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Francesc Junyent and V. Chandrasekar

Abstract

The CSU–CHILL radar is a dual-wavelength, dual-polarization weather radar system operating at S and X bands with coaxial beams. One of the capabilities of this radar system is the possibility of developing and/or validating algorithms across dual wavelengths and dual polarizations. This paper presents one such instance, showing how the rainfall field can be estimated either from the S- and X-band reflectivities or from the differential propagation phase at X band. To do so, the paper first presents a dual-wavelength attenuation correction method that uses the reflectivity measured at S band, as the constraint for the correction of the reflectivity measured at X band, and it describes how Mie scattering regions at X band may be detected from the retrieved path-integrated attenuation field. Then, the paper describes how the resulting specific attenuation field relates to rainfall and specific phase at X band, which can be obtained from dual-polarization data at a single wavelength as well, and shows examples. Finally, the paper looks at the relation between attenuation and the differential phase as a function of elevation angle for a few cases, which may be related to the drop size distribution and mean diameter, as well as temperature.

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Francesc Junyent and V. Chandrasekar

Abstract

A dense weather radar network is an emerging concept advanced by the Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA). In a weather radar environment, the specific radar units employed and the network topology will influence the characteristics of the data obtained. To define this, a general framework is developed to describe the radar network space, and formulations are obtained that can be used for weather radar network characterization.

The models developed are useful for quantifying and comparing the performance of different weather radar networks. Starting with system characteristics that are used to specify individual radars, a theoretical basis is developed to extend the concept to network configurations of interest. A general network elemental cell is defined and employed as the parameterized domain over which different coverage aspects (such as detection sensitivity, beam size, and minimum beam height) are studied using analytical tools developed in the paper. Other important parameters are the number of different radars with overlapping coverage at a given point in the network domain and the coverage area and number of radars of a network and its elemental cells. A combination of analytical and numerically derived expressions is employed to obtain these parameters for several configurations.

The radar network characterization tools developed are applied to the comparison of individual radar and networked radar configurations of interest. The values used in the calculations illustrate the CASA Integrated Project 1 (IP1) radar network and are compared to other radar systems.

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Francesc Junyent, V. Chandrasekar, and P. Kennedy

Abstract

The CSU–CHILL radar is a dual-wavelength, dual-polarization weather radar system operating at S and X band with coaxial beams. This radar system offers a unique environment to develop and/or validate algorithms that cut across its wavelengths and polarizations. This paper presents a method to retrieve resonance scattering regions from the difference in intrinsic reflectivities after attenuation correction, which is performed using measured reflectivity fields only. The algorithm to retrieve these regions dominated by non-Rayleigh scattering is applied to different storm events, and the obtained data field capturing the difference in S- and X-band reflectivities due to resonance effects (which we will call Mie signal for convenience) is compared to the collocated dual-polarization fields. The obtained Mie signal is also compared to hail reports. In both cases, the retrieved Mie signal is found to be consistent with the rest of the dual-polarization data fields, and in some situations, it is shown to bring information not directly discernible from the usual dual-polarization radar variables.

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Nitin Bharadwaj, V. Chandrasekar, and Francesc Junyent

Abstract

This paper describes the waveform design space and signal processing system for dual-polarization Doppler weather radar operating at X band. The performance of the waveforms is presented with ground clutter suppression capability and mitigation of range–velocity ambiguity. The operational waveform is designed based on operational requirements and system/hardware requirements. A dual–Pulse Repetition Frequency (PRF) waveform was developed and implemented for the first generation X-band radars deployed by the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA). This paper presents an evaluation of the performance of the waveforms based on simulations and data collected by the first-generation CASA radars during operations.

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Francesc Junyent, V. Chandrasekar, D. McLaughlin, E. Insanic, and N. Bharadwaj

Abstract

This paper describes the Collaborative Adaptive Sensing of the Atmosphere (CASA) Integrated Project 1 (IP1) weather radar network, the first distributed collaborative adaptive sensing test bed of the Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere. The radar network and radar node hardware and software architectures are described, as well as the different interfaces between the integrated subsystems. The system’s operation and radar node control and weather data flow are explained. The key features of the radar nodes are presented, as well as examples of different data products.

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Steven A. Rutledge, V. Chandrasekar, Brody Fuchs, Jim George, Francesc Junyent, Brenda Dolan, Patrick C. Kennedy, and Kyla Drushka

Abstract

A new, advanced radar has been developed at Colorado State University (CSU). The Sea-Going Polarimetric (SEA-POL) radar is a C-band, polarimetric Doppler radar specifically designed to deploy on research ships. SEA-POL is the first such weather radar developed in the United States. Ship-based weather radars have a long history, dating back to GATE in 1974. The GATE radars measured only reflectivity. After GATE, ship radars also provided Doppler measurements. SEA-POL represents the next advancement by adding dual-polarization technology, the ability to transmit and receive both horizontal and vertical polarizations. This configuration provides information about hydrometeor size, shape, and phase. As a result, superior rain-rate estimates are afforded by the dual-polarization technology, along with hydrometeor identification and overall improved data quality. SEA-POL made its first deployment as part of the Salinity Processes in the Upper Ocean Regional Study, second field phase (SPURS-2) fall 2017 cruise to the eastern tropical Pacific, sailing on the R/V Roger Revelle. SPURS-2 was a field project to investigate the fate of freshwater deposited on the ocean’s surface. Oceanographers are keenly interested in how fast these freshwater patches mix out by wind and upper-ocean turbulence, as the less dense rainfall sitting atop the salty ocean inhibits mixing through increased stability. To this end, during SPURS-2, SEA-POL produced rain maps identifying the location of freshwater lenses on the ocean’s surface thereby providing context for measurements of SST and salinity. Examples of SEA-POL polarization measurements are also discussed to assess microphysical processes within oceanic convection. Future ocean-based field campaigns will now benefit from SEA-POL’s advanced dual-polarization technology.

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Francesc Junyent, V. Chandrasekar, V. N. Bringi, S. A. Rutledge, P. C. Kennedy, D. Brunkow, J. George, and R. Bowie

Abstract

This paper describes the transformation of the Colorado State University–University of Chicago–Illinois State Water Survey (CSU–CHILL) National Radar Facility from a single-frequency (S band) dual-polarization Doppler weather radar system to a dual-frequency (S and X bands) dual-polarization Doppler system with coaxial beams. A brief history regarding the development of dual-wavelength radars is first presented. In the past, dual-wavelength measurements were used to detect hail using the dual-wavelength ratio defined as the ratio of intrinsic (or attenuation corrected) X-band reflectivity to the S-band reflectivity. Departures of this ratio from unity were taken to indicate the presence of hail, produced by Mie scattering at the shorter wavelength by hail. Most dual-wavelength radars were developed with attempts to match beams for S and X bands, which implies that the sample volumes for the two frequencies were essentially the same. The X-band channel of the CSU–CHILL radar takes a different approach, that of making use of the already existing dual-offset-fed antenna designed to give a 1° beamwidth at S band, resulting in an X-band beamwidth of approximately 0.3°, with very high gain. Thus, the X band provides about a factor of 3 more resolution than the S-band component while maintaining the same sensitivity as the S-band component. Examples of cold season and warm season data from the X-band and S-band radar components are presented, demonstrating the successful transformation of the CSU–CHILL radar into a unique multifrequency, multipolarization system. The new CSU–CHILL dual-wavelength, dual-polarization weather radar will serve as an important asset for the scientific community.

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Howard B. Bluestein, Michael M. French, Robin L. Tanamachi, Stephen Frasier, Kery Hardwick, Francesc Junyent, and Andrew L. Pazmany

Abstract

A mobile, dual-polarization, X-band, Doppler radar scanned tornadoes at close range in supercells on 12 and 29 May 2004 in Kansas and Oklahoma, respectively. In the former tornadoes, a visible circular debris ring detected as circular regions of low values of differential reflectivity and the cross-correlation coefficient was distinguished from surrounding spiral bands of precipitation of higher values of differential reflectivity and the cross-correlation coefficient. A curved band of debris was indicated on one side of the tornado in another. In a tornado and/or mesocyclone on 29 May 2004, which was hidden from the view of the storm-intercept team by precipitation, the vortex and its associated “weak-echo hole” were at times relatively wide; however, a debris ring was not evident in either the differential reflectivity field or in the cross-correlation coefficient field, most likely because the radar beam scanned too high above the ground. In this case, differential attenuation made identification of debris using differential reflectivity difficult and it was necessary to use the cross-correlation coefficient to determine that there was no debris cloud. The latter tornado’s parent storm was a high-precipitation (HP) supercell, which also spawned an anticyclonic tornado approximately 10 km away from the cyclonic tornado, along the rear-flank gust front. No debris cloud was detected in this tornado either, also because the radar beam was probably too high.

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David McLaughlin, David Pepyne, V. Chandrasekar, Brenda Philips, James Kurose, Michael Zink, Kelvin Droegemeier, Sandra Cruz-Pol, Francesc Junyent, Jerald Brotzge, David Westbrook, Nitin Bharadwaj, Yanting Wang, Eric Lyons, Kurt Hondl, Yuxiang Liu, Eric Knapp, Ming Xue, Anthony Hopf, Kevin Kloesel, Alfred DeFonzo, Pavlos Kollias, Keith Brewster, Robert Contreras, Brenda Dolan, Theodore Djaferis, Edin Insanic, Stephen Frasier, and Frederick Carr

Dense networks of short-range radars capable of mapping storms and detecting atmospheric hazards are described. Composed of small X-band (9.4 GHz) radars spaced tens of kilometers apart, these networks defeat the Earth curvature blockage that limits today s long-range weather radars and enables observing capabilities fundamentally beyond the operational state-of-the-art radars. These capabilities include multiple Doppler observations for mapping horizontal wind vectors, subkilometer spatial resolution, and rapid-update (tens of seconds) observations extending from the boundary layer up to the tops of storms. The small physical size and low-power design of these radars permits the consideration of commercial electronic manufacturing approaches and radar installation on rooftops, communications towers, and other infrastructure elements, leading to cost-effective network deployments. The networks can be architected in such a way that the sampling strategy dynamically responds to changing weather to simultaneously accommodate the data needs of multiple types of end users. Such networks have the potential to supplement, or replace, the physically large long-range civil infrastructure radars in use today.

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