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I am relatively new to GIS (about 4-5 months in) I did not receive any formal education about this so I am completely clueless about how to go about measuring/quantifying vegetation using satellite images. Can somebody please help? Is there any specific kind of image file I need to do this, if there is, how/where can I get them?

Thanks!

Enrique Roa Undergrad biology student

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Welcome to GIS.SE. please be more precise and give more information of what you achieve and what you had done till now. What you mean by "measuring/quantifying vegetation". –  rashad May 22 '13 at 12:39
    
Please see gis.stackexchange.com/faq how to write good questions. –  Mapperz May 22 '13 at 13:31
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1 Answer

up vote 6 down vote accepted

One of the most simple ways to characterize vegetation from imagery is to utilize NDVI. In short, NDVI takes the difference from the spectral band with the highest EMR reflectance (nIR) and the spectral band with the lowest reflectance (red) and normalizes this value by dividing by the sum of the highest reflectance (nIR) band and the lowest reflectance band (red). To put this together, the equation looks like:

(nIR - red)/(nIR + red)


How do we put this all together using QGIS?

  • First, find the appropriate imagery that has a nIR band and a red band. Two common products are NAIP imagery and Landsat imagery (Available from Earth Explorer). For each, band 4 = nIR and band 3 = red.
  • Next use QGIS's raster calculator to calculate the NDVI

enter image description here

  • When you display the NDVI, make sure to stretch to MinMax in the layer properties otherwise your image will appear to be solid gray.

Values in the NDVI range from -1 to 1. In other words, healthy green vegetation will have higher pixel values (i.e. closer to 1) and non-vegetation will have lower values (i.e. closer to -1)

enter image description here

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+1. Consider spending some time looking at the Earth Explorer link provided by @Aaron. Read the documentation and download some of the imagery. For some background information use wikipedia to look up the Landsat series of satellites - you'll get an idea of how they work and the data they can provide you with. –  Nick Ochoski May 22 '13 at 15:37
    
Thank you all for the help! I've already started reading journals regarding this, but I didn't quite get how to do it before. Right now I am going to start reading @Aaron's link to the earth explorer page to learn more. Anyway, thank you all for the help! I appreciate it a lot. :) –  Enrique Roa May 27 '13 at 13:56
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