基于模型模拟的植被NDVI与观测天顶角和LAI的关系

利用PROSPECT和SAIL模型模拟了不同叶绿素含量、不同LAI和不同观测天顶角下的植被冠层反射率,分析了NDVI随LAI、观测天顶角和叶绿素含量的变化规律。结果表明:叶绿素影响冠层反射率主要在可见光波段,冠层反射率随叶绿素含量的增加而下降；冠层反射率随观测天顶角的增加而增加,而LAI较高时,其受观测天顶角的影响较小。观测天顶角相同时,随叶绿素含量的增加NDVI呈上升趋势;叶绿素含量一定时,NDVI随LAI的增加而增加。LAI为1时,在不同叶绿素含量下,随观测天顶角的增加,NDVI呈先下降后上升的趋势,拐点在观测天顶角65°或70°处,而LAI为3、5和7时,NDVI呈现下降趋势。叶绿素含量较高时,NDVI受观测天顶角的影响较小。当LAI较大和叶绿素含量较低时,NDVI随观测天顶角的增加(>70°)下降较快。

Relationship between NDVI,View Zenith Angle and LAI based on Model Simulation

This paper uses PROSPECT and SAIL model to simulate vegetation canopy reflectance under different chlorophyll contents,LAI and view zenith angles.The changes of NDVI with different LAI,view zenith angles and chlorophyll contents are analyzed.This study results show that chlorophyll mainly affects canopy reflectance in visible band.Canopy reflectance decreases with the increasing of chlorophyll content.Canopy reflectance increases with the increasing of view zenith angle.However,the influence of view zenith angles on canopy reflectance decreases when LAI is high.Under the same view zenith angle,with the increase of chlorophyll contents,corresponding NDVI values increase.Under constant content of chlorophyll,NDVI increases with the increase of LAI.When LAI is 1,under different chlorophyll contents,with the increase of view zenith angles,NDVI shows a trend of first decrease and then increase where the inflection point is at the zenith angle of 65°or 70°.However,NDVI presents a decreasing trend when LAI is 3.5 or 7.When chlorophyll content is higher,the influence of view zenith angles on NDVI is low.When LAI is great and chlorophyll content is low,NDVI decreases rapidly with the increase of view zenith angle (>70°).