Change Detection for SAR (CCD)

Transcription

1 Change Detection for SAR (CCD) The purpose of this tutorial is to provide you with a friendly and easy to follow step-bystep guide for using change detection algorithms for synthetic aperture radar data in PCI Geomatica Geomatica 2012 introduces new algorithms to facilitate Coherent Change Detection. New algorithms include AUTOSHIFT, CCDINTEN, CCDPHASE, CCDWISH and CCDWM. The CCD functions are a complete set of tools designed specifically for the detection and analysis of changes extracted from a user-specified test and reference SAR image pair. This includes the following functions: AUTOSHIFT - Function to prepare data for Coherent Change Detection workflow. Allows a user to align a target image to a reference image. CCDINTEN - Measures the change in total radar backscattering between a test image and a reference image by comparing the sum of the intensities of the input channels. CCDPHASE - Measures change based on the average coherence (over a specified window size) between two co-registered single look complex SAR images. CCDWISH - Measures change between two single-look complex SAR images based on modified Wishart statistics. CCDWM - Combines the results from multiple change detection techniques in a weighted manner. GEOMATICA FOCUS 1. Start Geomatica Focus. Page 1

2 2. Load the SAR files you will be using to view change detection. Please note that the test and reference data files must be coherent (i.e. have the same viewing geometry (beam modes), polarizations and resolution). 3. Choose your preferences for the following windows. Page 2

3 RUN SARINGEST 1. Select SARINGEST from the Algorithm Librarian. This algorithm will convert the entire file to PCIDSK extracting the required meta-data. 2. In the SARINGEST Module Control Panel click the Input Params 1 tab. Click Browse and locate the appropriate folder and file for the data you are using. 3. In the SARINGEST Module Control Panel in the Files tab click Browse and locate the appropriate folder to save the output PCIDSK file. 4. Click Run. Page 3

4 5. Repeat steps 1-4 for the second image. The second image will be used as a reference image for the change detection algorithms. 6. Load images into Focus to view. RUN AUTOSHIFT Note: If AUTOSHIFT is not run, the co-registration is based upon the geocoding provided by the vendor. If AUTOSHIFT is run the comparison is based upon nearest neighbor in the test file to the pixel of interest in the reference file. 1. Select AUTOSHIFT from the Algorithm Librarian. AUTOSHIFT was developed to handle complex data and automatically computes a nominal offset for coherent data. AUTOSHIFT does not modify the image; it only adjusts the geocoding information of the output file to optimize the registration. Essentially the reference file and output file are identical except for the geocoding information. Co-registration of the images could also be improved by manually adding tie points of GCP s. Page 4

5 2. In the AUTOSHIFT Module Control Panel click Browse and locate the appropriate folder and files for the data you are using. 3. Click Browse in the Output Ports and save your output file. 4. Select the Input Params 1 tab. Change the Search radius (pixels) to 64. Change the Number or horizontal tiles to 8. Change the Number of vertical tiles to 8. It is recommended to use a Search radius between 16 and maximum offset of +5 as determined using Focus. 5. Click Run. The result will be the target image aligned to the reference image. 6. Repeat steps 1-4 for the second image which will be used as a reference image for the change detection algorithms. Page 5

6 Once the SAR data is co-registered; there are three options for change detection CCDINTEN, CCDPHASE and CCDWISH. The CCD* output contains (real valued) output channels. Channel 1 = Test File (sum of all polarizations) Channel 2 = Co-registered Reference File (sum of all polarizations) Channel 3 = Change metric (depending upon algorithm used) Channel 4 = Ranked change metric with 0 representing smallest change and 100 representing largest change. Examples of CCDINTEN and CCDWISH are found below. Run CCDINTEN 1. Select CCDINTEN from the Algorithm Librarian. CCDINTEN computes the change in intensity. 2. In the CCDINTEN Module Control Panel click Browse and locate the appropriate folder and files for the data you are using. 3. In the Input Params 1 tab in the CCDINTEN Module Control Panel select 5 as the Window size (pixels). Page 6

7 4. Click Browse in the Output Ports and save your output file. 5. Click Run. 6. Open the file in Focus. No change appears in yellow. Objects in purple signify changes in the test data but not the reference data whereas cyan objects signify changes in the reference data but not in the test data. Page 7

8 Run CCDWISH 1. Select CCDWISH from the Algorithm Librarian. CCDWISH is based upon changes in the Wishart distribution. Complex data (single, dual or quad) is required as input. 2. In the CCDWISH Module Control Panel click Browse and locate the appropriate folder and files for the data you are using. Page 8

9 3. In the Input Params 1 tab in the CCDWISH Module Control Panel select 5 as the Window size (pixels). 4. Click Browse in the Output Ports and save your output file. 5. Click Run. 6. Open the file in Focus. No change appears in yellow (R + G). Objects in purple signify changes in the test data but not the reference data (R + B) whereas cyan objects signify changes in the reference data but not in the test data (G + B). Page 9

10 CCDPHASE can also be selected from the Algorithm Librarian. CCDPHASE is based upon changes in coherence. Complex data (single, dual or quad) is required as input. 1. Select CCDPHASE from the Algorithm Librarian. CCDWISH is based upon changes in the Wishart distribution. Complex data (single, dual or quad) is required as input. 2. In the CCDWISH Module Control Panel click Browse and locate the appropriate folder and files for the data you are using. All of these Coherent Change Detection modules can be used in EASI. CCDWM can also be used in EASI as it permits the user to combine the results of the change detection algorithms by specifying a number of CCD output files and weights to provide a weighted metric for the channel of interest. This is usually channel 4 = Ranked change metric. For example if a pixel shows significant change for all CCD algorithms it will rank as more significant than a pixel which only ranks high in one metric but not the other two (e.g. high change in Intensity but small changes in Phase or Wishart would give a low change rank if weights = (1,1,1) and a higher rank if weights = (3,1,1) and very low if weights = (0.001, 10,10). Page 10