ANSI-C program: stokes.c
NAME
stokes - Calculate Stokes parameters from co-polarized and
cross-polarized linear polarization SLC images, for example HH
and HV, or VV and VH.
SYNOPSIS
stokes <SLC-1> <SLC-2> <SLC1_par>
<SLC2_par> <S> <S_par> <rlks>
<azlks> [loff] [nlines]
| <SLC-1> | (input) HH, VV, RH, LH single-look complex image (scomplex or fcomplex format) |
| <SLC-2> | (input) HV, VH, RV, LV single-look complex image
coregistered with SLC-1 (scomplex or fcomplex format) NOTE: 1. SLC images must be a co-pol and cross-pol pair with the same transmit polarization and linear receive polarization (HH, HV), (VV, VH), (RH, RV), or (LH, LV) 2. SCOMPLEX SLC data are scaled by .001 to increase dynamic range |
| <SLC1_par> | (input) SLC image parameter file of SLC-1 |
| <SLC2_par> | (input) SLC image parameter file of SLC-2 coregistered with SLC-1 |
| <S> | (output) root file name of 4 Stokes parameter files
with extensions .s0, .s1, .s2, .s3 (float) NOTE: expressed in the H,V polarization basis, BSA convention, the Stokes parameters given by: s0: <|E_h|**2 + |E_v|**2> s1: <|E_h|**2 - |E_v|**2> s2: 2Re<E_h E_v*> s3: -2Im<E_h E_v*> |
| <S_par> | (output) image parameter file associated with the Stokes parameter data files (enter - for none) |
| <rlks> | number of range looks used to calculate Stokes parameters |
| <azlks> | number of azimuth looks used to calculate Stokes parameters |
| [loff] | offset to starting line (default: 0) |
| [nlines] | number of SLC lines to process (enter - for default: entire file) |
EXAMPLE
stokes 20080415_HH.slc 20080415_HV.slc 20080415_HH.slc.par
20080415_HV.slc.par 20080415_HH_HV 20080415_HH_HV.mli.par 2
4
This calculates the 4 Stokes parameters s0, s1, s2, and s3 and stores them in the files 20080415_HH_HV.s0, 20080415_HH_HV.s1, 20080415_HH_HV.s2, 20080415_HH_HV.s3
DESCRIPTION
The Stokes parameters describe the polarization state of an electromagnetic field, see http://en.wikipedia.org/wiki/Stokes_parameters. The set of 4 parameters are given different designations in the literature with the letters (I, Q, U, V), (s0, s1, s2, s3), (s1, s2, s3, s4), (g0, g1, g2, g3) are also widely used. The parameters denote the amount of power in the different possible polarization basis: linear, 45 degree, and circular as well as the total power scattered by the scene.
The program stokes calculates the following terms given linear polarized H and V SLC radar data as input:
s0 = < |EH|2 + |EV|2 >
s1 = < |EH|2 - |EV|2 >
s2 = 2 Re<EH E*V>
s3 = -2 Im<EH E*V>
The single-pixel Stokes parameters are averaged over a rectangular region that is rlks by azlks in size and the average values are written to the individual output files. What is significant about the Stokes parameters is that they are real-valued parameters and can fully describe the polarization state of the field. s0 is the average total incident power while the other three parameters describe the difference of powers in each of the polarization bases. s1 gives the difference in power of the H and V linear components, s2 the difference of the linear components at 45 and 135 degrees, and s3 the difference between the right-hand and left-hand circularly polarized components. An electromagnetic field with random polarization will have components s1, s2, and s3 equal to 0. The degree of polarization m is defined as:
m = (s12 + s22 + s32)1/2 / s0
If the field is totally polarized, such as for a monochromatic plane wave:s0 = (s12 + s22 + s32)1/2
The Stokes parameters s1, s2, and s3 can be represented as a point in 3 dimensions on the Poincaré sphere, see http://en.wikipedia.org/wiki/Polarization_(waves) and http://spie.org/x32375.xml.
SEE ALSO
typedef_ISP.h, stokes_qm