Automated instrumentation for continuous monitoring of the dielectric properties of woody vegetation: system design, implementation, and selected in situ measurements

The design and implementation of a system for the automated and continuous in situ monitoring of the dielectric constant of woody vegetation tissue are presented. The implementation of both single-channel and multichannel systems is discussed. These systems permit unsupervised continuous and long-term monitoring of vegetation canopy dielectric behavior in remote field sites. Utilizing open-ended coaxial lines, the real and imaginary parts of the microwave dielectric constant of woody plant tissue are inferred from direct measurement of the magnitude and phase of the microwave reflection coefficient. Samples of in situ data from forests in contrasting ecological environments are presented. Measurements obtained with the authors' systems allow new insight into the dielectric behavior of vegetation with respect to the physiological and hydraulic function of trees. The observations provide a significant advance in our ability to link canopy physiological and hydraulic behavior to radar remote-sensing observations.