Three-dimensional synthetic aperture radar imaging of a fir tree: first results

A three-dimensional (3D) inverse synthetic aperture radar (ISAR) imaging experiment on a fir tree is described. Radar measurements on single trees under laboratory conditions can be performed in the scatterometric, with no aperture synthesis, and in the imaging (SAR) mode. Imaging an entire tree requires the use of a wideband radar and a two-dimensional (2D) aperture which may be synthetic or real. A 3D ISAR image can be obtained by processing- coherently the backscattered fields as a function of the frequency and two rotation angles about axes which are mutually orthogonal. With such a system, and by conveniently processing the acquired data, the major scatterers and their positions within the tree volume can be identified with a high spatial resolution. The obtained 2D and 3D polarimetric ISAR images show that this new technique can be used to support the understanding of the interaction of electromagnetic waves with natural targets and provide the basis for the validation and verification of existing models.