Exercises
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1. Start the LEOWorks software and File > Open the single-channel image file tm_23july2006_1.tif.
2. Use Image Information to see technical information about the image.
How many pixels is the image in height and width? What ground area does one pixel cover? How many kilometres is the image in width and height?
3. Get familiar with the image. You might want to use the zoom function.
Can you find the airstrip of Ny Ålesund? Write down its geographic position using View > Cursor Position/Value.
4. Use the Image > Measure Tool to measure some distances. Make sure that you change the Units in the Measure Tool menu bar to Meters.
How long is the airstrip? How far is it from Ny Ålesund (which lies close to the airstrip) to the front of the Kronebreen glacier? How wide are the calving fronts of Kronebreen and other glaciers?
5. Open other channels, for instance 4 and 5, or all channels.
6. Under View > Histogram you can look at the histograms of the different channels. The best way to do this is to change Properties > Scale to Logarithmic.
What does the histogram tell you? How do the histograms differ from channel to channel?
You can change/improve how the images look by changing their histograms. Enhance > Interactive Stretching (or Histogram Equalization methods). For interactive stretching, change the position of the upper and lower image values between which the histogram is stretched. Observe the changes in the output histogram and the satellite image.
7. Explore the different channels. Use the Cursor Position value.
How does the intensity of radiation differ between the different channels? Place the pointer over the lower part of the Kronebreen glacier. Read the image value at about the same place for each channel and write it down. Do the same for a site on the water and for a site on land that is not covered by glacier. You can now fill in a simple table:
| |
Channel 1
(Blue) |
Channel 2
(Green) |
Channel 3
(Red) |
Channel 4
(near-infrared) |
Channel 5
(shortwave
infrared) |
Channel 7
(=6 in your
image)
(shortwave
infrared) |
| Glacier |
148 (example) |
|
|
|
|
|
| Water |
|
|
|
|
|
|
| Land |
|
|
|
|
57 (example) |
|
What is the difference between the three channels for the three sites? What values did others find in your class?
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