A forward scattering model for foliage camouflaged complex targets

Detection and identification of hard targets inside vegetation canopies are among the challenging problems in remote sensing. The two challenging problems are (1) computation of the field propagation through and scattering from foliage; (2) characterization of the scattering from the target illuminated by the attenuated incident field and scattered field from foliage. An accurate hybrid method is proposed to characterize the effects of scatterings from forest components and their near field interactions with the hard target. Electromagnetic (EM) scattering from vegetation canopies can be simplified in terms of problems of scattering from individual dielectric cylinders and thin dielectric disks, modeling branches and leaves, arranged in a semi-deterministic fashion. The coherent summation of all the scattering contributions is considered in order to accurately compute the total field at a given point with in the forest canopy. The total field is composed of the mean field and scattered field and the mean field is derived, using Foldy´s approximation. The total field is used as the excitation to illuminate the hard target which may have complex geometry and material properties. In order to have some level of accuracy and computational efficiency, physical optics (PO) approximation, is proposed as a solution for the problem of scattering from electrically large objects. It is shown that reciprocity theorem can be effectively applied to derive the back scattered field from the induced PO currents on the target. By this, the interactions of target and foliage on both illumination and scattering are taken in to account. The challenging step in this process is to determine lit and shadowed points on the target, considering the very complex geometry of the target and very large number of the scatterers around the target, which act as a source of illumination for the target. A powerful technique is proposed to accurately and effectively calculate the induced current on the target including the effects of shadowing. This model has been applied to a simple geometry´ of PEC box and the reciprocity theorem is used to estimate the back scattered field from the object.