Change detection

From AWF-Wiki
Revision as of 12:30, 12 January 2018 by Hfuchs (Talk | contribs)

Jump to: navigation, search

Contents

Prerequisites of spatio-temporal image analysis

Correct the pixel intensities as much as possible for uninteresting differences:

  1. Sensor calibration
  2. Exact spatial co-registration of images (especially pixel-by-pixel comparision)
  3. Cloud and cloud shadow masking
  4. Haze reduction
  5. Atmospheric correction
  6. Topographic illumination correction (mountains)
  7. Clear definitions and classification scheme

Change detection techniques

Multi-temporal color composites

Multi temporal.png

Principal component analysis

  1. Add the raster layers of the years 1992 (tm_920526_mul.tif), 2000 (etm_000515_mul.tif) and 2005 (etm_050623_mul.tif) into a QGIS project. It should be available in the course data.
  2. Install PCA plugin under Plugins --> Manage and Install Plugins....
  3. Open PCA plugin Pca.png.
    • Set tm_920526_mul.tif as Input Raster File.
    • Set Number of output Principal Components to 1.
    • Save the Output Raster File as pca1992_1.
    • Repeat this procedure for the raster files of 2000 and 2005 and adapt the name of each Output Raster File.
  4. Merge the three output raster files with Toolbox --> GDAL/OGR --> [GDAL] Miscellaneous --> Merge.
  5. Load the three pca****_1.tif files as Input Layers, mark Layer Stack and save Merged output as pca_merge.

Amplitude

  1. Add the raster layers of the years 1992 (tm_920526_mul.tif), 2000 (etm_000515_mul.tif) and 2005 (etm_050623_mul.tif) into a QGIS project. It should be available in the course data.
  2. Open Toolbox --> OTB --> Miscellaneous --> Band Math.
  3. Calculate the amplitude for each raster layer (1992, 2000, 2005) with the use of the bands 5-4-3.
    • For the year 1992, set tm_920526_mul.tif as Input image list.
    • Type sqrt(im1b4^2 + im1b5^2 + im1b3^2) as Expression.
    • Save theOutput image as amplitude1992.
    • Repeat this procedure for the raster files of 2000 and 2005 and adapt the name of each Output Raster File.
  4. Merge the three output raster files with Toolbox --> GDAL/OGR --> [GDAL] Miscellaneous --> Merge
  5. Load the three amplitude****.tif files as Input Layers, mark Layer Stack and save Merged output as amplitude_merge.

NDVI ratio

  1. Add the raster layers of the years 1992 (tm_920526_mul.tif) and 2005 (etm_050623_mul.tif) into a QGIS project. It should be available in the course data.
  2. Open Toolbox --> OTB --> Feature Extraction --> Radiometric indices.
    • Set tm_920526_mul.tif as Input Image.
    • Set Red Channel to 4 and NIR Channel to 5.
    • Set Available Radiometric Indices to ndvi.
    • Save the Output Image as ndvi1992.
    • Repeat this procedure for the raster file of 2005 and adapt the name of the Output Image to ndvi_2005.
  3. Calculate the ratio of both raster images with the Raster --> Raster Calculator.
    • Choose ndvi_2005 from the Raster bands by double clicking on the raster name.
    • Choose the division operator from the Operators by clicking on /.
    • Choose ndvi_1992.tif from the Raster bands by double clicking on the raster name.
    • Save the Output layer as ndvi_ratio and press OK.
Personal tools
Namespaces

Variants
Actions
Navigation
Development
Toolbox
Print/export