5B.1

**A geometric approach to characterizing and interpreting dual-polarization radar meteorological observations**

Richard Scott, New Mexico Tech, Socorro, NM; and P. Krehbiel

The polarization state of a radar signal is fully characterized by four
quantities, and is determined by measuring the signal covariances or powers
in two orthogonal polarizations (e.g., H and V or RHC and LHC) and the
magnitude and phase of the cross-covariance between the two polarizations.
The covariance values are readily transformed to represent the polarization
state geometrically in terms of its location on the Poincare sphere. The
geometric representation provides a powerful way of understanding the dual
polarization measurements, both conceptually and analytically. Z_{DR}, phi_{DP},
and rho_{HV} of horizontally oriented particles such as rain change the
polarization state in orthogonal spherical directions in the Poincare space,
and the changes are azimuthally symmetric about the H-V axis
of the sphere. The polarization changes produced by randomly oriented
or shaped particles are due to a single quantity termed the sphericity
parameter and are azimuthally symmetric about the polar or LHC-RHC axis of the
sphere. These and other features of the polarization changes make it relatively easy to
understand the effect of transmitting different polarizations and how the
resulting observations can be interpreted. Particular examples concern
a) the effect of using simultaneous H and V transmissions, in the form of circular
or slant 45 linear polarizations, and comparison with alternating H and V
linear transmissions, and b) the use of polarization diverse measurements to
objectively determine the parameters of different classes of hydrometeors.

Supplementary URL: http://lightning.nmt.edu/radar/30_radar_met/index.html

Session 5B, Signal Processing—Polarization & Doppler Techniques (Parallel with Session 5A)

**Friday, 20 July 2001, 4:00 PM-6:00 PM**** Next paper
**