Change detection

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(→‎Prerequisites of multi-temporal image analysis)
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== Prerequisites of spatio-temporal image analysis ==
+
= Prerequisites of spatio-temporal image analysis =
 
Correct the pixel intensities as much as possible for uninteresting differences:  
 
Correct the pixel intensities as much as possible for uninteresting differences:  
 
# Sensor calibration
 
# Sensor calibration
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# Clear definitions and classification scheme
 
# Clear definitions and classification scheme
  
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== Change detection techniques ==
+
= Change detection techniques =
 +
== Bitemporal ==
 +
=== Post-classification Comparison ===
 +
=== Raster algebra: Difference ===
 +
=== Raster algebra: Ratio ===
 +
# 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|course data]].
 +
# Open {{mitem|text=Toolbox --> OTB --> Feature Extraction --> Radiometric indices}}.
 +
#* Set ''tm_920526_mul.tif'' as {{button|text=Input Image}}.
 +
#* Set {{button|text=Red Channel}} to 4 and {{button|text=NIR Channel}} to 5.
 +
#* Set {{button|text=Available Radiometric Indices}} to {{button|text=ndvi}}.
 +
#* Save the {{button|text=Output Image}} as ''ndvi1992''.
 +
#* Repeat this procedure for the raster file of 2005 and adapt the name of the {{button|text=Output Image}} to ndvi_2005.
 +
# Calculate the ratio of both raster images with the {{mitem|text=Raster --> Raster Calculator}}.
 +
#* Choose ''ndvi_2005'' from the {{button|text=Raster bands}} by double clicking on the raster name.
 +
#* Choose the division operator from the {{button|text=Operators}} by clicking on {{button|text= / }}.
 +
#* Choose  ''ndvi_1992.tif'' from the {{button|text=Raster bands}} by double clicking on the raster name.
 +
#* Save the {{button|text=Output layer}} as ''ndvi_ratio'' and press {{button|text=OK}}.
 +
 +
== Multi-temporal ==
 
=== Multi-temporal color composites ===
 
=== Multi-temporal color composites ===
 +
# 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|course data]].
 +
# Open {{mitem|text=Toolbox --> OTB --> Miscellaneous --> Band Math}}.
 +
# 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 {{button|text=Input image list}}.
 +
#* Type <tt>sqrt(im1b4^2 + im1b5^2 + im1b3^2)</tt> as {{button|text=Expression}}.
 +
#* Save the{{button|text=Output image}} as ''amplitude1992''.
 +
#* Repeat this procedure for the raster files of 2000 and 2005 and adapt the name of each {{button|text=Output Raster File}}.
 +
# Merge the three output raster files with {{mitem|text=Toolbox --> GDAL/OGR --> [GDAL] Miscellaneous --> Merge}}
 +
# Load the three ''amplitude****.tif'' files as {{button|text=Input Layers}}, mark {{button|text=Layer Stack}} and save {{button|text=Merged}} output as ''amplitude_merge''.
 
[[File:multi_temporal.png|250px]]
 
[[File:multi_temporal.png|250px]]
 +
 
==== Principal component analysis ====
 
==== Principal component analysis ====
 
# 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|course data]].
 
# 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|course data]].
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# Load the three ''pca****_1.tif'' files as {{button|text=Input Layers}}, mark {{button|text=Layer Stack}} and save {{button|text=Merged}} output as ''pca_merge''.
 
# Load the three ''pca****_1.tif'' files as {{button|text=Input Layers}}, mark {{button|text=Layer Stack}} and save {{button|text=Merged}} output as ''pca_merge''.
  
−
==== Amplitude ====
 
−
# 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|course data]].
 
−
# Open {{mitem|text=Toolbox --> OTB --> Miscellaneous --> Band Math}}.
 
−
# 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 {{button|text=Input image list}}.
 
−
#* Type <tt>sqrt(im1b4^2 + im1b5^2 + im1b3^2)</tt> as {{button|text=Expression}}.
 
−
#* Save the{{button|text=Output image}} as ''amplitude1992''.
 
−
#* Repeat this procedure for the raster files of 2000 and 2005 and adapt the name of each {{button|text=Output Raster File}}.
 
−
# Merge the three output raster files with {{mitem|text=Toolbox --> GDAL/OGR --> [GDAL] Miscellaneous --> Merge}}
 
−
# Load the three ''amplitude****.tif'' files as {{button|text=Input Layers}}, mark {{button|text=Layer Stack}} and save {{button|text=Merged}} output as ''amplitude_merge''.
 
−
 
−
=== NDVI ratio ===
 
−
# 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|course data]].
 
−
# Open {{mitem|text=Toolbox --> OTB --> Feature Extraction --> Radiometric indices}}.
 
−
#* Set ''tm_920526_mul.tif'' as {{button|text=Input Image}}.
 
−
#* Set {{button|text=Red Channel}} to 4 and {{button|text=NIR Channel}} to 5.
 
−
#* Set {{button|text=Available Radiometric Indices}} to {{button|text=ndvi}}.
 
−
#* Save the {{button|text=Output Image}} as ''ndvi1992''.
 
−
#* Repeat this procedure for the raster file of 2005 and adapt the name of the {{button|text=Output Image}} to ndvi_2005.
 
−
# Calculate the ratio of both raster images with the {{mitem|text=Raster --> Raster Calculator}}.
 
−
#* Choose ''ndvi_2005'' from the {{button|text=Raster bands}} by double clicking on the raster name.
 
−
#* Choose the division operator from the {{button|text=Operators}} by clicking on {{button|text= / }}.
 
−
#* Choose  ''ndvi_1992.tif'' from the {{button|text=Raster bands}} by double clicking on the raster name.
 
−
#* Save the {{button|text=Output layer}} as ''ndvi_ratio'' and press {{button|text=OK}}.
 
  
  
 
[[category:QGIS Tutorial]]
 
[[category:QGIS Tutorial]]

Revision as of 12:59, 12 January 2018

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

Bitemporal

Post-classification Comparison

Raster algebra: Difference

Raster algebra: 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.

Multi-temporal

Multi-temporal color composites

  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.

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.
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