Özet:
Predictions of the fourth-order small perturbation
method (SPM) are examined for scattering from two rough surfaces
in a layered geometry. Cross-polarized backscatter, in particular,
is emphasized because use of the fourth-order SPM is
required to obtain this quantity. The formulation of the SPM
fields and incoherent ensemble-averaged normalized radar cross
sections (NRCSs) up to the third and the fourth order in surface
rms heights, respectively, are reviewed. It is shown that the
fourth-order NRCS includes distinct contributions from upper
and lower interface roughnesses, as well as an “interaction” term
that couples the upper and lower interface roughnesses. A comparison
with NRCS values computed using the “numerically exact”
method of moments in the full bistatic scattering pattern is shown
for verification, and NRCS values at the second and the fourth
order are compared in order to assess the convergence of the
SPM series. Although the number of parameters inherent in the
two-layer rough surface scattering problem makes an exhaustive
study of scattering effects difficult, several illustrative examples
are presented to capture a range of scattering behaviors. The results
emphasize the importance of interactions between the rough
surfaces in producing cross-polarized backscattering and also
indicate an increased significance of fourth-order contributions in
the two-layer geometry as compared to the single-layer case.
