| | Landslide detection in Langtang Himal
This exercise is divided into two parts and requires the use of LEOWorks.
Part 1
Landslides are a severe threat to the local population. The destroying effects and side-effects of a landslide make the living in remote, high mountain areas a challenge. This is especially the case in sensitive mountainous ecosystems. Besides the direct effects and danger to the people, landslides often cut off essential transportation routes.
In the following exercise you will investigate a landslide area in Langtang Himal.
Download the necessary data from Himalayas_env4.zip.
Start LeoWorks and open the image 20001122¬_321.tif (natural colour) and 20001122_432.tif (false colour infrared) from your working directory.
As you can see, the images appear quite dark, and it is quite difficult to analyse the situation beside the snow-covered areas. In the previous exercise you applied a histogram equalisation. Here we will do an interactive stretching to have full control over the stretching.
Go to Enhance>Interactive stretching and a new window will appear. This window shows you the original histogram of each channel on the left-hand side, and the histogram after the interactive stretching process on the right-hand side. Now click on the pink bar on the very right of the original histogram, and drag it gently to the left. You will see that both the histogram on the right hand-side and the image in the viewer will change.
Histograms before and after interactive stretching
The interactive stretching makes it possible for the user to choose which parts of the image should be more visible. In this case, the snow-covered areas of the image are not part of our investigation, as we are interested in the land-covered areas. While dragging the pink bar to the left, the contrast for the snow-covered areas decreases, while the contrast for the other part increases. This makes it easier for the observer to distinguish between different kinds of land cover. Click 'apply' and examine the images.
1. Describe what you see.
2. Which types of landcover can you identify?
3. What is a landslide?
4. How do landslides work?
5. What are the reasons for landslides?
6. Where can landslides occur? What are the preconditions?
7. What can be done to predict landslides?
8. What can be done to prevent landslides?
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