Geology Reference
In-Depth Information
Table 8.2 Backscatter coefficient of ice types and OW during the early freezing period (September to December) in the
Eastern Arctic.
No. of
Homogeneous
Polygons
Initial Backscatter
from Homogenous
Polygons, b m (dB)
No. of
Heterogeneous
Polygons
Estimated Backscatter
from All Polygons,
b es (dB)
Difference,
b es b in (dB)
Ice Type
Incidence angle 20°-30°
OW
13
−6.344
240
−13.049
−6.705
NI
13
−15.224
194
−15.375
−0.151
Nilas
6
−18.995
32
−19.368
−0.373
GI
1
−14.687
195
−13.640
−1.047
GWI
1
−12.356
48
−15.339
−2.983
FY thin
3
−13.002
FY thick
7
−11.450
122
−11.184
0.266
SY
61
−11.346
MY
6
−12.394
203
−11.680
0.714
Incidence angle 30°-40°
OW
22
−18.680
240
−19.414
−0.734
NI
24
−19.450
184
−20.142
−0.692
Nilas
5
−21.802
38
−21.412
0.390
GI
7
−16.691
239
−17.036
−0.345
GWI
1
−15.000
18
−17.656
−2.656
FY thin
1
−27.122
FY thick
9
−12.525
179
−13.336
−0.811
SY
2
−14.120
38
−14.296
−0.176
MY
2
−12.828
210
−12.444
0.384
Incidence angle 40°-50°
OW
28
−20.834
277
−23.446
−2.612
NI
29
−21.573
247
−21.342
0.231
Nilas
−22.000
9
−21.548
0.452
GI
1
−21.168
153
−15.904
5.264
GWI
4
−19.119
12
−22.187
−3.068
FY thin
FY thick
5
−13.527
195
−14.612
−1.085
SY
1
−13.709
19
−15.820
−2.111
MY
3
−15.527
192
−13.717
1.810
Note : Data are obtained from CIS Radarsat analysis that incorporates IAPs of homogeneous as well as heterogeneous ice types.
Backscatter from homogeneous polygons is the arithmetic average from all pixels while backscatter from heterogeneous
polygons is calculated using the technique described in Shokr [2009].
view) generate more backscatter than the shallow angles
(at the far end of the swath). However, the local incidence
angle, which takes surface slope into consideration, is
the  parameter that actually determines the scattering
backscatter value. Moreover, higher backscatter is also
expected from rougher ocean surface (i.e., at higher wind
speed). Therefore, the backscatter from the ocean surface
is usually determined as a function of both wind speed
and radar incidence angle. A few empirical equations are
presented in the literature to describe this relationship.
Shokr [2009] developed an equation using two data
sources: (1) calibrated backscatter from Radarsat‐1
scenes in the Gulf of St. Lawrence, eastern Canada, dur-
ing the winter of 2003 and (2) nearly coincident wind
speed at 12 m above the sea level calculated from the
Global Environmental Multiscale (GEM) weather model
(the operational weather model used at the Canadian
Meteorological Centre). The equation takes form of a
second‐order surface polynomial (note that it applies to
the C‐band, HH polarization):
2
2
0
i i
dV
(8.8)
ij
i
0
j
0
where σ 0 is the backscatter coefficient in dB, V is the wind
speed in m/s and α , is the incidence angle in degrees. Data
were obtained from 6152 pixels of OW in several scenes.
The coefficients d ij are given in Table 8.3. The application
of this equation is limited to a range of α between 20° and
 
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