Change detection

Prerequisites of multi-temporal image analysis

1. Acquisition of remote sensing data by the same (or similar) sensor recorded using same spatial resolution, viewing geometry, spectral bands, time of day.
2. Optical calibrationcorrecting uninteresting differences due to illumination, atmospheric conditions, topography, sensor calibration. DNs are converted to physical units (surface reflectance).
3. Clear definitions and classification scheme
4. Exact spatial coregistration

Change detection techniques

Multi-temporal color composites

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 .
   • 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.