冠层是植被进行生态过程的主要层次,森林冠层结构影响冠层生化组分的遥感反演,因此对其光谱特征的分析有助于提高冠层生化组分反演的精度.以长白山温带阔叶红松林为研究对象,利用Hyperion高光谱数据提取不同林冠反射率,运用连续统去除和光谱一阶微分法进行光谱变换,定量分析森林冠层的光谱特征.通过计算样方阔叶树种优势度(BFDI),以及一系列光谱指数(NIR,NDVI,EVI,NDNI,SPRI*NDVI和SPRI*EVI),探讨冠层结构组成对其光谱特征及光谱指数的影响.结果表明:(1)相比阔叶林冠层,针阔混交林、美人松林和樟子松林冠层光谱的红边有左移趋势,斜率明显下降,蓝边、黄边斜率特征也相应减弱,近红外波段反射率明显下降,可见光波段的归一化反射率有上升趋势,表明不同林冠,尤其针叶林与阔叶林林冠之间的光谱特征差异明显.(2)BFDI对冠层NIR反射率和三边斜率有明显的影响,与光谱指数显著相关(P<0.01),表明BFDI影响森林光谱指数.BFDI与NDVI,EVI,SPRI*EVI,NIR,SPRI*NDVI,NDNI的R2分别达到0.90,0.83,0.83,0.81,0.68,0.59,揭示了BFDI对于冠层绿度、叶面积指数、植被生产力以及冠层叶氮浓度等植被参数存在一定影响.研究表明,利用星载高光谱数据结合地面样方调查可以很好地阐明林冠结构组成对于光谱特征的影响,也对优化植被冠层生化组分和森林生态系统生产力的遥感反演具有借鉴意义.

Canopy is a major structural layer for vegetation to carry out ecological activities.The differences of light radiative transfer processes in canopies caused by forest canopy structure directly influence remote sensing inversion of forest canopy biochemical composition.Thus an analysis of spectral characteristics between different canopy structures contributes to improve the accuracy of remote sensing inversion of forest canopy biochemical components.Based on a Hyperion hyperspectral image in the north Slope of Changbai Mountain Nature Reserve,through FLAASH(the Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes) atmospheric correction,different canopy reflectance spectra were extracted,and spectral transforms were carried out using continuum removal method and first derivative method for quantitative analysis of the spectral characteristics.A set of spectral indices were calculated,including NIR(near infrared reflectance),NDVI(normalized difference vegetation index),EVI(Enhanced Vegetation Index),NDNI(normalized difference nitrogen index),SPRI(normalized photochemical reflectance index)*NDVI and SPRI*EVI(vegetation productivity index).Combined with the broad foliar dominance index(BFDI),the relationships between the spectral indices and canopy structure composition were investigated.The characteristics of canopy structure composition impacting its spectral curve and indices were clarified in the temperate forest.The results showed that:(1) there existed significantly different spectral characteristics between different canopy structures:comparing to the spectrum of broad-leaved forest canopies,the red edge moved to the left and their slope decreased,blue edge and yellow edge features were also weakened,near-infrared reflectance decreased,normalized reflectance in visible region risen for the spectrum of conifer forest canopies;(2) the spectrum variation were controlled by BFDI.The correlations between BFDI and the spectral indices were significant(P<0.01).It was suggested the ratio of broad-leaved and conifer in canopy played an important role in variation of spectral indices.The coefficients of determination(R2) of BFDI and NDVI,EVI,SPRI*EVI,SPRI*NDVI and NDNI were 0.90,0.83,0.83,0.81,0.68 and 0.59 respectively.It was revealed that BFDI could control the variation of the canopy structure,greenness,leaf nitrogen concentration,leaf area index and productivity in temperate coniferous and broad-leaved mixed forests.Our findings were very significant foundation for accurate determination of forest type,quantitative extraction of canopy biochemical components,estimation of regional forest ecosystem productivity and other related researches.