PSPOLSYN

Description

PSPOLSYN creates a synthesized detected intensity SAR image for arbitrary transmit and receive polarizations from a fully polarimetric SAR (POLSAR) data set. Creating an image with polarizations that are different from the original ones may reveal information that is not apparent in the input data set.

Parameters

pspolsyn(fili, filo, tpsi, tchi, rpsi, rchi, scaletyp)

Name	Type	Caption	Length	Value range
FILI *	str	Input polarimetric SAR image	1 -
FILO *	str	Output synthesized detected SAR image	1 -
TPSI	List[float]	Transmitted orientation angle (degrees)	0 - 1	-90 - 90 Default: 45
TCHI	List[float]	Transmitted ellipticity angle (degrees)	0 - 1	-45 - 45 Default: 0
RPSI	List[float]	Received orientation angle (degrees)	0 - 1	-90 - 90 Default: 45
RCHI	List[float]	Received ellipticity angle (degrees)	0 - 1	-45 - 45 Default: 0
SCALETYP	str	Scaling	0 - 7	Decibel | Linear Default: Linear

* Required parameter

Parameter descriptions

FILI

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

The input data set 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 and a complete list of supported POLSAR sensors and data products, see the SARINGEST Help.

FILO

Specifies the name of the output detected SAR image that is to be synthesized. The output file has the same dimensions as the input SAR image, and one channel that contains the synthesized detected intensity radar backscatter image in the selected polarization, stored in floating-point pixel values. The physical quantity (beta0, sigma0, or gamma0) represented by the pixel values is the same as for the input SAR data set, but the values can be scaled to be either linear or decibel.

The specified file must not already exist.

TPSI

Optionally specifies the transmitted orientation angle (psi) of the polarization to be synthesized. The specified value must be between -90 degrees and +90 degrees; the default is 45 degrees.

Upon successful completion of this function, the user-specified transmit/receive values are written to the output file's metadata.

TCHI

Optionally specifies the transmitted ellipticity angle (chi) of the polarization to be synthesized. The specified value must be between -45 degrees and +45 degrees; the default is 0 degrees.

Upon successful completion of this function, the user-specified transmit/receive values are written to the output file's metadata.

RPSI

Optionally specifies the received orientation angle (psi) of the polarization to be synthesized. The specified value must be between -90 degrees and +90 degrees; the default is 45 degrees.

Upon successful completion of this function, the user-specified transmit/receive values are written to the output file's metadata.

RCHI

Optionally specifies the received ellipticity angle (chi) of the polarization to be synthesized. The specified value must be between -45 degrees and +45 degrees; the default is 0 degrees.

Upon successful completion of this function, the user-specified transmit/receive values are written to the output file's metadata.

SCALETYP

Optionally specifies the scaling (linear or decibel) of pixel values in the output image.

Details

PSPOLSYN creates a synthesized detected SAR image with linear, circular, or elliptical transmit and receive polarizations.

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

The input file must be a data set that is already imported into the PCIDSK format by SARINGEST. For more information and a complete list of supported polarimetric SAR sensors and data products, see the SARINGEST Help.

For a fully polarized electromagnetic wave, the tip of the electric field vector traces an ellipse on a plane that is perpendicular to the wave propagation direction. Two parameters define the polarization ellipse: orientation and ellipticity. The orientation of the ellipse, psi, can range from -90 degrees to +90 degrees. The ellipticity angle, chi, can range from -45 degrees to +45 degrees. The values specified for these parameters are written to the output file's metadata.

A circle and a straight line are the limiting cases of the ellipse. In the case of a straight line the ellipticity is zero, and the polarization is linear, with psi = 0 degrees (horizontal linear polarization, H) and psi = 90 degrees (vertical linear polarization, V) being the two most common orientations. In the case of a circle, the orientation is 0 degrees and the ellipticity is 45 degrees. An ellipticity of chi = +45 degrees corresponds to a left-circular polarization and chi = -45 degrees corresponds to a right-circular polarization.

The polarization properties of the synthesized image are defined by the transmitted and received orientation and ellipticity angles. They specify the orientation angle (psi) and ellipticity angle (chi) for the transmitted and received signals. The synthesized image is in the linear or decibel scale, depending on the setting of the scaling parameter.

If the synthesized backscatter cannot be computed at a pixel, the stored value depends on the output scaling. For linear scaling, the pixel value is set to zero. For decibel scaling, the pixel value is set to -10000.0.

Example

Create a synthesized backscatter image in the linear scale from a RADARSAT-2 data set that has already been imported to PCIDSK by SARINGEST. The two synthesized polarizations are circular: left for transmit and right for receive. For circular polarizations, the orientation (psi) is ignored and can be set to 0.

from pci.pspolsyn import pspolsyn

fili	=	"rsat2.pix"
filo	=	"rsat2_LR.pix"
tpsi	=	[0]
rpsi	=	[0]
tchi	=	[45]
rchi	=	[-45]
scaletyp	= ""

pspolsyn( fili, filo, tpsi, rpsi, tchi, rchi, scaletyp )

Algorithm

PSPOLSYN first creates the transmit and receive linear polarization unit vectors in the horizontal-vertical basis. The vectors are constructed from the orientation and ellipticity angles of the polarizations that are specified in the TPSI, RPSI, TCHI, and RCHI parameters.

For input data in the scattering matrix format, the unit vectors are combined directly with the matrix at each pixel. The transpose of the receive unit vector multiplies the matrix on the left, and the transmit unit vector multiplies the matrix on the right. The square of the absolute value of the resulting number is the synthesized intensity at the pixel.

For input data in the covariance and coherency matrix formats, the unit vectors are combined to derive a (4x1) vector for the non-symmetrized matrix and a (3x1) vector for the symmetrized matrix. The operation takes the Kronecker product (also called the outer product or tensor product) of the two unit vectors. For input data in the coherency matrix format, a scaling matrix is also used. The transpose of the derived vector then multiplies the input matrix on the left and the complex conjugate of the derived vector multiplies the matrix on the right. The resulting number is the synthesized backscatter intensity at the pixel.

For the input data in the Kennaugh matrix format, the Stokes vectors are formed for the synthesized transmit and receive polarizations. The transpose of the receive Stokes vector multiplies the matrix on the left and the transmit Stokes vector multiplies the matrix on the right. One-half of the resulting number is the synthesized backscatter intensity at the pixel.

The derived backscatter represents the same physical quantity (sigma0, beta0, or gamma0) as the input data, in the linear scale. If the output is requested in decibels in the SCALETYP parameter, the computed value is converted as follows:

bcksct_db = 10 * log10( bcksct_lin )
            

The bcksct_db is the output pixel value, in the decibel scale, log10() is the base 10 logarithm, and bcksct_lin is the derived backscatter value, in linear scaling.

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.