PSPOLSYNR

Description

PSPOLSYNR creates a synthesized backscatter image from a fully polarimetric SAR (POLSAR) data set. The transmitted and received polarizations used for synthesis are determined automatically by the program to maximize the backscatter for the target provided.

Parameters

Name	Type	Caption	Length	Value range
FILI*	String	Input polarimetric SAR image	1 - 192
TARGETS*	String	Input target layer (bitmap or vector)	1 - 192
FILO	String	Output synthesized detected SAR image	0 - 192
MONITOR	String	Monitor mode	0 - 3	ON, OFF Default: ON

* Required parameter

Parameter descriptions

FILI

The name of the input polarimetric SAR data set, which must be either nonsymmetrized or symmetrized fully polarimetric (quad-polarization) complex data. The input data set must be in scattering, covariance, coherence, or Kennaugh matrix format.

The input must be a data set that has already been imported into the PCIDSK (.pix) format by SARINGEST, or it may be the key file name of any GDB-supported POLSAR data set in its distribution format. For more information, including a complete list of supported POLSAR sensors and data products, follow the link to SARINGEST under Related functions at the end of this topic.

TARGETS

The name of the file that contains vector targets, bitmap targets, or both. The file must be in PCIDSK (.pix) format.

The vector layer or bitmap with the lowest segment number is used to delineate the target. All other vector layers or bitmaps in the file are ignored. Vector layers must overlap the imagery. If you use bitmaps, they must have the same dimensions as the input SAR image.

If necessary, you can create targets in CATALYST Professional Focus or import targets from another image. You can generate geocoded vector targets in Focus or CATALYST Professional SAR Polarimetry Target Analysis, or you can import the targets from another source.

FILO

The name of the output synthesized backscatter file that is created. The output file contains a single channel and has the same dimensions as the input SAR image. The output channel contains the synthesized radar backscatter image, which is stored as floating point pixel values in the linear scale. The polarizations used for synthesis are automatically determined by PSPOLSYNR to maximize the return from the specified target. If the synthesized backscatter cannot be computed at a pixel, the pixel value is set to zero. The optimal transmit and receive ellipticity and orientation values (in degrees) are written to the output file metadata.

The specified file must not already exist.

MONITOR

The program progress can be monitored by printing the percentage of processing completed. A system parameter, MONITOR, controls this activity.

Available options are:

• ON: Turns the monitor ON (default)
• OFF: Turns the monitor OFF (recommended if running in batch or background mode)

Details

PSPOLSYNR creates a synthesized backscatter image from a fully polarimetric SAR data set.

The input polarimetric SAR image must represent a nonsymmetrized or symmetrized, fully polarimetric (quad-polarization, complex) data set in the scattering (s4c or S3c), covariance (c4r6c or C3r3c), coherency (t4r6c or T3r3c), or Kennaugh (k16r or K9r) matrix format.

The polarizations used for synthesis are automatically selected by the program to maximize the returned signal of a selected target. The polarizations are determined by searching the full ranges of the orientation and ellipticity angles for the transmitted and received polarizations.

The identified transmitted and received polarizations are then used to synthesize the radar backscatter at every pixel in the input data set. The synthesis algorithm is the same as in PSPOLSYN.

Example

Create a synthesized backscatter image that maximizes the response of a target. The input image is a RADARSAT-2 quad-polarized SLC image that is already converted to the PCIDSK format. The target is represented by a bitmap that is created in the input file.

        EASI>FILI	=	"radarsat2.pix" 
        EASI>TARGETS	=	"radarsat2.pix" 
        EASI>FILO	=	"max_r_1.pix"

        EASI>run PSPOLSYNR     
      

Algorithm

PSPOLSYNR maximizes the return from the specified target. The sigma0 radar backscatter is shown here, but the computations can also use the gamma0 radar backscatter or beta0 radar brightness. The physical quantity is always the same as in the input data set.

In PSPOLSYNR, the radar backscatter of a target is expressed in terms of the Kennaugh matrix of the target, and the transmit and receive Stokes vectors. For target a, the expression is as follows:

        1
        (sigma0)a = - * Transpose(Fr) * ka * Ft
        2
      

Ft and Fr represent Stokes vectors for the transmit and receive polarizations, respectively; ka is the averaged nonsymmetrized Kennaugh matrices for the target a. For symmetrized data, the matrix Ka is used.

A Stokes vector (F) is defined by its orientation (psi) and ellipticity (chi) angles, as follows:

        F = Transpose( 1, cos(2*psi)*cos(2*chi), sin(2*psi)*cos(2*chi), sin(2*chi) )
      

The transmit and receive orientation and ellipticity angles are used for Ft and Fr, respectively.

If required, PSPOLSYNR first converts the input data to the Kennaugh matrix format. A symmetrized or nonsymmetrized matrix matches the symmetry of the input data set. PSPOLSYNR then computes the average Kennaugh matrix ka for the target a by averaging every matrix element over all pixels of the target.

PSPOLSYNR then searches for the transmit and receive polarizations that maximize the return from the specified target as follows:

• Initialize (sigma0)max = 0
• For psi, from -90 degrees to +90 degrees, in 1-degree increments
  • For chi, from -45 degrees to +45 degrees, in 1-degree increments
    • Derive the transmit Stokes vector Ft with the current values of the psi and chi angles
    • Derive the Stokes vector of the wave scattered by the target a as follows:

                    Fa = Transpose(Fa1, Fa2, Fa3, Fa4) = ka * Ft
                  

    • Derive the maximum backscatter (sigma0)a from target a for the current Ft as follows:

                    (sigma0)a = ( Fa1 + sqrt(Fa2^2 + Fa3^2 + Fa4^2) ) / 2
                  

    • If the computed backscatter represents a new maximum, the processing parameters are updated as follows:

                    (sigma0)max = (sigma0)a
                    (Ft)max = Ft
                    Transpose( sqrt(Fa2^2 + Fa3^2 + Fa4^2), Fa2, Fa3, Fa4 )            
                    (Fr)max =  ------------------------------------------------------- 
                    sqrt(Fa2^2 + Fa3^2 + Fa4^2)
                  

When the search is completed, the output image is synthesized from the Stokes vectors (Ft)max and (Fr)max, and from the input Kennaugh matrix k(i,j) at every image pixel, (i,j). The synthesized backscatter is computed as follows:

        1
        sigma0(i,j) =  - * Transpose((Fr)max) * k(i,j) * (Ft)max
        2 
      

Acknowledgements

PCI Geomatics gratefully acknowledges the financial support provided by the Canadian Space Agency through the Earth Observation Application Development Program (EOADP), contract number 9F028-034946.