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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
compatible with the radar look angle present the highest values
in the cross-polar signature. The case of z/4 titled dihedrals is
little presented in this figure, for high intensity of the cross-
polar components, an ellipticity angle equal to 45° and an
orientation angle close to 180°.
In the forest co-polar signature, the highest values of intensity
are observed for an ellipticity angle close to 0° and an
orientation angle close to 160° (figure 4). In this case,
polarization is almost horizontally oriented (i.e., Sy, presents
high value and S,, a value close to 0). Consequently, several
areas in the forest environment denote a dipole like scattering,
resulting from the a) volume scattering, i.e. wave scattered by
branches and/or leaves, b) contribution of two scattering types,
dihedral and surfaces. The latter occurs because a resolution
cell can represent either a trunk to ground interaction which
denotes the double scattering mechanism, or a uniform smooth
arca which denotes a surface scattering mechanism. Although
forest leaves are randomly oriented, they fit more to horizontal
dipoles. Thus, the forest signature presents low values of co-
polar intensity for an ellipticity angle close to 0° and an
orientation angle close to 70° (figure 4), i.e. for waves that are
vertically polarized (S,, presents a high value and S, à value
close to 0). In the forest cross-polar signature (figure 4), like in
that of urban areas, the radar look angle defines the orientation
of high cross-polar intensities. The case of n/4 titled dihedrals is
strongly presented in this figure for high intensity of the cross-
polar components, an ellipticity angle equal to 45° and an
orientation angle close to 180°.
(a) (b)
Figure 4. a) The co-polar and b) the cross-polar signature of the
forest area
In the vegetation co-polar signature, we observe high values of
intensity for an ellipticity angle close to 0°, and orientation
angles close to 160° and 80° respectively (figure 5). This means
high return of the wave scattered by horizontally and/or
vertically oriented dipoles. The low intensity values, which we
observe for an ellipticity angle close to -45° and an orientation
angle close to 0°, denotes the surface scattering type of smooth
surfaces like bare soil or sowed fields. In contrast to the forest
signature, vegetation signature denotes an organization of the
DEV TE
Figure 5. a) The co-polar and b) the cross-polar signature of the
vegetation
scatterers which allows them to act either as horizontal (leaves)
or vertical (trunks) dipoles. In the vegetation cross-polar
signature (figure 5), the case of 7/4 titled dihedrals is strongly
presented.
283
In the runway co-polar signature (figure 6), the lack of returned
wave is observed for almost the entire range of values of the
ellipticity angle, i.e. for random ellipses. Indeed, low intensity
values are observed for an orientation angle close to 0*.
Figure 6. a) The co-polar and b) the cross-polar signature of the
runway
Furthermore, this signature is similar to that of the vegetation -
dipole like scattering — presenting, however, lesser intensity
values. Dipoles are formed along the runway by the
contribution of two scattering types, dihedral and surfaces.
This occurs because a resolution cell can represent either a
grass to ground interaction which denotes the double scattering
mechanism, or a uniform smooth area which denotes the
runway surface. In the runway cross-polar signature (figure 6),
the case of 7/4 titled dihedrals is slightly presented.
3.2 Interpretation of the Pauli signatures
The Pauli components are computed as following:
Pauli 12 8, 758
Pauli 2 =
Pauli 3 =
i (16)
S In d: 5 vh
S hh + S
where Paulil denotes the even bounce component, Pauli2 the
45? titled even bounce component, and Pauli3 the odd bounce
component. For each of the 3 components we calculate the
absolute value, we scale it with an exponent of 0.7 and assign a
color. Red color is assigned to Paulil, green to Pauli2, and blue
to Pauli 3. Pauli signatures are extracted from the color
composition of the three components.
For the urban area the red color, i.e. dihedrals, dominates
(figure 7). The orientation of the streets is consequently
extracted. Surface scattering type (green) and 45" titled
dihedrals (blue) are less presented. There are also areas in
which all the scattering mechanisms detected by the Pauli
method are simultaneously presented. These areas are shown
with white
(c
Figure 7. Color composition of the Pauli analysis for the a)
urban, b) forest, c) vegetation, and d) runway class
