Constraints on Mueller matrices of polarization optics.
ABSTRACT The issue of physical realizability constraints on depolarizing scattering or imaging systems is addressed. In particular, the overpolarization problem, i.e., the problem of ensuring that the output degree of polarization is always smaller than (or equal to) unity, is discussed in detail. A set of necessary conditions for the elements of a Mueller matrix is derived. These conditions can be used to test the accuracy of polarimetric measurements and computations. Several recent experimental examples from polarization optics and radar are discussed.
- [show abstract] [hide abstract]
ABSTRACT: The Stokes scattering operator is noted to be the most useful characterization of incoherent scattering in radar imaging; the polarization that would yield an optimum amount of power received from the scatterer is obtained by assuming a knowledge of the Stokes scattering operator instead of the 2x2 scattering matrix with complex elements. It is thereby possible to find the optimum polarizations for the case in which the scatterers can only be fully characterized by their Stokes scattering operator, and the case in which the scatterer can be fully characterized by the complex 2x2 scattering matrix. It is shown that the optimum polarizations reported in the literature form the solution for a subset of a more general class of problems, so that six optimum polarizations can exist for incoherent scattering.IEEE Transactions on Antennas and Propagation 08/1987; · 2.33 Impact Factor
Conference Proceeding: Light scattering by hexagonal ice crystals[show abstract] [hide abstract]
ABSTRACT: A complete and traceable geometric ray-tracing solution for finite hexagonal columns and plates arbitrarily oriented in space has been developed by means of analytic geometry. In addition, an analytic expression for the cross-sectional area for arbitrarily oriented hexagons also has been derived based on which Fraunhofer diffraction and extinction and scattering cross sections in the limit of geometric optics can be computed exactly. The program involving geometrical reflection and refraction and Fraunhofer diffraction was used to compute the scattered intensities corresponding to two components of polarization for randomly oriented columns and plates in a horizontal plane and three-dimensional space. The scattered intensities were subsequently normalized to yield the nondimensional phase function commonly used in radiative transfer analyses. Numerical computations have been performed to study the effects of size, shape, orientation, and absorption on the scattering phase function and linear polarization. We show that the scattering phase functions for columns and plates, having approximately the same value, are quite similar except columns have a broader 22° halo pattern. The polarization patterns for these two shapes as well as for spheres and circular cylinders, however, are distinctly different, especially between 30 and 60° and between 130 and 140° scattering angles. We also show that hexagonal columns and plates randomly oriented in a horizontal plane do not generate a full scattering pattern of significant magnitude for an obliquely incident beam, and that the scattering patterns vary significantly with the oblique angle of the incident beam. At the 10.6 m infrared wavelength, because of the strong absorption of ice, the scattering pattern is basically attributed to diffraction and external reflection but with a noticeable 7° halo maximum due to two refractions. Comparisons with experimental results for plates having a mode radius of 20 m reveal a general agreement in regions from about 30-160° scattering angles.Conference on Light Scattering by Nonspherical Particles: Theory, Measurements and Applications, Goddard Institute for Space Studies, NY-USA, 29 Sept.-01 Oct. 1998; 01/1981
- [show abstract] [hide abstract]
ABSTRACT: Radar backscattering from reciprocal random targets is studied employing a covariance matrix approach. Polarization signatures for backscattered power and correlation observables are derived. Optimal polarization for the power return in two orthogonally polarized radar channels can be determined. Polarizations which extremize mean copolar power can be proved to reduce the correlation of the backscattered wave components exactly to zero. In the case of cross-polar optimal polarizations, a particular correlation difference rather than individual interchannel correlations tends to zero. The utilization of these necessary conditions for the power extrema, furthermore, allows the introduction of an efficient numerical algorithm to compute optimal polarization states for a given target covariance matrix. The presented polarimetric concept is demonstrated to generalize the well-established theory of characteristic polarizations. Analysis of chaff radar data illustrates the efficiency of the outlined approachIEEE Transactions on Geoscience and Remote Sensing 10/1990; · 3.47 Impact Factor