EFFECT OF TREE STRUCTURE ON X-BAND MICROWAVE SIGNATURE OF CONIFERS

Experimental studies are performed on some coniferous trees: Austrian pine, Nordmann spruce, and Norway spruce, to investigate the relation between the tree architecture and radar signal at X-band. For a single tree, the RCS is measured as a function of the scatterer location at 90-degrees incidence. It is found that the main scatterers are the lea fy branches and the difference between sigma(vv) and sigma(hh) is sign ificant at the upper portion of the tree. At the lower portion of the tree sigma(vv)o and sigma(hh)o have almost the same level. For a group of trees the angular trends of sigma(vv)o and sigma(hh)o are measured . It is found that the levels of sigma(vv)o and sigma(hh)o are of the same order, but their angular trends vary from one tree species to the other depending on the tree species structure. The interpretation of these experimental results is carried out with the help of a theoretic al model which accounts for the structure of the tree. According to th is theoretical study, the major scattering trend is due to the leaves, while the perturbation to the angular trend and the level difference between sigma(vv)o and sigma(hh)o are due to the branch orientation di stributions, e.g., the tree architecture.