Spectral indices
From AWF-Wiki
Vegetation index using the Raster Calculator
- Click the Open Data Source Manager
and then Add raster layer 
and select the file /geodata_lab01/raster/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:
- 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
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).
- Open the In the pulldown menu of Color ramp by clicking on
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 text=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.
- in the text field Available Radiometric Indices type:
Vegetation:NDVI Enter Water:NDWI Enter Soil:BI2 Enter. Click Run.
- Click Helpto find an overview on available spectral indices in three categories (vegetation, water, soil) and relevant channels of the input multiband image.
- Display the output multiband spectral indices image as a color composite in the canvas (Fig. B).
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