Geology Reference
In-Depth Information
volume scattering in this medium. For the rough melt
pond water
presented in dB. The SPAN represents backscatter, which
is usually expressed in dB. The other two parameters can
be presented in linear scale but they are presented in dB
to be consistent with the SPAN in the same graph. For
example, if
0
0
stabilizes beyond 40°. In general, the
hv
hv
can reach values below the noise floor of a space‐borne
SAR especially at high incidence angle. The authors
reported that all measurements presented in Figure 8.12
are consistent with model and experiments results from
snow‐covered FY ice presented by
Nghiem et al.
[1995]. It
appears that
0
is −12 dB, then the
co‐polarization ratio
R
hh
/
vv
in dB will be (
0
is −10 dB and
vv
hh
0 0
), i.e., 2.
On the linear scale it is 1.585. That is why some values of
R
vv
/
hh
are positive in the graph, meaning that
vv
hh
0
can be used to discriminate between ice
and rough water at low incidence angles. These measure-
ments, however, may not apply to open water in the
ocean.
The three polarimetric parameters in Figure 8.13 are
the total power (SPAN), the co‐polarization ratio (
R
vv
/
hh
),
and the depolarization correlation coefficient (
R
depol
)
[see definitions in section 7.6.2.3 and note that the co‐
polarization ratio presented in the figure is the inverse of
the ratio given in equation (7.82)]. All parameters are
0
is higher.
This is particularly noticeable in the case of rough melt
pond water at higher angles (60° and above), which are
around the Brewster angle (section 7.3.2).
The total power (SPAN) is dominated by the contribu-
tion from the co‐polarization backscatter as shown in
Figure 8.12. It decreases gradually with the incidence
angle for the smooth FY ice and hummock MY ice
surfaces and sharply in the case of rough pond water. As
expected, MY ice has higher values than FY ice. Its high
hv
vv
10
10
Smooth FY ice with a snow
cover of 41 cm
Snow-free MY ice hummoch
5
5
0
0
-5
-5
-10
-10
-15
-15
-20
-20
Span
R
depol
R
υυ
/hh
Span
R
depol
R
υυ
/hh
-25
-25
-30
-30
20
30
40
50
60
70
20
30
40
50
60
70
Incidence angle (deg.)
Incidence angle (deg.)
10
Rough melt pond on FY ice
5
0
-5
-10
-15
-20
Span
R
depol
R
υυ
/hh
-25
-30
20
30
40
50
60
70
Incidence angle (deg.)
Figure 8.13
Plots of three polarimetric parameters in the C‐band: SPAN, the depolarization correlation coefficient
(
R
depol
), and the co‐polarization ratio (
R
vv
/
hh
) from FY ice, MY ice, and wind‐roughened melt pond on FY ice. Data are
compiled from the three field experiments in the Arctic as mentioned in the text. Fit lines are quadratic equations.
Error bars represent standard deviation. All ratios are presented in dB [adapted from
Geldsetzer, et al.,
2007].
