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Mean NDVI value calculation

by mvardovs on ‎08-16-2016 02:48 AM (2,103 Views)

Question

How can I calculate mean NDVI value for each field?

Answer

Why it can be needed?

 

Having datasets for each crops growing stage and Mean NDVI value for each, you can create graphs for monitoring crop growth dynamic.

 

0.png

 

To do that you need to have two inputs:

1) NDVI image. Go to the Raster tab and from Classification group choose Unsupervised – NDVI to create it if you don’t have.

2) Vector file with fields borders.

 

  1. Load inputs to the Viewer.

image.png

 

  1. Select your Vector file in Contents window. Go to the Drawing tab and activate Enable Editing option.

2.png

 

  1. Go to the Raster tab and from Raster GIS group choose Thematic > Zonal Attributes.

3.png

 

  1. Your vector file will be automatically loaded as Vector Layer and NDVI image as Raster Layer. If not, do this manually.

zonal_attr.png

 

  1. In Zonal Functions block activate Mean function. Leave the attribute name by default.

5.png

 

  1. Click OK in Save Zonal Statistics to Polygon Attributes window.
  2. When done, select your shapefile in Contents window. Go to the Drawing tab and deactivate Enable Editing option.
  3. Go to the Table tab and click on Show Attributes 6.png. You will see in a table the mean NDVI values for each field.

7.png

 

This process can be optimized using Spatial Modeler. The model should look as following (in attachment as well):

 

model.png

 

 

 

Comments
by Man
on ‎08-13-2017 09:54 PM

Hi, I have question,

 

  1. How to recode color of NDVI
  2. Can I convert/subset area with certain range of NDVI to shp/aoi/etc.

Thank you.

by Forest
on ‎07-21-2018 08:44 AM

Hi.

 

I want to know, can i calculate NDVI from the Landsat 8 data set which download from USGS website. 

Or I must convert DN to reflectance first? and if i convert DN to reflectane already how can i calculate NDVI?

 

Thanks

 

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