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Extended polarimetric observations of chaff using the WSR-88D weather radar network
June 20, 2023
Journal Article
Published in:
IEEE Transactions on Radar Systems, vol. 1, pp. 181-192, 2023.
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Summary
Military chaff is a metallic, fibrous radar countermeasure that is released by aircraft and rockets for diversion and masking of targets. It is often released across the United States for training purposes, and, due to its resonant cut lengths, is often observed on the S-band Weather Surveillance Radar–1988 Doppler (WSR-88D) network. Efforts to identify and characterize chaff and other non-meteorological targets algorithmically require a statistical understanding of the targets. Previous studies of chaff characteristics have provided important information that has proven to be useful for algorithmic development. However, recent changes to the WSR-88D processing suite have allowed for a vastly extended range of differential reflectivity, a prime topic of previous studies on chaff using weather radar. Motivated by these changes, a new dataset of 2.8 million range gates of chaff from 267 cases across the United States is analyzed. With a better spatiotemporal representation of cases compared to previous studies, new analyses of height dependence, as well as changes in statistics by volume coverage pattern are examined, along with an investigation of the new "full" range of differential reflectivity. A discussion of how these findings are being used in WSR-88D algorithm development is presented, specifically with a focus on machine learning and separation of different target types.
Summary
Military chaff is a metallic, fibrous radar countermeasure that is released by aircraft and rockets for diversion and masking of targets. It is often released across the United States for training purposes, and, due to its resonant cut lengths, is often observed on the S-band Weather Surveillance Radar–1988 Doppler (WSR-88D)...
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CoSPA data product description
November 1, 2021
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-449
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Summary
This document contains a description of Consolidated Storm Prediction for Aviation (CoSPA) data products that are packaged and distributed for external users. As described in Rappa and Troxel, 2013 [1] for Corridor Integrated Weather System (CIWS) data products, CoSPA products are categorized as gridded and non-gridded. Gridded products are typically expressed as rectangular arrays whose elements contain a data value coinciding with uniformly-spaced observations or computed results on a 2-D surface. Gridded data arrays map to the earth's surface through a map projection, for example, Lambert Conformal or Lambert Azimuthal Equal-Area. CoSPA generates only gridded products; there are no non-gridded data for CoSPA.
Summary
This document contains a description of Consolidated Storm Prediction for Aviation (CoSPA) data products that are packaged and distributed for external users. As described in Rappa and Troxel, 2013 [1] for Corridor Integrated Weather System (CIWS) data products, CoSPA products are categorized as gridded and non-gridded. Gridded products are typically...
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The 2017 Buffalo Area Icing and Radar Study (BAIRS II)
May 14, 2020
Project Report
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MIT Lincoln Laboratory Report ATC-447
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Summary
The second Buffalo Area Icing and Radar Study (BAIRS II) was conducted during the winter of 2017. The BAIRS II partnership between Massachusetts Institute of Technology (MIT) Lincoln Laboratory (LL), the National Research Council of Canada (NRC), and Environment and Climate Change Canada (ECCC) was sponsored by the Federal Aviation Administration (FAA). It is a follow-up to the similarly sponsored partnership of the original BAIRS conducted in the winter of 2013. The original BAIRS provided in situ verification and validation of icing and hydrometeors, respectively, within the radar domain in support of a hydrometeor-classification-based automated icing hazard algorithm. The BAIRS II motivation was to: --Collect additional in situ verification and validation data, --Probe further dual polarimetric radar features associated with icing hazard, --Provide foundations for additions to the icing hazard algorithm beyond hydrometeor classifications, and --Further characterize observable microphysical conditions in terms of S-band dual polarimetric radar data. With BAIRS II, the dual polarimetric capability is provided by multiple Next Generation Weather Radar (NEXRAD) S-band radars in New York State, and the verification of the icing hazard with microphysical and hydrometeor characterizations is provided by NRC's Convair-580 instrumented research plane during five icing missions covering about 21 mission hours. The ability to reliably interpret the NEXRAD dual polarization radar-sensed thermodynamic phase of the hydrometeors (solid, liquid, mix) in the context of cloud microphysics and precipitation physics makes it possible to assess the icing hazard potential to aviation. The challenges faced are the undetectable nature of supercooled cloud droplets (for Sband) and the isotropic nature of Supercooled Large Drops (SLD). The BAIRS II mission strategy pursued was to study and probe radar-identifiable, strongly anisotropic crystal targets (dendrites and needles) with which supercooled water (and water saturated conditions) are physically linked as a means for dual polarimetric detection of icing hazard. BAIRS II employed superior optical array probes along with state and microphysical instrumentation; and, using again NEXRAD-feature-guided flight paths, was able to make advances from the original BAIRS helpful to the icing algorithm development. The key findings that are given thorough treatment in this report are: --Identification of the radar-detectable "crystal sandwich" structure from two anisotropic crystal types stratified by in situ air temperature in association with varying levels of supercooled water --with layer thicknesses observed to 2 km, --over hundred-kilometer scales matched with the mesoscale surveillance of the NEXRAD radars, --Development and application of a multi-sensor cloud phase algorithm to distinguish between liquid phase, mixed phase, and glaciated (no icing) conditions for purposes of a "truth" database and improved analysis in BAIRS II, --Development of concatenated hydrometeor size distributions to examine the in situ growth of both liquid and solid hydrometeors over a broad size spectrum; used, in part, to demonstrate differences between maritime and continental conditions, and --The Icing Hazard Levels (IHL) algorithm’s verification in icing conditions is consistent with previous work and, new, is documented to perform well when indicating "glaciated" (no icing) conditions.
Summary
The second Buffalo Area Icing and Radar Study (BAIRS II) was conducted during the winter of 2017. The BAIRS II partnership between Massachusetts Institute of Technology (MIT) Lincoln Laboratory (LL), the National Research Council of Canada (NRC), and Environment and Climate Change Canada (ECCC) was sponsored by the Federal Aviation...
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Enhanced signal processing algorithms for the ASR-9 Weather Systems Processor
October 1, 2015
Journal Article
Published in:
J. Atmos. Ocean. Technol., Vol. 32, No. 10, October 2015, pp. 1847-59.
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.
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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Evaluation of the baseline NEXRAD icing hazard project
September 17, 2015
Conference Paper
Published in:
37th Conference on Radar Meteorology, 14-18 September 2015
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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 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.
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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Aircraft in situ validation of hydrometeors and icing conditions inferred by ground-based NEXRAD polarimetric radar
June 15, 2015
Conference Paper
Published in:
SAE Int. Conf. on Icing of Aircraft, Engines, and Structures, ICE 2015, 15 June 2015.
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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 (
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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Measurements of differential reflectivity in snowstorms and warm season stratiform systems
March 1, 2015
Journal Article
Published in:
J. Appl. Meteor. Climatol., Vol. 54, No. 3, 2015, pp. 573-95.
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The organized behavior of differential radar reflectivity (ZDR) is documented in the cold regions of a wide variety of stratiform precipitation types occurring in both winter and summer. The radar targets and attendant cloud microphysical conditions are interpreted within the context of measurements of ice crystal types in laboratory diffusion chambers in which humidity and temperature are both stringently controlled. The overriding operational interest here is in the identification of regions prone to icing hazards with long horizontal paths. Two predominant regimes are identified: category A, which is typified by moderate reflectivity (from 10 to 30 dBZ) and modest +ZDR values (from 0 to 13 dB) in which both supercooled water and dendritic ice crystals (and oriented aggregates of ice crystals) are present at a mean temperature of -13 degrees C, and category B, which is typified by small reflectivity (from -10 to +10 dBZ) and the largest +ZDR values (from +3 to +7 dB), in which supercooled water is dilute or absent and both flat-plate and dendritic crystals are likely. The predominant positive values for ZDR in many case studies suggest that the role of an electric field on ice particle orientation is small in comparison with gravity. The absence of robust +ZDR signatures in the trailing stratiform regions of vigorous summer squall lines may be due both to the infusion of noncrystalline ice particles (i.e., graupel and rimed aggregates) from the leading deep convection and to the effects of the stronger electric fields expected in these situations. These polarimetric measurements and their interpretations underscore the need for the accurate calibration of ZDR.
Summary
The organized behavior of differential radar reflectivity (ZDR) is documented in the cold regions of a wide variety of stratiform precipitation types occurring in both winter and summer. The radar targets and attendant cloud microphysical conditions are interpreted within the context of measurements of ice crystal types in laboratory diffusion...
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Forecast confidence measures for deterministic storm-scale aviation forecasts
February 5, 2014
Conference Paper
Published in:
4th Aviation, Range, and Aerospace Meteorology Special Symp., 2-6 February 2014.
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Deterministic storm-scale weather forecasts, such as those generated from the FAA's 0-8 hour CoSPA system, are highly valuable to aviation traffic managers. They provide forecasted characteristics of storm structure, strength, orientation, and coverage that are very helpful for strategic planning purposes in the National Airspace System (NAS). However, these deterministic weather forecasts contain inherent uncertainty that varies with the general weather scenario at the forecast issue time, the predicted storm type, and the forecast time horizon. This uncertainty can cause large changes in the forecast from update to update, thereby eroding user confidence and ultimately reducing the forecast's effectiveness in the decision-making process. Deterministic forecasts generally lack objective measures of this uncertainty, making it very difficult for users of the forecast to know how much confidence to have in the forecast during their decision-making process. This presentation will describe a methodology to provide measures of confidence for deterministic storm-scale forecasts. The method inputs several characteristics of the current and historical weather forecasts, such as spatial scale, intensity, weather type, orientation, permeability, and run-to-run variability of the forecasts, into a statistical model to provide a measure of confidence in a forecasted quantity. In this work, the forecasted quantity is aircraft blockage associated with key high-impact Flow Constrained Areas (FCAs) in the NAS. The results from the method, which will also be presented, provide the user with a measure of forecast confidence in several blockage categories (none, low, medium, and high) associated with the FCAs. This measure of forecast confidence is geared toward helping en-route strategic planners in the NAS make better use of deterministic storm-scale weather forecasts for air traffic management.
Summary
Deterministic storm-scale weather forecasts, such as those generated from the FAA's 0-8 hour CoSPA system, are highly valuable to aviation traffic managers. They provide forecasted characteristics of storm structure, strength, orientation, and coverage that are very helpful for strategic planning purposes in the National Airspace System (NAS). However, these deterministic...
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Velocity estimation improvements for the ASR-9 Weather Systems Processor
February 2, 2014
Conference Paper
Published in:
American Meteorological Society Annual Meeting, 2-6 February 2014.
Summary
The Airport Surveillance Radar (ASR-9) is a rapid-scanning terminal aircraft detection system deployed at airports around the United States. To provide cost-effective wind shear detection capability at medium-density airports, the Weather Systems Processor (WSP) was developed and added on to the ASR-9 at 35 sites. The WSP on the ASR-9 is capable of utilizing dual fan-beam estimates of reflectivity and velocity in order to detect low-level features such as gust fronts, wind shear, and microbursts, which would normally be best detectable by a low-scanning pencil beam radar. An upgrade to the ASR-9 WSP, which is currently ongoing, allows for additional computational complexity in the front-end digital signal processing algorithms compared to previous iterations of the system. This paper will explore ideas for improving velocity estimates, including low-level dual beam weight estimation, de-aliasing, and noise reduction. A discussion of the unique challenges afforded by the ASR-9's block-stagger pulse repetition time is presented, along with thoughts on how to overcome limitations which arise from rapid-scanning and the inherent lack of pulses available for coherent averaging.
Summary
The Airport Surveillance Radar (ASR-9) is a rapid-scanning terminal aircraft detection system deployed at airports around the United States. To provide cost-effective wind shear detection capability at medium-density airports, the Weather Systems Processor (WSP) was developed and added on to the ASR-9 at 35 sites. The WSP on the ASR-9...
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Validation of NEXRAD radar differential reflectivity in snowstorms with airborne microphysical measurements: evidence for hexagonal flat plate crystals
September 16, 2013
Conference Paper
Published in:
36th Conf. on Radar Meteorology, 16 September 2013.
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Summary
This study is concerned with the use of cloud microphysical aircraft measurements (the Convair 580) to verify the origin of differential reflectivity (ZDR) measured with a ground-based radar (the WSR-88D KBUF radar in Buffalo, New York). The underlying goal is to make use of the radar measurements to infer the presence or absence of supercooled water, which may pose an icing hazard to aircraft. The context of these measurements is the investment by the Federal Aviation Administration in the use of NEXRAD polarimetric radar and is addressed in the companion paper by Smalley et al. (2013, this Conference). The highlight of the measurements on February 28, 2013 was the finding of sustained populations of hexagonal flat plate crystals over a large area northwest of the KBUF radar, in conditions of dilute and intermittent supercooled water concentration. Some background discussion is in order prior to the discussion of the aircraft/radar observations that form the main body of this study. The anisotropy of hydrometeors, the role of humidity and temperature in crystal shape, and the common presence of hexagonal flat plate crystals in the laboratory cold box experiment are all discussed in turn.
Summary
This study is concerned with the use of cloud microphysical aircraft measurements (the Convair 580) to verify the origin of differential reflectivity (ZDR) measured with a ground-based radar (the WSR-88D KBUF radar in Buffalo, New York). The underlying goal is to make use of the radar measurements to infer the...
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