A comparison of different polarization schemes for the radar sensing of precipitation

Abstract

Abstract. The equations of the radar covariances and cross covariances for linear vertical and horizontal polarization, slant linear +45 ø and -45 ø polarization, and left-hand and righthand circular polarization are presented for a model medium containing spheroidal particles. This model takes into account the distribution of canting angles but assumes the uniformity of the distribution function along the propagation path. Assuming the particles to be locally equioriented, equations for the intrinsic differential reflectivity and the mean canting angle are derived. Furthermore, for particles having the same orientations throughout the region of precipitation, the total differential phase shift is obtained. Reflectivity and depolarization ratios are also considered. A comparison of the three polarization schemes from a theoretical point of view is made and illustrated with data from the DLR C band Doppler and polarimetric weather radar. Since the DLR radar did not record the magnitude of the covariances and cross covariances, the comparison is only partially complete. The data confirm the theoretical prediction that depolarization is stronger in circular and slant linear polarization than in linear horizontal/vertical polarization.

Zenith/Nadir Pointing mm-Wave Radars: Linear or Circular Polarization?

“…From the above considerations, it is possible to conclude that, for scatterers with azimuthal symmetry, considering two antennas with the same cross-polar isolation, the dynamic range of CDR is always larger than the dynamic range of LDR by at least 3 dB. For anisotropic scatterers (when azimuthal symmetry is broken), the difference between CDR and LDR can be significantly larger than 3 dB [26], and implementation of the CDR mode emerges as an even better option for zenith/nadir pointing mm-wave radars. We emphasize the fact that the depolarization ratio dynamic range is dependent on its minimum measurable value, driven by the antenna cross-polar isolation.…”

“…In absence of azimuth symmetry, that is, in presence of aligned scatterers, polarimetric variables obtained at circular polarization (reflectivity, depolarization ratio, cross-polar coherence, degree of polarization) have a physical meaning that is more pertinent to the geometry of the problem, since they are independent from the specific alignment direction (with respect to the antenna ports) of the anisotropic scatterers potentially present in the radar resolution volume. Further, the presence of anisotropic scatterers additionally enhances the dynamic range of CDR with respect to the dynamic range of LDR [26].…”

The m‐chi decomposition of hybrid dual‐polarimetric radar data with application to lunar craters

“…In contrast, a hybrid dualpolarimetric architecture receives orthogonal linear polarizations, while transmitting circular polarization. The precedent for this architecture may be found in radars used for meteorological purposes [Bringi and Hendry, 1990;Torlaschi and Holt, 1998], and in the early days of radar astronomy. In the 1960s the Moon was illuminated from the Arecibo Observatory by circular polarization, and the lunar backscatter was transformed into coherent linear dual-polarized components.…”

The m-chi decomposition of hybrid dual-polarimetric radar data

“…These radars are hybrid dual-polarimetric, receiving orthogonal linear polarizations, while transmitting circular polarization (CL-pol) [3]. The precedent for this architecture may be found in radars used for meteorological measurements [4], and radar astronomy [5]. The Mini-RF and Mini-SAR radars offer the same suite of polarimetric information from lunar orbit as Earth-based radar astronomical observations of the Moon, since both types measure the 2x2 covariance matrix of the backscattered field.…”