Detection of Rice Yellow Mottle at the Asymptomatic Stage by Hyperspectral Fluorescence and Reflectance Spectroscopies

Rice yellow mottle is considered the most destructive disease threatening rice production in Africa. Early detection of this infection in rice is essential to limit its expansion and proliferation. However, there is no research devoted to the spectral detection of rice yellow mottle virus (RYMV) infection, especially in the asymptomatic or early stages. This work proposes the use of hyperspectral fluorescence and reflectance data at leaf level for the detection of this disease in asymptomatic stages. A greenhouse experiment was therefore conducted to collect hyperspectral fluorescence and reflectance data at different stages of infection. These data allowed to calculate nine vegetation indices: one from fluorescence spectra and eight from reflectance spectra. A t-test made it possible to identify, from the second day after infection, four relevant reflectance vegetation indices to discriminate healthy leaves from those infected: these are Photochemical Reflectance Index (PRI), Transformed Chlorophyll Absorption in Reflectance Index (TCARI), Structure Intensive Pigment Index (SIPI) and Simple Ratio Pigment Index (SRPI). The fluorescence index was less sensitive in detecting infection. The four significant vegetation indices for the detection of RYMV were then used to build and evaluate models for discriminating plants according to their health status by the supervised classification of support vector machine (SVM) at different stages of infection. The maximum overall accuracy is 92.5% six days after inoculation (6 DAI). The sixth day after inoculation would be the adequate day to detect RYMV. This plants discrimination was validated by the mean reflectance spectra and by the histograms showing the differences between the average reflectance vegetation indices values of the two types of plants. Our results demonstrate the feasibility of differentiating RYMV-infected samples. They suggest that support vector machine learning models could be developed to diagnose RYMV-infected plants based on vegetation indices derived from spectral profiles at early stages of disease development.

On the Temperature Dependent Excitation and Reflection Spectra of Ln₃Al₅O₁₂:Ce³⁺Ceramics (Ln = Y, Lu) for White LEDs

Yttrium aluminum garnet (YAG) and Lutetium aluminum garnet (LuAG) doped with Ce3+ are widely applied phosphor powders or ceramics for the conversion of blue into green to yellow light in the rapidly expanding market of white light emitting high power LEDs. Surprisingly, the temperature dependent reflection and excitation spectra of these well-established materials have not been investigated until today. In this work, we report the temperature dependence of the reflection and excitation spectra of Ce3+ doped YAG and LuAG in the temperature range from 300 to 800 K.

Quantitative Relationship between Leaf Area Index and Canopy Reflectance Spectra of Rice under Different Nitrogen Levels

Monitoring rice growth by spectral remote sensing technology can provide scientific basis for the high yield and efficient production of rice. Field experiments with different nitrogen application amounts using Tianyouhuazhan rice as test sam- ples were set up to study the relationship between rice leaf area index （LAI） and canopy reflectance spectral. The results showed that： the LAI increased with the amount of applied nitrogen; the canopy reflectance spectral showed significant re- sponse characteristics to groups with different nitrogen application levels; the corre- lation coefficient of LAI and canopy spectral reflectance reached the maximum at 720 nm red edge region. The mathematical model was constructed to predict the LAI according to the canopy reflectance spectra of rice.

Effect of HITRAN Database Improvement on Retrievals of Atmospheric Carbon Dioxide from Reflected Sunlight Spectra in the 1.61-μm Spectral Window

A large number of experimental and theoretical investigations of carbon dioxide （CO 2 ） spectra have been conducted since the most recent update of the High-Resolution Transmission Molecular Absorption （HITRAN） database. To maintain optimal parameters, the HITRAN 2004 CO 2 line list has been completely replaced by HITRAN 2008 data in the near-infrared region from 4300 cm-1 to 7000 cm-1 . To examine the effect of this change on the retrieval of CO 2 vertical column data from reflected sunlight spectra in the 1.61-μm spectral window, synthetic measurements for a given atmospheric state and instrument setup were generated and compared using radiative transfer model with the line-transition parameters from the HITRAN 2004 and 2008 databases. Simulated retrievals were then performed based on the optimal estimation retrieval theory. The results show that large systematic errors in atmospheric CO 2 column retrievals were induced by the differences in the HITRAN laboratory line parameters in the 1.61-μm region. The retrieved CO 2 columns were underestimated by 10 ppm using the HITRAN 2004 data, and improvements resulting from the use of the improved HITRAN database were more pronounced at a higher spectral resolution.

应用衰减全反射红外光谱无损鉴别中国传统手工纸的方法研究

纤维种类鉴别是古代纸张保护的重要基础工作。探究中国传统手工纸的无损纤维鉴别的方法对中国古籍、档案及纸质文物的研究和保护具有重要意义。该研究应用衰减全反射傅里叶变换红外光谱(ATRFTIR)对已知纤维成分的17类64种中国传统手工纸标准样品进行了无损分析,参考纤维素和木质素的红外峰位及部分纸样的X射线衍射(XRD)分析结果确认纸样中的所有红外谱峰归属;并采用分波段比较分析的方法对相似度极高的谱图进行比对分析,分别总结各类纸张在4000~1800、1800~1500、1500~1200和1200~600cm^(-1)四个波段的谱图特征;同时对4cm^(-1)精度的谱图进行二阶导数处理,分别总结各类纸张在1500~1200和1200~900cm^(-1)两个波段的二阶导数谱图特征;最后通过红外结晶指数及其他峰高和峰面积比值计算结果实现对纸类更细致的区分。应用上述方法对16个盲测样品进行了有效性测试,红外分析结果与显微纤维鉴别结果一致,初步证明了该方法在中国传统手工纸无损纤维鉴别上的可行性和有效性。实验结果表明,应用ATR-FTIR无损分析法可对麻、桑构皮、檀皮、瑞香皮和竹几大类原料的传统手工纸纤维类型作出快速而准确的鉴别,对于混料的宣纸也同样适用;但对于显微分析也难以鉴别的亲缘关系较近的植物原料如桑、构皮之间的精细鉴别仍有一定局限性。

基于可见光谱特征波长提取和分类算法的柑橘黄龙病快检研究

柑橘黄龙病(HLB)是由亚洲韧皮杆菌引起的一种严重病害,目前无法根治。其防控具有重要意义和经济价值。当前利用健康和患病叶片的光谱差异对其进行诊断显示了良好的应用前景。因患病叶片在叶绿素反射区及O—H伸缩振动区的可见光谱与健康叶片存在显著差异,而可见光谱检测在采集和数据处理方面具有成本低、简便的优势,研究可见光谱的黄龙病快速检测方法具有可行性和重要意义。为了减少光谱数据冗余和计算量,实现精准的黄龙病的早期鉴别以及降低黄龙病相似病症的误诊率,采集了黄龙病患病地区共160个叶片样本。经qPCR测定分别将其分类标定为健康、轻度疾病、重度疾病和缺镁症四类。根据叶片样本在可见光波段450~800 nm的反射光谱特征,通过S-G平滑以及降采样等预处理光谱数据后,为了优选出尽可能囊括光谱特征信息的特征波长,分别使用遗传算法(GA)、连续投影算法(SPA)以及竞争自适应重加权采样法(CARS)对采集到的可见光谱数据进行特征波长提取和降维优选出特征波长,进一步降低模型复杂度,提高预测精度。综合泛化能力及检测速度的考量,在定性判别分析模型的选择中采用训练速度快,分析准确率高的最小二乘支持向量机(LS-SVM)以及随机森林(RF)对两种变量筛选算法降维后的数据进行分类判别。通过对不同的模型的验证优选,筛选出最佳的快检方案。对比发现,在建立的模型中,SPA-RF模型与其他模型比较,对于训练集和测试集的判别准确率分别达到了100%和97.5%。结果表明,连续投影算法以及随机森林的组合分类模型可以很好地实现黄龙病早期的病理鉴别,同时也能够很好地识别出黄龙病病叶与其他相似病症的差异,为柑橘黄龙病快速检测及防治提供了一种方法依据。

Investigation on Physiological Status of Regional Vegetation Using Pushbroom Hyperspectral Imager Data

To extract vegetation pigment concentration and physiological status has been studied in two test areas covered with swamp and flourish vegetation using pushbroom hyperspectral imager (PHI) data which flied in September of 2000 at Daxing'anling district of Heilongjiang Province, China. The ratio analysis of reflectance spectra (RARS) indices, which were put forward by Chappelle et al (1992), are chosen in this paper owing to their effect and simpleness against both comparison with various methods and techniques for exploration of pigment concentration and characteristics of PHI data. The correlation coefficients between RARS indices and pigment concentration of vegetation were up to 0.8. The new RARS indices modes are established in the two test areas using both PHI data and spectra of different vegetations measured in the field. The indices' parameter images of chlorophyll a (Chl a), chlorophyll b (Chl b) and carotenoids (Cars) of the test areas covered with swamp and flourish vegetation are acquired by the new RARS indices modes. Furthermore, the regional concentration of Chl a and Chl b are extracted and quantified using regression equations between RARS indices and pigment concentrations, which were built by Blackburn (1998). The results showed the physiological status and variety clearly, and are in good agreement with the distribution of vegetation in the field.

探测几何反射光谱测量系统设计

地物反射光谱是地面遥感的基础,现有的测量装置多基于复杂的机械传动平台与控制系统,整体结构庞大笨重、成本较高、便携性差。为解决上述问题,该文设计了一种探测几何反射光谱测量系统,该系统主要由探测几何支架、光谱采集系统、卤钨聚光光源、载物台四个部分组成,探测几何支架采用模块化设计,通过各组成模块的灵活装配定位,可实现较大的角度、距离探测几何范围,该系统采用一分多光纤,可实现较大的光谱波段覆盖范围。通过对该系统的试制与调试,以及地物样品光谱采集测试实验,验证了其探测几何及波段范围。该系统结构简单、互换性好、安装携带方便、实用性较强、满足室内与野外使用需求的特点。

Statistical and Spatial Analyses of Correlations Between Spectral Signatures and Chemical Data of Lichens for Environmental Pollution Assessing

Aim of the study is to evaluate the environmental impact of geothermic activities by the use of in site spectral analyses of different environmental com- ponents.These activities can cause the heavy metal （Hg,Sb,S,B,As,H2S）drifting from power plants to around areas.Different analytical techniques

Charge Transfer Spectra (CTS) in CaS:Ce^(3+) Phosphors

This paper describes the excitation spectra nearby 220hm of CaS:Ce^(3+),Na^+ and CaS:Ce^(3+),X^-(X=F,Cl or Br).It is considered that the charge transfer excitation is caused by electron transfer of S^(2-)on 3p^6 to the 4f shell of Ce^(3+).It has been discussed that,when halogen ions act as coactivators,this excitation band shifts to low- er wavenumber.

Estimating Directional Distribution for Co-Existent Field of Incident and Reflected Waves

In the nearshore, the wave field contains reflected and incident waves in which there is correlation between their phases due to the effect of reflection by some obstacles. Based on the extended eigenvector method (EEV) derived by Guan et al., a modified method (MEEV) is proposed as a general and practical approach to estimating directional spectra for the co-existent field of incident and reflected waves and a formula is given for direct calculation of the reflection coefficient. The results of numerical simulations show that MEEV is superior to EEV in resolution power, and the computed reflection coefficient agrees well with the real value within a certain range of incident angle.

The transmission enhancement of a THz pulse through an Ag/Ag_2 O layer detected by terahertz time-domain spectroscopy

This paper reports a new way to detect the enhanced transmission of a THz electromagnetic wave through an Ag/Ag2O layer by THz-TDS （time-domain spectroscopy）. As the THz beam illuminates the sub-wavelength Ag particles gained by Ag2O thermal decomposition, the evanescent wave is generated. The evanescent wave is coupled by a 500μm-GaAs substrate, which attaches behind the Ag/Ag2O layer, and then it transmits to the far field to be detected. The experimental results indicate that the transmitting amplitude is enhanced, as well as the frequent shifting and spectra broadening.

Visible and Ultraviolet Reflectivity of Hg_(0.8)Cd_(0.2)Te

The fundamental reflectivity spectra of Hg_(0.8)Cd_(0.2)Te have been investigated.The feature of the spectra is the presence of E_(1) and E_(2) peaks within the fundamental absorption region.A three dimensional saddle point is used to fit the E_(1) and E_(1)+Δ_(1) critical point and some simulated calculation is done for E_(2) at X point.The measured and calculated reflectivities are compared and prominent features of the reflectivity spectra are identified with critical point transition at the and X points in the Brillouin zone.

Analysis of Spectral Signatures of Silicone-Based Sealant Materials Used in Residential and Commercial Buildings

In the construction industry, silicone is primarily used as sealant material to fill gaps and cracks providing water and air-tightness to vertical construction projects reducing energy usage bills and enhancing the integrity of construction materials. This paper reports the results of spectral analysis of commonly used building sealant materials used in residential and commercial buildings. A dozen commercially available silicone-based sealant materials composed of different ingredients representing three manufacturer brands are characterized using Raman and UV-VIS-NIR spectroscopic techniques. The characteristic vibrational fingerprints of the selected sealant materials are summarized, and the Raman and reflectance spectra of the samples are also presented. It is observed that most of the samples appear to have similar vibrational band assignments and reflectance spectra. However, analysis of the Raman spectral positions and the reflectance spectra reveals that there are distinct differences among the sealant materials.

土壤磷组分的可见-近红外反射光谱特征及其光谱分析

磷在可见-近红外反射光波段具有极微弱的吸收,在土壤磷的光谱分析中,其特征光谱有赖于同其他组分的相关性,因此磷的光谱模型的稳定性较差。为此,本研究另辟蹊径,通过分离不同磷组分,分别以标准白板和残渣样品为参考光谱,间接和直接采集了不同磷组分的可见-近红外反射光谱。发现各磷形态具有显著不同的反射光谱特征,光谱形状、反射率大小及峰/谷位置均不同,能够被现有可见-近红外光谱(200~1000 nm)定性和定量。在现有研究波段内,250~750 nm是土壤磷的敏感波段。利用本敏感波段,建立土壤磷的光谱模型优于全谱波段建立的光谱模型。最后,本研究评价了现有土壤磷及其不同组分的光谱分析的技术指标,包括测量范围、分辨率和误差。本研究突破了理论限制,创造性的解决了土壤磷的光谱分析,为其他同类参数的光谱分析提供了有效参考。

查干湖冰封期光谱特征及影响因素

湖冰光谱特征是湖冰遥感反演的物理基础,是研究湖冰光学特性和空间分布的理论依据。本文以查干湖为例,使用ASD Field Spec 4便携式地物光谱仪采集冰封期不同类型湖冰、积雪和水体光谱,利用Savitzky-Golay滤波法和包络线去除法分析白冰、灰冰、黑冰、雪冰、积雪和水体的反射光谱特征,探索气泡对湖冰反射光谱特征的影响。积雪和雪冰、白冰和灰冰、黑冰和水体的反射特征随着波长的变化特征基本一致,冰的反射率介于积雪和水体之间,其中白冰的反射率高于灰冰和黑冰,在包络线去除结果中,黑冰和水体在440 nm吸收谷处的吸收面积为5.184和10.878、吸收深度为0.052和0.106,雪、雪冰、白冰、灰冰在800和1030 nm吸收谷处的吸收面积和吸收深度的变化表现为雪<雪冰<灰冰<白冰。气泡是影响湖冰光谱特征的重要因素,气泡使白冰反射率减小和黑冰反射率增大,并且气泡使得白冰在800/1030 nm和黑冰在440 nm处的吸收面积和吸收深度减小,其中气泡大小和疏密程度的不同会导致湖冰反射率的影响程度存在差异。同时,本文选取时间同步的Landsat 8 OLI遥感影像,在完成辐射校正、大气校正和Fmask去云处理后,根据实测光谱特性差异选取敏感波段和最佳遥感指数实现湖冰遥感分类。结果显示,红波段和近红外波段是湖冰遥感分类的最佳波段,结合光谱特征、波段运算和阈值法能有效区分积雪、湖冰和水体。

利用高光谱数据对作物群体叶绿素密度估算的研究

叶绿素是农作物生长中重要的因素。叶绿素含量既表明作物生长的状况 ,又表征了作物的生产能力。而叶绿素密度 (单位面积农作物的叶绿素含量 )是估计农作物群体生产力的重要指标。对早播稻、晚播稻和玉米的多时相的群体光谱测量数据和相应的叶片叶绿素密度的测量数据进行了相关分析 ,结果表明早播稻、晚播稻和玉米的群体光谱的反射率数据以及其导数光谱数据与叶绿素密度具有很好的相关性 ,并且可以对这几种农作物建立统一的线性回归关系。利用这几种农作物的导数光谱在近红外波段 76 2nm处与叶绿素密度的高相关性 ,选取样本建立了回归方程。并利用其余样本对估计方程进行检验 ,结果表明估计的标准偏差为 0 .2 72g/m2 ,估计精度约为 80 6 %。

基于反射光谱预测土壤重金属元素含量的研究

本文利用实验室实测的土壤反射光谱以及铅、镉、汞等重金属元素数据,进行土壤重金属元素含量快速预测的可行性研究。本文利用偏最小二乘回归方法,研究了反射率(R)、一阶微分(FDR)、反射率倒数的对数(lg(1/R))和波段深度(BD)等对预测精度的影响,对这几种光谱指标预测土壤重金属含量的能力进行了分析和评价,同时分析了多光谱数据估算土壤重金属元素含量的可行性。结果表明,反射率倒数的对数lg(1/R)是估算土壤重金属元素含量最好的光谱指标,尤其是Cd和Pb,检验精度R超过0.82。有机质、铁锰氧化物和黏土矿物对土壤重金属元素的吸附是可见光—近红外—短波红外光谱估算其含量的机理。多光谱数据同样具有估算土壤重金属元素含量的能力,但实际数据则要考虑多种因素的影响。

西北荒漠草甸植被光谱反射特征研究

选取位于西北干旱内陆地区的安西荒漠草场为观测试验区,分别对盐生低地草甸、极旱荒漠草甸和荒漠灌丛三类草地进行了地面反射光谱测定,并分析了主要荒漠草甸植被光谱反射的一般特征和红边参数特征,进而探讨了形成草地光谱特征差异的主要内在原因和影响因素。结果表明:在近红外波段,由于荒漠植被类别间叶片内部结构变化大,因此冠层光谱反射率差异较大;同一植被冠层光谱反射率的大小主要受植被长势的影响;受沙地背景的影响,在近红外波段,植被冠层的光谱反射率要明显小于叶片的光谱反射率;荒漠植被冠层光谱的红边也具有“双峰”现象,红边特征的参数表现为:沙地植被>绿洲植被>沙漠植被。对安西荒漠植被光谱特征的分析研究,对于研究干旱区荒漠植被的理化性能、遥感反演、植被分类、植被调查等都具有重要的意义。

基于高分辨率反射光谱的土壤营养元素估算模型

研究了土壤中营养元素含量(N、P、K)与土壤可见光/近红外光谱之间的关系。在对原始光谱进行预处理分析后,计算出了4种光谱指标:反射率Reflectance、一阶导数FDR、倒数之对数log(1/R)和波段深度Depth。通过偏最小二乘回归分析建立了营养元素与4种光谱指标的经验模型,并且利用验证样本集对回归模型进行了验证。结果表明,可见光/近红外反射光谱具有快速估算土壤中营养元素含量的潜力。