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I am creating a variety of NDVI for different periods in time, so per season for four years. I used the raster calculator on arcgis but i keep getting different max and min values.

Do I need to make all the min-max values the same to be able to compare all the NDVI's and, if so, how do I do this?

I tried using the min-max function in stretch in the symbology tab of layer properties but this just makes all the values alter that everything turns green.

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  • Please keep in mind that ESRI samples the raster to derive the statistical moments. As such, you cannot take the min-max values as absolute values. If you would like the software to show the correct values, recalculate the statistics and set the skip value to 1. You can then view the correct statistics under the layer properties > source tab. And, yes NDVI values can vary. – Jeffrey Evans Apr 20 '18 at 15:05
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This most known and used vegetation index is a simple, but effective VI for quantifying green vegetation. It normalizes green leaf scattering in the Near Infra-red wavelength and chlorophyll absorption in the red wavelength.

Values description: The value range of an NDVI is -1 to 1. Negative values of NDVI (values approaching -1) correspond to water. Values close to zero (-0.1 to 0.1) generally correspond to barren areas of rock, sand, or snow. Low, positive values represent shrub and grassland (approximately 0.2 to 0.4), while high values indicate temperate and tropical rainforests (values approaching 1).

From sentinel-hub.com

There is nothing wrong with your values, and you can compare them as they are now because the NDVI is already normalized (that´s the N in NDVI)

So to answer your question directly:

Do I need to make all the min-max values the same to be able to compare all the NDVI's and, if so, how do I do this?

Depending on what you are trying to achieve, but if you simply want to compare the NDVI of an AOI during different periods then you don't need to make the min-max values the same.

If you are trying to normalize the colors for the visualization, just make sure that you set the same break rules for the stretch in every raster.

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For visual comparison, you need to make all min-max the same, but not for analysis.

In your case, the most simple workaround is to import the symbology of Automn 2014-2 for all your layer (because it contains both the min and the max values of all the rasters shown in your print screen).

Otherwise, using the min-max of the symbology tab sounds good, so I would need more details to understand why it is going wrong. Just make sure that you don't have a problem with comas instead of points for the decimal separating symbol (could be linked with your regional parameters)

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In order to compare them, you need to make sure the product you are using is comparable. You are not supposed to compare two different images if they haven't been properly corrected since the atmospheric variations may be the cause of some of the observed differences.

As long you make sure all your NDVI images have been corrected, meaning you need to work with Surface Reflectance products, your values can be compared. It is completely normal to have different ranges and you of course have to symbolize them with the same palette and ranges.

If you are working with Landsat data you can get Level-2 products (Surface Reflectance) on demand. Check this: https://landsat.usgs.gov/landsat-surface-reflectance-data-products

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