David Brunkow

A Description of the CSU-CHILL National Radar Facility

The subject of this paper is the Colorado State University‐University of Chicago‐Illinois State Water Survey (CSU‐CHILL) National Radar Facility’s S-band polarimetric research radar. Key features of this system include polarization agility (provided by the dual-transmitter, dual-receiver design), a recently updated signal processor, and a low (234 dB, two way) integrated cross-polar ratio (ICPR 2) antenna system. After reviewing the technical description of the radar, the authors present a new differential reflectivity ( ZDR) calibration technique and data examples collected in different polarization modes. Although the CSU‐CHILL radar is transportable, it can also be operated in a dual-Doppler configuration with the CSU‐Pawnee radar, an 11-cm Doppler radar system situated 48 km north of the CSU‐CHILL Greeley field site. Used together, these radars provide three-dimensional kinematic and hydrometeor information in precipitating cloud systems.

Design and Performance Characteristics of the New 8.5-m Dual-Offset Gregorian Antenna for the CSU–CHILL Radar

The Colorado State University‐University of Chicago‐Illinois State Water Survey (CSU‐CHILL) national weather radar facility has been operated by the Colorado State University under a cooperative agreement with theU.S.NationalScienceFoundationfrom1990tothepresent. Theradar isconfiguredtomeasuretheelements of the 3 3 3 polarimetric covariance matrix based on using a two-transmitter and two-receiver system in the horizontal‐verticalpolarizationbasis.ThisS-bandDoppler,dual-polarizedradarfacilityisusedforobservations of precipitation with the highest possible data quality. To achieve this, a new dual-offset 8.5-m Gregorian antenna was custom designed and built by VertexRSI (now General Dynamics SATCOM) in Kilgore, Texas, to replace the circa 1994 center-fed parabolic reflector antenna. Here, the design features used to achieve the stringent specifications in terms of the sidelobe envelope and off-axis cross-polar levels are described, and the way in which they were validated at the manufacturer’s long- and short-range pattern measurement facility. Measurements in several different storm types, including stratiform rain and an intense hailstorm, and ground clutter (from mountains) are used to illustrate the new antenna performance. The linear depolarization ratio(LDR)systemlimitis shownto be 240 dBor better,whichshould leadtomore insightsinto the microphysics of convective precipitation at subfreezing temperatures (e.g., hail formation, improved hydrometeor-type classification), and in winter precipitation in general (e.g., aggregation processes, rimed versus unrimedparticles).In the case of the intense hailstorm,it is shownthat measurement artifacts resulting from strong cross-beam gradients of reflectivity, up to 40 dB km 21 at 40-km range, have been greatly reduced or eliminated. Previously noted measurement artifacts with the 1994 antenna at storm tops in intense convection have been eliminated with the dual-offset antenna. The ground (mountain) clutter example shows greatly reduced returns (in terms of near-zero mean Doppler velocity areas) because of rapid falloff in the sidelobe levels with increasing elevation angle. The greatly improved antenna performance as compared with the 1994 antenna are expected to result in corresponding data quality improvements leading to more accurate measurement of rain rate and hydrometeor classification.

Transformation of the CSU–CHILL Radar Facility to a Dual-Frequency, Dual-Polarization Doppler System

AbstractThis 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 appro...

Use of the CSU–CHILL Radar in Radar Meteorology Education at Colorado State University

Abstract A recent example illustrating the use of the CSU–CHILL Doppler radar in a graduate-level course in radar meteorology at Colorado State University (CSU) is described. In addition to providing students in the Department of Atmospheric Science with “hands-on” experience in the operation of a multiparameter Doppler radar, the data collected by this radar provided a unique opportunity to conduct case-study analyses for a variety of weather situations that occurred in northeastern Colorado. A total of six case studies were analyzed by the students in the class, and ranged from the study of a mesocyclone in a tornadic storm to snowbands in a winter cyclone. The case studies were presented by student groups in the format of a “miniconference” held during the final exam period for this class. Several of the case studies are described herein. The data collected in each of these case studies is available to the atmospheric sciences community as part of a “case-study archive” maintained at the CSU–CHILL rada...

Virtual CSU-CHILL Radar: The VCHILL

Abstract The Virtual CHILL (VCHILL) system makes it possible to transfer the educational and research experience of the Colorado State University dual polarization radar to remote locations over the Internet. The VCHILL operation includes remote control of radar and display of radar images, as well as the ability to locally process high-bandwidth radar data transferred over data networks. The low-bandwidth VCHILL operation allows the distant users to access the archived and real-time data estimated at the radar site and simultaneously display them on their local systems. A parallel receiver was developed exclusively for the high-bandwidth VCHILL. End-system architectures were designed to accommodate the demands of the high-bandwidth VCHILL operations in real time. A graphic user interface was also developed with the objective of easy installation and usage at various end-user institutions. The VCHILL not only expands the education experience provided by the radar system, but also stimulates the developmen...

Networking CSU-CHILL and CSU-Pawnee to Form a Bistatic Radar System

This paper describes how the synchronization and networking capabilities of the transmit and receive chain used at the CSU-CHILL and CSU-Pawnee radars are used to form a bistatic radar system capable of observing clear air echoes from atmospheric boundary layer. An overview of the bistatic radar geometry and resolution volume are presented, along with a discussion of the methods used to achieve timing coherence. Some preliminary results from clear-air observations are included.

Chill Radar Dual Polarization

The CHILL radar was originally designed as dual polarization radar. It was put into operation in late 1971. The original concept was a dual frequency X-band and S-band system. In 1972, the idea of using it as polarization radar was suggested by Drs. Tom Seliga and Viswanathan Bringi. After several years, the X-band radar was discarded and the system became a dual polarization radar instead. This discussion outlines the changes that were preformed on the system to make it a good polarization system. The radar was dual polarization capable from the beginning with a switch which changed the polarization of the transmit signal. A short list of the changes that were made in the radar and there success and problems are presented. The changes started with an electrical operated switch (original design) which took a second to switch but no special processing; a modified processor and the same switch changing to a 4 second cycle; a ferrite switch with 2 microseconds switching time and changing the processor to one with more channels; two channel separate transmitter and receiver; new antenna; and finally a second new antenna. Most of these upgrades also involved signal processing updates.

Architecture and implementation for high-bandwidth real-time radar signal transmission and computing application

he design, architecture, and implementation for the high-throughput data transmission and high-performance computing,which are applicable for various real-time radar signal transmission applications over the data network, are presented. With a client-server model, the multiple processes and threads on the end systems operate simultaneously and collaborately to meet the real-time requirement. The design covers the Digitized Radar Signal (DRS) data acquisition and data transmission on the DRS server end as well as DRS data receiving, radar signal parameter computation and parameter transmission on the DRS receiver end. Generic packet and data structures for transmission and inter-process data sharing are constructed. The architecture was successfully implemented on Sun/Solaris workstations with dual 750 MHz UltraSPARC-III processors containing Gigabit Ethernet card. The comparison in transmission throughput over gigabit link between with computation and without computation clearly shows the importance of the signal processing capability on the end-to-end performance. Profiling analysis on the DRS receiver process shows the work-loaded functions and provides guides for improving computing capabilities.

NETWORK TRANSFER, DIGITAL SIGNAL PROCESSING AND DISPLAY OF CSU CHILL DIGITIZED RADAR SIGNALS

Colorado State University (CSU) operates a radar at Greeley, Colorado. The CSU-VCHILL (Virtual-CHILL) project is aimed at developing and implementing protocols for providing the raw radar data to researchers in real-time over the internet. The Next Generation Internet has features, which could be used to transfer raw time-series data generated by the radar. In this project we have developed a network transfer application with TCP as the underlying protocol. This network transfer application has been successfully tested to provide throughput of 90 Mbps over a 100 Mbps link and 300 Mbps over gigabit link. We have also implemented a software digital signal-processing module. A network transfer application with User Datagram protocol as the underlying protocol was also developed. The performance of the software digital signal processing unit and the TCP version of the application to transfer the data across the network meet the requirements in most areas.

Development of a virtual radar environment

The CSU-CHILL radar facility has embarked on an initiative to enable the real time operation of the radar over the Internet called VCHILL or Virtual CHILL. The concept of operation over the Internet can be implemented at several levels. The simplest one is to make the routine CHILL images available on the Internet as soon as the scans are completed. This type of data dissemination has been available with CSU-CHILL over 5 years. However such images are clearly not sufficient for aircraft coordination or actively conducting coordinated scans with rapid updates. The VCHILL initiative has a more ambitious goal of providing the same quality of service (QoS) at remote locations as at the radar site. In addition, the goal of the VCHILL initiative is to provide the educational experience of polarimetric radar at a remote location, without compromising on features of an on-site radar console. This paper describes some progresses and plans of the VCHILL initiative.