Image Processing Reference
InDepth Information
k
y
k
x
Back scattered data
Forward scattered data
Figure 5.1
Spatial frequency space or
k
space map showing that the forward scattered field data lies close
to the origin and backscattered data lies furthest from the origin assuming that the target is illuminated from the

x
direction.
Green's function, which for this (and most) cases is assumed to be Green's
function for free space (Chew, 1995; Lin and Fiddy, 1990). It is this assumption
that also leads to the Fourier transform relationship being exploited as seen
elsewhere in this text on the discussion on the Born approximation. However,
as mentioned above, the back propagation step generates a field distribution in
k
y
k
(
r
inc

r
sct
)
Ewald
limiting circle

k
r
sct

k
r
inc
k
x
2
k
2k
2
k
Ewald circle
Figure 5.2
Fourier space (
k
space) of the object as a result of interaction of different incident plane waves
with scattering object. The direction of the incident field
r
inc
and the direction
r
sct
of a particular plane wave compo
nent of the scattered field define a point at the Ewald circle. Changing incident field directions
r
inc
fills the interior
of Ewald limiting circle.
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