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 deciduous trees. Two-dimensional (2D) images are produced in a format familiar 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 experimental 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° to the vertical axis. The series of images obtained for VV-, VH-, and HH-combinations of the transmit-receive antennas indicate that the polarization purity of this prototype system is better than -35 dB. Results are presented for three different species of tree, ash (Fraxinas 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 provided by the imaging system reveals detailed information on the structure of each tree. The different RCS responses of living and dead branches are clearly demonstrated, and the presence of multiple reflections between adjacent branches is seen. Differences between the VV-, VH-, and HH-images correlate well with the orientation of the various components of each tree