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For industrial regions, which contain buildings mostly clad
in metallic materials, the slope of the roof will also be
important. If the roof is positioned such that the radar is
incident perpendicular to the surface the radiation will be
reflected directly back to the antenna. The radar
backscatter will be exceptionally high due to the roofs
high conductivity.
POLARISATION SIGNATURES IN THE URBAN
ENVIRONMENT
Multipolarised radar provides much more information than
individual cross or co-polarised radar. The polarisation
signature shows the co-polarised or cross-polarised
backscatter received as a function of the radars
transmitting polarisation. The polarisation of a wave can
be described by its ellipticity and orientation angle (Ulaby
and Elachi, 1990). The ellipticity describes the flatness of
the ellipse, from a line (where the ellipticity angle is 09),
to a circle (ellipticity angle is 450 ). The orientation angle
describes the orientation of the major axis of the ellipse
with respect to the horizontal. For example, a plane
polarised horizontal wave would have an ellipticity of O 0
and an orientation of 90°, while a circularly polarised
wave would have an ellipticity of 459 or -459 and an
orientation between -90° and 90.
A polarised wave may also be described as containing a
vertical and horizontal component separated by a phase
difference. A perfectly conducting dihedral corner reflector
(Figure 4a) undergoes a phase shift of 180 degrees
during reflection, whilst a smooth flat surface undergoes
almost no phase shift. These are commonly termed
double and single bounce, or even and odd bounce
scattering mechanisms.
The polarisation signature contains valuable information
for determining the characteristics of a surface. Trees, for
example, can give a high cross-polarised response which
may help distinguish between some residential and
commercial classes since residential areas are more
likely to contain a higher proportion of trees (both in
gardens and along roads).
Figure 2. Simulated Backscatter from Components of Residential Building with
respect to Radar Look Direction.
RN RWI lo Te TRE Gral
£a
= front wall
o
s VUE AK e o D 7 5 E au o ef IM mA IB: TX dique front roof
5
i gif eer 7 back roof
=
#4 es ET A S o o XY 1 d rr PTT side wall
phi (degrees)
Figure 3. Simulated Backscatter from Components of Industrial Building with
respect to Radar Look Direction.
(v? HRI tal
ea
= front wall
= "IEEE SEAT en. RAM RAR AA. A uou d | oes
3 = front roof
£ sssssanensncn DACK TOOË
a
X :1080:d. c4 ^! neu VIC — 1 NM .DBXBM LEA AD AR es side wall
A ; à NE eo se
duds; + 85% SES AS Mb RR
phi (degrees)
HELF
711
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
