基于反射光谱的PCA及BP神经网络法预测甘蔗叶片叶绿素含量

叶绿素是植物进行光合作用的重要色素,叶绿素含量可以作为评价植物生长状况的重要参数。本研究基于甘蔗叶片的反射光谱,利用PCA及BP神经网络算法,建立了甘蔗叶片的叶绿素含量预测模型。PCA算法可以在尽可能少地丢失有用光谱信息的前提下,降低输入光谱矩阵的维数,最大限度地减少冗余信息。BP神经网络算法因其良好的非线性逼近能力可大大提高该模型的预测精度。研究发现：基于PCA和BP算法建立的叶绿素含量预测模型,其预测值与实测值之间的R2达0.8929,表明该模型具有较高的预测能力。     

水稻叶片叶绿素含量的光谱反演研究

通过研究不同叶绿素含量的水稻叶片的光谱特性，发现叶绿素含量与光谱特性之间具有明显的相关性，并建立了水稻叶片叶绿素含量的光谱反演模式。研究表明，水稻叶片光谱反射率及其一阶导数的峰值参数与叶绿素含量之间具有很强的相关性，复相关系数均达到0．4以上，经多元线性回归分析显示回归显著，线性相关密切，回归方程的复相关系数为0.63，可作为水稻叶片叶绿素含量反演的方法，并为大面积水稻冠层叶绿素含量遥感监测提供理论依据。     

基于Cubist的中国植被区域叶绿素荧光数据重建

日光诱导叶绿素荧光(Solar-Induced chlorophyll Fluorescence,SIF)是植物在太阳光照条件下,在光合作用过程中发射出的光谱信号(650～800 nm),SIF相比于植被指数等参数更能直接地反映植被光合作用的相关信息,为大尺度GPP估算带来了新的途径.但目前卫星SIF数据或存在分辨率较...     

Hyperion数据玉米叶绿素含量制图

采用星地同步观测方法,对Hyperion影像进行预处理并提取玉米专题信息,计算与遥感影像同步获取的玉米地面实测光谱及其一阶微分形式,作物光谱指数参量与叶绿素含量之间的相关性。结果表明:作物叶绿素含量预测指数TCARI/OSAVI与叶绿素a和叶绿素b的相关性最好,R²分别为0.5694和0.5313。采用其与叶绿素含量进行回归分析,建立叶绿素反演模型。将回归结果应用到提取的玉米区域,得出叶绿素a和叶绿素b含量的空间分布图,直观显示玉米的长势状况,为农业估产和植被长势监测提供重要的数据源。     

基于JavaScript的叶绿素荧光信号特征点自动定位软件设计

几乎所有光合作用过程都可通过叶绿素荧光反映出来,叶绿素荧光动力学技术已经成为研究植物生理最广泛的技术之一,本软件分析叶绿素荧光参数,辅助研究光合作用过程中光系统II对光能的吸收、传递、耗散、分配等过程。程序从excel表中批量读取叶绿素荧光仪测量得到的数据,在网页中运用JavaScript语言编程,自动绘制OJIP曲线,以及相应的OJIP曲率曲线、一阶导数曲线、二阶导数曲线。用户能在交互式OJIP曲线上设定区间,根据设定算法,自动定位符合条件的I点与J点,手工调整与优化特征点位置,将定位的特征点结果作为文件导出并保存,使叶绿素荧光信号研究更加方便快捷。     

应用叶绿素荧光估算植被总初级生产力研究进展

日光诱导叶绿素荧光作为光能在叶片上光合作用的伴生产物，包含丰富的光合信息，被认为是可以表征植物光合作用的快速、无损“指示器”。叶绿素荧光在研究植物胁迫、病虫害监测、估算植被总初级生产力（Gross Primary Production， GPP）等方面发挥着独特的作用。陆地植被GPP是研究全球气候、碳循环变化、全球生态系统等的重要内容。准确、及时地掌握GPP的时空分布特征，有利于深入理解生物圈与大气圈之间的相互作用，可为开展减缓全球气候变化的生态过程管理提出相应建议和对策。相比于植被指数，叶绿素荧光对植被光合作用的敏感程度更高，已被证实可以更直接有效地监测GPP，显著优于传统的GPP估算方法。深入探讨了叶绿素荧光在遥感估算GPP领域的基本原理、方法、不确定性以及最新进展，并对其面临的挑战和未来趋势进行了分析。     

北京麦蚜虫害的光谱测量与分析

通过测定小麦生育期内叶绿素含量变化及分析叶绿素含量与麦蚜量间的动态关系,提出小麦蚜虫灾害遥感监测的植物生理学依据。通过1995、1996和1998年的地面光谱测量,绘制出蚜量同小麦光谱的相关性曲线,证明利用小麦的反射光谱植被指数RVI值监测麦蚜的可行性,并给出了确定小麦蚜虫防治点即百株蚜量500头左右的RVI值方法。为确定麦蚜虫害最佳防治时间提供依据。     

成像角度与叶龄对叶片叶绿素荧光成像的影响研究

叶绿素荧光成像作为一种高效的植物光合作用和生理状态信息获取手段,常被应用于智慧农业信息感知等众多领域。现阶段的大尺度叶绿素荧光成像技术缺少与微观的叶片级叶绿素荧光成像之间的机制上联系,忽略成像角度与叶片叶龄对叶绿素荧光成像产生的影响,限制了其在大尺度农业智能评估与决策中应发挥的作用。针对上述问题,设计了一套可多角度成像的叶绿素荧光采集设备,用以探究叶绿素荧光成像与成像角度和叶片叶龄之间存在的联系,并利用绿萝、樟树和大叶黄杨这三种分别代表藤本、乔木和灌木的植物共计60片叶子进行成像实验,分析荧光强度、Fv/Fm和Rfd三个典型荧光指标。实验结果表明成像角度对叶绿素荧光成像存在显著影响,成像角度的增大会导致荧光参数值的减小,对不同种类植物的影响也不同。叶片的叶龄也会影响叶绿素荧光成像,成长期叶片的成像参数指标优于成熟期叶片。     

基于光谱分析的长江口湿地互花米草叶片叶绿素含量反演研究

互花米草是我国滨海湿地主要入侵植物之一,对当地生态系统产生深远影响,其叶绿素含量信息是湿地生态系统关键生态功能定量化研究的重要基础数据。以长江口崇明东滩湿地为研究区,以实测互花米草叶片光谱反射率和总叶绿素含量为数据源,在400~1 000nm范围内研究原始光谱反射率和一阶导数光谱反射率的比值形式(RVI)与归一化差值形式(NDVI)组合,与叶绿素含量的相关性分析,并构建叶绿素含量估算模型。结果表明:基于原始光谱反射率的RVI和NDVI植被指数形式所构建的模型的精度最高,均方根误差RMSE分别达到0.24和0.25;一阶导数光谱反射率因噪声影响较大,其估算效果不佳;从模型所入选波段来看,红边波段在互花米草叶绿素含量估算中尤为重要。     

离子选择性电极催化电位法测定植物中的微量锰

锰是植物中的微量元素之一,它对植物具有增强光合作用、刺激生长等作用。分析测定植物中锰含量,对于研究锰在植物叶绿素的合成和碳水化合物的运输中的生理功能等具有重要意义。本文用离子选择性电极催化电位法——高碘酸根电极指示跟踪锰(Ⅱ)催化的     

Curve-fit analysis of chlorophyll fluorescence spectra: Application to nutrient stress detection in sunflower

The in vivo laser-induced chlorophyll fluorescence (LICF) spectra of healthy and nutrient-deficient sunflower plants were measured on a Jobin Yvon monochromator with He---Ne laser excitation. To correctly determine the peak center and to evaluate the relative contributions of the bands in the total fluorescence spectrum, the steady state LICF spectra were analyzed with a nonlinear iterative procedure using Gaussian, Lorentzian, Pearson, Voigt, and exponential Gaussian spectral functions. It was observed that curve fitting performed by using two Gaussian peaks centered at 690 and 730 nm usually fits well to the chlorophyll fluorescence spectra. After curve fitting, the mean peak centers of the red and far-red chlorophyll bands of control plants were observed at 688.2 and 725.4 nm, respectively. A blue shift of as much as 9 nm in the peak position of the far-red band was observed with nutrient stress, whereas the shift in position of the red band was only of the order of a few nanometers. Further, the width at half maximum of the far-red band was found to increase by as much as 20 nm with nutrient stress. Curve fitting could thus separate out the red and far-red fluorescence spectra from a pair of normally distributed curves centered at 690 and 730 nm wavelengths, thereby differentiating the effects due to reabsorption from those due directly to changes in photosynthetic electron transport. The F690/F730 fluorescence intensity ratio obtained from curve-fitted parameters was found to be more sensitive to plant stress than were fluorescence values alone. Results indicate that a curve-fitting analysis of LICF spectra using Gaussian spectral functions is a very useful and sensitive method of evaluating spectral features from a statistical point of view and for accurate determination of contributions from constituent bands in the whole leaf fluorescence spectrum.     

Developing a Fuzzy Bicluster Regression to Estimate Heat Tolerance in Plants by Chlorophyll Fluorescence

This paper presents a straightforward and useful fuzzy regression approach to estimate heat tolerance of plants by chlorophyll fluorescence measurement. The chlorophyll fluorescence measurement is an indicator of functional change of photosynthesis and is sensitive to temperature. Using the fluorescence–temperature curves, the experimenter may determine the heat tolerance ($T_{c}$) of plants by intersections of two linear regression lines. However, as traditional statistical regression analysis shows, the experiment may contain uncertain factors or phenomena such as leaf nature and growth environment, which concludes that data may vary among individual plants and different species. This research presents a fuzzy bicluster regression (FBCR) analysis with genetic algorithms, which helps derive a fuzzy intersection set and fuzzy heat tolerance of plants, in addition to the traditional statistical regression analysis. A fuzzy clustering concept and simultaneously optimal determination of data clusters is also developed. Especially, when there are nonlinear inflections in data curves, due to the imperative use of linear regression models, the traditional regression analysis may become unable to sufficiently model the uncertainties exhibited. The FBCR analysis can resolve this problem effectively due to the nonlinear tolerance of the system, even in a linear model. To demonstrate the FBCR analysis, it was applied to estimate the heat tolerance of five plant species. The results derived appeared to be more suitable than that of the conventional method. The approach may provide a useful means for the experimenters to derive more credible results from their chlorophyll fluorescence–temperature data.      

Associated changes in physiological parameters and spectral reflectance indices in olive (Olea europaea L.) leaves in response to different levels of water stress

This study aimed to determine whether modification of physiological parameters could be detected remotely by monitoring the spectral reflectance of olive leaves in response to different degrees of drought. Three different drought intensities were simulated: (a) a mild drought by feeding abscisic acid to detached branches; (b) a rapid and severe drought by detaching leaves and letting them dry over several hours; (c) a relatively slow drought caused by withholding water to potted olive plants. The three degrees of stress affected gas exchange and chlorophyll fluorescence. When the inhibition of photosynthesis occurred within an hour it was not accompanied by a parallel reduction in chlorophyll concentration in the carotenoid to chlorophyll ratio. Consequently, changes in spectral reflectance in the visible region, e.g. in PRI (photochemical reflectance index) and FRI (fluorescence reflectance indices) were not significantly induced. In contrast, when the inhibition of photosynthesis caused by slow developing drought was prolonged (i.e. more than 24 hours) and led to a decrease in chlorophyll concentration and to a simultaneous increase in carotenoid to chlorophyll ratio, there were significant changes in the visible region of the leaf spectral reflectance and, in turn, in PRI and FRI. We defined 16 new reference wavelengths, from visible to SWIR regions, which are sensitive to both fast‐developing and slow‐developing stresses. These reference wavelengths were used to develop an algorithm, the Relative Reflectance Increment (RRI), that was linearly related to changes in relative water content (RWC, r ² = 0.733). This algorithm showed that the 1455 nm wavelength is highly affected by drought. This wavelength was therefore used to elaborate the water content reflectance index that was inversely related to RWC (r ² = 0.702).     

叶绿素荧光检测电路设计

荧光检测法测叶绿素溶液浓度含量具有实时、快速和原位检测等优点.以1 kHz方波作为载波信号,对激发光源进行调制,光源照射叶绿素溶液发出荧光,经光电转换后通过高信噪比的前级放大、二阶带通滤波器、后级放大、有效值检波和16位AD采样,得到的信号再经单片机处理.实验表明叶绿素浓度与荧光强度具有很好的相关性(相关系数R2 ＞0.99),满足叶绿素溶液浓度检测要求.     

太湖水体时间序列叶绿素浓度与反射光谱特征分析

对2008年5月到2009年5月采集的太湖水体反射光谱数据进行了异常数据检测、归一化等预处理后,计算了常用于叶绿素浓度反演的特征参量,包括荧光峰高度、荧光面积、特征波段比值、反射率微分;并分析建立了这些特征参量与对应叶绿素浓度的相关模型。研究表明：荧光面积、特征波段比值等与实测叶绿素浓度具有较好的相关性,而蓝绿光波段反射率比值对内陆水体叶绿素浓度反映不明显。湖泊水体的光学特征能够较好反映蓝藻的不同生长状态,太湖蓝藻随时间变化的规律大致可分为5月～11月,12月～4月两个阶段。本研究结果可为湖泊水体富营养化高光谱遥感监测的波段选择提供参考。     

A new instrument for passive remote sensing: 1. Measurements of sunlight-induced chlorophyll fluorescence

Under natural sunlight illumination, the chlorophyll fluorescence emitted by the vegetation represents less than 3% of the reflected light in the near infrared part of the spectrum. This small amount is difficult to quantify except at certain wavelengths, where the solar spectrum is attenuated (Fraunhofer lines). An instrument measuring the in-filling of the atmospheric oxygen absorption band at 760 nm by chlorophyll fluorescence has been designed and constructed at the “Laboratoire pour l'Utilisation du Rayonnement Electromagnetique” in Orsay, France. The system was calibrated against a pulsed fluorimeter (FIPAM), especially developed for monitoring chlorophyll fluorescence at distance. The penetration of diuron, a herbicide acting on photosynthesis, was monitored by the passive instrument for several days on a corn canopy. A good agreement was found between gas exchange and variable chlorophyll fluorescence at the canopy level and variable fluorescence at the leaf level. The potential application of the passive chlorophyll fluorescence measurements for long range vegetation remote sensing is discussed.     

FluorMODleaf: A new leaf fluorescence emission model based on the PROSPECT model

A new model of chlorophyll a fluorescence emission by plant leaves, FluorMODleaf, is presented. It is an extension of PROSPECT, a widely used leaf optical properties model that regards the leaf as a pile of N absorbing and diffusing elementary plates. In FluorMODleaf, fluorescence emission of an infinitesimal layer of thickness dx is integrated over the entire elementary plate. The fluorescence source function is based on the excitation spectrum of diluted isolated thylakoids and on the emission spectra of isolated photosystems, PSI and PSII, which are the main pigment-protein complexes involved in the initial stages of photosynthesis. Scattering within the leaf is produced by multiple reflections within and between elementary plates. The input variables of FluorMODleaf are: the number of elementary plates N, also called leaf structure parameter, the total chlorophyll content C_ab, the total carotenoid content C_cx, the equivalent water thickness C_w, and the dry matter content C_m (or leaf mass per area), as in the new PROSPECT-5, plus the σ_II/σ_I ratio referring to the relative absorption cross section of PSI and PSII, and the fluorescence quantum efficiency of PSI and PSII, τ_I and τ_II, that are introduced here as mean fluorescence lifetimes. The model, which considers the reabsorption of emitted light within the leaf, allows good quantitative estimation of both upward and downward apparent spectral fluorescence yield (ASFY) at different excitation wavelengths from 400 nm to 700 nm. It also emphasizes the role of scattering in fluorescence emission by leaves having high chlorophyll content.     

Early detection of nutrient and biotic stress in Phaseolus vulgaris

Prerequisites for optimal, high crop yield are disease‐free growth and an equilibrated supply of nutrients. Early signatures of stress‐altered physiology, before appearance of symptoms in the visible spectrum, allow timely treatment. Early detection of stress development was carried out on phaseolus vulgaris bean infected with the agriculturally important grey mould pathogen and under conditions of magnesium deficiency, limiting photosynthesis. During stress development, bean plants were monitored by time‐lapse imaging with thermal, video and chlorophyll fluorescence cameras, mounted on a gantry robot system. For early detection of grey mould infection, chlorophyll fluorescence imaging proved to be the most sensitive. This technique detected magnesium deficiency at least three days before visual symptoms appeared. Further development of non‐contact technology for plant health monitoring will help to achieve optimal productivity in greenhouse and field cultures. Associated establishment of a stress catalogue based on early symptoms will allow swift diagnosis.