利用半球图像法提取植被冠层结构特征参数

植被冠层结构深刻地影响着植物群落与环境的相互作用,对植被冠层结构的研究是深入理解植被生态系统格局、过程及其运作机制的重要基础。冠层结构特征参数的快速测量方法是植被冠层结构研究的前提,目前测量方法主要是基于实际测量的地面法,地面法一般费时费力,受人为因素影响较大,因此本文探索利用半球图像法获取植被冠层结构特征参数。通过对半球图像进行几何纠正并建立参数图层,与分类后的植被冠层图层进行运算提取植被冠层结构特征参数。将该方法应用于祁连山旺腰沟流域青海云杉冠层结构特征参数的提取,包括植被冠幅、冠层面积、冠层周长等,结果显示：半球图像法能够较好的提取植被冠层结构特征参数,该方法具有简单、客观、可重复等优点,也可作为植被冠层结构变化的监测方法。     

辽西不同针叶被害率的油松冠层光谱特征

通过对辽宁西部大面积油松冠层反射光谱的测定,分析了不同针叶被害率的油松冠层光谱反射率的差异.结果表明:在可见光波段,健康植被和不同针叶被害率的油松冠层光谱均符合绿色植物的光谱特征,但针叶被害率大于60％的油松冠层的红谷不十分明显;在近红外波段,随着针叶被害率的减少,780～1350 nm波段范围的光谱反射率增大,1450～1800和1950 ～2350 nm波段范围的光谱反射率下降.随着针叶被害率的增加,红边拐点波长位置向短波方向移动,即出现“蓝移”现象.不同针叶被害率与红边特征参数和多种植被指数均具有显著或极显著的相关关系,其中,以DVI(1470,860)为参数所建模型能更好地监测油松冠层针叶被害率.     

PROSPECT5耦合4SAIL模型的亚热带典型森林冠层反射率时间序列模拟

冠层反射率在森林植被类型精确解译、森林碳同化关键参数如叶面积指数(LAI)、叶绿素等遥感反演等方面具有重要意义.本研究以亚热带毛竹林、雷竹林和常绿落叶阔叶混交林3种典型森林类型为研究对象,通过耦合PROSPECT5和4SAIL模型模拟其冠层反射率时间序列.首先,对PROSPECT5和4SAIL模型参数进行敏感性分析,探讨模型参数对冠层反射率的影响;其次,利用实测反射率对不敏感参数进行优化,并确定其参数值;最后,耦合PROSPECT5和4SAIL模型模拟3种亚热带森林冠层反射率,并与MODIS反射率进行对比.结果表明:LAI对第1、2、3、5、7波段最敏感,各波段的总敏感指数分别为0.80、0.83、0.94、0.66、0.47;叶绿素含量对第4波段最敏感,总敏感指数为0.59;叶片含水量对第6波段的敏感性最大,总敏感性指数为0.54;叶子结构参数、类胡萝卜素、热点参数、干物质含量和土壤干湿比等参数对各个波段都不敏感或敏感性较小.优化后的PROSPECT5和4SAIL模型模拟得到的冠层反射率能够真实反映3种典型森林的季节性变化规律,通过与MODIS反射率对比分析发现,模拟冠层反射率和MODIS反射率之间具有较高的决定系数,分别为0.86、0.90、0.93,均方根误差(RMSE)也较小,分别为0.09、0.07、0.05,且模拟反射率能在一定程度上解决MODIS反射率数据冬季易受雨雪、混合像元影响等问题.     

基于机载高光谱影像的植被冠层叶绿素反演

利用黑龙江省伊春市带领区凉水国家级自然保护区机载高光谱数据,提取了红边面积、三角形植被指数、归一化植被指数等15个光谱参数,结合坡度、坡向、海拔、郁闭度和植被总盖度5个地理参数,并利用叶绿素计SPAD-502对研究区植被冠层叶绿素相对含量进行同步测量,分析了叶片光谱反射率、反射率的一阶导数及其他变形分别与SPAD值的相关性,采用基于核变换的偏最小二乘原理建立了叶绿素相对含量的估测模型,用该模型对研究区植被冠层叶绿素相对含量进行定量估算.结果表明:当分段数为3、提取的主成分数为10时,所建模型的效果较好,模型决定系数达到0.855,平均绝对百分误差为9.6％,预测精度为89.7％.     

基于PROSAIL辐射传输模型的毛竹林分冠层反射率模拟研究

冠层光谱反射率直接关系到毛竹（Phyllostachys pubescens Mazel）林冠层参数的反演,对毛竹林地土壤肥力间接估测具有重要意义。以PROSPECT5、PROSAIL模型为基础,从叶片尺度和冠层尺度分析模型参数对叶片和冠层反射率的影响,构建毛竹冠层叶面积指数（LAI）-冠层反射率查找表并通过代价函数选取最优冠层反射率,从而实现毛竹林分冠层反射率的准确模拟。结果表明,在叶片尺度,PROSPECT模型参数敏感性从高到低依次为叶肉结构参数（N） > 叶绿素含量（C_ab） > 等效水厚度（EWT） > 干物质含量（C_m） > 类胡萝卜素含量（C_ar）;在冠层尺度,PROSAIL模型参数敏感性从高到低依次为LAI > C_ab > EWT > C_m > N > C_ar > ALA（平均叶倾角）;叶片尺度反射率整体大于冠层尺度反射率;在400~900 nm波长范围内,PROSAIL模型模拟的冠层光谱反射率与实测光谱反射率拟合效果较好,相对误差为6.71%。     

广东省2004-2016年植被冠层降雨截留模拟及时空变化特征

评价植被冠层降雨截留能力,是生态系统水循环的重要研究内容。以广东省中小流域为例,结合地面监测站点的降雨量数据和MODIS叶面积指数遥感数据,利用植被冠层降雨截留模型,定量模拟和分析了广东省流域尺度2004-2016年的地表植被冠层降雨截留能力及其时空变化特征。结果表明：（1）2004-2012年广东省年均植被冠层降雨截留率持续下降,2016年略有上升,并且随着时间的推移,流域之间的植被冠层降雨截留率差异越来越小。（2）广东省植被冠层降雨截留能力呈现山区东西两翼高,山区中部以及沿海地区低的显著空间差异格局,这种空间格局与植被覆盖LAI主要呈现由珠三角向外围递增的圈层空间格局特征密切相关,而与由南向北逐渐递减的降雨空间格局特征相关性不大。（3）森林覆盖对流域植被冠层降雨截留能力有着一定的影响,其中流域内阔叶林占森林面积的比例对这种影响的程度起着最为关键的作用。     

4-Scale几何光学模型冠层反射率模拟的空间尺度适用性

明确4-Scale模型模拟森林冠层反射率适用的空间尺度,有助于提高其应用于不同植被类型冠层反射率模拟时的精度,进而提升其开展叶面积指数、郁闭度和其他参数的反演精度。以黑龙江省尚志市帽儿山实验林场2块100 m×100 m森林样地(阔叶林与混交林各一块)为研究对象,分别分割为10、20、30、40和50 m空间尺度,使用4-Scale模型模拟森林冠层反射率,采用局部平均法、最邻近法、双线性内插法和立方卷积法对空间分辨率为10 m的Sentinel-2影像升尺度转换至其他尺度并评价,对比分析模拟冠层反射率和遥感像元反射率,明确混交林和阔叶林适合4-Scale模型高精度反演参数的空间尺度。结果表明：4-Scale模型整体低估了像元森林冠层反射率,混交林和阔叶林冠层反射率在20 m尺度的模拟效果均最差,红光波段和近红外波段的均方根误差(RMSE)和平均绝对偏差(MAE)均较大;>20 m尺度的模拟效果开始变好,混交林40 m、阔叶林30 m时模型的适用性最佳,红光波段和近红外波段下,模拟值与遥感像元反射率之差的均值和标准差最小,RMSE和MAE同样最小;10 m尺度混交林和阔叶林模拟结果...     

植被冠层尺度生理生态模型的研究进展

随着人们对植物生命活动各个过程研究的不断深入,以植物生理过程、物理过程为基础的各种生理生态学模型逐渐发展起来,而植被冠层尺度生理生态学过程模型已成为生态系统模型的核心之一。目前植被冠层尺度的大叶模型、多层模型、二叶模型以其成熟的理论基础及对植被冠层的光合作用、蒸腾作用较为成功的模拟,得到了广泛的应用。3个模型都以光合作用-气孔导度-蒸腾作用耦合模型为基础,但又具有各自的特点。本文对3种模型的结构及特点进行了总结,并对其进行了比较,简要介绍了目前植被冠层尺度生理生态学模型的应用及存在的问题和发展状况。     

多组分植被方向反射系数的解析计算模型

基于植被介质中的辐射传输理论和几何光学原理,提出了一个计算非随机、多组分植被多波段、多角度反射光谱的综合解析模型.此模型以作者以前建立的叶冠层模型和多组分模型为基础,通过对任意空间取向植被组分对冠层“热点”效应贡献的定量计算及在多次散射系数的估算中考虑冠层所有组分的作用,全面、深入地概括了植被冠层的多种组分以及它们的几何结构和光学性质的空间变化对植被多角度反射光谱的影响。模拟与实测结果的比较得出:模型基本上能抓住多组分植被反射光谱的角度分布特征,模拟出叶冠层模型所不能得到的自然植被方向反射系数和冠层“热点”效应的非对称性分布.模型的模拟结果表明,冠层“热点”效应在冠层组分的平均倾角约20°时达最大,然后随平均倾角的增大,“热点”效应明显减弱.     

植被生化组分光谱模型抗土壤背景能力分析

应用LOPEX'93(Leaf Optical Properties Experiment)数据,分析了统计回归模型在进行植被叶绿素和水分反演中抗土壤背景影响的能力,模型参数分别使用了:反射率及其变化形式、光谱位置变量、植被指数。在LOPEX'93数据库的植被波谱中分别加入10%-90%的实测土壤光谱信息,得到植被与土壤的混合光谱,并分析混合光谱对植被生化组分的响应。结果表明:应用反射率及其变化形式进行植被叶绿素反演时,以730nm和400nm组合的反射率和反射率倒数的对数为参数的模型具有最高的抗土壤背景能力,在土壤背景所占比例从低到高的变化过程中,以二者反射率组合为参数的模型与叶绿素的相关系数,始终保持在0.645附近,以二者反射率倒数的对数为参数的模型与植被叶绿素的相关系数保持在0.650附近;应用反射率及其变化形式进行植被含水量反演时,以1100,1170,1000,1040,1080nm组合的反射率为参数的模型以及以1170,960,1210,1090,1080,950,1220,1210nm反射率倒数的对数组合为参数的模型具有较高的稳定性,在土壤组分变化的过程中,以上模型与植被含水量的相关系数均稳定的高于0.99;对于光谱位置变量的分析中,以红边-绿峰-红谷组合的模型与植被叶绿素含量具有较高、而且稳定的相关系数,在土壤背景所占比例变化的情况下,相关系数稳定在0.53附近;在应用植被指数进行叶绿素的反演过程中,植被指数与叶绿素的相关系数在土壤背景所占比例变化的情况下变化较大,抗土壤背景的能力均较差;在应用植被指数进行植被水分含量的反演时,以水分指数Ratio975和Ratio1200相关系数最高,且在不同比例土壤背景变化下稳定,相关系数分别分布在0.980附近和0.960附近。该结果可用于指导不同植被覆盖条件下植被冠层参数的反演,提高反演的稳定性和准确性。     

Plant ecophysiological processes in spectral profiles: perspective from a deciduous broadleaf forest

The need for progress in satellite remote sensing of terrestrial ecosystems is intensifying under climate change. Further progress in Earth observations of photosynthetic activity and primary production from local to global scales is fundamental to the analysis of the current status and changes in the photosynthetic productivity of terrestrial ecosystems. In this paper, we review plant ecophysiological processes affecting optical properties of the forest canopy which can be measured with optical remote sensing by Earth-observation satellites. Spectral reflectance measured by optical remote sensing is utilized to estimate the temporal and spatial variations in the canopy structure and primary productivity. Optical information reflects the physical characteristics of the targeted vegetation; to use this information efficiently, mechanistic understanding of the basic consequences of plant ecophysiological and optical properties is essential over broad scales, from single leaf to canopy and landscape. In theory, canopy spectral reflectance is regulated by leaf optical properties (reflectance and transmittance spectra) and canopy structure (geometrical distributions of leaf area and angle). In a deciduous broadleaf forest, our measurements and modeling analysis of leaf-level characteristics showed that seasonal changes in chlorophyll content and mesophyll structure of deciduous tree species lead to a seasonal change in leaf optical properties. The canopy reflectance spectrum of the deciduous forest also changes with season. In particular, canopy reflectance in the green region showed a unique pattern in the early growing season: green reflectance increased rapidly after leaf emergence and decreased rapidly after canopy closure. Our model simulation showed that the seasonal change in the leaf optical properties and leaf area index caused this pattern. Based on this understanding we discuss how we can gain ecophysiological information from satellite images at the landscape level. Finally, we discuss the challenges and opportunities of ecophysiological remote sensing by satellites.

     

水稻多组分双向反射模型的研究

利用1999-2000年的水稻田间试验实测光谱数据,对水稻不同生长期特性建立的水稻多组分双向反向模型进行了一些主要因子的敏感性分析及模型模拟值与实测值的比较分析。结果表明,考虑水稻冠层叶、茎干、穗等作用及水稻不同生长期特点的水稻多组分双向反向模型,能较好地反映水稻多组分反向光谱的角度分布特征,较准确地模拟水稻不同条件下水稻的自然方向反向系数和冠层"热点"效应的非对称性分布。得到了薄层水体和土壤背景的一次反向辐射以及在冠层内部、薄层水体和土壤表面相互间的多次反向辐射随水稻各组分平均倾角的变化规律,冠层双向反向率随叶面积指数LAI的变化特征。     

不同水氮条件下水稻冠层反射光谱与植株含水率的定量关系

研究了不同土壤水氮条件下水稻 (Oryzasativa) 冠层光谱反射特征和植株水分状况的量化关系。结果表明, 水稻冠层近红外光谱反射率随土壤含水量的降低而降低, 短波红外光谱反射率随土壤含水量的降低而升高。相同土壤水分条件下, 高氮水稻的冠层含水率高于低氮水稻的冠层含水率 ;同一水分条件下, 高氮处理的可见光区和短波红外波段光谱反射率低于低氮处理, 近红外波段光谱反射率高于低氮处理。发现拔节后比值植被指数 (R810 /R460 ) 与水稻叶片含水率和植株含水率呈极显著的线性相关, 模型的检验误差 (RootmeansquareError, RMSE) 分别为 0.93和 1.5 0。表明比值植被指数R810 /R460 可以较好地监测不同生育期水稻叶片和植株含水率。     

An analytical model for bidirectional reflectance factor of multicomponent vegetation canopies

Based on radiative transfer theory in vegetation and geometric-optical principles, an analytical physi-cal mode] for calculating multiangular, multispectral reflectance over a non-random, multiple component vegetation canopy is developed. This model is derived by taking advantages of the previous leaf canopy and multicomponent canopy BRF models. It quantitatively accounts for both the impact of foliage elements' orientation on the canopy hotspot through an innovative algorithm to estimate the hotspot function for any arbitrarily oriented foliage element and contributions of all foliage elements to the reflectance by multiple scattering. Thus, it is characterized by more com-pletely considering the integrative influence of spatial variations in optical and structural properties of all foliage ele-ments on canopy reflectance than any previous analytical BRF models. Simulation results from this model demonstrate that canopy hotspot becomes strongest when the mean inclination angle of foliage elements is ar     

光谱分析在植物生理生态研究中的应用

本文介绍了光谱分析技术在植物生理生态研究中的应用。通过分析植物叶片和冠层的反射光谱特征,可以快速、无损伤地研究不同环境条件下植物的各种色素含量、叶黄素循环组分、营养状况、水分状况、光能利用效率、植被盖度以及冠层结构等生理生态特征,此外光谱分析还能用来监测湖泊、河流中水华的发生和分布、研究生态系统中CO_2和H_2O的通量以及各种逆境胁迫和放牧等对植物生长的影响。     

Structure is more important than physiology for estimating intracanopy distributions of leaf temperatures

Estimating leaf temperature distributions (LTDs) in canopies is crucial in forest ecology. Leaf temperature affects the exchange of heat, water, and gases, and it alters the performance of leaf‐dwelling species such as arthropods, including pests and invaders. LTDs provide spatial variation that may allow arthropods to thermoregulate in the face of long‐term changes in mean temperature or incidence of extreme temperatures. Yet, recording LTDs for entire canopies remains challenging. Here, we use an energy‐exchange model (RATP) to examine the relative roles of climatic, structural, and physiological factors in influencing three‐dimensional LTDs in tree canopies. A Morris sensitivity analysis of 13 parameters showed, not surprisingly, that climatic factors had the greatest overall effect on LTDs. In addition, however, structural parameters had greater effects on LTDs than did leaf physiological parameters. Our results suggest that it is possible to infer forest canopy LTDs from the LTDs measured or simulated just at the surface of the canopy cover over a reasonable range of parameter values. This conclusion suggests that remote sensing data can be used to estimate 3D patterns of temperature variation from 2D images of vegetation surface temperatures. Synthesis and applications. Estimating the effects of LTDs on natural plant–insect communities will require extending canopy models beyond their current focus on individual species or crops. These models, however, contain many parameters, and applying the models to new species or to mixed natural canopies depends on identifying the parameters that matter most. Our results suggest that canopy structural parameters are more important determinants of LTDs than are the physiological parameters that tend to receive the most empirical attention.     

Diverse Optical and Photosynthetic Properties in a Neotropical Dry Forest during the Dry Season: Implications for Remote Estimation of Photosynthesis1

Using optical and photosynthetic assays from a canopy access crane, we examined the photosynthetic performance of tropical dry forest canopies during the dry season in Parque Metropolitano, Panama City, Panama. Photosynthetic gas exchange, chlorophyll fluorescence, and three indices derived from spectral reflectance (the normalized difference vegetation index, the simple ratio, and the photochemical reflectance index) were used as indicators of structural and physiological components of photosynthetic activity. Considerable interspecific variation was evident in structural and physiological behavior in this forest stand, which included varying degrees of foliage loss, altered leaf orientation, stomatal closure, and photosystem II downregulation. The normalized difference vegetation index and the simple ratio were closely related to canopy structure and absorbed radiation for most species, but failed to capture the widely divergent photosynthetic behavior among evergreen species exhibiting various degrees of downregulation. The photochemical reflectance index and chlorophyll fluorescence were related indicators of photosynthetic downregulation, which was not detectable with the normalized difference vegetation index or simple ratio. These results suggest that remote sensing methods that ignore downregulation cannot capture within‐stand variability in actual carbon flux for this diverse forest type. Instead, these findings support a sampling approach that derives photosynthetic fluxes from a consideration of both canopy light absorption (e.g., normalized difference vegetation index) and photosynthetic light‐use efficiency (e.g., photochemical reflectance index). Such sampling should improve our understanding of controls on photosynthetic carbon uptake in diverse tropical forest stands.     

稻麦叶片氮积累量与冠层反射光谱的定量关系

作物氮素积累动态是评价作物群体长势及估测产量和品质的重要指标,对于作物氮素的实时监测和精确管理具有重要意义。该文以5个小麦(Triticum aestivum)品种和3个水稻(Oryza sativa)品种在不同施氮水平下的3年田间试验为基础,综合研究了稻麦叶片氮积累量与冠层反射光谱的定量关系。结果表明,不同试验中拔节后叶片氮积累量均随施氮水平呈上升趋势;稻麦冠层光谱反射率在不同施氮水平下存在明显差异,可见光区(460~710 nm)反射率一般随施氮水平的增加逐渐降低,近红外波段(760~1 220 nm)反射率却随施氮水平的增加逐渐升高;就单波段而言,810和870 nm处的冠层光谱反射率均与稻麦叶片氮积累量具有相对较高的相关性;在光谱参数中,比值植被指数(Ratio vegetation index, RVI)(870,660)和RVI(810,660)均与稻麦叶片氮积累量具有高度的相关性,且相关系数明显高于单波段反射率,尤其是水稻作物;对于小麦和水稻,均可以利用统一的波段和光谱指数来监测其叶片氮积累量,并可以采用统一的回归方程来描述其叶片氮积累量随单波段反射率和反射光谱参数的变化模式,但若采用单独的回归系数则可以提高稻麦叶片氮积累量估测的准确性。     

Review of optical-based remote sensing for plant trait mapping

Plant trait data have been used in various studies related to ecosystem functioning, community ecology, and assessment of ecosystem services. Evidences are that plant scientists agree on a set of key plant traits, which are relatively easy to measure and have a stable and strong predictive response to ecosystem functions. However, the field measurements of plant trait data are still limited to small area, to a certain moment in time and to certain number of species only. Therefore, remote sensing (RS) offers potential to complement or even replace field measurements of some plant traits. It offers instantaneous spatially contiguous information, covers larger areas and in case of satellite observations profits from their revisit capacity.In this review, we first introduce RS concepts of light–vegetation interactions, RS instruments for vegetation studies, RS methods, and scaling between field and RS observations. Further we discuss in detail current achievements and challenges of optical RS for mapping of key plant traits. We concentrate our discussion on three categorical plant traits (plant growth and life forms, flammability properties and photosynthetic pathways and activity) and on five continuous plant traits (plant height, leaf phenology, leaf mass per area, nitrogen and phosphorous concentration or content). We review existing literature to determine the retrieval accuracy of the continuous plant traits. The relative estimation error using RS ranged between 10% and 45% of measured mean value, i.e. around 10% for plant height of tall canopies, 20% for plant height of short canopies, 15% for plant nitrogen, 25% for plant phosphorus content/concentration, and 45% for leaf mass per area estimates.The potential of RS to map plant traits is particularly high when traits are related to leaf biochemistry, photosynthetic processes and canopy structure. There are also other plant traits, i.e. leaf chlorophyll content, water content and leaf area index, which can be retrieved from optical RS well and can be of importance for plant scientists.We underline the need that future assessments of ecosystem functioning using RS should require comprehensive and integrated measurements of various plant traits together with leaf and canopy spectral properties. By doing so, the interplay between plant structural, physiological, biochemical, phenological and spectral properties can be better understood.     

Contribution à l'analyse des structures forestières 2. Caractérisation et analyse du toit de la végétation

Data used come from point-height analysis. 100 sample points are arranged in 4 lines of 25, with 24 m between lines and 1 m between points on lines. At each point, vertical lists of species are compiled, by measurement strata. Such strata depth is 10 cm when mean vegetation height in the stand is lower than 4–5 m and 50 cm when heigher. A synthetic vegetation profile is obtained by sum of species presences in each measurement stratum for all 100 observations. When these profiles are bimodal, vegetation can be divided in two at the secondary minimum level: the upper part is the canopy, the lower the understorey. Only the canopy structure is dealt with in this tudy. Several parameters, describing vertical structure of woody vegetation, are defined and measured. They are: (1) maximum height, (2) upper and lower canopy limits, (3) canopy depth and (4) density. Delimitation of canopy is achieved by calculating the hypegeometric probability of realisation groups of vegetation presence, or absence, in the vertical line of sight. The thickness is the difference between the two previous values (2) and (3) and density the number of intercepts between them. Horizontal variations in those structural parameters are revealed by cumulative sum method which demonstrates different types of pattern. Relations between horizontal variations are studied by pairs; actual values compared by linear correlation analysis while concordance between patterns are characterised by the coefficient of simple concordance ofSokal etMitchner and by a binary autocorrelation coefficient.Shannon's formula enables an overall appreciation of canopy homogeneity. an example is applied to some stands ofNothofagus antarctica (Forest) Verst. in Southern Chile and Argentina. The upper canopy limits are the same upper vegetation intercepts so canopies are smooth. High correlation exists between upper and lower limits of the canopies, and low correlation between the latter and thickness and density, so canopies are uniform.