Diurnal-Scale Time Lag between Canopy Temperature and Environmental Factors of Winter Wheat

Abstract

Exploring and quantifying the lag effect between environment factors and canopy temperature can improve the accuracy of using environmental factors to predict canopy temperature. In order to quantitatively analyze the lag relationship, we continuously monitored the canopy temperature (Tc) of winter wheat, and simultaneously collected the data of such environmental factors as net radiation (Rn), atmospheric temperature (Ta), relative humidity (RH) and soil heat flux (SHF). With the synchronous diurnal time series, we analyzed the lag relationships between Tc-Rn, Tc-Ta, Tc-RH and Tc-SHF using the bivariate plot; calculated the lag time at jointing stage, heading stage and filling stage using time-lagged correlation analysis; established the Tc lag response model based on Rn, Ta, RH and SHF respectively using the least square. The results indicated that: in sunny days, (1) the hysteresis loops of Tc-Rn, Tc-Ta, Tc-RH were approximately bow-shaped, Tc-SHF was approximately “figure-8”-shaped, and their directions were anticlockwise, clockwise, anticlockwise and clockwise; (2) in the jointing, heading and filling stages of wheat, Tc was 50 min behind Rn; Ta 40, 30 and 30 min behind Tc respectively; RH 30, 40 and 10 min behind Tc respectively; and no lag was found between Tc and SHF; (3) lag effect could improve the accuracy of the Tc response model, because in the jointing, heading and filling stages, the Radj2(adjusted coefficient of determination) of Tc response model based on Rn (Rn-Tc) had increased 13.46%, 13.64% and 12.32% respectively; the Radj2 of Ta-Tc increased 9.02%, 6.31% and 5.56%; and the Radj2 of RH-Tc increased 6.53%, 9.33% and 1.61%. This study may provide some reference for the research on mechanism influencing canopy temperature change.