CCDWISH

Description

CCDWISH measures change between two single-look complex SAR images based on modified Wishart statistics. The statistical probability of the area of interest being "the same" is computed within the defined analysis window. Areas with a high probability are considered to be unchanged, while areas with a low probability are considered to be changed; that is, they have a low probability of being the same.

Parameters

Name	Type	Length	Value range
Input: Input complex SAR image *	Raster port	1 -
Reference: Reference complex SAR image *	Raster port	1 -
Output: Output Wishart change metric raster *	Raster port	1 -
Window Size	Integer	0 - 1	3 | 5 | 7 | 9 | 11 | 13 | 15 | 17 | 19 | 21 | 23 | 25 | 27 | 29 | 31 | 33 Default: 5

* Required parameter

Parameter descriptions

Input: Input complex SAR image

Specifies the SAR image input layers.

This data must be a complex SAR image in scattering matrix format (symmetrized or non-symmetrized) and it must have the same georeferencing, pixel size, and viewing geometry as the reference image file.

Reference: Reference complex SAR image

Specifies the reference SAR image layers.

The data must be a complex SAR image in scattering matrix format (symmetrized or non-symmetrized), and it must preserve the same structure as the input test image. This file must have the same georeferencing, pixel size, viewing geometry, bit depth, matrix representation, and calibration type as the specified input image.

Output: Output Wishart change metric raster

Specifies the name of the output file that is created. The output file will consist of the overlap area, and four channels that describe:

• the intensity value (or sum of intensities) of the input test data
• the intensity value (or sum of intensities) of the reference data
• the Wishart metric (written in decibels)
• the change, as percentiles, ranked from 0% (no change) to 100% (maximum change)

The direction of change is inferred by visual inspection of the output.

The specified file must not already exist.

Window Size

Optionally specifies the size of the square window that is moved over the images. All of the pixels in the window are averaged together for the value of the center pixel. The window size value must be an odd integer between 3 and 33. The default value of 5 defines a processing window of 5 pixels by 5 lines.

Details

CCDWISH uses Wishart statistics to test the equality of two complex covariance matrices that are assumed to follow a Wishart distribution. When the backscatter coefficients are very close, but either the phase or the correlation coefficient between the co-polarization have changed, the Wishart test statistic is much more sensitive to the differences than test statistics based only on the intensity. In other words, CCDWISH may highlight changes that are not detected by CCDINTEN.

Both the input and the reference images must have been ingested through SARINGEST and must overlap. It is recommended that you check the pixel alignment (or run AUTOSHIFT) before computing the change. The input layers and reference layers must be comparable on a corresponding basis (for example, the first layers from each image must have the same polarizations).

References

Conradsen, K.; Aasbjerg, A.; Schou, J.; Skriver, H.; "A Test Statisitc in the Complex Wishart Distribution and its Application to Change Detection in Polarimetric SAR Data" IEEE Trans. Geosci Remote Sensing, 41, no. 1 (2003): 4-19.