Geology Reference
In-Depth Information
It concluded that at wind speeds <13 m/s OW can be
effectively discriminated from all ice types except thin ice.
A study of polarimetric backscatter measurements from
newly formed sea ice using a ship‐based scatterometer is
presented in
Isleifson et al.
[2010]. Once again, it offers
a limited data set, but it shows the sensitivity of the
co‐polarizarion ratio
R
hh
/
vv
to the thickness of thin ice.
It also shows the effect of some surface conditions such
as frost flowers on polarimetric parameters. By removal
of frost flowers a decrease in backscatter coefficient
(from co‐ and cross‐polarization signals) was noticed.
The decrease was quantified as 4.5, 8.3, and 7.0 dB for
image, for example, thin ice is the dark areas, MY ice
floes are the bright areas, and the gray areas are FY ice.
Visual interpretation reveals a few observations about the
performance of each parameter. The co‐polarization and
the SPAN images can be used for ice type classification.
The entropy and alpha‐angle images enhance the identifi-
cation of ridges and can add to the discrimination capa-
bility of the co‐polarized image. The pixel values from
MY ice in both images are considerably smaller than the
values from FY ice. Small entropy values mean that the
scattering is limited to one mechanism (presumably ran-
dom volume scattering from hummock ice surface). On
the other hand, small alpha‐angle values means that the
scattering is from smooth surface (again, presumably
smooth hummocky surface). The scattering from FY
ice encompasses single, double, and random volume
bouncing due to its variety of surface structure. Note
the similarity between the entropy and alpha‐angle
0
, respectively.
Figure 8.15 shows images of polarimetric parameters
of a sea ice scene from the Arctic in the summer. It
includes the three major ice types (thin, FY, and MY ice),
which can be visually identified in the co‐polarization
(HH or VV) images and in the SPAN images. In the HH
0
,
0
, and
hv
vv
hh
HH
VV
HV
SAPN
Anisotropy
Entropy
Alpha angle
Correlation
Figure 8.15
Images of polarimetric parameters (section 7.6.2.3) of summer sea ice scene in the Arctic.
