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 irt situ monitoring of the dielectric constant of woody vegetation tissue a re presented. The implementation of both single-channel and multichannel sy stems is discussed. These systems permit unsupervised continuous and long-t erm monitoring of vegetation canopy dielectric behavior in remote field sit es. Utilizing open-ended coaxial lines, the real and imaginary parts of the microwave dielectric constant of woody plant tissue are inferred from dire ct measurement of the magnitude and phase of the microwave reflection coeff icient. Samples of in situ data from forests in contrasting ecological envi ronments are presented. Measurements obtained with our systems allow new in sight into the dielectric behavior of vegetation with respect to the physio logical and hydraulic function of trees. The observations provide a signifi cant advance in our ability to link canopy physiological and hydraulic beha vior to radar remote-sensing observations.