The latest generation of fully polarimetric, ultra wideband (UWB), wide ang
le, low frequency, foliage and ground-penetrating synthetic aperture radars
(SARs) record huge amounts of data that must he processed to focus high qu
ality images. At the same time only a few small subimages contain important
information. We investigate the relationship between the focused image and
the reflectivity profile and show that a linear shift-invariant model adeq
uately represents the overall process when the focusing is done with a back
projection algorithm over a constant integration angle, The derived signal
model can be used to replace many computationally expensive processing tech
niques, previously performed on the raw data, with equivalent postprocessin
g algorithms which can be applied selectively to subimages.