Optimal vegetation index for assessing leaf water potential using reflectance factors from the adaxial and abaxial surfaces

Leaf water potential (LWP) is an effective indicator of plant water deficit. Determining the LWP by remote sensing can contribute to quick and non-destructive drought assessment. The purpose of this study was to investigate the quantitative relationship between LWP and different vegetation indices (VIs). Some previous indices and new indices proposed in this study were used to determine LWP. Our results showed that most of the previously published vegetation indices had a strong correlation with LWP based on measurements conducted on the adaxial leaf surface; however, the correlation between LWP and VIs derived from the reflectance factor of both the abaxial and adaxial surfaces was relatively poor. Based on the optimization process of the reflectance factor indices, a modified DATT (MDATT) index (R-1740-R-2370)/(R-1740-R-1750), which had the strongest correlation with LWP, is proposed as a new indicator for the remote assessment of LWP considering different leaf structures (R-2 = 0.85, P < 0.01 for two leaf types based on measurements from both the adaxial and abaxial surfaces). This new index is insensitive to the adaxial and abaxial leaf surface structures; therefore, LWP can be accurately estimated. This new index can provide scientific guidance for monitoring the water status, growth, and health conditions of vegetation.