【作者】 王强；

【导师】 罗传文；

【作者基本信息】 东北林业大学 ， 森林经理学， 2009， 博士

【摘要】 森林遥感在几十年的发展过程中,已经取得了很大的成绩,尤其是光学遥感,已经成功地获取到了全球性的森林分类图、森林叶面积指数图,从而使人类对地球上的森林二维面状信息有了全面的了解。但是森林是三维的客观存在,森林的三维信息主要通过森林中树木的平均高度、叶面积指数等空间结构参数来反映。从理论上讲,要准确地得到森林空间结构参数,这需要得到更多维度的遥感信息,相对于遥感技术在空间分辨率、时间分辨率、光谱分辨率已经实现了多元的拓展,而在观测的角度分辨率方面,尽管出现了少数多角度传感器,但是目前在理论体系完善以及开展应用方面都还有很多工作要做。为充分发挥多角度遥感技术在森林资源监测过程中的作用,首先需要认识遥感信号产生的机理,了解植被冠层辐射传输的过程,建立合适的数学模型进行定量描述,最终达到从遥感信号中提取植被信息的目的。本文以多角度遥感机理出发研究植被冠层BRDF与林分空间分布格局的内在联系,引入均匀度定量的描述林分空间格局并寻求两者之间的关系,为以往几何光学模型假设植被群体为随机分布所导致模拟的BRDF信号存在误差进行必要修正,和前人相关领域进行的研究比较,本文工作的主要特色在于:1、本文针对传统的研究方法仅将林木空间分布格局定性地描述为均匀分布、随机分布或聚集分布,且这些方法过于笼统,不能用于详细地分析林木空间分布格局对BRDF影响的缺点入手,引入均匀度来研究两者的关系。均匀度是对点集格局的一种测度,可以连续地度量空间分布格局的均匀性,而不像经典的格局指数那样只能分辨格局类型。利用光学遥感模型定量地模拟分析了林木空间分布格局对BRDF的影响。研究结果表明,对于红光波段,在大于树冠尺度上均匀度可以有效地刻画林木空间分布格局对BRDF曲线的影响,均匀度与BRDF之间呈现负指数关系,同时这种关系还在一定程度上受郁闭度的影响,郁闭度越大,林木空间分布格局对BRDF影响也越大。对于近红外波段,由于受多次散射的影响,BRDF与林木空间格局之间的关系更为复杂,均匀度尚未有效描述此关系。2、本文根据仅适合于垂直单角度观测的GeoSAI1模型,改进得到适合于各种角度观测的MGeoSAIL模型,它是几何光学模型和辐射传输模型的结合,具备两种模型的优点使MGeoSAIL模型更具准确性、实用性。几何光学模型用来计算场景内不同情况下阴影和照亮成分的比例,辐射传输模型(SAIL)考虑冠层内的辐射传输计算得到树冠的反射率和传输率,将其权重加和生成场景反射率。该模型是利用冠层组分的光学属性,树的形状,太阳天顶角和冠层覆盖度来计算场景反射率,模拟结果表明该模型简单适用,在可见光与近红外波段均能反应出“热点”效应,在近红外波段能描述出“碗边”效应,且更适合于低密度、大个体、不连续稀疏林分冠层的BRDF模拟。3、根据各种模型的特点按不同密度森林场景选择适用的模型,模拟植被冠层BRDF与树木各空间参数之间的关系,建立查找表反演LAI,与试验区真实数据比较验证查找表的有效性。更多还原

【Abstract】 Forest remote sensing has achieved a lot in the past decades.Researchers have realized global forest distribution and leaf area index mapping,which enables a whole 2-D picture of the forests on the earth.However,forest is a 3-D being.Forest 3-D information not only refers to spatial distribution but also canopy height,vertical stratification and leaf area index of a tree. In order to acquire more forest spatial structure parameters,we need to get versatile information from possible remote sensing means,such as spatial,temporal,spectral,and angular dimensions.Comparing to the progress in the former three dimensions,research on angular dimension still lacks enough understanding in both theoretical and applicable aspects. In order to quantitatively and correctly estimate the parameters of forest from remote sensing measurements,it is important to thoroughly understand the interacting processes of electromagnetic radiation with foliage elements,and construct an appropriate mathematical model to describe such processes.The paper study relation of tree pattern and BRDF of the foliage canopy through the mechanism of multiple-angle remote scening,the uniform index was used to continuously describe forest pattern and find the relation of them.Based on the relation,the error that is from the old GO model which only suppose foliage colony be random distribution was corrected. The main features of this paper include following points:1、The paper contrapose the limitation that tranditional methods only qualitatively distinguished the types of tree pattern as regular distribution,random distribution and clumped distribution,and can not describe how the BRDF is effected by tree pattern in detail.The uniform index is used to study the relations of them,which is a measure of points set pattern,and continuously describes the spatial relationship in the points set,rather than the traditional method that only distinguishs the types of points pattern.This paper used the optical remote sensing model to simulate and analyse the effect.The results showed that in red band the uniform index could describe the relationship between tree pattern and BRDF,the relationship between uniform index and BRDF appears to be negative exponential.In addition the relationship berween tree pattern and BRDF is affected by crown cover,the crown cover is bigger the effect is greater.The relationship between BRDF and tree pattern is more complicated in near infrared band because of the multiple-scatter,however the uniform index could not describe the relationship effectively.2、In this paper,we extend GeoSAIL model that was adapt to one direction to MGeoSAIL model that is adapt to mulit-angular observation.It combines geometric-optical model with radiation transfer model and has the merits of two models,which makes the model more accuracy and applied.The GO model provides the amount of shadowed and illuminated components in a scene,the radiation tranfer model(SAIL) calculates the reflectance and transmittance of the tree crowns.To calculated the reflectance of scene,reflectance of each component in the scene is weighted by its fractional area and summed.The model make use of the optical attribute of crown components,the shape of tree,the sun zenith angle,the forest canopy density to calculate reflectance of scene.The result show that model is appliable and simple,describes the "hot" spot in both visible and near infrared bands,describes the "bowl" shape in the near infrared band.Especially the model is more adapt to low density,big unit、discontinuous and open forest.3、Based on characteristic of the each model,the appropriates were chosed for different density forestry scene,and construct look-up table for retrieving LAI to validate with measure data.更多还原