| The Assiniboine River near Virden, Manitoba |
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Natural Resources Canada > Earth Sciences Sector > Priorities > Canada Centre for Remote Sensing
Tour Canada from space The Assiniboine River near Virden, Manitoba
 This airborne radar image was acquired on April 22, 1995 during a major flood of the Assiniboine River. It is easy to identify the area which has been flooded. The very dark tones represent the maximum extent of the flood waters. The bright curvilinear feature contains the main river channel (thin, dark line) surrounded by flooded vegetation (bright, irregular areas). The town of Virden is visible in the western portion of the image. Wetlands and ponds, fluvial features and agricultural fields are all recognizable components of this radar image.
Question: Why is the vegetation along the main river channel so bright? Or in other words, why is there so much radar
backscatter from these features? [ Answer ]
About this Image
| Location: |
The Assiniboine River near Virden, Manitoba |
| NTS map(s): |
62 F (1:250,000) |
 Location Map: |
See a detailed map (1:1M) of the region |
| Image Date: |
April 22, 1995 |
| Satellites/Sensors: |
CRS airborne Synthetic Aperture Radar (SAR), C-Band HH-Polarized |
| Resolution: |
30 m pixels |
| Image Area: |
13 km by 18 km |
| Image Features: |
River, flooded landscape, agricultural fields, wetlands, lakes, town, roads, railroad |
| Related Tour Images: |
Melfort, Saskatchewan |
| Related Glossary Terms: |
These terms from the CCRS Glossary may help you to understand this image and its interpretation:
dihedral reflector, SAR, backscatter, tone |
| Related Tutorial Sections: |
These sections of the "Fundamentals of Remote Sensing" tutorial by CCRS will help you to better understand this image and its interpretation:
3.5 3.6 5.5
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| Image Credits: |
Collected, processed and provided by the Canada Centre for Remote Sensing |
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Additional
Information: | The Assiniboine River is a typical meandering river with a single main channel embanked within a flat, shallow valley. Since 1967, the flow of the Assiniboine River has been controlled by a dam located at Shellmouth. However, several important tributaries of the Assiniboine River are drained downstream of the dam, thus increasing the stream flow during a runoff period. During the spring of 1995, above normal snow fall was experienced in much of the countryside that drains into the Assiniboine. When the spring melt arrived, a tremendous runoff and then flood was experienced. The highest flow rates recorded since the construction of the dam were made at a number of local monitoring stations. For more information regarding the Assinboine's flow rates during the flood, please see Flood Mapping of the Assiniboine River. Synthetic Aperture Radar (SAR) imagery is particularly useful for monitoring catastrophic events such as floods. SAR instruments carried by satellites (such as RADARSAT) will make it timely and convenient to map and monitor such events, even in darkness or through cloudy conditions. |
| Question: |
Why is the vegetation along the main river channel so bright? Or in other words, why is there so much radar backscatter from these features? |
| Answer: |
An interesting radar phenomenon is responsible for this. When radar energy is emitted from the sensor it is first deflected directly away from the antenna by the smooth water surface (a specular reflector). After bouncing off the water, the radar beam encounters the vertical trees and is directed back to the antenna, resulting in a strong and therefore bright signal in those parts of the scene. This is termed "corner reflection". This combination of flat water and standing vegetation is a particularly good example of a "natural" corner reflector. |
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