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I would like to calculate average NDVI values. I have 3 values of NDVI:

  1. high:243 low:0
  2. high:243 low:0
  3. high:238 low:0

How can I use a a raster calculator to calculate the average valvue

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    Which software do you use? Have you tried to google solution for your issue? – SS_Rebelious Dec 1 '14 at 14:23
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    Please make a minimal attempt to research your question and provide detail on what you have tried and your preferred software. A GUI software solution will vary considerably from a programming one. I performed search for "NDVI time" (gis.stackexchange.com/search?q=NDVI+time), on this site, and immediately found several threads that answer your question using various solutions. – Jeffrey Evans Dec 1 '14 at 18:38
  • possible duplicate of How do I average a set of rasters? – Erica Dec 2 '14 at 14:18
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There are several ways to approach this. One option is to use the Raster Calculator, as you indicated. I see that your NDVI values have been rescaled from floating point (-1 to 1) to unsigned 8-bit integer (0 - 255). This is the syntax you would use in the raster calculator:

("ndvi_1" + "ndvi_2" + "ndvi_3") / 3

You can also use Cell Statistics (Spatial Analyst) with the "MEAN" statistic to perform the same calculation.

  • thanks so much for the answers however I would like the NDVI values to be ranged from (-1 to 1) not (0-255) as it is being shown now so that I may come up with a graph showing variations of NDVI in a year. how should I go about it – favour Dec 2 '14 at 15:21
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    You should consider updating your question to reflect that you need to rescale 8-bit unsigned integer to float. If you have access to Erdas, this is easily accomplished with the rescale tool: gis.stackexchange.com/a/114262/8104. However, you would want to set the min max range different than the example. – Aaron Dec 2 '14 at 15:34
  • Yes Aaron, I need to rescale the bit-integer to float. how can I do it in ArcGIS 9.3, I don't have Erdas at the moment – favour Dec 3 '14 at 3:05

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