4.7 Radar Images of Terrains

4.7 Radar Images of Terrains

The biggest effect of microwave backscattering on variations in the radar image is due to terrain features. It is larger than the effect of permittivity. Particularly the effect of incident beam angle in terms of off nadir angle and terrain slope will produce various effects such as foreshortening, layover and shadow as already explained in section 4.4.

Normally in the closer range from SAR, called near range, layover may occur while in the far range more shadow may be seen. This means that care should be taken with the flight direction and range direction in interpretation of terrain features.

Figure 4.7.1 shows an example of a SAR image of SEASAT around the mountainous areas of Geneva, Switzerland.

Figure 4.7.2 shows the effect of terrain and off nadir angle on foreshortening, layover and shadow.

Usually foreshortening and layover appear as a bright response around the summit or ridge, while shadow appears black without any information in the shadow area.

As seen in the figure, the effect of microwave back scattering can be better seen along the track or azimuth direction than in the cross track direction.

By interpreting the radar image, land form classification, lineament analysis, mineral resources exploration, monitoring of active volcanoes, land slide monitoring, geological structure analysis and so on can be carried out.

Two parallel flights may produce a stereo pair which will offer the elevation information on terrain features. Recent work is Canada has demonstrated that terrain elevation information can also be derived from the use of interferometry with a single flight line.