Electromagnetic Scattering from Foliage Camouflaged Targets

Mojtaba Dehmollaian and Kamal Sarabandi

Characterization
of scattering from camouflaged targets is one of the most challenging problems
in the area of remote sensing. Fig.1 describes such a problem scenario, where a
complex target is reradiated by myriads of nearby foliage particles. In order
to solve the forward problem, the scattering problem is divided into three
parts: 1) modeling of propagation through and scattering from the forest, and
2) calculation of scattering from the hard targets, illuminated by an arbitrary
field, and 3) computation of scattering interaction between the hard target and
foliage around it.

The first part of the
problem is solved by employing a single scattering foliage model. This is a coherent model that
preserves the geometry of tree structures using a statistical Lindermayer system. Tree constituents are modeled by
dielectric cylinders and disks, whose scatterings are analytically derived
using high- and low-frequency techniques which are valid in both the near-field
and far-field regions of the foliage scatterers. The
scattered field from all tree components and the attenuated incident field are
used as the excitation for the hard target. The second part, computation of the
scattered field form an isolated target, can be solved using exact or
approximate numerical methods. For relatively low frequencies, we used the
finite difference time domain (FDTD) technique to compute the scattered field
from the hard target. For higher frequencies on the other hand we employed the
iterative physical optics (IPO) approximation. The connection between these two
models, that accounts for the interaction between the
foliage scatterers and the target and vice versa, is
accomplished through the application of the reciprocity theorem.

As
an example the backscattered RCS of a camouflaged metallic tank inside a pine
stand forest as a function of incidence angle is shown in Fig.2. In this
simulation frequency of operation is 2 GHz and the scattering effect of two
adjacent trees is taken into account. Pine trees are generated by the
statistical L-system having an average height of 15 *m*, crown radius of 3 *m*, crown height of 10 *m*, trunk radius of 10 *cm*. Each tree consists of about 5000 scatterers.

Fig.1 Fig.2