Revision as of 14:56, 17 November 2018

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).

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).

Figure A: Single band NDVI displayed with color table RdYlGn

Figure B: Color composite of three spectral indices: RGB=NDVI, BI2, NDWI