Retrieval Of Conifer LAI In Changbai Based On The Multiple-angle Model

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.