Scenarie Simulation And Spectral Analysis Of Wet Land Species Using A 3D Radiative Transfer Model

As one of the terrestrial ecosystems,wetland is a critical kind of land cover area for climate change and carbon cycle research.However,it is susceptible to invasive species,which leads to a series of ecological problems.Phragmites australis is one of the main local wetland species in the Yangtze River estuary.In recent years,due to the introduction and diffusion of Spartina alterniflora,the growth of Phragmites australis has been greatly inhibited.In order to control the expansion of Spartina alterniflora effectively,it is urgent to use the advanced technology such as remote sensing to explore the dynamic distribution characteristics of Phragmites australis and competition mechanism.As spectrums of the two wetland vegetation are similar,the mixed distribution in the ecotone is complicated and the wetland can be poorly entered.In this paper,the three-dimensional radiative transfer model is used to carry out the wetland vegetation simulation and spectral analysis,which is intended to provide a theoretical basis for the research and application of remote sensing,such as species identification,analysis of ecotone competition,quantitative inversion of biophysical and biochemical parameters.The main contents and results were as follows:1.The field experiment of Phragmites australis and Spartina alterniflora was designed and carried out in Chongming Dongtan wetland.The data needed for plant model such as plant height and leaf size were obtained,and other data for scene simulation such as plant density,soil reflectance were also measured;2.The plant models of Phragmites communis and Spartina alterniflora were established by 3Dmax.The PROSPECT + DART coupling model was used to simulate the scenarie of pure Phragmites communis and Spartina alterniflora at different densities,and the mixed scene with equal parts.3.Analyzed the effects of leaf and canopy chlorophyll content on vegetation index by adjusting the-model and,scene parameters:The results showed that the sensitivity of vegetation index to chlorophyll content was significantly affected by scale effect,the canopy chlorophyll content can be disturbed by LAI,and the bias was larger when vegetation index was used to estimate canopy chlorophyll content.4.Simulated canopy reflectance of Phragmites australis and Spartina alterniflora at different densities.The reflectance of the near-infrared band was significantly affected by the vegetation densities,and raising up with the increasing of the plant density.However,the two species showed different response to the change of density in the visible band.As a result,the discrimination abilities of vegetation index at plant density were different.5.The canopy reflectance of mixed scene with equal parts of Phragmites australis and Spartina alterniflora was simulated.Compared with the pure scene,the mixed one can be distinguished by the reflectance of near-infrared band and simple ratio vegetation index(SR).