236.

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Figure 1.17 The relationship between angle θ_j and radar shadow.

if one knew what effects are occurring at a given pixel, then one could use suitable algorithms to carry out calibration. As in the case of topographic calibration of optical imagery described above, geometric and radiometric correction of radar images requires a co-registration to a DEM. However, the calibration procedures are generally more complicated. Kwok et al. (1987) and Curlander and McDonough (1991) provide descriptions.

1.6.3 Factors affecting radar backscatter

It has already been noted that a radar image is a record of the strength of the backscatter from the targets making up the imaged area. The stronger the backscatter, the brighter is the corresponding image element. The level of backscatter is determined by terrain conditions (such as roughness and electrical characteristics), and also by the parameters of the radar system. Understanding the factors affecting radar backscatter can help analyse landscape properties more knowledgeably.

1.6.3.1 Surface roughness

Radar backscatter is stronger where the ground surface is rough relative to the radar wavelength. The roughness of a surface is dependent on both the wavelength of the incident energy and the angle of incidence. Rough surfaces act as Lambertian reflectors (Section 1.4), so that incident microwave energy is scattered in all directions and a portion is reflected back to

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