【作者】 宋金玲；

【导师】 王锦地；

【作者基本信息】 北京师范大学 ， 地图学与地理信息系统， 2006， 博士

【摘要】 植被BRDF模型的研究是支撑多角度植被遥感技术的理论基础,它的发展大大地推动了再生资源定量遥感的进程。因此,植被BRDF模型研究已经成为当前遥感科学中一个十分活跃的领域,先后出现的辐射传输模型、几何光学模型、混合模型和计算机模拟模型被用来定量计算地面目标的方向反射特性。本研究中采用了计算机模拟模型的辐射度方法,它由两大模块组成:(1)根据植被的生长规律,生成植被真实三维场景结构;(2)以生成的真实结构为基础,利用辐射度方法模拟植被场景冠层二向反射特性。为了能顺利展开对计算机模拟模型的研究,论文工作中进行了大量实验,积累了丰富的实验数据,一方面为模型研究提供了条件数据,同时也为模型结果验证提供了依据。本论文以植被结构特征的定量描述与场景模拟为基础,利用辐射度方法模拟了农作物(冬小麦和夏玉米)以及阔叶林地冠层的二向反射特性。并利用几何光学模型的思想,简化了阔叶树冠的结构,进而扩展了辐射度方法模拟的应用尺度。本论文的主要研究内容和创新点归结如下:(1)首先得到冬小麦整个生长期LAI变化估算模型,以LAI为控制因子,利用辐射度方法模拟了冬小麦不同LAI的冠层二向反射特性及NDVI的变化。并将计算机模拟结果与实测数据、Prosail模型模拟结果以及MISR多角度数据进行比较,取得了很好地一致性。(2)研究了不同时期冬小麦茎组分对冠层BRF的影响,分析了茎组分、入照和垄向对冠层二向反射特性的敏感性。(3)模拟了夏玉米与杂草不同下垫面的两种混合场景,分析了下垫面对农作物冠层二向反射特性的敏感性。(4)为了进一步扩展计算机模拟模型研究的真实场景观测尺度,以真实结构林地场景为研究目标。首先改进了林冠结构的模拟,分析了不同LAI条件下冠层二向反射特性变化趋势。(5)为了拓展辐射度方法的适用尺度,解决大尺度林地场景的模拟,简化林地树冠结构,将树冠抽象为椭球体,结合几何光学模型的思想完成了大尺度林冠场景冠层二向反射特性的模拟。(6)发挥计算机模拟模型的优势,模拟了不同条件下的植被结构场景,分析了植被空间分布、入照以及下垫面等对农作物和林冠场景冠层二向反射特性的敏感性。更多还原

【Abstract】 The researches on vegetation BRDF (Bi-directional reflectance distribution function) models are the theoretical basis to support multi-angle remote sensing techniques of vegetations, which promote the process of quantitative remote sensing and apply to many fields, such as military, and space remote sensing, meteorological and ecological environment fields. Therefore, vegetation BRDF models (such as, Radiation Translation(RT) model, Geometry Optical(GOMS), model GORT model and Computer Simulation model have become the hot field in remote sensing science to calculate vegetation canopy bi-directional reflectance .In this study, Radiosity method is used to simulate the canopy BRF (bi-directional reflectance factor) of vegetation, which is one of the methods of computer simulation model. The Radiosity method composes of two modules: 1) using L-system to render the 3D realistic structured scenes; 2) based on the rendering scenes, simulating the canopy bi-directional reflectance using Radiosity method. In order to successfully carry out researches on the computer simulation model, some experiments have been done, and accumulated lots of experimental data, which are the conditional data for model study, and also are the validation authority for simulation results.In this paper, taking crops (winter wheat and summer maize) and broadleaf trees as research objects, their canopies BRF have been simulated by Radiosity method. In addition, in order to extend the simulated scale for Radiosity method, the crown structures are simplified. In this paper, the major research contents and innovations points are as following:(1) Based on the measured leaf area index(LAI) and relative cumulated temperature, and used Logistic function, the model is fitted to depict the LAI changes in the entire crop growth stages. Taking LAI as the control factor, we simulate canopy bi-directional reflectance and NDVI for different LAI, and analyzing their change. Computer simulated results(canopy BRF and hyperspectrum data) are compared with field measured data ,Prosail simulated data and MISR BRF data, and they have made good consistency.(2) Based on canopy BRF simulation of winter wheat, studying on the influence of winter wheat stem to canopy bi-directional reflectance regime in different growth stages, and analyzing the effect of stem on the day change of canopy bi-directional reflectance. In addition, the realistic structured scenes for two different ridges are simulated. The study shows that the ridge has some influence on canopy BRF of winter wheat.(3) In order to analyze the influence of underlying surface on crop canopy bi-directional reflectance regime, two mixed scenes of maize and grass with different types of underlying surfaces are simulated: one is soil and sparse grass, and the other is soil and bushy grass. One conclusion is shown that the influence of underlying surface with bushy grass is great, which can accumulate the priori knowledge to reverse the structure parameters.(4) In order to extent the scale of realistic structured scene for computer simulation study, forest is taken as the experiment object. Based on the simulated realistic structured broadleaf forest scene, canopy radiation regime is analyzed. In addition, we also study on the change trend of canopy BRF for different LAI.(5) Because of the complexity of crown 3D structures, and the facets are too many to calculate canopy BRF by radiosity method. So in order to extent the simulated scale and solve the problem of larger scale simulation, an idea is to abstract the crown as an ellipsoid and to simplify the scene structures. When facets in the scenes are given optical properties, the probability of crown gap is considered, and combined with the thoughts of Geometry Optical model to complete canopy BRF simulation at larger scale.(6) Take advantage of computer simulation model, based on vegetation scenes in many different conditions, analyzing the sensitivity of parameters to vegetation canopy bi-directional reflectance regime. The parameters conclude the spatial distribution, sun direction and underlying surface in simulated scenes.更多还原