An investigation of the relationship between tree water potential and dielectric constant
Results of of the EOS Synergism Study which was carried out near Fresno, California in the summer of 1987 indicate that a strong correlation may exist between the microwave dielectric constant of trees and their xylem water potential as evaporation of water vapor occurs through the leaves. Although this correlation is apparent, no studies have been performed that attempt to explain the nature of this phenomenon. This paper describes an experiment that has been performed to verify the relationship between the dielectric constant of several tree species and their respective water potentials. The water potential, xylem flow and dielectric properties of five tree species were continuously monitored while simultaneously manipulating canopy transpiration and water status. An analysis of the data recorded during these manipulations is presented. Results of this analysis demonstrate a clear coincidence of change in dielectric constant and water status. The implication of this relationship on the utilization of remotely sensed data to study canopy water relations is explored. Preliminary backscatter modeling results demonstrate that the changes in dielectric constant that occur as a result of changes in water status are significant enough to be observable with microwave radar.
