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50°. The backscatter values calculated for that range
using a practical range of surface wind speeds are pre-
sented in Figure 8.6. Results are also grouped into bins of
α and V as shown in Table 8.4. These results compare well
with previous results of backscatter measurements and
model output from OW, obtained at different incidence
angles under different wind speeds [ Mouche et al ., 2006].
Shokr [2009] found also that backscatter from OW in the
C‐band HH SAR increases with the wind speed at a rate
less than that of its decrease with incidence angle. In other
words it is more sensitive to the wind speed than incidence
angle. The rate of variation with incidence angle is calcu-
lated from equation (8.8) at wind speed values 10, 20, 30,
and 40 m/s and presented in Figure 8.7. It is interesting to
note that at a wind speed of 35 m/s, the gradient of back-
scatter decrease with incidence angle becomes independ-
ent of the angle (about −0.46 dB/deg.). Studying the
effect of wind speed over ocean on backscatter leads to
developing a capability for wind speed retrieval from
backscatter. Using equation (8.8) for that purpose is
possible, although the solution of such a nonlinear
equation is not straightforward.
A demonstration of the combined effects of radar inci-
dence angle and surface wind speed on the radar
backscatter is shown in Figure  8.8. The figure presents
two Radarsat images of the Gulf of St. Lawrence
acquired on 22 January and 22 February 2003. The
images on the left show the ice analysis polygons deline-
ated during the Radarsat image analysis at CIS by an
ice  analyst. The polygons are colored to represent the
Table 8.3 Coefficients d ij of the nonlinear relation [equation
8.8] that gives the radar backscatter coefficient of the open
water as a function of radar incidence angle (deg.) and wind
speed (m/s) on the other hand for OW.
Angle ( α )
Wind ( V )
i = 0
i = 1
i = 2
j = 0
5.2674
−1.2299
0.01273
j = 1
1.2226
−0.0259
5.35 × 10 −5
j = 2
−0.0338
0.00133
−1.16 × 10 −5
0
-5
-10
-15
-20
-25
Table 8.4 Backscatter coefficient of OW for different wind
speeds and radar incident angle ranges.
Wind speed
0-10 m/s
(dB)
10-20 m/s
(dB)
20-30 m/s -1
(dB)
Angle ( α )
20°-30°
Figure 8.6 Three‐dimenttional graph showing variation of
backscatter from OW with surface wind speed for different
radar incidence angle. Backscatter is calculated from equation
(8.1) [Shokr, 2009].
−13.015
−9.394
−7.375
30°-40°
−19.931
−15.903
−14.314
40°-50°
−22.747
−20.949
−18.714
0.2
inc. angle =20°
inc. angle =30°
inc. angle =40°
inc. angle =50°
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
0
5
10
15
Surface wind speed (m/s)
20
25
30
35
40
45
Figure 8.7 Gradient of backscatter from OW (with respect to radar incidence angle) at different surface wind
speeds at different radar incidence angle. The gradient is calculated using equation (8.8) [ Shokr , 2009].
 
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