Help Content > Polarimetry and PolInSAR Module > Reference Guide Polarimetric Interferometry

Purpose

The coregistration of a pair of polarimetric Single Look Complex acquisitions is performed. This step is necessary to get a correspondence, with sub-pixel accuracy, between the Reference and Secondary acquisition in order to enable the further interferometric processing.

It must be noted that, for a proper execution of the polarimetric interferometric processing, calibrated data are required.

Although a full-polarimetric dataset acquired in linear polarization (HH, HV, VH, VV) is the default usage of this functionality, the input file list may be composed by any number of SLC data (linear or synthesized polarization or any other data type).

Technical Note

The Secondary to Reference coregistration is performed first by means of the orbital parameters, then using a cross-correlation function between the two Intensity images, and finally the shift is refined by automatically selecting a series of image "chips" where mini-interferograms are calculated. If the coherence is too low the number of points for the fine shift estimate can be not sufficient to optimize the coregistration process. In this case the coregistration will be carried out using the orbits and an improved cross correlation based fit, which allow a coregistration with sub-pixel accuracy.

In case the two acquisitions are very much different in terms of areal coverage, the smallest one should be used as "Input Reference files" in order to avoid the coregistration windows to be located in areas with null pixel values, which can eventually cause the coregistration process to fail.

The two input list must be consistent between each other, e.g. Input Reference HH and HV, Input Secondaru HH and HV.

The first file of the list is used to compute the coregistration parameters. Typically the HH polarization is the most suitable for this purpose.

It is possible to perform the coregistration in a manual way, by manually locating the center of the windows (i.e. Cross-correlation Grid and Fine Shift Parameters) in the Input reference file (see input "Coregistration file" below).

It must be noted that the output coregistered Reference and Secondary data are over sampled (i.e. multiplied by a factor two) in range direction. This has to be taken into account for a proper execution of the further processing steps.

Input Files

Input Reference files

Input file names of the Reference polarimetric data set (_slc, _slc_list). These files are mandatory.

Input Secondary files

Input file names of the Secondary polarimetric data set (_slc,_slc_list). These files are mandatory.

Optional Files

Geometry GCP File

A previously created Ground Control Point file (.xml), with the points used for the manual coregistration (.xml), is automatically loaded. These points represent the center of the coregistration windows. This file is optional.

Shift Parameter file

Name of the file with the shift parameters used for the coregistration (_par). This file is mandatory. If the Compute shift parameter flag is set, it is generated as output.

ScanSAR-TOPSAR Spectral Diversity Avoid Area

Spectral Diversity is used to improve the coregistration along the Azimuth direction of the ScanSAR-TOPSAR mode data. Without a perfect coregistration along the azimuth direction phase slopes will appear along the same direction. Issues may arise when the spectral diversity is calculated on areas that show phase slopes along the azimuth direction related to real and strong surface displacement event (e.g. earthquakes); in such circumstances the tool could interpretate the phase ramp as a consequence of a miss-coregistration. To avoid this behavior the user can draw the area where the spectral diversity should not be performed. The shapefile of the avoid area must be geocoded (lat-long). All the ScanSAR or TOPSAR bursts which intersect this shapefile will be avoided during the Spectral Diversity estimation step. This file is optional.

Parameters - Principal Parameters

Compute Shift Parameters

By setting this flag, the coregistration shifts between Reference and Secondary image are calculated and saved into the _par file.

Coregistration With DEM

This parameter can not be defined by the user.

Parameters - Global

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

Parameters - Coregistration

It brings to the coregistration section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

Parameters - Other Parameters

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

Output Files

Output Reference File list

Output file names of the Reference polarimetric data set (_slc). These files are mandatory.

Output Secondary File list

Output file names of the Secondary polarimetric data set (_slc). These files are mandatory.

_slc_rsp / _slc_list_rsp

Coregistered data with the associated header files (.sml, .hdr).

_sint

Synthetic phase with the associated header files (.sml, .hdr).

_srdem

Digital Elevation Model, in slant range geometry, with the associated header files (.sml, .hdr).

rg_sint

Synthetic phase in range with the associated header files (.sml, .hdr).

az_sint

Synthetic phase in azimuth with the associated header files (.sml, .hdr).

_par

ASCII file containing the coregistration shift parameters in range and azimuth. This file is generated only if the shift parameters are calculated.

_orbit_off.shp

Shape file with the points used to estimate the orbit based shift. This file contains the following information:

•Pixel position in range direction (Range), in Single Look pixel units.

•Pixel position in azimuth direction (Azimuth), in Single Look pixel units.

•Shift measured in range direction (Dr), in Single Look pixel units.

•Shift measured in azimuth direction (Da), in Single Look pixel units.

•Calculated polynomial shift, to apply in range direction (Drfit), in Single Look pixel units.

•Calculated polynomial shift, to apply in azimuth direction (Dafit), in Single Look pixel units.

The file, which is generated only when the shift parameters are calculated, is over sampled (i.e. multiplied by a factor two) in range direction.

_winCC_off.shp

Shape file with the points used to estimate the cross correlation based shift from the Intensity data. In addition to the information provided by the "_orbit_off.shp" file, this file contains also the cross-correlation value (it is dimensionless and it can vary from 0 to 1) and the following two residual shift measurements (calculated with respect to the orbit and topography related shift):

•Residual shift in range direction (Dr).

•Residual shift in azimuth direction (Da).

The file, which is generated only when the shift parameters are calculated, is over sampled (i.e. multiplied by a factor two) in range direction.

_winCoh_off.shp

Shape file with the points used to estimate the coherence based shift from the complex data (fine shift estimate). In addition to the information provided by the "_orbit_off.shp", this file contains also the following information:

•Signal to Noise Ratio (SNR), which is a linear dimensionless value.

•Coherence value. It is dimensionless and it can vary from 0 to 1.

The file, which is generated only when the shift parameters are calculated, is over sampled (i.e. multiplied by a factor two) in range direction.

Details specific to the Units of Measure and Nomenclature of the output products can be found in the Data Format section.

General Functions

Exec

The processing step is executed.

Store Batch

The processing step is stored in the batch list. The Batch Browser button allows to load the batch processing list.

The window will be closed.

Help

Specific help document section.

Specific Function(s)

None.

Polarimetry and PolInSAR - Polarimetric Interferometry - SLC Coregistration

Polarimetry and PolInSAR - Polarimetric Interferometry - SLC Coregistration