This is a tutorial about the use of the tool Band calc that allows for the raster calculation for bands. In particular, we are going to calculate the NDVI (Normalized Difference Vegetation Index) of a Landsat image, and then apply a condition in order to refine a land cover classification (see Tutorial 2: Land Cover Classification of Landsat Images ) basing on NDVI values (a sort of Decision Tree Classifier).
The Band calc can perform multiple calculations in sequence. We are going to apply a mask to every Landsat bands in order to exclude cirrus and cloud pixels from the NDVI calculation, and avoid anomalous values. In particular, Landsat 8 includes a Quality Assessment Band ) that can be used for masking cirrus and cloud pixels.
The values that indicate with high confidence cirrus or clouds pixels are (for the description of these codes see the table at http://landsat.usgs.gov/L8QualityAssessmentBand.php ):
- 61440;
- 59424;
- 57344;
- 56320;
- 53248;
- 31744;
- 28672 .
In particular, the Quality Assessment Band of the sample dataset includes mainly the value 53248 indicating clouds. Therefore, in this tutorial we are going to exclude the pixels with the value 53248 from all the Landsat bands.
Following the video of this tutorial.
Following the video of this tutorial.