture exemplifies excited-state reconfiguration of solvate. Both systems are known to produce nonexponential fluorescence decay, attributed to the existence of multiple species (rotamers) or to the effects of slow dipolar relaxation, for (1) and (2), respectively. In the latter case a substantial dependence of decay on the excitation wavelength is expected. Indeed such dependence is observed for indole in water/glycerol mixture but not for Trp zwitterion in buffer. Therefore, excitational dependence can be used as a criterion to distinguish effects of multiple conformations in the ground state from effects of excited state reactions on tryptophan decays in proteins. The example of the bee venom peptide melittin indicates that both phenomena are important for interpretation of heterogeneity of decay, and therefore, caution should be exercised when assigning individual decay components to conformational subspecies in proteins.     

苹果花期的冠层高光谱特征研究

系统分析苹果花期冠层高光谱特征,探明其敏感光谱波段,为大面积苹果树信息提取与营养状况的遥感反演等提供理论依据。利用ASD Field Spec 3便携式地物光谱仪实测的120个苹果花期的冠层高光谱数据,在分析了不同累计样本容量对花期冠层高光谱特征影响的基础上,采用方差分析的方法,明确了苹果花期的冠层高光谱特征及反映花期冠层高光谱的敏感波段。结果表明,随着累计样本容量的增加,苹果花期的高光谱曲线趋于稳定、平滑。在550 nm绿峰处和760～1 300 nm的反射高原区,反射率随着花量的增多而减小,在670 nm的红谷处,反射率随着花量的增多而增大;在350～400 nm,400～500 nm,600～680 nm,760～1 300 nm波段的方差分析结果极显著,是反映花期冠层光谱的敏感波段;随着花量的增多,红边位置、红边斜率和红边面积有逐渐减小的趋势。     

Fluorescence Characterization of the Hydrophobic Pocket of Cyclophilin B

Human cyclophilin B is a monomeric protein that contains two tryptophan residues, Trp104 and 128. Trp128-residue belongs to the binding site of cyclosporin A and is the homologous of Trp 121 in CyPA, while Trp104 residue belongs to the hydrophobic pocket. In the present work, we studied the dynamics of Trp residue(s) of cyclophilin B and of the CyPB_w128A mutant and of TNS-mutant complex. Our results showed that Trp-104 and TNS show restricted motions within their environments and that energy transfer between the two fluorophores is occurring.