Exercise 1: Inspecting the images from 1972 to 2009 (cont'd)
In order to highlight differences in vegetation, we will produce a false colour composite. In a combined image, the colours do not correspond to what we expect to see in real life. Instead, it highlights specific vegetated features of different land cover classes based on their spectral signatures.
Create a new band combination. Now select band 4 (near infrared) for the red colour, band 5 (mid infrared) for the green colour, and band 3 (red band) for the blue colour. If necessary, use Interactive Stretching to increase the contrast of the image.
Save this colour composite as 2009_Cordoba_453 in a folder on your computer.
Compare the two images you’ve just created.
Cordoba city and surroundings in a true (left) and a false (right) colour image
7. Based on the information found in the section on Spectral signatures, explain why the colours are different in the two colour composites.
8. Observe and describe the visible homogeneity or smoothness of each land cover class, considering the three main classes:
- Urban (built-up area, city, industry)
- Bare soil (non-vegetated fields)
- Vegetation (crop fields, forests, parks).
Close the images.
b) Detecting urban sprawl by comparing images from 1972 to 2009
Now that you are familiar with creating colour composites, we will try to detect urban sprawl by comparing three images: one of 1972, one of 1992 and one of 2009.
Open these three images as false colour composites, just like you did in the previous exercise. Be aware that the image of 1972 has fewer bands than the other two because it was acquired by the MSS sensor. Use bands 4, 3 and 2 to create the RGB (red green blue) image.
The city of Cordoba in three different years (1972, 1992, 2009) showing urban growth
9. Do you see a difference between densely built-up area and urban land with a lower dwelling density? Use the Córdoba/Argentina image found in Google Earth to identify these two land cover classes.
10. Can you see where the city expands the most? Can you see in which period this happened?
11. Judging from the extension of reddish colours (vegetation!), can you explain the main difference between 1992 and 2009? Could it be because of the prevailing weather in the respective periods?
12. Between 2000 and 2004 there was a gradual change from an economy based on livestock to large-scale agriculture. Can you see that in the images?
Close the images.
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