Segmentaion

Segmentation (A trivially simple example)

Data

• For the Example:

  • october_ndvi.tif

• Also bag these files for the challenge:

  • Sentinel-2 median composite image, near Susques Argentina, 2025-04-01 to 2025-10-26

  • Sentinel-2 max composite image, near Susques Argentina, 2025-04-01 to 2025-10-26

A simple example of segmentation

Start a QGIS project ad set the project crs 20 EPSG:6339.

1. Open october_ndvi.tif.
2. What should you do before starting?
3. Use the raster calculator to create a binary raster where NDVI > 0.2.
4. Use Raster > Conversion > Polygonize to make polygons from the raster
5. Use the field calculator to calculate area (expression: $area)
6. What units is area in?
7. Remove tiny polygons based on area.
8. What did you do?

Challenge!

You know about spectral indices (There’s an index for that!). You know about (very basic) segmentation. You know about zonal statistics.

1. Segment the lithium brine evaporation ponds using Sentinel-2 median composite image and/or Sentinel-2 maximum composite image (near Susques Argentina, 2025-04-01 to 2025-10-26).
2. Calculate their total area.
3. What is the difference in mean SWIR1 (band 11) within and outside of evaporation ponds in the image?
4. What is a median composite image? A maximum composite image?