条件植被温度指数的多尺度特性分析与应用

基于2008-2013年关中平原冬小麦单产数据和条件植被温度指数（vegetation temperature condition index，VTCI）的干旱监测结果，分别采用Morlet、Mexican Hat和Paul（m=4）3种非正交小波的功率谱分析冬小麦单产和主要生育期VTCI和单产的多时间尺度特征，借助小波互相关度进一步确定两个时间序列在时频域局部相关的密切程度，并以此构建主要生育期加权VTCI与冬小麦单产间的线性回归模型。结果表明，基于同一小波函数确定的主要生育期VTCI的振荡能量不同，而基于不同小波函数确定的同一生育期VTCI的主振荡周期及其与单产对应的小波互相关系数也存在差异，但各生育时期VTCI均存在着6 a左右的主振荡周期。基于Paul（m=4）小波的各生育时期VTCI与单产时间序列的多尺度相关性分析的效果最佳（R2=0.521），且Paul（m=4）对应的模型的单产估测结果与实测单产的平均相对误差较之于Morlet和Mexican Hat小波函数获得的相对误差分别降低了0.78%和0.30%，表明Paul（m=4）小波函数能更好地用于干旱对冬小麦单产的影响评估研究，也可用于多尺度的干旱影响评估研究。

Analysis and Application of the Multi-scale Characteristics of Vegetation Temperature Condition Index

Based on the collected wheat yields in the years of 2008-2013 in the Guanzhong Plain, China and the drought monitoring results of vegetation temperature condition index(VTCI), the Morlet, Mexican Hat and Paul(m=4) were used to study droughts. Wavelet power spectra of the three non-orthogonal wavelet functions were applied to analyze the multi-time scale characteristics and the cross-correlation degrees of the wheat yields and the VTCIs at the main growth stages of winter wheat. Linear regression models between the yields and the weighted VTCIs at the main growth stages were compared for selecting a better wavelet function for assessing drought impact. The results show that the oscillation energy of the VTCIs using the same wavelet function is different. There are differences of the main oscillation periods determined by three wavelet functions at the same growth stage of wheat, and further there are differences in the wavelet cross-correlation coefficients. The time series VTCIs at the four growth stages of wheat all have a 6-year main oscillation period. The Paul(m=4) wavelet is most applicable to analyze the multi-scale correlation between the VTCIs and wheat yields, and assess the multi-scale drought impact.