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Table of Contents
Foreword
Preface
Glossary

Chapter 16: Water Resources

16.42: 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 east bank, facing the direction from which waves were propagated, is light-toned 5 compared with the west bank 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 1 and the flooded area 2, which are light-toned, are visible, some parts are obscured by cloud 3. In contrast to the radar image, treed areas are dark-toned 4, and PR 259 is light-toned 5 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

Figure 16.42: Comparison of a Radar Image and a Vertical Air Photo of Flooding in the Assiniboine Valley Near Virden

A.    Radar Image

Platform: Convair 580 Plane

Imaging system: Synthetic Aperture Radar (SAR)

C Band

HH Transmit/receive polarization

Scale: 1:31,700 (approx.)

Date: April 22, 1995

Location: Township 10 and 11; Range 25WI

Map sheets: 1:250,000 62F Virden

              1:50,000 62F/15 Virden

B.    Air Photo

Flight height: ; lens focal length:

Scale: 1:19,000 (approx.)

Date: April 22, 1995

Location: Township 10 and 11; Range 25WI

Map sheets: 1:250,000 62F Virden

                                1:50,000 62F/15 Virden