SAR Change Detection module

Description

The SAR Change Detection module detects differences between two input SAR images. Typically, the two images are a reference image and the image with which to compare and, subsequently, in which change, if any, occurs. The images must be from the same SAR sensor.

Parameters

Name	Caption
Polarimetric File	Image to compare with reference image
Polarimetric Reference File	Reference image to compare with input polarimetric image
Output File	File name of output file
Absolute Difference	Whether to calculate absolute difference
Overwrite Results	Overwrite existing results

Parameter descriptions

Polarimetric File

The path and file name of the image to compare with the reference image; that is, the new file that contains the raster data after change occurs.

The supported format of the file is PCIDSK (.pix).

Polarimetric Reference File

The path and file name of the reference (ref) image to compare with the input polarimetric image; that is, the file that contains the raster data before change occurs.

The supported format of the file is PCIDSK (.pix).

Output File

The path and file name of the output image in which change, if any, occurs between the reference and comparison image.

The georeferencing of the output file will be based on that of the reference. The extents of the output file will be the overlap area of the reference and comparison files. For more information about the content of the output file, see Job results.

Absolute Difference

Select this check box to calculate the absolute difference between the new and reference image. For each overlapping pixel in the images, the following calculation is performed:

Absolute difference: abs(new – ref)
Difference: new – ref

Where:

new is the pixel value in the polarimetric image
ref is the pixel value in the reference image

To calculate only the difference, clear the check box.

Overwrite Results

Select this check box to overwrite the existing output files, if any exist. If this check box is left clear, and an output file exists in the relevant folder, the status of the job displays a message informing you of the existence and name of the output file. The message is also written to the event log of the job.

Details

General job details

Preprocessing requirements

Before running this module, the following requirements must be met to ensure the job processes successfully and produces accurate results:

Both images must be the following:

Overlapping
Aligned at the pixel level
Of the same spatial resolution
Of the same number of channels
From the same SAR sensor

For optimum results:

Both images must be coregistered and normalized radiometrically

Module details

The algorithm used to detect change is Channel Difference. The Channel Difference algorithm creates an output channel of the next-highest bit depth to the two input channels. For example, if both the input channel and the input reference channel are 8U, the output channel will be 16S. Similarly, if the input channel is 8U and the input reference channel is 16U, the output channel will be 32R.

Job results

On successful completion, the SAR Change Detection module creates an output PCIDSK (.pix) file. The output file has the same number of channels as that specified as input. Each output channel indicates changes between the new and reference image. The pixel values in the output file depend on the input channels, and on whether the Absolute Difference check box is selected. If the input file contains a NO_DATA_VALUE metadata tag, pixels having a NoData value in either of the input files will be NoData in the output.