Exercise 1: Correlation of repeated images (LEOWorks 3)
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Start LEOWorks and File > Open both ast_20jan2001.tif and ast_20nov2001.tif. Study the images. You might want to use the zoom buttons (+) and (-), or the Magnifying Glass.
1. Locate the glacier shown in the ASTER overview image.
2. Describe the glacier from south to north. How can you distinguish between the accumulation and ablation zones?
Use View > Image Information, or the [ i ]-button to see technical information about the image.
3. How many pixels is the image in height and width?
4. One pixel represents 15 x 15 m. How many kilometres is the image in width and height?
Animate both ASTER images. In order to do this, click on Tools > Image Animation. CTRL-select both images ast_20jan2001.tif and ast_20nov2001.tif and start the animation. Adjust the Animation Speed. Alternatively, stop the animation using the pause button || and go through the images using the slider bar in the Animation Frame rectangle. You can also click on the Animation Frame slider and use the left and right arrows on your keyboard.
5. Do you see the glacier flow?
6. Observe and describe the displacements between both images in different image sections. Where are they minimal? Where are they important?
What are your conclusions?
7. What other changes besides ice flow do you see between both images?
8. Describe the changes in snow cover and have a closer look at the glacier lake in front of the glacier.
Close the animation and keep both images open. On the January 2001 image zoom in 2 or 3 times and choose one or more distinct crevasses. Open the menu GIS > GIS Tools or use the [GIS] button. Under File > New Theme, choose a name for the layer (e.g. crevasses) and Polyline as type. Press OK.
Choose Edit > Start Edit in the GIS Tool menu bar and digitise a line on several crevasses. By right-clicking on your mouse you can terminate one polyline and start a new one. Try to distribute crevasse lines over the entire glacier. Digitise the ice front of the glacier lake. Edit > Stop Editing terminates the polyline editing. File > Save Theme using the name ‘crevasses.shp’.
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