Spectral indices

Spectral vegetation index using Raster Calculator

• Click the Open Data Source Manager and then Add raster layer 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). Here the rank of 10 bands is B2,B3,B4,B5,B6,B7,B8,B8A,B11,B12.
• 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 Symbology tab. Under Render type select Singleband pseudocolor.
  • Open the the pulldown menu of Color ramp by clicking on Select All color ramps --> RdYlGn. Under Mode select Equal interval. Set the number of Classes to 10. In the pulldown menu of Color ramp select Invert Color Ramp.

• • To finish, click Apply (see Fig. A).

Several spectral indices at once using OTB

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 once and store them in a multiband file click Help to find definitions of available spectral indices in three categories (vegetation, soil, water) and relevant channels of the input multiband image.
• In the text field Available Radiometric Indices type with apostrophs:

"Vegetation:NDVI Water:NDWI2 Soil:BI2"

• Click Run.

Figure A: Single band NDVI (color table = RdYlGn)

Figure B: Spectral composite (RGB = NDVI,BI2,NDWI)