【摘要】 为了解成像几何关系对叶绿素含量与红边光谱响应之间关系的影响,利用无人机搭载高光谱成像仪对大豆和玉米进行多角度观测并构建二向反射分布函数(BRDF)模型,分析红边波段反射率与叶绿素相对含量(SPAD)的相关性在观测主平面中随观测角度变化的规律。研究发现:1)两种作物红边波段反射率与SPAD值均为负相关,在714 nm处具有最大相关系数(约-0.5);2)BRDF特性的差异导致观测角度对大豆的影响超过玉米,即:后向40°～45°观测可显著提升大豆SPAD值的相关性,而玉米在-30°～30°内不敏感;3)BRDF校正可显著提升无人机航测结果与冠层SPAD值的相关性。结果表明,遥感观测的角度效应严重影响红边波段对冠层叶绿素含量的光谱响应,且不同作物类型间差异巨大;研究结果可为高精度的农作物冠层叶绿素含量反演提供依据。更多还原

【Abstract】 In order to understand the influence of imaging geometry on the relationship between chlorophyll content and "red edge" spectral response,the hyperspectral imaging sensor carried by unmanned aerial vehicle(UAV)was used to observe soybeans and maize from different angles.The correlation between reflectance of red edge bands in the main observing plane and relative chlorophyll content(SPAD) was analyzed by the bidirectional reflectance distribution function(BRDF) model.The results are summarized as follows.1) The reflectance of red-edge bands of soybeans and maize is negatively correlated with the SPAD value,and the maximum correlation coefficients of the two crops are about-0.5,both at 714 nm.2) Soybean and maize show different BRDF characteristics.In addition,the observation angle has more influence on soybean than maize.That is to say,for almost all the red-edge bands,backward 40°～45° observation can significantly improve the correlation of soybean′s SPAD values,while the results of maize are not sensitive to observation angles within-30° to 30°.3) The BRDF correction can significantly improve the correlation between UAV measurements and canopy SPAD values,which is raised from ±0.15 to around-0.3(soybean) and-0.5(maize),respectively.It should be pointed out that,in remote sensing,the angular effect of observation seriously affected the spectral response of red edge bands to the chlorophyll content of canopy,and there were great differences among different crop types.The results can provide guidance for high-accuracy inversion of the chlorophyll content of crop canopy.更多还原