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MackenzieDelta_TerraSAR-X.jpg

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Dr. Dick van der Wateren

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remote sensing, radar satellite, TanDEM-X, satellite image

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First images from TanDEM-X satellite

01.07.2010, Age: 2849 days

The first images from TanDEM-X, Germany's new radar satellite were published on the website of Infoterra GmbH.

Mackenzie River Delta, Northwest Territories, Canada. Composite of images taken by TerraSAR-X on 21 September, 13 and 24 October 2009. This image is an example of Infoterra's Amplitude Change Detection Product (ACD) showing the northern extent of the Mackenzie River Delta in Canada's North West Territory.

Acquisitions of the high-resolution radar satellite TerraSAR-X combined in this way are a rapid and easy mechanism for change detection (in this case the freeze-up over a period of time) as the presence and kind of colour represents changes in signal backscatter on the different acquisition dates. 

The colour in the composite contains information about the relative strength of the signal on a certain date: For example, areas that display a relative purity of a primary colour show that the backscatter of the surface was particularly bright in comparison to the other acquisition dates. Areas that do not have a predominance of colour represent a backscatter signal about equal between the three acquisition dates.  

Thus, in this example, the composite reveals the progression of freeze-up over the course of the time period.

The dominance of reddish tones on land areas points to a significant decrease in surface roughness after the first acquisition (Sept 21st) - this could be first snow that fell and reduced the surface roughness of the vegetation during the two subsequent acquisition dates in October. 

In SAR images, due to the specular reflection of the radar signal away from the sensor, calm water areas will appear dark, while the formation of ice increases surface roughness and thus, brightness. So the presence of blue and green tones dominating the water areas indicates the formation of ice in the Beaufort Sea on the two October acquisitions.  

The channels of the Mackenzie River are dominated by blue - indicating the increased backscatter on the last date (Oct 24th) compared to the other two, and thus, representing the freeze-up of the channels.

Some areas are dominated by green, meaning strongest signal on the middle date (Oct 13th) - this indicates the movement of ice during freeze-up. In areas that are cyan (combination of green and blue), no significant movement of ice has occurred between the second and third acquisition date.

(Text from Infoterra GmbH.)


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