Oft-chdet.bash

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oft-chdet.bash automated change detection

Usage: oft-chdet.bash <input1> <input2> <output> <nodata_value> [threshold]

Description This tool performs automated change detection between 2 input images. The script uses the Iteratively Re-weighted Multivariate Alteration Detection (MAD) algorithm (Canty and Nielsen, 2008). Input imagery must have the same format, extent, resolution, number of bands and type of data.

<input1> - Input raster 1 (with extension).

<input2> - Input raster 2 (with extension).

<output> - A raster consisting of binary values (0 or 1) indicating pixels of likely change between the two dates. Values of 1 indicate change. Values of 0 indicate no-change.

<nodata_value> - Value indicating no-data within the image.

[threshold] - Default 0.99. Specifies the threshold value of the cumulative frequency distribution (of the resulting Chi-square layer...see Reference below) above which pixels are identified as changed. Higher threshold values indicate more stringent limits for detecting changes and, thus, produce less changed area than lower thresholds. Threshold values must be specified as a proportion using 0.XX notation.

Reference:

M. J. Canty and A. A. Nielsen (2008), Automatic radiometric normalization of multitemporal satellite imagery with the iteratively re-weighted MAD transformation RSE 112(3), 1025-1036.

Example:

To automatically find changes between a landsat image from year 2000 and 2005 using a threshold of 0.85:

oft-chdet.bash landsat00.tif landsat05.tif change00_05.tif 0 0.85


Exercise:

  • Get Example data set
  • For this exercise following tools are used: oft-chdet.bash

Identify changed areas between year 2000 and 2012 using Landsat imagery using landsat_t1.tif and landsat_t2.tif

1. Open your working directory using

cd /home/...

2. Unpack the data

3. Now we run oft-chdet.bash to do the automated change detection using the input Landsat data

oft-chdet.bash landsat_t1.tif landsat_t2.tif change_0012.tif 0 0.85

Outputs include the following:

A file beginning with imad-[name of outfile].tif. This file contains the raw results of the IMAD process, one for each input band and the chi-squared layer (see Reference).

The specified output file:

This file contains 1's and 0's; 1's indicate areas of change and 0's indicate areas of no change.



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