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Applications in Low-Power Phased Array Weather Radars
Low-cost X-band radars are an emerging technology that offer significant advantages over traditional systems for weather remote sensing applications. X-band radars provide enhanced angular resolution at a fraction of the aperture size compared to larger, lower frequency systems. Because of their low cost and small form factor, these radars can now be integrated into more research and commercial applications. This work presents research and development activities using a low-cost, X-band (9410 MHz) Phase-Tilt Radar. The phase-tilt design is a novel phased array architecture that allows for rapid electronic scanning in azimuth and mechanical tilting in elevation, as a compromise between cost and performance.
This work focuses on field studies and experiments in three meteorological applications. The first stage of research focuses on the real-world application of phased array radars in forest fire monitoring and observation. From April to May 2013, a phase-tilt radar was deployed to South Australia and underwent a field campaign to make polarimetric observations of prescribed burns within and around the Adelaide Hills region. Measurements show the real-time evolution of the smoke plume dynamics at a spatial and temporal resolution that has never before been observed with an X-band radar. This dissertation will perform data analysis on results from this field campaign. Results are compared against existing work, theories, and approaches.
In the second stage of research, field experiments are performed to assess the data quality of X-band phased array radars. Specifically, this research focuses on the measurement of and techniques to improve the variance of weather product estimators for dual-polarized systems. Variability in the radar products is a complicated relationship between the radar system specifications, scanning strategy, and the physics governing precipitation. Here, the variance of the radar product estimators is measured using standard radar scanning strategies employed in traditional mechanical antenna systems. Results are compared against adaptive scan strategies such as beam multiplexing and frequency diversity. This work investigates the improvement that complex scanning strategies offer in dual-polarized, X-band phased array radar systems.
In the third stage of research, simulations and field experiments are conducted to investigate the performance benefits of adaptive scanning to optimize the data quality of radar returns. This research focuses on the development and implementation of a waveform agile and adaptive scanning strategy to improve the quality of weather product estimators. Active phased array radars allow radar systems to quickly vary both scan pointing angles and waveform parameters in response to real-time observations of the atmosphere. As an evolution of the previous research effort, this work develops techniques to adaptively change the scan pointing angles, transmit and matched filter waveform parameters to achieve a desired level of data quality. Strategies and techniques are developed to minimize the error between observed and desired data quality measures. Simulation and field experiments are performed to assess the quality of the developed strategies
Applied Radar Meteorology
This is a textbook focused on operational and other aspects of applied radar meteorology. Its primary purpose is to serve as a text for upper-level undergraduates and graduate students studying meteorology, who wish to work as professional operational meteorologists in the U.S. National Weather Service or the Air Force Weather Agency. In addition to a detailed description of operational weather radar systems operating in the United States, this text also provides a brief historical overview of the subject as well as a basic review of the physics of electromagnetic radiation and other theoretical aspects of weather radar. The last two chapters discuss a sample of other radar systems (such as the Doppler on Wheels and the Canadian and European operational networks), and future directions of weather radar, including its use as an input for high-resolution, rapid refresh computer models
Investigation of Advanced Radar Techniques for Atmospheric Hazard Detection with Airborne Weather Radar
In 2013 ProSensing Inc. conducted a study to investigate the hazard detection potential of aircraft weather radars with new measurement capabilities, such as multi-frequency, polarimetric and radiometric modes. Various radar designs and features were evaluated for sensitivity, measurement range and for detecting and quantifying atmospheric hazards in wide range of weather conditions. Projected size, weight, power consumption and cost of the various designs were also considered. Various cloud and precipitation conditions were modeled and used to conduct an analytic evaluation of the design options. This report provides an overview of the study and summarizes the conclusions and recommendations
Frequency diversity wideband digital receiver and signal processor for solid-state dual-polarimetric weather radars
2012 Summer.Includes bibliographical references.The recent spate in the use of solid-state transmitters for weather radar systems has unexceptionably revolutionized the research in meteorology. The solid-state transmitters allow transmission of low peak powers without losing the radar range resolution by allowing the use of pulse compression waveforms. In this research, a novel frequency-diversity wideband waveform is proposed and realized to extenuate the low sensitivity of solid-state radars and mitigate the blind range problem tied with the longer pulse compression waveforms. The latest developments in the computing landscape have permitted the design of wideband digital receivers which can process this novel waveform on Field Programmable Gate Array (FPGA) chips. In terms of signal processing, wideband systems are generally characterized by the fact that the bandwidth of the signal of interest is comparable to the sampled bandwidth; that is, a band of frequencies must be selected and filtered out from a comparable spectral window in which the signal might occur. The development of such a wideband digital receiver opens a window for exciting research opportunities for improved estimation of precipitation measurements for higher frequency systems such as X, Ku and Ka bands, satellite-borne radars and other solid-state ground-based radars. This research describes various unique challenges associated with the design of a multi-channel wideband receiver. The receiver consists of twelve channels which simultaneously downconvert and filter the digitized intermediate-frequency (IF) signal for radar data processing. The product processing for the multi-channel digital receiver mandates a software and network architecture which provides for generating and archiving a single meteorological product profile culled from multi-pulse profiles at an increased data date. The multi-channel digital receiver also continuously samples the transmit pulse for calibration of radar receiver gain and transmit power. The multi-channel digital receiver has been successfully deployed as a key component in the recently developed National Aeronautical and Space Administration (NASA) Global Precipitation Measurement (GPM) Dual-Frequency Dual-Polarization Doppler Radar (D3R). The D3R is the principal ground validation instrument for the precipitation measurements of the Dual Precipitation Radar (DPR) onboard the GPM Core Observatory satellite scheduled for launch in 2014. The D3R system employs two broadly separated frequencies at Ku- and Ka-bands that together make measurements for precipitation types which need higher sensitivity such as light rain, drizzle and snow. This research describes unique design space to configure the digital receiver for D3R at several processing levels. At length, this research presents analysis and results obtained by employing the multi-carrier waveforms for D3R during the 2012 GPM Cold-Season Precipitation Experiment (GCPEx) campaign in Canada
Signal Processing Techniques and Concept of Operations for Polarimetric Rotating Phased Array Radar
The Weather Surveillance Radar 1988 Doppler (WSR-88D) network has been operational for over 30 years and is still the primary observational instrument employed by the National Weather Service (NWS) forecasters to support their critical mission of issuing severe weather warnings and forecasts in the United States. Nevertheless, the WSR-88Ds have exceeded their engineering design lifespan and are projected to reach the end of operational lifetime by 2040. Technological limitations may prevent the WSR-88D to meet demanding functional requirements for future observational needs. The National Oceanic and Atmospheric Administration (NOAA) has started considering radar systems with advanced capabilities for the eventual replacement of the WSR-88D. Unique and flexible capabilities offered by Phased Array Radar (PAR) technology support the required enhanced weather surveillance strategies that are envisioned to improve the weather radar products, making PAR technology an attractive candidate for the next generation of weather radars. If PAR technology is to replace the operational WSR-88D, important decisions must be made regarding the architecture that will be needed to meet the functional requirements. A four-faced planar PAR (4F-PAR) is expected to achieve the requirements set forth by NOAA and the NWS, but deploying and maintaining an operational network of these radars across the U.S. will likely be unaffordable. A more affordable alternative radar system is based on a single-face Rotating PAR (RPAR) architecture, which is capable of exceeding the functionality provided by the WSR-88D network. This dissertation is focused on exploring advanced RPAR scanning techniques in support of meeting future radar functional requirements. A survey of unique RPAR capabilities is conducted to determine which ones could be exploited under an RPAR Concept of Operations (CONOPS). Three capabilities are selected for further investigation: beam agility, digital beamforming, and dwell flexibility. The RPARs beam agility is exploited to minimize the beam smearing that results from the rotation of the antenna system over the collection of samples in the coherent processing interval. The use of digital beamforming is investigated as a possible way to reduce the scan time and/or the variance of estimates. The RPAR's dwell flexibility capability is explored as a possible way to tailor the scan to meteorological observations with the goal of improving data quality. Three advanced RPAR scanning techniques are developed exploiting these capabilities, and their performance in support of meeting the radar functional requirements is quantified. The proposed techniques are implemented on the Advanced Technology Demonstrator (ATD), a dual-polarization RPAR system at the National Severe Storms Laboratory (NSSL) in Norman, OK. Data collection experiments are conducted with the ATD to demonstrate the performance of the proposed techniques for dual-polarization observations. Results are verified by quantitatively comparing fields of radar-variable estimates produced using the proposed RPAR techniques with those produced by a well-known collocated WSR-88D radar simultaneously collecting data following an operational Volume Coverage Pattern (VCP). The techniques introduced are integrated to operate simultaneously, and used to design an RPAR CONOPS that can complete a full volume scan in about one minute, while achieving other demanding functional requirements. It is expected that the findings in this dissertation will provide valuable information that can support the design of the future U.S. weather surveillance radar network
Assessing scanning strategies with all-digital phased array weather radars for characterization and detection of microbursts
Microbursts are a rapidly evolving, vertically oriented meteorological phenomena that can be extremely hazardous to aviation, and other human activities, if left undetected. The temporal resolution and vertical sampling of the current operational weather radar network (NEXRAD) is too coarse to properly observe the evolution of microbursts and their precursor signatures. However, a potential polarimetric phased array weather radar (PAR) should be able to improve both temporal resolution and spatial sampling of the atmosphere to provide better observation of rapidly evolving hazards such as microbursts. All-digital PAR technology is extremely flexible as a wide array of scanning techniques are available to use; however, this flexibility is not without trade-offs, and these trade-offs are important for understanding how a potential PAR network would operate.
This thesis will lay out a framework and tool set for the study of microbursts and their precursor signatures with varying PAR scanning strategies. This project is the first of its kind to investigate the question of what trade-offs are associated with different scanning strategies when using a planar, mechanically rotating, all-digital PAR to observe and detect microbursts and their precursor signatures, including dual-polarization variables. The scanning strategies analyzed include a traditional volume coverage pattern (VCP) 212, a true range-height indicator (RHI) scan, and imaging at three different spoiled beamwidths in elevation. VCP 212 represents the current operational capacity for microburst observation and detection. True RHI scanning and imaging are more feasible on a PAR system, and they can provide faster temporal resolution and finer vertical sampling.
The framework and tools developed herein are tested in a proof-of-concept analysis by looking at a single wet microburst producing storm generated within a numerical weather prediction (NWP) simulation. Using this NWP simulation data, scanning strategies are implemented through the use of a radar emulator, RSim. These emulations are then analyzed both qualitatively and quantitatively to compare the size, shape, and intensity observations of different microburst precursor signatures: descending reflectivity columns (DRCs), specific differential phase (KDP) cores, and mid-level convergence. Because of
the use of NWP simulations, error analysis is also performed to characterize the impact of estimation errors. The results of this test case analysis of one wet microburst imply that, when utilizing imaging, there is a limit to the benefits provided by increased temporal resolution. This limit occurs at temporal resolutions equal to 30 s and an imaging spoil factor of 5 degrees. When utilizing any spoil factor larger than 5 degrees , the effects of data degradation become too great for the scanning strategy to overcome, the representativeness of the model environment is degraded, and estimation errors become large. However, these results can only be considered preliminary because the analysis only serves as a proof-of-concept
Coherent Receiver Arrays for Astronomy and Remote Sensing
Monolithic Millimeter-wave Integrated Circuits (MMICs) provide a level of integration that makes possible
the construction of large focal plane arrays of radio-frequency detectors—effectively the first “Radio
Cameras”—and these will revolutionize radio-frequency observations with single dishes, interferometers,
spectrometers, and spacecraft over the next two decades. The key technological advances have been
made at the Jet Propulsion Laboratory (JPL) in collaboration with the Northrop Grumman Corporation
(NGC). Although dramatic progress has been made in the last decade in several important areas, including
(i) packaging that enables large coherent detector arrays, (ii) extending the performance of amplifiers
to much higher frequencies, and (iii) reducing room-temperature noise at high frequencies, funding to
develop MMIC performance at cryo-temperatures and at frequencies below 150GHz has dropped nearly
to zero over the last five years. This has severely hampered the advance of the field. Moreover, because
of the high visibility of < 150GHz cryogenic detectors in astrophysics and cosmology, lack of progress in
this area has probably had a disproportionate impact on perceptions of the potential of coherent detectors
in general.
One of the prime objectives of the Keck Institute for Space Studies (KISS) is to select crucial areas of
technological development in their embryonic stages, when relatively modest funding can have a highly
significant impact by catalyzing collaborations between key institutions world-wide, supporting in-depth
studies of the current state and potential of emerging technologies, and prototyping development of key
components—all potentially leading to strong agency follow-on funding.
The KISS large program “Coherent Instrumentation for Cosmic Microwave Background Observations”
was initiated in order to investigate the scientific potential and technical feasibility of these “Radio
Cameras.” This opens up the possibility of bringing support to this embryonic area of detector development
at a critical phase during which KISS can catalyze and launch a coherent, coordinated, worldwide
effort on the development of MMIC Arrays. A number of key questions, regarding (i) the importance and
breadth of the scientific drivers, (ii) realistic limits on sensitivity, (iii) the potential of miniaturization into
receiver “modules,” and (iv) digital signal processing, needed to be studied carefully before embarking on
a major MMIC Array development effort led by Caltech/JPL/NGC and supported by KISS, in the hope
of attracting adequate subsequent government funding. For this purpose a large study was undertaken
under the sponsorship and aegis of KISS. The study began with a workshop in Pasadena on “MMIC
Array Receivers and Spectrographs” (July 21–25, 2008)1, immediately after an international conference
“CMB Component Separation and the Physics of Foregrounds” (July 14–18, 2008)2 that was organized in
conjunction with the MMIC workshop. There was then an eight-month study period, culminating in a
final “MMIC 2Workshop” (March 23–27, 2009).3 These workshops were very well attended, and brought
together the major international groups and scientists in the field of coherent radio-frequency detector
arrays. A notable aspect of the workshops is that they were well attended by young scientists—there
are many graduate students and post-doctoral fellows coming into this area. The two workshops focused
both on detailed discussions of key areas of interest and on the writing of this report. They were
conducted in a spirit of full and impartial scrutiny of the pros and cons of MMICs, in order to make an
objective assessment of their potential. It serves no useful purpose to pursue lines of technology development
based on unrealistic and over-optimistic projections. This is crucially important for KISS, Caltech,
and JPL which can only have real impact if they deliver on the promise of the technologies they develop.
A broad range of opinions was evident at the start of the first workshop, but in the end a strong consensus
was achieved on the most important questions that had emerged. This report reflects the workshop
deliberations and that consensus.
The key scientific drivers for the development of the MMIC technology are: (i) large angular-scale Bmode
polarization observations of the cosmic microwave background—here MMICs are one of two key
technologies under development at JPL, both of which are primary detectors on the recently-launched
Planck mission; (ii) large-field spectroscopic surveys of the Galaxy and nearby galaxies at high spectral
resolution, and of galaxy clusters at low resolution; (iii) wide-field imaging via deployment as focal plane
arrays on interferometers; (iv) remote sensing of the atmosphere and Earth; and (v) wide-field imaging in
planetary missions. These science drivers are discussed in the report.
The most important single outcome of the workshops, and a sine qua non of this whole program,
is that consensus was reached that it should be possible to reduce the noise of individual HEMTs or
MMICs operating at cryogenic temperatures to less than three times the quantum limit at frequencies up
to 150 GHz, by working closely with a foundry (in this case NGC) and providing rapid feedback on the
performance of the devices they are fabricating, thus enabling tests of the effects of small changes in the
design of these transistors. This kind of partnership has been very successful in the past, but can now be
focused more intensively on cryogenic performance by carrying out tests of MMIC wafers, including tests
on a cryogenic probe station. It was felt that a properly outfitted university laboratory dedicated to this
testing and optimization would be an important element in this program, which would include MMIC
designs, wafer runs, and a wide variety of tests of MMIC performance at cryogenic temperatures.
This Study identified eight primary areas of technology development, including the one singled out
above, which must be actively pursued in order to exploit the full potential of MMIC Arrays in a timely
fashion:
1. Reduce the noise levels of individual transistors and MMICs to three times the quantum limit or
lower at cryogenic temperatures at frequencies up to 150 GHz.
2. Integrate high-performing MMICs into the building blocks of large arrays without loss of performance.
Currently factors of two in both noise and bandwidth are lost at this step.
3. Develop high performance, low mass, inexpensive feed arrays.
4. Develop robust interconnects and wiring that allow easy fabrication and integration of large arrays.
5. Develop mass production techniques suitable for arrays of differing sizes.
6. Reduce mass and power. (Requirements will differ widely with application. In the realm of planetary
instruments, this is often the most important single requirement.)
7. Develop planar orthomode transducers with low crosstalk and broad bandwidth.
8. Develop high power and high efficiency MMIC amplifiers for LO chains, etc.
Another important outcome of the two workshops was that a number of new collaborations were
forged between leading groups worldwide with the object of focusing on the development of MMIC
arrays
General aviation weather avoidance sensor study
General aviation weather avoidance sensor stud
The Atmospheric Imaging Radar for High Resolution Observations of Severe Weather
Mobile weather radars often utilize rapid scan strategies when collecting obser- vations of severe weather. 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 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 Atmospheric Radar Research Center at the University of Oklahoma 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 and temporal resolution. Specifically, point target analysis was performed using several digital beamform- ing techniques. Adaptive algorithms allow for the improved resolution and clutter rejection when compared to traditional techniques. Additional experiments were conducted during three severe weather events in Oklahoma, including an isolated cell event with high surface winds, a squall line, and a non-tornadic cyclone. Sev- eral digital beamforming techniques were tested and analyzed, producing unique, simultaneous multi-beam measurements using the AIR.The author made specific contributions to the field of radar meteorology in several areas. Overseeing the design and construction of the AIR was a signif- icant effort and involved the coordination of many smaller teams. Interacting with the members of each group and ensuring the success of the project was a primary focus throughout the venture. Meteorological imaging radars of the past have typically focused on boundary layer or upper atmospheric phenomena. The AIR's primary focus is to collect precipitation data from severe weather. Ap- plying well defined beamforming techniques, ranging from Fourier to adaptive algorithms like robust Capon and Amplitude and Phase Estimation (APES), to precipitation phenomena was a unique effort and has served to advance the use of adaptive array processing in radar meteorology. Exploration of irregular antenna spacing and drawing from the analogies between temporal and spatial process- ing led to the development of a technique that reduced the impact of grating lobes by unwrapping angular ambiguities. Ultimately, the author leaves having created a versatile platform capable of producing some of the highest resolution weather data available in the research community today, with opportunities to significantly advance the understanding of rapidly evolving weather phenomena and severe storms
An Atmospheric and Spatiotemporal Examination of Lightning-Initiated Terrestrial Gamma-ray Flashes Detected by the Fermi Satellite and TETRA II
Terrestrial Gamma-ray Flashes (TGFs) are sub-millisecond bursts of the highest naturally occurring light-energy found within Earth’s atmosphere. TGFs are associated with the electric fields produced in thunderstorms and are geolocated by coincident sferics from lightning strokes. Though billions of lightning strokes occur globally each year, fewer than 1,000 TGFs are detected via satellite and ground-based sensors and only a small fraction are geolocated via sferics.
To date, few studies have focused on individual thunderstorms and climates that produce TGFs. This dissertation examines TGFs from two differing data samples: 1) NASA\u27s Fermi Gamma-Ray Burst Monitor (2013-2018) and 2) The TGF and Energetic Thunderstorm Rooftop Array (TETRA-II) (2016-2019) as a means to identify influences of climate, topography, and electric and atmospheric conditions that produce TGFs.
Getis Ord Gi* and Anselin Moran\u27s I spatial cluster analyses reveal several statistically significant cluster patterns of the 1,341 sferic-associated TGFs detected in tropical latitudes by Fermi. Clusters tend to occur in coastal areas heavily influenced by land-sea interaction. A disproportionate number of Fermi TGFs (65\%) occur over ocean, where lightning is infrequent. Additionally, TGFs in this sample do not necessarily coincide with the highest lightning dense regions, suggesting the production of TGFs require a specific atmospheric conditions rather than occurring as a ratio function of lightning activity.
TETRA II detected 20 sferic-associated TGF events across three detector arrays in tropical and subtropical climates. An examination of lightning frequency within 10 km of TETRA II indicates that events occur within mature thunderstorm cells exhibiting both high and low frequency lightning flash rates (1-46 flashes/min) within(8km-15.5km). One low-altitude, cold-weather event confirms a probable satellite detection bias as proposed by Chronis et al. 2016. NEXRAD-monitored events occur withinproduction, a relationship to the development of the mixed-phase updraft region is present
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