Polarimetric radar studies of atmospheric ice particles

Abstract

Abstract-Single scattering properties of ice crystals are described at microwave frequencies using discrete dipole approximations and Rayleigh scattering techniques. For a given shape, the average bulk densities of ice crystals can be estimated using the ratio of the copolarized radar signal in a linear (horizontal, vertical) polarization basis. Reflectivity depends on the ice content (g . m-3 ) , and also on both size distribution parameters and average bulk density of the scatterers. Differential propagation phase is primarily a function of shape, ice water content, and is independent of size distribution parameters. Thus, by using a combination of polarimetric radar measurements, average ice content, bulk density, and shape of distributed scatterers can be inferred. These techniques become quite complex in the case of a winter storm where scatterers can exist with varying shape and bulk densities. Polarimetric radar properties of such complex distributed scatterers are modeled. Physical variations in the relation among ice water content, reflectivity, and differential propagation phase are considered with respect to change in the shape of size distribution, bulk density, and average shape of the scatterers. Also, simultaneous polarimetric radar observations and in situ aircraft measurements are shown to demonstrate practical applicability of the techniques.

Optimal Polarized Beampattern Synthesis Using a Vector Antenna Array

“…Among current radar systems, polarimetric radar that transmits waveforms with both horizontal and vertical orientations has been developed and adopted in a wide range of applications [12]. In fact, polarization diversity not only provides more complete information about the target, but also is a degree of freedom of the transmit waveforms that can be exploited in response to the dynamic targets and environments.…”

State and parameter estimation

“…Some polarimetric radar simulators already exist in the literature (Brandes et al 1995;Brandes et al 2004b;Zhang et al 2001;Vivekanandan et al 1994;Ryzhkov et al 1998;Huang et al 2005). However, they are either incomplete in terms of utilizing all available model parameters and state variables or are too expensive for use within DA systems.…”

“…Ryzhkov et al (1998) and Vivekanandan et al (1994) have proposed that polarimetric methods can estimate ice water content more accurately than the one that only uses reflectivity (Z H ). An accurate estimate of the amounts of hydrometeors and DSDs using polarimetric radar data can contribute to the improvement and verification of microphysical parameterizations in cloud and mesoscale models.…”

“…While many polarimetric radar emulators are mainly interested in single-phase hydrometeor concentration (Brandes et al 1995;Brandes et al 2004b;Ryzhkov et al 1998;Vivekanandan et al 1994;Zhang et al 2001;Capsoni et al 2001), only a handful of complete polarimetric radar emulators exist in the literature that utilizes all parameters available in the model. Huang et al (2005) developed a simulator based on T-matrix scattering calculations (Waterman 1969;Vivekanandan et al 1991 constant model is physically questionable because it assumes a high-density melting core with a low-density shell.…”

“…Brandes et al (1995;, Zhang et al (2001) offer the expressions for rain. Vivekanandan et al (1994) and Ryzhkov et al (1998) propose formulae that can be applied to ice particles ranging from ice crystals to snow aggregates. Because of the lack of sufficient understating of the polarimetric measurements for ice and mixed phases because of their complex behaviors and non-linear interactions, general expressions that are applicable to each of the hydrometeor categories are generally unavailable.…”