基于无人机载遥感的水分胁迫下冬小麦叶绿素变化及冠层光谱响应

Response of Winter Wheat Canopy Spectra to Chlorophyll Changes Under Water Stress Based on Unmanned Aerial Vehicle Remote Sensing

为探究水分胁迫下冬小麦冠层反射率在各生育期响应叶片叶绿素变化的特性,针对2020年-2021年小麦生长季11个品种(分为强、一般和弱3个抗旱性品系),设置了2次灌溉(拔节、扬花)、 1次灌溉(冬季、返青、拔节、拔节后7天和拔节后14天)以及无灌溉总共3个水分梯度处理,分析了叶绿素与反射率之间的相关性,利用波长随机组合方式[简单比值(SRSI)、简单差值(SDSI)和归一化(NDSI)]与线性拟合方法,筛选了对叶绿素最为敏感的窄波段光谱指数。结果表明:(1)所有品系叶绿素含量在各生育期均差异显著,从拔节到灌浆大致表现为降低-升高-降低态势,但冬季和返青期灌溉处理下的抗旱性一般品系、以及返青期灌溉处理下的抗旱性较差品系除外;(2)随着发育进程推移和品种抗旱性减弱,不同处理间在近红外区域的冠层反射率差距逐渐增大。(3)叶绿素与窄波段光谱指数的线性拟合决定系数高值区集中在绿(445~591 nm)和红边(701~755 nm)波段。抗旱性较强品系和抗旱性较差品系的SRSI指数均在开花期反演叶绿素的精度最高,分别达0.762和0.811;抗旱性一般品系的NDSI指数在灌浆期精度最高,为0.732。该研究对于揭示水分胁迫下叶绿素变化的反射率响应在冬小麦各关键生育期以及品种间差异等,具有一定参考价值,可为基于无人机载高光谱技术的抗旱小麦品种高效筛选奠定基础。

In order to explore the characteristics of canopy reflectance of winter wheat responding to leaf chlorophyll changes in each growth period under water stress,a total of three water gradient treatments were set for 11 wheat varieties(divided into strong,general and weak drought resistant strains)in the growth season from 2020 to 2021,including two irrigation treatments(jointing and flowering),one irrigation treatment(winter,turning green,jointing,7 days after jointing and 14 days after jointing)and no irrigation,The correlation between chlorophyll and reflectance was analyzed.The narrow band spectral indexes most sensitive to chlorophyll were selected by using the random combination of wavelengths(simple ratio(SRSI),simple difference(SDSI)and normalization(NDSI))and linear fitting methods.The results showed that:(2)With the development process and the drought resistance of varieties weakened,the difference of canopy reflectance in near-infrared region between different treatments gradually increased.(3)The high value of the linear fitting determination coefficient of chlorophyll and narrow band spectral index is concentrated in the green(445~591 nm)and red edge(701~755 nm)bands.The SRSI index of drought resistant and drought-resistant strains had the highest precision of chlorophyll retrieval at the flowering stage,reaching 0.762 and 0.811 respectively;The NDSI index of general drought-resistant strains had the highest precision at the filling stage,which was 0.732.This study has a certain reference value for revealing the reflectance response of chlorophyll change under water stress in different key growth stages of winter wheat and differences among varieties.It can lay a foundation for efficient screening of drought-resistant wheat varieties based on unmanned aerial hyperspectral technology.