Exercise 1: Exploring and learning about the volcano - continued
False Colour Composites (FCC) of Landsat image taken on 11 December 2001
Band Combinations and Visual Interpretation
Using combinations of three different bands which are assigned to be displayed in the colours red, green, and blue, we can create an RGB composite. The Landsat combination band 3-2-1 is also called 'Natural Colour Composite’ or 'True Colour Composite' because of the combination of bands in the part of the electromagnetic spectrum’s visible light, and comes closest to what we would see with human eyes.
Other combinations are called False Colour Composites (FCC), where wavelengths are assigned as red, green, and blue, which human eyes would not see. Be careful when using the stretched bands, or you will have to stretch the FCC again (see Tutorial page 34).
Natural colour composite: Image > Combine from > RGB > 3-2-1
False colour composite: Image > Combine from > RGB > 4-3-2
Try out RGB 4-5-3, 7-4-1 or 7-4-2. …
Save the images by choosing Image > Save As
13. Play with different colour combinations.
About the volcanoes:
14. Where can you best identify volcanic lava?
15. Find volcanic cones.
16. Why does the lava appear almost the same colour in one FCC, and in totally different colours in another FCC?
17. In which FCC can you clearly distinguish different types of lava?
18. How far does the volcanic lava go? Can you find indications about lava flows of the 20th century and even earlier online?
To help you with the last question, go to the Global Volcanism Program website and search for the Nyiaragongo and Nyamuragira volcanoes (under Volcano Names / Find Volcanoes / By Name and then check the Monthly Reports, and the Eruptive History).
Around the volcanoes
19. Can you identify vegetation in the different images?
20. Can you see the boundaries of the Virunga National Park?
21. Can you identify infrastructure such as cities, villages, and roads?
22. What are the names of these cities/villages and how far are they from the volcano? (use Google Earth / Google Maps to help you)
23. Think about why people live so close to dangerous volcanoes.
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