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Exercise 2 : NDVI Animation
NDVI image composite over South America
The main objective of this exercise is to create an animation of the vegetation dynamics for the whole South American continent. We will be using a TIFF image of South America that contains twelve SPOT-NDVI images for the year 2000 (one for each month of the year). Images are referred to as ‘channels’ and numbered from 1 to 12, 1 corresponding to January, 2 to February and so on.
Before continuing, find out more about vegetation indices, NDVI, and SPOT Vegetation imagery in the background articles (see right).
Download the Year2000.zip file from the menu on the right.
We are going to work with one image at a time, because we need to convert these images to “image with LUT” in order to be able to apply a Look Up Table (LUT) that will allow us to easily observe the NDVI changes. The next step will consist in saving the image created as a BMP, PNG, JPG or TIFF. Once the twelve images are saved, we will create the animation.
- Open the TIFF image: File/Open/*.TIFF (Year2000.tiff).
- Open Year2000.tif Channel 1 as grayscale and convert it into an image with LUT (Image/Covert to/Image with LUT).
- A colour bar will appear at the bottom of the image. Click twice on the bar and the LUT Editor will appear. The LUT Editor will allow us to change the colour palette from a greyscale palette to a colour palette.
- Click on Open LUT and select the ndvi .pal file. The .pal extension tells us that this file is an ASCII file that contains a table of numbers. Each of the 256 lines are separated into three columns and have values that range between 0 and 255. Each value corresponds to a different colour.
- Save the image created as a BMP, PNG, JPG or TIFF. Do this for all images. Assign a name to each image and keep the correct order for the months of the year, e.g. by naming the first month of the year, January (i.e. channel 1 in the tiff image) with the number one: “1_2000.png”.
- Once all twelve images are saved, open Tools/Image Animation. This will bring up the 'Select Files for Animation' window. Choose the proper animation speed. You can see the number of the slide by activating the Active Slider. You can save the animation as an mpeg file by clicking on Write MPEG.
Observe and describe the variation in the NDVI value during the year 2000.
2. In what months is the NDVI at its maximum in the Amazon basin? Can you explain why?
3. Observe the December image for the northeastern part of Brasil along the Atlantic coast and inland. Can you explain the vegetation pattern?
4. Can you explain the variation in vegetation along the Pacific coast?
5. Compare the information on climate as described in the maps in a normal school atlas with the NDVI images. How are the yearly changes of the location of the Inter-Tropical Convergence Zone (ITCZ) reflected in the NDVI images?
Vegetation in South America
BackgroundVegetation in South AmericaMain EcosystemsVegetation IndicesSPOT VEGETATION imageryThe MERIS sensor and the Globcover Project
ExercisesExercise 1: NDVI - Vegetation from spaceExercise 3: NDVI dynamics by biogeographical zones
Eduspace - SoftwareLEOWorks 3
Eduspace - DownloadYear2000.zip