Computer session on measurement and analysis of waves and turbulence

6th COSPAR Capacity Building Workshop

Sinaia, Romania, June 4-16, 2007

Ondrej Santolik


4. Stokes parameters in the polarization plane

The Stokes parameters are widely used in optics and radioastronomy to describe the polarization state of electromagnetic waves in the plane perpendicular to their group velocity. In the case of waves in an anisotropic medium (low frequency waves in a magnetized plasma) it is useful to determine the Stokes parameters in the plane perpendicular to the wave vector since its direction may be very different from the group velocity. Multicomponent wave measurements can be first analyzed using the singular value decomposition (SVD) technique to obtain the polarization plane. The input spectral matrix is then transformed to the frame of the principal axes of the polarization ellipsoid. In this frame the Stokes parameters can be calculated.

Instructions:

  1. Download the following IDL procedures:
  2. Read the comments and try to understand the code (the above sequence of files is recommended)
  3. Run the procedure stokes_svd.pro using the spectral matrix data read by read_sm.pro and check the result.
  4. Re-run the program using different different spectral matrices in the data set. You may also want to use the results of the programming assignment #5.

Reading: There are many texts on the Stokes parameters, for an example of their application to wave measurements in the Earth's magnetosphere see
Hanas J. et al., Dynamic spectra of the Stokes parameters for the dayside and nightside Auroral Kilometric Radiation, Geophys. Res. Lett. 27, 1631-1634, 2000.

To read about using the SVD to obtain the polarization plane: Santolik, O., M. Parrot, and F. Lefeuvre, Singular value decomposition methods for wave propagation analysis, Radio. Sci. 38(1), 1010, doi:10.1029/2000RS002523, 2003.