Spectral indices

From AWF-Wiki
(Difference between revisions)
Jump to: navigation, search
(Spectral indices using Processing Toolbox)
(Spectral indices using Processing Toolbox)
Line 17: Line 17:
 
* Open it with a double click.  
 
* Open it with a double click.  
 
* Assign the bands in the multiband file to the correct spectral sensitivity.
 
* Assign the bands in the multiband file to the correct spectral sensitivity.
* If you want to calculate a single spectral index type in the text field ''Available Radiometric Indices'': {typed|text="Vegetation:NDVI"}}
+
* If you want to calculate a single spectral index type in the text field ''Available Radiometric Indices'': {{typed|text="Vegetation:NDVI"}}
 
* If you want to calculate several spectral indices at one time and store them in a multiband file click {{button|text=Help}} to find definitions of available spectral indices in three categories (vegetation, water, soil) and relevant channels of the input multiband image.
 
* If you want to calculate several spectral indices at one time and store them in a multiband file click {{button|text=Help}} to find definitions of available spectral indices in three categories (vegetation, water, soil) and relevant channels of the input multiband image.
 
* Click {{button|text=Run}}.
 
* Click {{button|text=Run}}.

Revision as of 13:55, 11 June 2020

Vegetation index using the Raster Calculator

  • Click the Open Data Source Manager QGIS 3.0 datasource.png and then Add raster layer QGIS 2.0 addrast.png and select the file /geodata/lucc/s2/Subset_S2A_MSIL2A_20170619T_MUL.tif.
  • Check the rank and spectral range of bands in the multiband file (e.g. see table Changing Raster Layer Style).
  • After clicking Open, the raster layer appears in the QGIS canvas.
  • Click Raster --> Raster calculator.
  • A powerful normalization is realized by the normalized difference vegetation index that forms the basis of most vegetation indices $NDVI = (Nir - Red) / (Nir + Red)$. It can be implemented using Raster Calculator as seen in the following screenshot:

Qgis raster calc ndvi.png

  • Define path and file name of the output layer. OK.
  • Map visualization: Open the raster layer properties by right-clicking the ndvi raster in the TOC selecting Properties, or by simply double clicking.
  • Select the Style tab. Under Render type select Singleband pseudocolor.
    • Open the In the pulldown menu of Color ramp by clicking on Qgis pull down.png Select All color ramps --> RdYlGn. In the Mode select Equal interval. Set the number of Classes to 10 and click Classify.
    • To finish, click Apply (see Fig. A).

Spectral indices using Processing Toolbox

A convenient module for calculating one or several spectral indices at the same time can be found in the QGIS processing toolbox.

  • Type Radiometric into the search field and find the OTB --> Feature Extraction --> Radiometric Indices) tool.
  • Open it with a double click.
  • Assign the bands in the multiband file to the correct spectral sensitivity.
  • If you want to calculate a single spectral index type in the text field Available Radiometric Indices: "Vegetation:NDVI"
  • If you want to calculate several spectral indices at one time and store them in a multiband file click Help to find definitions of available spectral indices in three categories (vegetation, water, soil) and relevant channels of the input multiband image.
  • Click Run.
  • In the text field Available Radiometric Indices type with apostrophs:"Vegetation:NDVI Water:NDWI2 Soil:BI2"
Qgis radiometric composite.png
Figure A: False color composite RGB = 4,3,2
Figure B: Single band NDVI
Personal tools
Namespaces

Variants
Actions
Navigation
Development
Toolbox
Print/export