INSADJUST

Description

INSADJUST adjusts the phase of interferograms to eliminate low-frequency fringes due to small errors in the interferometric perpendicular base line caused by orbital errors in position, velocity, or both. The module uses fast Fourier transform (FFT) in the spectral domain to remove residual orbital fringes.

Parameters

insadjust(fili, dbic_ocs, dbic, filo, maxiter)

Name	Type	Caption	Length	Value range
FILI*	str	Name of database input file	1 -
DBIC_OCS*	List[int]	Source channel of orbital correction	1 - 1
DBIC	List[int]	List of database input channels	0 -
FILO*	str	Name of database output file	1 -
MAXITER	List[int]	Maximum number of iterations	0 - 1	1 - 20 Default: 10

* Required parameter

Parameter descriptions

FILI

The name of the PCIDSK file from which to read uncorrected interferogram data.

DBIC_OCS

The input interferogram channel to use to derive the orbital corrections. The channel must have 32-bit complex values, and an InSARContent metadata tag set to one of the following:

• RawInterferogram
• TopographicInterferogram
• DeformationInterferogram

DBIC

The input interferogram channel or channels to correct with the orbital adjustments derived from the source orbital-correction channel you specify. Each channel must have 32-bit complex values, and have the appropriate InSARContent metadata tag. If you specify the default value, only the source channel of orbital correction will be corrected.

The same correction is applied to each channel you specify.

FILO

The name of the output PCIDSK file to which to write phase values corrected for orbital adjustment. The coherence value of the interferogram remains unchanged.

MAXITER

The maximum number of iterations for removing the residual fringes, up to a maximum of 20. The iteration process is monitored and may end before reaching the number of iterations you specify depending on the number of cycles per image and whether any oscillation correction occurs.

The default value is 10; typically, however, the process converges in fewer steps.

For more information about the iteration process, see Details.

Details

INSADJUST removes low-frequency, residual-phase errors in SAR interferograms by applying a correction algorithm in the fast Fourier transform domain (FFT). The input file must be in slant-range geometry, and the incident-angle-array segment must be available in the metadata. The channel or channels you specify must have pixel values that are 32-bit complex and stored in the Real, Imaginary (Cartesian) format.

The correction is derived from the interferogram in the source channel you specify as input: select the interferogram with the highest coherence as the source channel. The derived correction is then applied to all interferogram channels you specify as input interferograms. INSADJUST writes the processed channels to the output file in the order you specify.

The FFT is derived for the entire interferogram you specify as the source channel for orbital correction. The x and y sizes are set to the smallest power-of-two values equal to, or higher than, the pixel-and-line dimensions of the input file. The transform is written to a temporary file and, on completion of processing, deleted.

INSADJUST allocates sufficient memory to contain the entire input channel and all the FFT data, but will not exceed 60 percent of system memory. If there is insufficient memory to accommodate processing buffers, the image and FFT are processed as tiles. This reduces processing speed, but does not effect the result. Large images may take longer to process.

The algorithm iteratively detects the residual low-frequency signal in the FFT domain, and then removes it in the image domain.

The iteration process may end before reaching the number of iterations you specify. The process is system-monitored, and ends if the current-iteration adjustment is smaller than 0.001 cycles per image (checked separately for the horizontal and vertical image dimensions). The process may also end when an oscillating correction occurs. This condition is detected when the derived current-iteration adjustment is larger than the adjustment in the previous iteration. With oscillating solutions, the output image reflects the correction applied in the iteration prior to the one that diverged.

In typical processing scenarios, you run INSADJUST after running topographic correction with INSTOPO.

On successful processing, the output file you create will have corrected interferograms with no strongly attenuated, low-frequency noise (residual fringes), and an average of zero radians in their phases.

Example

Remove the orbital fringes from a single-channel interferogram by using a maximum of 10 iterations (default).

from pci.insadjust import *

fili	=	'InSAR_1_2.pix'
dbic_ocs=	[1]
dbic	=	[]
filo	=	'InSAR_1_2_Adjusted.pix'
maxiter =	[10]

insadjust ( fili, dbic_ocs, dbic, filo, maxiter )

Algorithm

Convert the interferogram from the spatial domain to spectral. INSADJUST identifies iteratively the maximum horizontal and vertical fringe rates and adjusts the interferometric phase to remove the fringes by using the known viewing geometry. The iterative process continues until one of convergence, oscillation, or the maximum number of iterations occurs.

Acknowledgements

The PCI Interferometric SAR (InSAR) project was funded in part by the Canadian Space Agency under the Earth Observation Application Development Program (EOADP) contract (9F043-130644/006/MTB), Application Development for Environmental Monitoring and Remediation.