晚霜冻影响下冬小麦冠层红边参数比较

Comparison of Red Edge Parameters of Winter Wheat Canopy under Late Frost Stress

冬小麦受晚霜冻影响的外部症状短期内不明显的特点,为红边光谱的应用提供了契机。利用田间移动式霜箱和低温室系统分别开展不同温度梯度的霜冻试验,基于冻后第1天测定的冬小麦冠层光谱数据,使用最大一阶导数(FD)、四点线性插值(FPI)、多项式拟合(POLY)、倒高斯拟合(IG)和线性外推(LE)等方法分别提取红边参数。通过相关分析、线性回归建模以及波动分析,从早期性、敏感性和稳定性方面对红边参数检测冬小麦晚霜冻的能力进行定量研究。结果表明,LE方法提取的红边位置(REP)与霜冻温度的相关性为极显著(显著性水平达到0.01),二者相关系数高于其他方法;REP随霜冻温度的降低而呈蓝移现象,温度越低,蓝移趋势越明显。FD方法提取的最小振幅(Drmin)和红边振幅与最小振幅比值(Dr/Drmin)对霜冻敏感性的表现最佳,其次是FD和IG方法提取的红边振幅与红边面积比值(Dr/SDr),敏感性最差的是LE方法提取的REP。总的来看,FD方法提取的Drmin和Dr/Drmin检测冬小麦晚霜冻的综合能力最强。以上结论可为基于冠层红边特征的冬小麦晚霜冻害早期诊断研究提供依据。

In the present study,late frost experiments were implemented under a range of subfreezing temperatures （-1^-9℃）by using a field movable climate chamber （FMCC）and a cold climate chamber,respectively.Based on the spectra of winter wheat canopy measured at noon on the first day after the frost experiments,red edge parameters REP,Dr,SDr,Drmin ,Dr/Drmin and Dr/SDr were extracted using maximum first derivative spectrum method （FD）,linear four-point interpolation method （FPI）,polynomial fitting method （POLY）,inverted Gaussian fitting method （IG）and linear extrapolation technique （LE）,re-spectively.The capacity of the red edge parameters to detect late frost stress was explicated from the aspects of the early,sensi-tivity and stability through correlation analysis,linear regression modeling and fluctuation analysis.The result indicates that ex-cept for REP calculated from FPI and IG method in Experiment 1 ,REP from the other methods was correlated with frost tem-peratures （P＆lt;0. 05）.Thereinto,significant levels （P）of POLY and LE methods all reached 0. 01.Except for POLY method in Experiment 2,Dr/SDr from the other methods were all significantly correlated with frost temperatures （P＆lt;0. 01）.REP showed a trend to shift to short-wave band with decreasing temperatures.The lower the temperature,the more obvious the trend is.Of all the REP,REP calculated by LE method had the highest correlation with frost temperatures which indicated that LE method is the best for REP extraction.In Experiment 1 and 2 ,only Drmin and Dr/Drmin calculated by FD method simultaneously achieved the requirements for the early （their correlations with frost temperatures showed a significant level P＆lt;0. 01）,sensitivity （abso-lute value of the slope of fluctuation coefficient is greater than 2. 0 ）and stability （their correlations with frost temperatures al-ways keep a consistent direction）.Dr/SDr calculated from FD and IG methods always had a low sensitivity in Experiment 2 .In Experiment 1 ,the sensitivity of Dr/SDr from FD was moderate and IG was high.REP calculated from LE method had a lowest sensitivity in the two experiments.Totally,Drmin and Dr/Drmin calculated by FD method have the strongest detection capacity for frost temperature,which will be helpful to conducting the research on early diagnosis of late frost injury to winter wheat.