Jim George

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...

Development of an Off-The-Grid X-band radar for weather applications

The Student Led Test Bed (STB) is part of the NSF Engineering Research Center CASA and is currently focused in developing low-cost and low infrastructure radar networks to fill lower atmosphere gaps not covered by current technology. The first radar node, which is part of a small region radar network, will significantly improve the time and spatial resolution of the radar data measured for the lower atmosphere. This paper describes the development of an Off-The-Grid (OTG) X-band radar node that requires minimum infrastructure for its deployment and can operate using solar energy and wireless communication links. The OTG radar was developed for meteorological applications modifying a commercially available marine radar. Hardware modifications for meteorological purposes were performed as well as the design and implementation of a photovoltaic system to power the radar using solar energy. The system was moved to the Colorado State University (CSU)-CHILL National Weather Radar facility for a cross-calibration and system evaluation. Satisfactory results were obtained where it was demonstrated that the OTG radar can provide precipitation measurements with improved spatial and temporal resolution, both necessary to have better lower troposphere measurements. This OTG node is the first prototype of a low infrastructure X-band weather radar network to aid forecasts in the western region of Puerto Rico.

Implementation of blind zone and range-velocity ambiguity mitigation for solid-state weather radar

This paper addresses the blind-zone problem associated with pulse compression techniques used to overcome the low peak power of solid-state transmitters, as well as interpulse coding techniques that take advantage of high duty cycles to mitigate range-velocity ambiguities. The implementation of these techniques on the CSU Wideband Experimental X-band (WiBEX) radar is presented.

Considerations in Pulse Compression Design for Weather Radars

Pulse compression is a useful technique for weather radar, as an enabling technology to facilitate use of low-power solid state transmitters. It also has the benefit of improving the dynamic range and range resolution of the radar, permitting rapid scanning of a volume. The nonlinear FMpulse waveform described produces the low sidelobe levels required for weather radar applications, while remaining Doppler-tolerant within the range of radial velocities expected for weather radar (plusmn100 m/s). Traditional pulse compression waveforms must be modified to reduce their range sidelobes to levels suitable for use in weather radar. The use of pulse compression involves some changes to the methods used during radar calibration, and places some restrictions on the design and implementation of the RF and IF components of the radar.

Dual-frequency dual-polarized Doppler radar (D3R) system for GPM ground validation: Update and recent field observations

Dual wavelength precipitation radar (DPR) is planned to be deployed in the GPM core satellite. The DPR is expected to provide improved characterization of the raindrop size distribution ( DSD), as well as rainfall rate estimation from a combination of Ku band and Ka band radar measurement [1]. The Ku band radar is nearly same as the TRMM Precipitation radar. The Ka band provides higher sensitivity and can be useful in the measurement of snow and light rain. In contrast to TRMM the dual wavelength retrieval methods will use two DSD parameters to characterize the precipitation medium. The underlying precipitation structures, hydrometeors and DSDs dictate the type of models or retrieval algorithms that can be used to estimate precipitation. Having dual wavelength radar on the ground, with the potential for in-situ observations, or coordinated observations provide excellent opportunity to develop microphysical and system models for retrievals. Therefore a beam aligned dual-wavelength system consisting of Ku and Ka bands can be very useful as a ground validation tool. In addition if these systems can be dual-polarized, then these can be self-consistent cross validation tools. This paper describes the NASA Dual polarized, dual frequency Doppler radar, developed for the ground validation program.

Waveform coding for dual polarization weather radars

Polarimetric variables are an essential part of algorithms for improved rainfall rate estimation, attenuation correction and hydrometeor identification. In such systems the transmit polarization state changes according to some fixed pattern that is repeated. The simultaneous mode and alternating mode waveforms are commonly used in weather radars. In the simultaneous mode of operation the horizontal and vertical polarization states are transmitted simultaneously and samples of both horizontal and vertical co-polar return are obtained A drawback of the current implementation of simultaneous mode is its inability to measure cross-polar parameters such as linear depolarization ratio. In this paper a technique to estimate cross- polar signals with a simultaneous mode waveform is presented. In this method, the horizontally and vertically polarized transmit waveforms are coded with orthogonal phase sequences. The performance of the phase coded waveform is determined by the properties of the phase codes. This paper presents the performance of the cross-polar and co-polar parameter estimation based on the simulation as well as data collected from CSU- CHILL radar.

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.

Dual-polarization spectral decompositions: Application to radar parameter estimation and quality control

Spectral decompositions of dual polarization observation allows for extending of analysis of polarimetric radar data to the new dimension, namely Doppler frequency domain. In this paper it is shown how this new paradigm can be used for improving quality of radar data. On an example of the CSU- CHILL observations it is demonstrated that this analysis can be used to design a spectral filter that allows for both ground clutter mitigation and radar sensitivity improvement.