Plant Water Stress Detection Using Radar: The Influence Of Water Stress On Leaf Dielectric Properties

Wednesday, 17 December 2014
Tim Hans Martin van Emmerik1, Susan C Steele-Dunne1, Jasmeet Judge2 and Nick Van De Giesen1, (1)Delft University of Technology, Faculty of Civil Engineering and Geosciences, Delft, 5612, Netherlands, (2)Univ Florida, Gainesville, FL, United States
Recent research on an agricultural maize canopy has demonstrated that leaf water content can change considerably during the day and in response to water stress. Model simulations suggest that these changes have a significant impact on backscatter, particularly in times of water stress. Radar is already used for several vegetation and soil monitoring applications and might be used for water stress detection in agricultural canopies. Radar observations of the land surface are sensitive because it results in two-way attenuation of the reflected signal from the soil surface, and vegetation contributes to total backscatter from the canopy itself. An important driver that determines the impact of vegetation on backscatter is the dielectric constant of the leaves, which is primarily a function of their moisture content. Understanding the effects of water stress on the dynamics of leaf dielectric properties might shed light on how radar can be used to detect vegetation water stress. Previous studies have investigated the dielectric properties of vegetation. However this has mainly been done using destructive sampling rather than in-vivo measurements. Unfortunately, few in-vivo measurements of vegetation dielectric properties exist. This study presents datasets of in-vivo dielectric measurements of maize leaves, taken during two field experiments. One experiment was done using was done during a period of water stress, the other during a period without. Field measurements revealed a vertical profile in dielectric properties during both the period with and without water stress. During a period of increased water stress, the diurnal dynamics of leaves at different heights responded differently to a decrease in bulk moisture content. This study provides insight in the effect of water stress on vegetation dielectric properties and highlights the potential use of radar for water stress detection in agricultural canopies.