Monitoring of Wheat Stripe Rust Using Red Band SIF Modified by Pseudokurtosis

The red band of solar-induced chlorophyll fluorescence (SIF) is closely related to the photosynthetically active radiation absorbed by chlorophyll, which is of great significance in stress monitoring. The scattering and reabsorption of red band SIF by the vegetation canopy caused significant changes in the spectral intensity and shape of SIF, which affected the relationship between SIF and crop stress. We proposed a method to modify the red band SIF by using SIF spectral shape characteristic parameters to reduce the influence of chlorophyll reabsorption and canopy geometry on the red band SIF intensity. We used the full-spectrum SIF spectral curve to calculate the red band pseudokurtosis (PKB) parameters that can characterize the spectral shape features. Based on the SCOPE model, the photosynthetic physiological mechanism of PKB was analyzed, and the expression of PKB to modify red-band SIF was constructed. To evaluate the performance of modified red band SIF in monitoring the severity of wheat stripe rust, the correlation between red band SIF and the disease severity level (SL) before and after PKB modification and its model accuracy were compared and analyzed by using measured data. The results showed that the introduction of PKB increased the Pearson correlation coefficient between the red band SIF and the SL in the plot control experiment and the natural disease field experiment (53.44% and 5.17%), and the root mean squared error between the predicted SL and the measured SL decreased from 0.166 to 0.148. We further verified the effectiveness of the shape feature parameter PKB on red band SIF revision by using the red band SIF after VI fusion. The results showed that the red band SIF modified by PKB could weaken the effect of chlorophyll reabsorption and canopy geometry on red band SIF and improve the ability of red band SIF to detect stress information.