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<< Click to Display Table of Contents >> Polarimetry and PolInSAR - Polarimetry - Polarimetric Calibration Matrix |
  
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<< Click to Display Table of Contents >> Polarimetry and PolInSAR - Polarimetry - Polarimetric Calibration Matrix |
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Purpose
Polarimetric calibration allows, in general, to minimize the impact of non ideal behaviours of a full-polarimetric SAR acquisition system, to obtain an estimate of the scattering matrix of the imaged objects as accurate as possible from their available measurement.
The calibration (or distortion) matrix is annotated within the header file (PolarimetricCalibrationParameters section) of the calibrated products.
In case of originally calibrated products (e.g. ALOS PALSAR data in JAXA format), this step has not to be executed unless a new - and more accurate - calibration matrix was available.
Technical Note
The terms of the matrixes that multiply the true target scattering matrix S, that represent non ideal behaviours of the acquisition system, like imbalance and cross-talk, are usually estimated using reference targets of well-known polarimetric response, like dihedral or trihedral Corner Reflectors as well as natural distributed random targets like forests and water areas. The N noise terms are normally neglected during the calibration process. The purpose of this processing step is to perform the matrix products to obtain an estimate of the S matrix from the measured Z one, using either a user-provided calibration matrix or a default one, as typically available with the original product. It shall be noticed that such a calibration matrix may be expected as quite constant along the life of a spaceborne sensor (i.e. ALOS PALSAR) or subject to periodic updates, but not to be estimated for every single scene.
The relationship between the true and the measured scattering matrixes S and Z of a target are expressed by the following equation:
Where:
| S | = Scattering matrix |
| f1,2 | = Channel amplitude imbalance |
| δ1,2 | = Cross talk |
| N | = Thermal noise |
| Ω | = Faraday rotation |
| A | = Absolute calibration |
Input Files
Input HH File
Input file name of the uncalibrated HH data (_slc). This file is mandatory.
Input HV File
Input file name of the uncalibrated HV data (_slc). This file is mandatory.
Input VH File
Input file name of the uncalibrated VH data (_slc). This file is mandatory.
Input VV File
Input file name of the uncalibrated VV data (_slc). This file is mandatory.
Optional Files
Input Calibration Matrix
Calibration matrix set by the user (.sml). This optional file must be formatted as follows:
<?xml version="1.0" ?>
<HEADER_INFO xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.sarmap.ch/xml/SARscapeHeaderSchema
_version_1.0.xsd">
<PolarimetricCalibrationParameters>
<DT_Real>
<MatrixDouble NumberOfRows = "2" NumberOfColumns = "2">
<MatrixRowDouble ID = "0">
<ValueDouble ID = "0">1</ValueDouble>
<ValueDouble ID = "1">-0.028047</ValueDouble>
</MatrixRowDouble>
<MatrixRowDouble ID = "1">
<ValueDouble ID = "0">0.0316404</ValueDouble>
<ValueDouble ID = "1">0.9352351</ValueDouble>
</MatrixRowDouble>
</MatrixDouble>
</DT_Real>
<DT_Immaginary>
<MatrixDouble NumberOfRows = "2" NumberOfColumns = "2">
<MatrixRowDouble ID = "0">
<ValueDouble ID = "0">0</ValueDouble>
<ValueDouble ID = "1">-0.0029335</ValueDouble>
</MatrixRowDouble>
<MatrixRowDouble ID = "1">
<ValueDouble ID = "0">-0.0103815</ValueDouble>
<ValueDouble ID = "1">0.4073565</ValueDouble>
</MatrixRowDouble>
</MatrixDouble>
</DT_Immaginary>
<DR_Real>
<MatrixDouble NumberOfRows = "2" NumberOfColumns = "2">
<MatrixRowDouble ID = "0">
<ValueDouble ID = "0">1</ValueDouble>
<ValueDouble ID = "1">-0.0369903</ValueDouble>
</MatrixRowDouble>
<MatrixRowDouble ID = "1">
<ValueDouble ID = "0">0.0211591</ValueDouble>
<ValueDouble ID = "1">0.7249998</ValueDouble>
</MatrixRowDouble>
</MatrixDouble>
</DR_Real>
<DR_Immaginary>
<MatrixDouble NumberOfRows = "2" NumberOfColumns = "2">
<MatrixRowDouble ID = "0">
<ValueDouble ID = "0">0</ValueDouble>
<ValueDouble ID = "1">0.0008454</ValueDouble>
</MatrixRowDouble>
<MatrixRowDouble ID = "1">
<ValueDouble ID = "0">0.0056483</ValueDouble>
<ValueDouble ID = "1">0.0005536</ValueDouble>
</MatrixRowDouble>
</MatrixDouble>
</DR_Immaginary>
<ReceiverGainForLikePolatizedDB>24</ReceiverGainForLikePolatizedDB>
<ReceiverGainForCrossPolatizedDB>24</ReceiverGainForCrossPolatizedDB>
</PolarimetricCalibrationParameters>
</HEADER_INFO>
Parameters - Principal Parameters
Calibration Type
The selection of one of the following operations is mandatory:
-Use Alos Palsar Calibration Matrix
It is intended to apply the calibration estimates - the same available in the standard JAXA SLC products - on SLC data generated with the Focusing module.
-Revert Calibration
The calibration matrix is inverted, removing the effect of a previous calibration.
As an example, SLC products provided by JAXA are calibrated with a reference matrix. If more accurate calibration estimates are available, the calibration process is inverted to perform a new (more accurate) one.
-Use Input Calibration Matrix
The Parameter file containing the relevant calibration matrix (Input Matrix file) is used.
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 - 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 HH File
Output file name of the calibrated HH data (_slc). This file is mandatory.
Output HV File
Output file name of the calibrated HV data (_slc). This file is mandatory.
Output VH File
Output file name of the calibrated VH data (_slc). This file is mandatory.
Output VV File
Output file name of the calibrated VV data (_slc). This file is mandatory.
_cal_slc
Calibrated scattering matrix (HH, HV, VH, VV) with the associated header files (.sml, .hdr).
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.
Close
The window will be closed.
Help
Specific help document section.
Specific Function(s)
None.
Task, SARscapeBatch object, SARscapeBatch script example
References ESA, Polarimetric SAR Interferometry tutorial A. Freeman. "SAR calibration: an overview". IEEE Transactions on Geoscience and Remote Sensing, Vol. 30, No. 6, 1992. S. Quegan. "A unified algorithm for phase and cross-talk calibration of polarimetric data-theory and observations". IEEE Transactions on Geoscience and Remote Sensing, Vol. 32, No. 1, 1994.