Redmond Kelley

The Atmospheric Imaging Radar: Simultaneous Volumetric Observations Using a Phased Array Weather Radar

AbstractMobile weather radars often utilize rapid-scan strategies when collecting observations of severe weather. Various techniques have been used to improve volume update times, including the use of agile and multibeam radars. Imaging radars, similar in some respects to phased arrays, steer the radar beam in software, thus requiring no physical motion. In contrast to phased arrays, imaging radars gather data for an entire volume simultaneously within the field of view (FOV) of the radar, which is defined by a broad transmit beam. As a result, imaging radars provide update rates significantly exceeding those of existing mobile radars, including phased arrays. The Advanced Radar Research Center (ARRC) at the University of Oklahoma (OU) is engaged in the design, construction, and testing of a mobile imaging weather radar system called the atmospheric imaging radar (AIR). Initial tests performed with the AIR demonstrate the benefits and versatility of utilizing beamforming techniques to achieve high spatial...

PX-1000: A Solid-State Polarimetric X-Band Weather Radar and Time–Frequency Multiplexed Waveform for Blind Range Mitigation

In this paper, a compact, transportable, and dual-polarization X-band weather radar was developed at the Advanced Radar Research Center of the University of Oklahoma. The radar was designed using a software-defined radio (SDR) approach for waveform versatility. One of the key innovations in this paper is the combination of SDR design and the mitigation of blind range, which is inherent in pulse compression radars, using a time-frequency multiplexed waveform while compression is performed in pure software architecture. Internally, this radar has been referred to as the PX-1000. It is primarily used as a platform for waveform studies and various signal processing techniques, such as pulse compression, polarimetric signal processing, refractivity retrieval, and support of various field campaigns. The radar system has been completed and is operational. It has two identical and independent power amplifiers, one for each polarization. The system also features a 1.2-m parabolic reflector dish with dual-polarization feed, which provides a 1.8 ° beamwidth. A majority of the components are housed above the turntable of an azimuth-over-elevation pedestal. We also took this opportunity to design and develop a new software suite that includes signal processing, system control, and graphical user interface. The raw I/Q time series can be recorded and streamed out of the radar system in real time. In this paper, a detailed description of the radar and some experimental data will be presented.

Leveraging Software-Defined Radio Techniques in Multichannel Digital Weather Radar Receiver Design

This paper describes the instrumentation, design, and implementation of an inexpensive nearly all-digital field-programmable gate-array (FPGA)-based radar receiver useful in a variety of applications including single-/dual-polarization weather radar, sidelobe cancellation, subarray modules for a digital beam-forming phased-array radar, and other applications where a compact, low-power, and low-cost receiver is needed. The design of the receiver includes a minimal analog radio-frequency front-end followed by an analog-to-digital converter utilizing a bandpass sampling technique which allows the FPGA to produce baseband in-phase (I) and quadrature (Q) signals without the use of multipliers or lookup tables.

Compact Digital Receiver Development for Radar Based Remote Sensing

This paper is the first of a series of publications that discusses the design and implementation of an inexpensive, nearly all-digital FPGA-based radar receiver which can be used in a variety of applications including single/dual-polarization weather radar, sidelobe cancellation, a subarray module for a digital beam-forming phased-array radar, and other applications where a compact, low-power, low-cost receiver is needed. The design of the receiver includes a minimal analog RF front-end followed by an analog-to-digital converter utilizing a bandpass sampling technique which allows the FPGA to produce baseband in-phase (I) and quadrature (Q) signals without the use of multipliers or look-up tables. The primary difference between the efforts of others and the efforts here is the use of single or multiple frequency channels in the receiver. The efforts of others have had applications in multi-channel military radars and in software defined radios that receive a variety of information. Here, only one frequency channel is needed for environmental observations, which provides a unique impetus to facilitate low-cost, low-power designs by leveraging software defined radio techniques.

Multichannel Receiver Design, Instrumentation, and First Results at the National Weather Radar Testbed

When the National Weather Radar Testbed (NWRT) was installed in 2004, a single-channel digital receiver was implemented so that the radar could mimic typical Weather Surveillance Radar (WSR) version 1988 Doppler (WSR-88D) capability. This, however, left unused eight other channels, built into the antenna. This paper describes the hardware instrumentation of a recently completed project that digitizes the radar signals produced by these channels. The NWRT is the nations first phased array devoted to weather observations, and this testbed serves as an evaluation platform to test new hardware and signal processing concepts. The multichannel digital data will foster a new generation of adaptive/fast scanning techniques and space-antenna/interferometry measurements, which will then be used for improved weather forecasting via data assimilation. The multichannel receiver collects signals from the sum, azimuth-difference, elevation-difference, and five broad-beamed auxiliary channels. One of the major advantages of the NWRT is the capability to adaptively scan weather phenomena at a higher temporal resolution than is possible with the WSR-88D. Access to the auxiliary channels will enable clutter mitigation and advanced array processing for higher data quality with shorter dwell times. Potential benefits of higher quality and higher resolution data include: better understanding of storm dynamics and convective initiation; better detection of small-scale phenomena, including tornadoes and microbursts; and crossbeam wind, shear, and turbulence estimates. These items have the distinct possibility to ultimately render increased lead time for warnings and improved weather prediction. Finally, samples of recently collected data are presented in the results section of this paper.

Dual-Polarization Frequency Scanning Microstrip Array Antenna With Low Cross-Polarization for Weather Measurements

The design of a dual-polarization frequency scanning array of microstrip patch antennas is presented. The coupling between the patch elements and the transmission lines is realized using microstrip directional couplers. Cross polarization suppression is achieved by applying a differential feed configuration to each element for the vertical polarization and an imaged feed arrangement with respect to the columns for the horizontal polarization. The antenna has been fabricated and test results are provided verifying the accuracy of the simulated results. In addition, the imaged feed configuration is used for two neighboring columns of the array to compensate for the spurious radiations and achieve a lower cross polarization level.

Direct digital synthesizer architecture in multichannel, dual-polarization weather radar transceiver modules

The Atmospheric Radar Research Laboratory (ARRC) of the University of Oklahoma is building a teamwork-oriented, cylindrical, dual-pol, phased array radar, and this paper addresses the hardware development of the waveform generation and digital receiver portions of the project (namely, a digital transceiver). Direct Digital Synthesizers (DDS) are being utilized to generate digital waveforms for the radar. DDSs will allow for smooth communication between array nodes and efficient beamsteering in this application so long as a synchronization technique ensures the operation of an accurate master clock. The paper describes a synchronous technique for generating waveforms over multiple channels of the radar and the architecture of each channels transmitter is examined. The functions, utilization, and synchronization scheme of DDSs in this application are also discussed. Finally, a digital receiver solution is explored. Combining these two ideas introduces a low-cost, custom digital transceiver with a small form factor. This transceiver has been designed and built at the ARRC and utilizes waveform generators and digital receivers to be used in multi-channel radar platforms.

An update on the multi-channel phased array Weather Radar at the National Weather Radar Testbed

The first phased array radar dedicated to weather observation and analysis is now instrumented with eight, simultaneous digital receivers. The multi-channel receiver will collect signals from the sum, azimuth-difference, elevation-difference, and five broad-beamed auxiliary channels. The multi-channel receiver will allow the direct implementation of interferometry techniques to estimate crossbeam wind, shear and turbulence within a radar resolution volume. Access to the auxiliary channels will enable clutter mitigation and advanced array processing for high data quality with short dwell times. Potential benefits of high quality and high resolution data together with angular shear and turbulence include better understanding of storm dynamics and convective initiation, as well as better detection of small-scale phenomena including tornado and microbursts, ultimately leading to increased lead time for warnings, and improved weather prediction. This paper will describe the system concept, system installation and early results from fielded weather data returns.

The Atmospheric Imaging Radar (AIR) for high-resolution observations of severe weather

Rapid updates are a highly desired feature in the field of mobile weather radars. Various techniques have been used to improve volume update times, including the use of agile and multi-beam radars. Imaging radars, similar in some respects to phased arrays, steer the radar beam in software, thus requiring no physical motion. In contrast to phased arrays, imaging radars gather data for an entire volume simultaneously within the field-of-view (FOV) of the radar, which is defined by the broad transmit beam. As a result, imaging radars provide update rates exceeding those of existing mobile radars, including phased arrays. The Atmospheric Radar Research Center (ARRC) at the University of Oklahoma (OU) is currently engaged in the design and fabrication of the worlds first mobile imaging weather radar.

Cylindrical polarimetric phased array radar: Hardware design and mobile demonstrator

This paper describes the design of a mobile Cylindrical Polarimetric Phased Array Radar (CPPAR) developed at the Advanced Radar Research Center (ARRC). The primary purpose of the radar is to prove the concept of a CPPAR and demonstrate its inherent polarimetric advantages. Since these advantages become most apparent in the context of the polarimetric weather radar mission, the ability to make meaningful weather measurements with the system is desired. With limited resources, a novel system has been designed which both can demonstrate the CPPAR concept and serve as a platform for general phased array research in the future.