potential to be variable given that the incident angle of the ScanSAR Narrow beam
varied from 20 to 40
. However, it was possible to proceed with a constant pixel
spacing of 25 m for the β
0 images as these images were rectified (at 25-m resolution) by CSA (RADARSAT International 2004), prior to their implementation.
As speckles can hinder the interpretation of radar images, a Gamma-map filter
(with a moving-window of 5 Â 5 pixels) was employed to suppress speckles. Before
filtering, the β
0 values (in dB) were converted to a power-scale, and then
re-calculated into dB values as outlined in Wickel et al. (2001). The three images
were co-registered by simply shifting the images using a stable high backscattering
feature or corner reflector in both the x- and y-directions, as described in Hasan
et al. (2003). Then, these images were geo-coded by using ground control points
Fig. 15.2 Workflow in the
generation of the Wetness
Index (WI)-values and their
comparison to soil water
content (SWC), either
measured in the field or
modeled with the SWAT
model
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Q.K. Hassan and C.P.-A. Bourque