Publications
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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The 2013 Buffalo Area Icing and Radar Study (BAIRS)
March 6, 2015
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-419
Summary
The Next Generation Weather Radar (NEXRAD) network completed a dual polarization upgrade in 2013. The radars now can be used to sense the type of scatterers that cause the radar returns. The scatterers can be hydrometeors, biologicals, or earth-sourced. The ability to reliably interpret the 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. That assessment for Federal Aviation Administration (FAA) purposes would necessarily be performed by automated algorithms based in hydrometeor classification terms. The truth as to the icing hazard aloft (where the radar scans) is required to ascertain the value of such algorithms. The Buffalo Area Icing and Radar Study (BAIRS) of 2013 was a partnership between MIT Lincoln Laboratory (LL) and the National Research Council of Canada (NRC) to perform in situ icing missions within the surveillance range of the dual polarization NEXRAD in Buffalo, NY. The goal of these 2013 missions, and the subject of this report, was to target specific winter weather scenarios known to exhibit an aviation icing hazard for the purpose of quantifying the microphysical properties of the target zones and verifying the presence of supercooled liquid water (SLW) to support validation of hydrometeor classification algorithms. These are the first such missions to execute in situ measurements within a NEXRAD's surveillance range running with the fielded, operational NEXRAD hydrometeor classifier. NRC's Convair-580 instrumented research plane was used for three icing missions covering 14 hours. Three distinctly different winter weather scenarios were encountered. This document details the analysis of in situ data such as particle type and liquid water content (LWC) with NEXRAD dual polarization parameters for the three missions. The BAIRS analysis identified these key findings: -NEXRAD radar returns are prevalent in conditions of supercooled water, -NEXRAD classification shows positive results based on particle imagery, -NEXRAD "dry snow" class masks the presence of mixed phase potential icing hazard, -NEXRAD "unknown" class contains diverse regions of icing hazard potential, and there are methods to classify some of these regions, and -In situ aircraft observations are an important tool to both verify algorithm performance and guide further development.
Summary
The Next Generation Weather Radar (NEXRAD) network completed a dual polarization upgrade in 2013. The radars now can be used to sense the type of scatterers that cause the radar returns. The scatterers can be hydrometeors, biologicals, or earth-sourced. The ability to reliably interpret the radar-sensed thermodynamic phase of the...
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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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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 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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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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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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Dual polarization radar winter storm studies supporting development of NEXRAD-based aviation hazard products
September 29, 2011
Conference Paper
Published in:
35th Conf. on Radar Meteorology, 26-30 September 2011.
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The Next Generation Weather Radar (NEXRAD) dual polarization upgrade has begun adding a functional enhancement to classify hydrometeors. MIT Lincoln Laboratory (LL) develops NEXRAD-based weather radar products for Federal Aviation Administration (FAA) weather systems such as Corridor Integrated Weather System (CIWS), Integrated Terminal Weather System (ITWS), and Weather and Radar Processor (WARP). Without dual polarization, those products are limited to providing information on precipitation location and intensity. With dual polarization, LL is now developing new aviation weather products to determine locations of hydrometeor-based hazards. A product for Icing Hazards Level (IHL) is expected to benefit the FAA. LL has partnered with Valparaiso University (VU) in northern Indiana near Chicago since 2008 to study the evolution of winter storms prior to the NEXRAD dual polarization upgrade. VU contributes to the study a C-band dual polarization weather radar, an on-demand local sounding capability, and a surface winter weather verification team. Additionally, the Wolcott, IN wind profiler is about 70 km south within viewing range of the VU radar, and provides information on the fall speeds of the hydrometeors of interest. This resource-rich location has allowed for substantive study of many winter storm types: synoptic, lake effect, and frontal passages. A key to development of the IHL product is the ability to interpret dual polarization radar signatures from the winter microphysical states and precipitation structures. Evolution of the structures is a response to the microphysical water and ice saturation (sub or super) states. The magnitude of the vertical lift may affect the saturation states. Methods to segregate the radar signatures will be important regarding the inferred presence of a supercooled water icing hazard. The blizzard of Feb. 1 and 2, 2011 produced four distinct precipitation periods (snow, sleet, freezing drizzle, and lake effect snow), all of which will be discussed. The paper and presentation will also detail findings from the study of multiple winter storms and how they inform the development of the IHL product.
Summary
The Next Generation Weather Radar (NEXRAD) dual polarization upgrade has begun adding a functional enhancement to classify hydrometeors. MIT Lincoln Laboratory (LL) develops NEXRAD-based weather radar products for Federal Aviation Administration (FAA) weather systems such as Corridor Integrated Weather System (CIWS), Integrated Terminal Weather System (ITWS), and Weather and Radar...
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Wind-shear system cost-benefit analysis
August 1, 2010
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 18, No. 2, August 20, pp. 47-68.
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Mitigating thunderstorm wind-shear threats for aircraft near the ground has been an important issue since the 1970s, when several fatal commercial aviation accidents were attributed to wind shear. Updating the knowledge base for airport wind-shear exposure and effectiveness of detection systems has become critical to the Federal Aviation Administration as they consider options for aging systems and evaluations of new systems.
Summary
Mitigating thunderstorm wind-shear threats for aircraft near the ground has been an important issue since the 1970s, when several fatal commercial aviation accidents were attributed to wind shear. Updating the knowledge base for airport wind-shear exposure and effectiveness of detection systems has become critical to the Federal Aviation Administration as...
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Development of dual polarization aviation weather products for the FAA
October 5, 2009
Conference Paper
Published in:
34th Conf. on Radar Meteorology, 5-9 October 2009.
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Weather radar products from the United States' NEXRAD network are used as key components in FAA weather systems such as CIWS, ITWS, and WARP. The key products, High Resolution VIL (HRVIL) and High Resolution Enhanced Echo Tops (HREET), provide primary information about precipitation location and intensity. The NEXRAD network will become dual polarization capable beginning in late 2010 adding the ability to classify hydrometeors. This new aspect from radar remote sensing of the weather offers opportunity to provide new aviation weather products and augment existing ones. This paper will detail the dual polarization product development program at MIT Lincoln Laboratory (LL) in support of FAA system needs. Current development efforts focus on four products. Two new products will provide volumetric analysis seeking aviation hazards (icing and hail). Two existing products, HRVIL and HREET, will be invigorated by dual polarization data to yield improved data quality and mitigation of partial beam blockage. The LL program has partnered with NCAR and NSSL subject matter experts to bring their most advanced research results into these new and improved products. The LL program also has partnered with Valparaiso University for them to provide dual polarization and local sonde sounding data especially during suspected icing conditions. The new Icing Hazards Level (IHL) product is expected to provide the most benefit to the FAA. Its development also poses the greatest challenge both in scope and in the ability of S-band radar to sense the phenomena of interest. Icing phenomena include supercooled drops/droplets and ice crystals and the associated aviation hazard could be aloft or near/at the surface. Graupel is an indication that supercooled water has accreted to ice particles. The initial NEXRAD hydrometeor classifier will not have an explicit supercooled water class or the benefit of supporting data. It will have ice crystal and graupel classes. The LL approach will utilize at least some additional data (vertical thermodynamic profiles). Techniques applied to the development of IHL will likely have applicability to the other products as well. Aspects of the IHL development will also be discussed in the paper.
Summary
Weather radar products from the United States' NEXRAD network are used as key components in FAA weather systems such as CIWS, ITWS, and WARP. The key products, High Resolution VIL (HRVIL) and High Resolution Enhanced Echo Tops (HREET), provide primary information about precipitation location and intensity. The NEXRAD network will...
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Redeployment of the New York TDWR - technical analysis of candidate sites and alternative wind shear sensors
September 14, 2009
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-351
Summary
The John F. Kennedy International Airport (JFK) and LaGuardia Airport (LGA) are protected from wind shear exposure by the New York Terminal Doppler Weather Radar (TDWR), which is currently located at Floyd Bennet Field, New York. Because of a September 1999 agreement between the Department of the Interior and the Department of Transportation, this location is required to be vacated no later than January 2023. Therefore, a study based on model simulations of wind shear detection probability was conducted to support future siting selection and alternative technologies. A total of 18 candidate sites were selected for analysis, including leaving the radar where it is. (The FAA will explore the feasibility of the latter alternative; it is included in this study only for technical analysis.) The 18 sites are: Six candidate sites that were identified in the initial New York TDWR site-survey studies in the 1990s (one of which is the current TDWR site), a site on Staten Island, two Manhattan skyscrapers, the current location of the WCBS Doppler weather radar in Twombly Landing, New Jersey, and eight local airports including JFK and LGA themselves. Results clearly show that for a single TDWR system, all six previously surveyed sites are suitable for future housing of the TDWR. Unfortunately, land acquisition of these sites will be at least as challenging as it was in the 1990s due to further urban development and likely negative reaction from neighboring residents. Evaluation results of the on-airport siting of the TDWR (either at JFK or at LGA) indicate that this option is feasible if data from the Newark TDWR are simultaneously used. This on-airport option would require software modification such as integration of data from the two radar systems an dimplementation of "overhead" feature detection. The radars on the Manhattan skyscrapers are not an acceptable alternative due to severe ground clutter. The Staten Island site and most other candidate airports are also not acceptable due to distance and/or beam blockage. The existing Airport Surveillance Radar (ASR-9) Weather Systems Processor (WSP) at JFK and the Bookhaven (OKX) Weather Surveillance Radar 1988-Doppler (WSR-88D, commonly known as NEXRAD) on Long Island cannot provide sufficient wind shear protection mainly due to limited wind shear detection capability and/or distance.
Summary
The John F. Kennedy International Airport (JFK) and LaGuardia Airport (LGA) are protected from wind shear exposure by the New York Terminal Doppler Weather Radar (TDWR), which is currently located at Floyd Bennet Field, New York. Because of a September 1999 agreement between the Department of the Interior and the...
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Wind-shear system cost benefit analysis update
May 13, 2009
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-341
Summary
A series of fatal commercial aviation accidents in the 1970s led to the development of systems and strategies to protect against wind shear. The Terminal Doppler Weather Radar (TDWR), Low Level Wind Shear Alert System (LLWAS), Weather Systems Processor (WSP) for Airport Surveillance Radars (ASR-9), pilot training and on-board wind shear detection equipment are all key protection components. While these systems have been highly effective, there are substantial costs associated with maintaining and operating ground-based systems. In addition, while over 85% of all major air carrier operations occur at airports protected by one of these ground-based wind-shear systems, the vast majority of smaller operations remain largely unprotected. This report assesses the technical and operational benefits of current and potential alternative ground-based systems as mitigations for the low-altitude wind-shear hazard. System performance and benefits for all of the current TDWR (46), ASR-9 WSP (35), and LLWAS (40) protected airports are examined, along with 40 currently unprotected airports. We considered in detail several alternatives and/or combinations for existing ground-based systems. These included the option to use data from current WSR-88D (or NEXRAD) and two potential future sensor deployments: (1) a commercially built pulsed-Doppler Lidar and (2) an X-band commercial Doppler weather radar. Wind-shear exposure estimates and simulation models for each wind shear protection component were developed for each site in order to accurately comare all alternatives. For the period 2010-2032, the current combination of wind-shear protection systems reduces teh $3.0 billion unprotected NAS overall wind-shear safety exposure to just $160 million over the entire study period. Overall, tehre were few alternatives that resulted in higher benefits than the TDWR, TDWR-LLWAS, and WSP configurations that currently exist at 81 airports. However, the cheaper operating costs of NEXRAD make it a potential alternative especially at LLWAS and non-wind-shear protected sites.
Summary
A series of fatal commercial aviation accidents in the 1970s led to the development of systems and strategies to protect against wind shear. The Terminal Doppler Weather Radar (TDWR), Low Level Wind Shear Alert System (LLWAS), Weather Systems Processor (WSP) for Airport Surveillance Radars (ASR-9), pilot training and on-board wind...
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