PSPHDIFF

Description

PSPHDIFF derives the phase-angle difference between two polarizations of a polarimetric SAR (POLSAR) data set. Processing of dual-polarization, compact-polarization, and quad-polarization polarimetric data is supported. The phase difference is noisy for single-look complex data and for multi-look data with an effective number of looks (ENL) of less than 25. The phase difference can be written as radians or degrees.

Parameters

psphdiff(fili, filo, pol1, pol2, angletyp)

Name	Type	Caption	Length	Value range
FILI*	str	Input polarimetric SAR image	1 -
FILO*	str	Output phase difference raster	1 -
POL1	str	First input polarization	0 -	Default: HH
POL2	str	Second input polarization	0 -	Default: VV
ANGLETYP	str	Angle units	0 - 7	Degrees | Radians Default: Degrees

* Required parameter

Parameter descriptions

FILI

The name of the input polarimetric SAR data set, which must be either dual-polarization, compact-polarization, or non-symmetrized or symmetrized fully polarimetric (quad-polarization) complex data. The input data set must be in one of the following matrix formats: scattering, covariance, coherence, or Kennaugh. Detected input data sets (single-look detected, multi-look detected) cannot be used: information about phase is insufficient. To minimize noise, it is recommended that the input data set have an equivalent number of looks (ENL) of at least 25, which can be done by applying a polarimetric filter to the image, such as boxcar, before computing phase difference.

The input data set must have already been imported into the PCIDSK (.pix) format with SARINGEST. Input can also 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 SAR sensors and data products, follow the link to SARINGEST at the end of this topic.

FILO

The name of the output file to which to write the phase-difference channel. The output file has the same dimensions as the input, and one floating-point channel that contains the phase-angle difference between the two selected polarizations at every pixel.

The file name you specify must not already exist.

POL1

The first polarization in the input file to use. The default value is HH.

With full-quad data sets, you can, as an option, synthesize any polarization of interest. For more information, follow the link to PSPOLSYN at the end of this topic, and see the Details section.

Standard configurations, such as linear-horizontal (H), linear-vertical (V), left-circular (L), and right-circular (R) are supported. Non-standard configurations require four floating-point values; orientation and ellipticity for transmit, followed by orientation and ellipticity for receive. Valid orientation angles range from -90 to 90. Valid ellipticity angles range from -45 to 45.

• rh: case-insensitive, predefined transmit and receive
• Rh: case-insensitive, predefined transmit and receive
• rH: case-insensitive, predefined transmit and receive
• 0,-45,H: transmit TPSI and TCHI followed by predefined receive
• 0,-45,h: transmit TPSI and TCHI followed by predefined receive
• R,0,0: predefined transmit followed by receive RPSI and RCHI
• r,0,0: predefined transmit followed by receive RPSI and RCHI
• 0,-45,0,0: transmit TPSI and TCHI followed by receive RPSI and RCHI

This parameter is optional.

POL2

The second polarization in the input file to use. The default value is VV. The behavior of this parameter is identical to that of POL1.

This parameter is optional.

ANGLETYP

The angle units for the output phase difference channel, in degrees or radians. The default unit is degrees.

This parameter is optional.

Details

PSPHDIFF computes the phase-angle difference between two polarizations of a polarimetric SAR data set at every pixel. You can select any combination from the available polarizations.

The input data set must contain either non-symmetrized or symmetrized fully polarimetric (quad-polarization complex) data in one of the following matrix formats: scattering (s4c or S3c), covariance (c4r6c or C3r3c), coherency (t4r6c or T3r3c), or Kennaugh (k16r or K9r).

The polarizations provided by the ENVISAT ASAR alternating-polarization mode have no Doppler overlap. The two polarizations are incoherent, relative to each other, and the phase difference between them is not expected to provide any useful information.

RADARSAT-2 dual-polarized products provide combinations of copolarization and cross-polarization (HH+HV or VV+VH). Over most targets, the phase difference between copolarized and cross-polarized channels is noisy (even with multi-looking) and provides little information. The phase difference between the copolarized channels (HH - VV) is of greater interest. For point targets, the phase difference between HH and VV should be low; for double-bounce targets, the phase difference should be close to 180 degrees.

Example

Derive the phase angle difference between the two copolarizations of a dual-pol RADARSAT-2 data set that has already been imported into the PCIDSK (.pix) format. The output phase angle is in degrees.

from pci.psphdiff import *

fili	=	"radarsat2.pix"
filo	=	"ph_HH_VV.pix"
pol1	=	"HH"
pol2	=	"VV"
angletyp	=	"degrees"

psphdiff( fili, filo, pol1, pol2, angletyp )
      

Algorithm

If the input data is not stored as a covariance matrix, the input data file is automatically converted to covariance. If the requested polarizations are available, they are selected. If the input data is full-quad, and if the requested polarization is not available, the requested polarizations are automatically synthesized. The phase difference (phi) is computed as the arctangent of the covariance of the requested polarizations.

Phi = atan2 [Imag (P1*conj(P2)), Real (P1*conj(P2))] where conj is the complex conjugate and P1 and P2 are the complex values of the requested polarizations.

Depending on the value specified for the ANGLETYP parameter, results are returned between -180 and 180 degrees, or between -PI and PI radians.

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.