Environmental Engineering Reference
In-Depth Information
(a)
W/m 2
1400
60N
40N
1200
1000
850
750
650
550
450
350
270
190
110
70
20N
EQ
20S
40S
60S
30
0
40E
80E
120E
160E
160W
120W
80W
40W
0
(b)
W/m 2
1400
1200
1000
850
750
650
550
450
350
270
190
110
70
60N
40N
20N
EQ
20S
40S
60S
30
0
40E
80E
120E
160E
160W
120W
80W
40W
0
Figure 14-12. Maps of mean wind power density derived from QuikSCAT for (a) boreal
winter (December, January, and February) and (b) boreal summer (June, July, and August),
for the 8-year period between 2000 and 2007. The gray scale corresponds to topography.
Source: Liu et al., 2008 (9).
interest. 5 Unfortunately, SAR images are expensive. The commercial price for a single
image ranges from a few hundred to a few thousand US dollars, depending on the
satellite and distributor, whereas several dozen to hundreds of images are required
for a statistically reliable estimate of the annual mean wind speed. (Images stored in
archives are significantly cheaper, and some may be available for free through gov-
ernment institutes or research projects sponsored by the European Space Agency or
Canadian Space Agency, for instance.)
For the foreseeable future, SAR is likely to be used as a complement to, rather
than replacement for, on-site measurements and numerical wind flow modeling. Its
importance is likely to grow, however, if SAR image prices come down and methods
of processing large numbers of images improve. One potentially useful application of
5 For a well-distributed sample of SAR images, the total uncertainty on the mean wind speed decreases
approximately as one over the square root of the number of images.
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