Weather Radar Polarimetry Research Articles

Polarization Weather Radar Development from 1970–1995: Personal Reflections

The modern era of polarimetric radar begins with radiowave propagation research starting in the early 1970s with applications to measurement and modeling of wave attenuation in rain and depolarization due to ice particles along satellite–earth links. While there is a rich history of radar in meteorology after World War II, the impetus provided by radiowave propagation requirements led to high-quality antennas and feeds. Our journey starts by describing the key institutions and personnel responsible for development of weather radar polarimetry. The early period was dominated by circularly polarized radars for propagation research and at S band (frequency near 3 GHz) for hail detection. By the mid to late 70s, a paradigm shift occurred which led to the dominance of linear polarizations with applications to slant path attenuation prediction as well as estimation of rain rates and inferences of precipitation physics. The period from the early 1980s to 1995 can be considered as the “golden” period of rapid research that brought in meteorologists, cloud physicists, and hydrologists. This article describes the evolution of this technology from the vantage point of the authors. Their personal reflections and “behind the scenes” descriptions offer a glimpse into the inner workings at several key institutions which cannot be found elsewhere.

Understanding Weather Radar Polarimetry [Book\/Software Reviews

Weather Radar Polarimetry, by Dr. Guifu Zhang, provides the fundamentals and principles of weather radar polarimetry by exploring wave scattering and propagation in clouds and precipitation. The book describes the correlation between physical state parameters and radar observables so that readers understand the polarimetric radar signatures of typical weather conditions. This book includes advanced signal processing and retrieval algorithms to help readers interpret polarimetric radar data (PRD) and provides data analysis tools and methods. Because it uses hundreds, if not thousands, of acronyms and symbols, the tables in the appendices are a helpful tool. It also includes many highresolution color photos and quality graphic charts to provide clarity.

Unraveling hydrometeor mixtures in polarimetric radar measurements

Abstract. Radar-based hydrometeor classification typically comes down to determining the dominant type of hydrometeor populating a given radar sampling volume. In this paper we address the subsequent problem of inferring the secondary hydrometeor types present in a volume – the issue of hydrometeor de-mixing. The present study relies on the semi-supervised hydrometeor classification proposed by Besic et al. (2016) but nevertheless results in solutions and conclusions of a more general character and applicability. In the first part, oriented towards synthesis, a bin-based de-mixing approach is proposed, inspired by the conventional coherent and linear decomposition methods widely employed across different remote-sensing disciplines. Intrinsically related to the concept of entropy, introduced in the context of the radar hydrometeor classification in Besic et al. (2016), the proposed method, based on the hypothesis of the reduced random interferences of backscattered signals, estimates the proportions of different hydrometeor types in a given radar sampling volume, without considering the neighboring spatial context. Plausibility and performances of the method are evaluated using C- and X-band radar measurements, compared with hydrometeor properties derived from a Multi-Angle Snowflake Camera instrument. In the second part, we examine the influence of the potential residual random interference contribution in the backscattering from different hydrometeors populating a radar sampling volume. This part consists in adapting and testing the techniques commonly used in conventional incoherent decomposition methods to the context of weather radar polarimetry. The impact of the residual incoherency is found to be limited, justifying the hypothesis of the reduced random interferences even in a case of mixed volumes and confirming the applicability of the proposed bin-based approach, which essentially relies on first-order statistics.

Weather Radar Polarimetry [Book Review

This book is a valuable reference book on weather radars and their associated algorithms, and it is written by a vital member of the University of Oklahoma Advanced Radar Research Center. As someone who originally studied physics for his B.S. degree and then, apparently, became an enthusiast of the physical interactions occurring around hydrometeorological targets, the author has poured all of the necessary physical explanations, relevant equations, and measurement techniques involving modern polarimetric weather radar into this book. The work is impressively organized in the ascending complexity of the topics it covers. An engineer or scientist who is new to the subject will find it very easy to read, since it covers almost all of the necessary preliminary information in a highly descriptive manner—amazingly, without forcing the reader to check many of the previous references.

Eigenvalue Signal Processing for Weather Radar Polarimetry: Removing the Bias Induced by Antenna Coherent Cross-Channel Coupling

We present a novel digital signal processing procedure, named eigenvalue signal pocessing (henceforth ESP), patented by the first author with Brookhaven Science Associates in 2013. The method enables the removal of the bias due to antenna coherent cross-channel coupling and is applicable in the LDR mode, the ATSR mode and the STSR orthogonal mode of weather radar measurements. In this paper, we focus on the LDR mode and consider copolar reflectivity at horizontal transmit $({\rm Z}_{\rm HH})$ , cross-polar reflectivity at horizontal transmit $({\rm Z}_{\rm VH})$ , linear depolarization ratio at horizontal transmit $({\rm LDR}_{\rm H})$ and degree of polarization at horizontal transmit $({\rm DOP}_{\rm H})$ . The ESP (ESP) method is substantiated by an experiment carried out in November 2012 using C-band weather radar with a parabolic reflector located at the Selex ES—Gematronik facilities in Neuss, Germany. The experiment involved comparison of weather radar measurements taken 1.5 minutes apart in two hardware configurations, namely with cross-coupling on (cc-on) and cross-coupling off (cc-off). It is experimentally demonstrated that eigenvalue-derived variables are invariant with respect to antenna coherent cross-channel coupling. This property had to be expected, since the eigenvalues of the Coherency matrix are SU(2) invariant.

Efficient Ways to Learn Weather Radar Polarimetry

The U.S. weather radar network is currently being upgraded with dual-polarization capability. Weather radar polarimetry is an interdisciplinary area of engineering and meteorology. This paper presents efficient ways to learn weather radar polarimetry through several basic and practical topics. These topics include: 1) hydrometeor scattering model and calculation of radar variables; 2) characteristics of polarimetric radar measurements and radar echo classification; and 3) rain microphysics retrieval. The supporting files, data, codes, and results are provided on the Web site http://arrc.ou.edu/~guzhang/Polarimetry/main.html. The study modules provide hands-on experience in the area of weather radar polarimetry and related fields.

Estimation of Specific Differential Phase and Differential Backscatter Phase From Polarimetric Weather Radar Measurements of Rain

The estimation of the specific differential phase particularly in the presence of the differential backscatter phase and nonuniform propagation paths is a long-standing goal in weather radar polarimetry. Furthermore, a reliable estimator of the differential backscatter phase for precipitation measurements has not been proposed yet, although it contains valuable information about the presence of non-Rayleigh scattering and the microphysics of precipitation. In this letter, we introduce a novel method to estimate the specific differential phase and the differential backscatter phase from polarimetric weather radar measurements of rain. This estimation does pay off particularly at the X-band where the scattering regime is non-Rayleigh already in moderate rain. In this case, the differential backscatter phase is useful as an additional weather radar observable with manifold applications such as rain rate estimation, microphysical retrieval, and operational radar calibration. The novel method also provides an improved range resolution of the specific differential phase compared to conventional estimators. We illustrate the estimation of the differential phases with data from the Delft University of Technology's polarimetric X-band International Research Centre for Telecommunications and Radar drizzle radar.

Polarimetry for Weather Surveillance Radars

This paper is an overview of weather radar polarimetry emphasizing surveillance applications. The following potential benefits to operations are identified: improvement of quantitative precipitation measurements, discrimination of hail from rain with possible determination of sizes, identification of precipitation in winter storms, identification of electrically active storms, and distinction of biological scatterers (birds vs insects). Success in rainfall measurements is attributed to unique properties of differential phase. Referrals to fields of various polarimetric variables illustrate the signatures associated with different phenomena. It is argued that classifying hydrometeors is a necessary step prior to proper quantification of the water substance. The promise of polarimetry to accomplish classification is illustrated with an application to a hailstorm.

Weather Radar Polarimetry–Trends Toward Operational Applications

This is a version of a speech presented at the 27th Conference on Radar Meteorology. Relative advantages of polarimetry are contrasted with the advantages accrued by the introduction of radar into meteorology and by the addition of Doppler measurements. A description of present interests as perceived by the author follows, and possible future trends are suggested.

A multiparameter radar case study of the microphysical and kinematic evolution of a lightning producing storm

We examine the co-evolving microphysical, kinematic, and electrical characteristics of a multi-cell thunderstorm observed on 21 May 1993 along the Front Range of Colorado using data collected with the 11 cm, multiparameter, CSU-CHILL Doppler radar. The measured polarimetric variables provide information on the size, shape, orientation, and thermodynamic phase of hydrometeors. Recent modeling and observational advances in weather radar polarimetry now permit the inference of bulk-hydrometeor types and mixing ratios, and the measurement of precipitation rate in mixed-phase (i.e., hail and rain) environments. We have employed these and other radar techniques, such as dual-Doppler analyses, to investigate the correlation between the convective life cycle of a multi-cell storm and the evolution of lightning type and flash rate.

Workshop on Weather Radar Polarimetry for Research and Operational Applications

A workshop on weather radar polarimetry for research and operational applications was held on 22 and 23 February 1994 at the National Center for Atmospheric Research. Polarization radar can provide estimates of the shapes, sizes, phase, and fall orientations of hydrometeors. This information can be used to remove some of the ambiguities present when only the reflectivity is measured. The morning of 22 February was devoted to 16 short presentations highlighting recent advances in polarimetric radar. The afternoon was dedicated to four discussion sessions that further developed important topics. On the following day, plans for the upgrading and development of the existing NCAR polarization radar capability were presented and debated. The workshop resulted in four recommendations: three of which proposed specific field measurement programs to quantify the potential improvements provided by the polarization techniques.