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A new radio frequency interference filter for weather radars

July 1, 2017
  |
Journal Article
Author:
John Y. Cho
Published in:
J. Atmos. Ocean. Technol., Vol. 34, No. 7, 1 July 2017, pp. 1393-1406.
Topic:
algorithms
R&D area:
R&D group:

Summary

A new radio frequency interference (RFI) filter algorithm for weather radars is proposed in the two-dimensional (2D) range-time/sample-time domain. Its operation in 2D space allows RFI detection at lower interference-to-noise or interference-to-signal ratios compared to filters working only in the sample-time domain while maintaining very low false alarm rates. Simulations and real weather radar data with RFI are used to perform algorithm comparisons. Results are consistent with theoretical considerations and show the 2D RFI filter to be a promising addition to the signal processing arsenal against interference with weather radars. Increased computational burden is the only drawback relative to filters currently used by operational systems.
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Summary

A new radio frequency interference (RFI) filter algorithm for weather radars is proposed in the two-dimensional (2D) range-time/sample-time domain. Its operation in 2D space allows RFI detection at lower interference-to-noise or interference-to-signal ratios compared to filters working only in the sample-time domain while maintaining very low false alarm rates. Simulations...

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A new radio frequency interference filter for weather radars

A polarization technique for mitigating low-grazing-angle radar sea clutter

June 4, 2017
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Conference Paper
Author:
Molly K. Crane
…
Published in:
IEEE Int. Microwave Symp., 4-9 June 2017.
Topic:
radar
R&D area:
R&D group:

Summary

Traditional detection schemes in conventional maritime surveillance radars may suffer serious performance degradation due to sea clutter, particularly in low-grazing-angle (LGA) geometries. In such geometries, typical statistical assumptions regarding sea clutter backscatter do not hold. Trackers can be overwhelmed by false alarms, while objects of interest can be challenging to detect. Despite several decades of attempts to devise a means of mitigating the effects of LGA sea clutter on traditional detection schemes, minimal progress has been made in developing an approach that is both robust and practical. To supplement work exploring whether polarization information might offer an effective means of enhancing target detection in sea clutter, MIT Lincoln Laboratory (MIT LL) collected a fully polarimetric X-band radar dataset on the Atlantic coast of Massachusetts Cape Ann in October 2015. Leveraging this dataset, MIT LL developed Polarimetric Co-location Layering (PCL), an algorithm that uses a fundamental polarimetric characteristic of sea clutter to retain detections on objects of interest while reducing the number of false alarms in a conventional singlepolarization radar by as many as two orders of magnitude. PCL is robust across waveform bandwidths, pulse repetition frequencies, and sea states. Moreover, PCL is practical: It can plug directly into the standard radar signal processing chain.
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Summary

Traditional detection schemes in conventional maritime surveillance radars may suffer serious performance degradation due to sea clutter, particularly in low-grazing-angle (LGA) geometries. In such geometries, typical statistical assumptions regarding sea clutter backscatter do not hold. Trackers can be overwhelmed by false alarms, while objects of interest can be challenging to...

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A polarization technique for mitigating low-grazing-angle radar sea clutter

Wind turbine interference mitigation using a waveform diversity radar

April 27, 2017
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Journal Article
Author:
Steven I. Krich
…
Published in:
IEEE Trans. Aerosp. Electron. Syst., Vol. 53, No. 2, April 2017, pp. 805-15.
Topic:
radar
R&D area:
R&D group:

Summary

Interference from the proliferation of wind turbines is becoming a problem for ground-based medium-to-high pulse repetition frequency (PRF) pulsed–Doppler air surveillance radars. This paper demonstrates that randomizing some parameters of the transmit waveform from pulse to pulse, a filter can be designed to suppress both the wind turbine interference and the ground clutter. Furthermore, a single coherent processing interval (CPI) is sufficient to make an unambiguous range measurement. Therefore, multiple CPIs are not needed for range disambiguation, as in the staggered PRFs techniques. First, we consider a waveform with fixed PRF but diverse (random) initial phase applied to each transmit pulse. Second, we consider a waveform with diverse (random) PRF. The theoretical results are validated through simulations and analysis of experimental data. Clutter-plus-interference suppression and range disambiguation in a single CPI may be attractive to the Federal Aviation Administration and coastal radars.
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Summary

Interference from the proliferation of wind turbines is becoming a problem for ground-based medium-to-high pulse repetition frequency (PRF) pulsed–Doppler air surveillance radars. This paper demonstrates that randomizing some parameters of the transmit waveform from pulse to pulse, a filter can be designed to suppress both the wind turbine interference and...

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Wind turbine interference mitigation using a waveform diversity radar

WSR-88D chaff detection and characterization using an optimized hydrometeor classification algorithm

January 23, 2017
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Conference Paper
Author:
James M. Kurdzo
…
Published in:
18th Conf. on Aviation, Range, and Aerospace Meteorology, 23-26 January 2017.
Topic:
radar
R&D area:
R&D group:

Summary

Chaff presents multiple issues for aviation, air traffic controllers, and the FAA, including false weather identification and areas where flight paths may need to be altered. Chaff is a radar countermeasure commonly released from aircraft across the United States and is comprised of individual metallic strands designed to reflect certain wavelengths. Chaff returns tend to look similar to weather echoes in the reflectivity factor and radial velocity fields, and can appear as clutter, stratiform precipitation, or deep convection to the radar operator or radar algorithms. When polarimetric fields are taken into account, however, discrimination between weather and non-weather echoes has relatively high potential for success. In this work, the operational Hydrometeor Classification Algorithm (HCA) on the WSR-88D is modified to include a chaff class that can be used as input to a Chaff Detection Algorithm (CDA). This new class is designed using human-truthed chaff datasets for the collection and quantification of variable distributions, and the collected chaff cases are leveraged in the tuning of algorithm weights through the use of a metaheuristic optimization. A final CDA uses various image processing techniques to deliver a filtered output. A discussion regarding WSR-88D observations of chaff on a broad scale is provided, with particular attention given to observations of negative differential reflectivity during different stages of chaff fallout. Numerous cases are presented for analysis and characterization, both as an HCA class and as output from the filtered CDA.
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Summary

Chaff presents multiple issues for aviation, air traffic controllers, and the FAA, including false weather identification and areas where flight paths may need to be altered. Chaff is a radar countermeasure commonly released from aircraft across the United States and is comprised of individual metallic strands designed to reflect certain...

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WSR-88D chaff detection and characterization using an optimized hydrometeor classification algorithm

Scalable prototyping testbed for MMW imager system

October 18, 2016
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Conference Paper
Author:
Huy T. Nguyen
…
Published in:
6th Int. Symp. on Phased Array Systems and Technology, PAST 2016, 18-21 October 2016.
Topic:
radar
R&D area:
R&D group:

Summary

A prototyping testbed for an experimental millimeter-wave multiple-imput multiple-output (MIMO) radar system for security applications in high foot-traffic areas will be presented. The system is designed for flexible operation at a 10 Hz video rate, enabled by high-speed electronic scanning and real-time signal processing. Overall imaging system costs are reduced by the use of an innovative ultra-sparse multistatic radar solution and a 3-D near-field beamforming image construction technique targeted for low-cost high-throughput GPU processors. The testbed is architected with FPGAs, GPUs, CPU storage, and networking, capable of supporting future growth in capabilities, such as interference suppression & advanced signal processing algorithms, auxiliary sensing modalities, near-sensor analytics, and integration into a system-of-systems security architecture.
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Summary

A prototyping testbed for an experimental millimeter-wave multiple-imput multiple-output (MIMO) radar system for security applications in high foot-traffic areas will be presented. The system is designed for flexible operation at a 10 Hz video rate, enabled by high-speed electronic scanning and real-time signal processing. Overall imaging system costs are reduced...

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Scalable prototyping testbed for MMW imager system

The threat to weather radars by wireless technology

July 1, 2016
  |
Journal Article
Author:
Elena Saltikoff
…
Published in:
Amer. Meteor. Soc., Vol. 97, No. 7, 1 July 2016, pp. 1159-67, doi: 10.1175/BAMS-D-15-00048.1.
Topic:
radar
R&D area:
R&D group:

Summary

Wireless technology, such as local area telecommunication networks and surveillance cameras, causes severe interference for weather radars, because they use the same operational radio frequencies. One or two disturbances can be removed from the radar image, but the number and power of the interfering wireless devices are growing all over the world, threatening that one day the radars could not be used at all. Some agencies have already changed or are considering changing frequency bands, but now even other bands are under threat. Use of equipment at radio frequencies is regulated by laws and international agreements. Technologies have been developed for peaceful co-existence. If wireless devices use these technologies to protect weather radars, their data transmission capabilities become limited, so it is tempting to violate the regulations. Hence, it is an important task for the worldwide weather community to involve themselves in the radio-frequency management process and work in close contact with their National Radio Authorities to ensure that meteorological interests be duly taken into account in any decision making process toward the future usage of wireless devices.
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Summary

Wireless technology, such as local area telecommunication networks and surveillance cameras, causes severe interference for weather radars, because they use the same operational radio frequencies. One or two disturbances can be removed from the radar image, but the number and power of the interfering wireless devices are growing all over...

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The threat to weather radars by wireless technology

The evolution to modern phased array architectures

October 20, 2015
  |
Journal Article
Author:
Jeffrey S. Herd
…
Published in:
Proceedings of the IEEE, Vol. 104, No. 3, March 2016, pp. 519-529.
Topic:
radar
R&D area:
R&D group:

Summary

Phased array technology has been evolving steadily with advances in solid-state microwave integrated circuits, analysis and design tools, and reliable fabrication practices. With significant government investments, the technologies have matured to a point where phased arrays are widely used in military systems. Next-generation phased arrays will employ high levels of digitization, which enables a wide range of improvements in capability and performance. Digital arrays leverage the rapid commercial evolution of digital processor technology. The cost of phased arrays can be minimized by utilizing high-volume commercial microwave manufacturing and packaging techniques. Dramatic cost reductions are achieved by employing a tile array architecture, which greatly reduces the number of printed circuit boards and connectors in the array.
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Summary

Phased array technology has been evolving steadily with advances in solid-state microwave integrated circuits, analysis and design tools, and reliable fabrication practices. With significant government investments, the technologies have matured to a point where phased arrays are widely used in military systems. Next-generation phased arrays will employ high levels of...

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The evolution to modern phased array architectures

Enhanced signal processing algorithms for the ASR-9 Weather Systems Processor

October 1, 2015
  |
Journal Article
Author:
John Y. Cho
Published in:
J. Atmos. Ocean. Technol., Vol. 32, No. 10, October 2015, pp. 1847-59.
Topic:
algorithms
R&D area:
R&D group:

Summary

New signal processing algorithms for the Airport Surveillance Radar-9 (ASR-9) Weather Systems Processor (WSP) are introduced. The Moving Clutter Spectral Processing for Uneven-Sampled Data with Dealiasing (MCSPUDD) algorithm suite removes isolated moving clutter targets and corrects aliased velocity values on a per-range-gate basis. The spectral differencing technique is applied to the low- and high-beam data to produce a dual-beam velocity estimate that is more accurate than the current autocorrelation-lag-1-based approach. Comparisons with Terminal Doppler Weather Radar (TDWR) data show that estimate errors are reduced by 8%, 15%, and 15% for the low-, high-, and dual-beam velocities, respectively.
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Summary

New signal processing algorithms for the Airport Surveillance Radar-9 (ASR-9) Weather Systems Processor (WSP) are introduced. The Moving Clutter Spectral Processing for Uneven-Sampled Data with Dealiasing (MCSPUDD) algorithm suite removes isolated moving clutter targets and corrects aliased velocity values on a per-range-gate basis. The spectral differencing technique is applied to...

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Enhanced signal processing algorithms for the ASR-9 Weather Systems Processor

Evaluation of the baseline NEXRAD icing hazard project

September 17, 2015
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Conference Paper
Author:
Michael F. Donovan
…
Published in:
37th Conference on Radar Meteorology, 14-18 September 2015
Topic:
aviation weather
R&D area:
R&D group:

Summary

MIT Lincoln Laboratory has developed an icing hazard product that is now operational throughout the NEXRAD network. This initial version of the Icing Hazard Levels (IHL) algorithm is predicated on the presence of graupel as determined by the NEXRAD Hydrometeor Classification Algorithm (HCA). Graupel indicates that rime accretion on ice crystal aggregates is present. It is inferred that the riming process occurs at the altitude that HCA reports graupel as well as to some vertical depth above. To capture some of that depth, temperature and relative humidity interest fields are computed from meteorological model data based on the technique used in the National Center for Atmospheric Research's Current Icing Potential Product and utilized within IHL as warranted. A critical aspect of the IHL development has focused on the verification of the presence of icing. Two methods are used. For the first, pilot reports of icing (PIREPs) are used to score the performance of IHL. Since PIREPs are provided with inherent time and space uncertainties, a buffer of influence is associated with each PIREP when scoring IHL. Results show the IHL as configured is an effective indicator of a potential icing hazard when HCA graupel classifications are present. Results also show the importance of radar volume coverage pattern selection in detecting weak returns in winter weather. For the second, in situ icing missions were performed within range of a dual pol NEXRAD to provide quantitative data to identify the presence of supercooled liquid water. Comparisons of in situ data to HCA classifications show that HCA graupel indications do not fully expose the icing hazard and these findings are being used to direct future attention of IHL development. This paper will describe the verification method and performance assessment of the IHL initial capability.
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Summary

MIT Lincoln Laboratory has developed an icing hazard product that is now operational throughout the NEXRAD network. This initial version of the Icing Hazard Levels (IHL) algorithm is predicated on the presence of graupel as determined by the NEXRAD Hydrometeor Classification Algorithm (HCA). Graupel indicates that rime accretion on ice...

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Evaluation of the baseline NEXRAD icing hazard project

Aircraft in situ validation of hydrometeors and icing conditions inferred by ground-based NEXRAD polarimetric radar

June 15, 2015
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Conference Paper
Author:
Earle R. Williams
…
Published in:
SAE Int. Conf. on Icing of Aircraft, Engines, and Structures, ICE 2015, 15 June 2015.
Topic:
aviation weather
R&D area:
R&D group:

Summary

MIT Lincoln Laboratory is tasked by the U.S. Federal Aviation Administration to investigate the use of the NEXRAD polarimetric radars for the remote sensing of icing conditions hazardous to aircraft. A critical aspect of the investigation concerns validation that has relied upon commercial airline icing pilot reports and a dedicated campaign of in situ flights in winter storms. During the month of February in 2012 and 2013, the Convair-580 aircraft operated by the National Research Council of Canada was used for in situ validation of snowstorm characteristics under simultaneous observation by NEXRAD radars in Cleveland, Ohio and Buffalo, New York. The most anisotropic and easily distinguished winter targets to dual pol radar are ice crystals. Accordingly, laboratory diffusion chamber measurements in a tightly-controlled parameter space of temperature and humidity provide the linkage between shape and the expectation for the presence/absence of water saturation conditions necessary for icing hazard in situ. In agreement with the laboratory measurements pertaining to dendritic and hexagonal flat plate crystals, the aircraft measurements have verified the presence of supercooled water in mainly low concentrations coincident with regions showing layered anomalies of positive differential reflectivity (ZDR) by ground-based radar, otherwise known as +ZDR 'bright bands'. Extreme values of ZDR (up to +8 dB) have also been found to be coincident with hexagonal flat plate crystals and intermittent supercooled water, also consistent with laboratory measurements. The icing conditions found with the anisotropic description are considered non-classical (condensation/collision-coalescence) and require the ascent of air and availability of ice nuclei. A modest ascent rate (
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Summary

MIT Lincoln Laboratory is tasked by the U.S. Federal Aviation Administration to investigate the use of the NEXRAD polarimetric radars for the remote sensing of icing conditions hazardous to aircraft. A critical aspect of the investigation concerns validation that has relied upon commercial airline icing pilot reports and a dedicated...

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Aircraft in situ validation of hydrometeors and icing conditions inferred by ground-based NEXRAD polarimetric radar
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