MICROWAVE PERMITTIVITY MEASUREMENTS OF 2 CONIFERS

Complex permittivity spatial distributions of two conifers, a 5.0-m hi gh Caucasian fir (Abies Normanniana) and a 1.9-m high spruce (Picea Om orika), have been measured in the frequency range 1-10 GHz. Unlike ear lier studies, particular attention was paid to the anisotropy of the d ielectric properties. The measurements were performed in the frame of polarimetric scattering, and imaging experiments conducted on both tre es in the European Microwave Signature Laboratory (EMSL), Space Applic ations Institute, Joint Research Centre, Ispra, Italy. They will be us ed, together with carefully established architectural models of the tr ees, to validate forest remote-sensing algorithms. The measurement met hod was based on an open-ended coaxial probe reflection technique with a rational function approximation model for the probe tip aperture ad mittance. With this model, no calibration on reference liquids is requ ired and sufficiently accurate results for the dielectric constant and loss factor can be obtained. Results are presented for branches, part s of the trunks, and needles from different tree heights. Values obtai ned with the probe oriented along different stem directions of the tru nk confirm the anisotropic nature of wood. The longitudinal complex pe rmittivity is roughly 1.5-three times higher than the transverse compo nent. Inside the trunk, early and late wood layers and small heterogen eities give rise to fluctuations; the phloem layer and the new needles have the highest complex permittivity, Representative average values for trunks, branches, and needles for modeling purposes are also given .