Dynamic Change in Rice Leaf Area Index and Spectral Response under Flooding Stress

Analysis of the canopy structure change and spectral response mechanism of rice under flooding stress is an important prerequisite for large-scale monitoring of rice flooding disasters. The leaf area index (LAI) was used as the characterization indicator. The response rule of the canopy spectrum to flooding stress intensity was analyzed. The sensitive spectral characteristic parameters were screened to construct the LAI spectral response model of rice under flooding stress. The results showed that the rice LAI under flooding stress decreased with an increase in waterlogging depth. The spectral reflectance of the rice canopy under flooding stress significantly changed in the near-infrared band and decreased with an increase in waterlogging depth. In 680–760 nm, the double peak in the first-order differential spectrum of the rice canopy was more obvious with advancement of the growth process and a multiple peak appeared during the late growth stage. The blueshift of the red edge parameters was the most obvious in the submerged top during the tillering stage. A power function regression model based on the ratio of the first-order differential spectral amplitude at 737 nm to 719 nm in the red edge range was the optimal LAI response model for rice under flooding stress. A field waterlogging experiment was used to simulate and analyze the influence of flooding on the rice canopy structure and the canopy spectral response rule, providing a reference for the subsequent analysis of rice growth and disaster loss assessment under flooding stress.