The incident angle of microwave to a target is the angle from the normal line while the aspect angle is the supplementary angle as shown in Figure 4.4.1. The smaller the incident angle , the larger the back scattering intensity .

Off nadir angle is the angle between the microwave and the nadir, while the depression angle is the angle from the horizon, as shown in Figure 4.4.2. There occurs a geometric distortion or shadow depending on the relationship between the off nadir angle and the terrain relief, as shown in Figure 4.4.3 and Figure 4.4.4. Foreshortening occurs when the ground range difference (horizontal distance X ) is reduced to the slant range difference DR, because the slant range to the top and the bottom are not proportional to the horizontal distances, as shown in the right hand example of Figure 4.4.5.

When the shortening becomes greater, the image of the top of a feature such as a mountain will be closer to the antenna than the bottom, which causes loss of, the slope image, as shown in the left hand example of Figure 4.4.5. This is called layover.

Such phenomena will occur when the terrain relief is greater and the off nadir angle is smaller.

However for large off nadir angles, there will be a shadow area, as called radar shadow, behind a hill or mountain, which makes the image very dark as shown in Figure 4.4.5.

The radar shadow will occur if the following relationship is satisfied.

+ > 90

where : slope angle of back slope
: off nadir angle

The slant range of the shadow is given as sec as shown in Figure 4.4.4.

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