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Manitoba from the Air
Image Options
Show Trace
Description
Comparison of a Radar Image and a Vertical Air Photo of Flooding in the Assiniboine Valley Near Virden

A. Radar Image

Radar has the advantage over air photographs in that it is not light dependant; images can be obtained at night, and if the correct wave length is used it can penetrate clouds. Shown here is a large-scale radar image with a vertical photograph taken at the same time to the right of it. As in figure 16.41 the very dark tones delimit the flooded area 1, the river channel 2, and one oxbow 3. The very light-toned areas on the flood plain are the tree-covered areas 4; the rough surface of the treetops sends back a strong signal. The eastern valley wall, facing the direction from which radar waves were propagated, is light-toned 5 compared with the west-facing valley wall which is dark-toned 6. PR 259, which has a smooth surface and is therefore dark-toned 7, crosses the Assiniboine spillway. The very light-toned spots, north of the road, are pylons 8 carrying an electrical power line. Two other lines of pylons can be seen further south 9, 10.

B. Air Photo

The air photo taken at this same time has a slightly larger scale. Although most of the river channel 11 and the flooded area 12, which are light-toned, are visible, some parts are obscured by cloud 13. In contrast to the radar image, treed areas are dark-toned 14, and PR 259 is light-toned 15 due to light reflection from its gravel surface. There is no evidence of the power lines.

 

Figure 16.42

Comparison of a Radar Image and a Vertical Air Photo of Flooding in the Assiniboine Valley Near Virden