High-resolution microwave polarimetric imaging of small trees

A planar near-field monostatic imaging system is employed at a frequency of 10 GHz to examine the polarimetric scattering characteristics of small dec iduous trees. Two-dimensional (2-D) images are produced in a format familia r to the human visual system, and the technique is intended to be of value in synthetic aperture radar (SAR) image interpretation. The theory utilized for the plane-to-plane imaging algorithm is presented, and the experimenta l configuration used is described. The polarimetric response of the system is evaluated by using a target composed of thin copper wires orientated at 0, 45, and 90 degrees to the vertical axis. The series of images obtained f or VV-, VH-, and HH-combinations of the transmit-receive antennas indicate that the polarization parity of this prototype system is better than -35 dB , Results are presented for three different species of tree, ash (Fraxinus excelsior L.), sycamore (Acer pseudoplatanus L,), and willow (Salix species ), with heights in the range 1-1.6 m. The high spatial resolution of 2 cm p rovided by the imaging system reveals detailed information on the structure of each tree, The different RCS responses of living and dead branches are dearly demonstrated, and the presence of multiple reflections between adjac ent branches is seen. Differences between the VV-, VH-, and HH-images corre late well with the orientation of the various components of each tree.