CCDPHASE

Description

CCDPHASE measures change based on the average coherence (over a specified window size) between two co-registered single-look complex SAR images. Coherence values will range between zero and one, where areas of change will have coherence values close to zero (that is, they are incoherent) while unchanged areas will have higher values (that is, will be coherent).

Parameters

ccdphase(fili, filref, dbic, filo, winsize)

Name	Type	Caption	Length	Value range
FILI *	str	Input complex SAR image	1 -
FILREF *	str	Reference complex SAR image	1 -
DBIC	List[int]	Input complex SAR image channels	0 -
FILO *	str	Output phase change metric raster	1 -
WINSIZE	List[int]	Window size (pixels)	0 - 1	3 | 5 | 7 | 9 | 11 | 13 | 15 | 17 | 19 | 21 | 23 | 25 | 27 | 29 | 31 | 33 Default: 5

* Required parameter

Parameter descriptions

FILI

Specifies the name of the input file that contains the test SAR image data.

The 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.

FILREF

Specifies the name of the file that contains the reference SAR image data.

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.

DBIC

Optionally specifies the list of input channels to be processed. The specified channels must exist for both the input and reference images, and must be comparable; that is, they must have the same data type and polarization. By default, all channels from the input test and reference file are used to compute the change.

FILO

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 absolute value of the intensity ratio (written in decibels) between the test and reference average coherence
• 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.

WINSIZE

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

CCDPHASE performs change detection based on phase information. It computes the intensity and polarimetric coherence value for each pixel in the overlap area, and determines the magnitude of the average coherence value. Change is determined based on the ratio of the computed total power for each pixel, to the magnitude of the average coherence value of the images. The computed change is written to cumulative percentiles, where negative values represent a "loss" and positive values represent a "gain" with respect to the reference image.

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.

Example

This example uses two Radarsat-2 Fine QuadPol images created by SARINGEST to measure the changes between September 19th and September 25th, based on phase information.

from pci.ccdphase import ccdphase

fili	=	'rsat2_FQ15_sep19.pix'	# input image file name
filref	=	'rsat2_FQ15_sep25.pix'	# reference image file name
dbic	=	[]	# uses all polarizations to detect change
filo	=	'rsat2_FQ15_sep25_ccdphase.pix'	# output file name
winsize	=	[]	# use default processing window of 5 by 5

ccdphase(fili, filref, dbic, filo, winsize)