Publications
Achieving higher integrity in NEXRAD products through multi-sensor integration
January 10, 1999
Conference Paper
Published in:
8th Conf. on Aviation, Range, and Aerospace Meteorology (ARAM), 10-15 January 1999.
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Summary
The initial operational concept for the NEXRAD focused on support for the operational forecaster based on longstanding practice in use of weather radars by the National Weather Service (NWS) and Air Force as well as difficulties in developing reliable, fully automated phenomena detection algorithms [Crum, 1998]. By contrast, achieving high integrity in the narrow band products provided by NEXRAD to external users has received much less attention in the NEXRAD product development process thus far. However, other government weather information systems [especially the FAA's Integrated Terminal Weather System (ITWS) and the Weather and Radar Processor (WARP)] and non-meteorologist external users of the NEXRAD products through the NEXRAD Information Distribution System (NIDS) vendors need very high integrity NEXRAD products. In the NWS context, the direct utilization of NEXRAD products into numerical weather prediction models will also create much more stringent requirements for integrity of the NEXRAD base data. Achieving very high integrity through automated analysis of only the data from a single NEXRAD is very difficult. In this paper, we consider the use of a much wider range of contextual information to create high integrity external user products. For instance, with the NEXRAD Open RPG and connectivity to AWIPS and ITWS, a system architecture will exist that will facilitate the implementation of NEXRAD product quality control algorithms that utilize information from other sensors. In the following sections, we present some examples of how information from various other sources might be used to improve the quality of the data from a NEXRAD. We first show an example of how data from adjacent NEXRADs can be used to help edit out the anomalous propagation (AP) ground clutter which currently is corrupting a number of the NEXRAD reflectivity products intended for air traffic controller use. In cases where the NEXRAD is near a major metropolitan area, data from the FAA's TDWR can be used to improve the integrity of the NEXRAD reflectivity products used for hydrology. Similarly, gridded wind fields estimated from multiple Doppler analyses, aircraft reports, and numerical models can be used to help address difficult challenges in Doppler ambiguity resolution for a single NEXRAD radar. The paper concludes with suggestions for near term demonstration and evaluation of multi sensor approaches to achieving high integrity in the NEXRAD products.
Summary
The initial operational concept for the NEXRAD focused on support for the operational forecaster based on longstanding practice in use of weather radars by the National Weather Service (NWS) and Air Force as well as difficulties in developing reliable, fully automated phenomena detection algorithms [Crum, 1998]. By contrast, achieving high...
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A refinement of thunderstorm climatology for the terminal radar control airspace
January 10, 1999
Conference Paper
Published in:
8th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 10-15 January 1999.
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Convective storms pose a significant threat to aviation safety, and often result in substantial fl ight delays for the commercial aviation industry. The overall impact of these storms is typically based on thunderstorm climatologies and are often one of the factors used in decisions by the US government regarding the operational benefits and allocation of its weather surveillance resources. These climatologies are based on the average number of days that a thunderstorm is observed at a particular airport. Due to the nature of the criteria used to identify a thunderstorm, the climatological statistics often do not accurately represent the number of thunderstorms that impact an airport's operations. The present study utilizes data from the Dallas Ft. Worth International Airport (DFW) and the Orlando International Airport (MCO) to identify deficiencies in the climatological data as it applies to aviation applications. A spatially representative climatology is presented as a more accurate climatology for use in evaluating the impact of convection on an airport's operations. This type of climatological estimate of thunderstorm frequency significantly increases the estimated number of thunderstorms impacting an airport and their associated costs.
Summary
Convective storms pose a significant threat to aviation safety, and often result in substantial fl ight delays for the commercial aviation industry. The overall impact of these storms is typically based on thunderstorm climatologies and are often one of the factors used in decisions by the US government regarding the...
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Addressing the weather delay problems of the New York City airports with the Integrated Terminal Weather System
January 10, 1999
Conference Paper
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8th Conf. on Aviation, Range, and Aerospace Meteorology, 10-15 1999.
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The three major New York City (NYC) air carrier airports (Kennedy, LaGuardia, Newark) currently experience high delays due to adverse terminal weather, both in an absolute sense and relative to other major airport complexes. Significantly expanding the NYC airports (e.g., by adding new runways) to reduce delays is not feasible. One alternative is to provide aviation weather decision support systems to air traffic, airline, and airport operations personnel to help them operate more safely and effectively with the existing runway/taxiway complexes. Under an innovative partnership between the Port Authority of New York and New Jersey and the Federal Aviation Administration (FAA), Massachusetts Institute of Technology, Lincoln Laboratory has installed and is currently operating a functional prototype Integrated Terminal Weather System (ITWS) to conduct research on improving the safety and efficiency of operations at the NYC airports during adverse weather. The New York terminal area provides a stringent test of the ITWS ability to safely reduce delays due to both the meteorology and the operational usage challenges not found at the earlier ITWS test locations of Orlando, Memphis, and Dallas. In this paper, we describe key features of the New York terminal environment and the ITWS prototype, the initial experience in addressing the meteorological and operational usage challenges of the New York terminal area, and describe plans for the coming years.
Summary
The three major New York City (NYC) air carrier airports (Kennedy, LaGuardia, Newark) currently experience high delays due to adverse terminal weather, both in an absolute sense and relative to other major airport complexes. Significantly expanding the NYC airports (e.g., by adding new runways) to reduce delays is not feasible...
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Aviation user needs for convective weather forecasts
January 10, 1999
Conference Paper
Published in:
8th Conf. on Aviation, Range, and Aerospace Meteorology (ARAM), 10-15 January 1999.
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Summary
The prediction of convective weather is very important to aviation, since almost half of the serious delay at major airports in the warm season is caused by thunderstorms. The need for accurate 0-6 hr forecasts for NAS users has been the subject of extensive publications, forums, and advisory committees in the aviation weather community over the last several years (Wolfson, et al; 1997). The Convective Weather Product Development Team (PDT), a core team of scientists and engineers from NCAR, NSSL, and MIT LL, was formed in 1996 as part of the reorganization of the FAA Aviation Weather Research Program. The team is developing convective weather forecast algorithms that produce operationally useful products for both the terminal area and enroute airspace. The products are designed to meet specific users' air traffic planning and safety needs. Before major algorithm development began, PDT members visited terminal and enroute Air Traffic (AT) personnel and airline dispatchers to understand the forecast products that were currently available to them and their needs for a near future product. Also, in order to reach the pilot community, a pilot survey about existing convective weather information and how to improve it, was created and distributed at the OshKosh Fly-In in August of 1997. This needs assessment took advantage of interviewees that had extensively used state-of-the-art weather information products (ITWS) in an operational setting for years. Their requirements, based on personal experiences with operational products during convective weather events, were less stringent than those reported in the recent requirements document pertaining to ARTCC TMUs (Browne, et al; 1999). The results of these investigations were used in the creation of the DFW Terminal Convective Weather Forecast (TCWF) product and the National Convective Weather Forecast (NCWF) products that were demonstrated throughout the summer of 1998 (Hallowell, et al; 1999; Mueller, et al; 1999). These demonstrations also provided additional insight into user needs. In this paper we describe Air Traffic users and their specific responsibilities. We then summarize AT and airline needs based on interviews conducted in 1997 and 1998. Information on pilots' needs for convective weather information is presented at the end.
Summary
The prediction of convective weather is very important to aviation, since almost half of the serious delay at major airports in the warm season is caused by thunderstorms. The need for accurate 0-6 hr forecasts for NAS users has been the subject of extensive publications, forums, and advisory committees in...
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Nowcasting requirements for the aircraft vortex spacing system (AVOSS)
January 10, 1999
Conference Paper
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8th Conf. on Aviation, Range, and Aerospace Meteorology, 10-15 Jan. 1999, pp. 340-344.
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Aircraft wake vortices are counter-rotating tubes of air that are generated from aircraft as a consequence of the lift on the aircraft. The safety concern of wake vortices, particularly when lighter aircraft are following heavy planes, has caused the Federal Aviation Administration (FAA) to enact minimum separation requirements during the arrival phase of flight. These separation standards are imposed at the arrival threshold during Instrument Flight Rules (IFR) and are a significant constraint on arrival capacity at the largest U.S. airports. Any movement toward increasing air traffic efficiency, such as concepts toward free-flight, must address increasing runway capacity if they are to be fully effective. Decades of past wake vortex measurements clearly show that current wake vortex separations are overconservative in many weather conditions, and that adapting the separations to the current weather state could safely reduce these separations...This paper describes the known meteorological influences on vortex behavior and gives an overview of AVOSS. Airport climatology is studied to discuss the prevalence of conditions that are conducive to capacity increases with AVOSS technology. Finally, additional constraints on AVOSS nowcasts are discussed.
Summary
Aircraft wake vortices are counter-rotating tubes of air that are generated from aircraft as a consequence of the lift on the aircraft. The safety concern of wake vortices, particularly when lighter aircraft are following heavy planes, has caused the Federal Aviation Administration (FAA) to enact minimum separation requirements during the...
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Optimizing the ITWS algorithm designed to remove anomalous propagation ground clutter from the ASR-9 precipitation product
January 10, 1999
Conference Paper
Published in:
8th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 10-15 January 1999.
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A key product within the Integrated Terminal Weather System (ITWS) Initial Operating Capability (IOC) product suite removes anomalous propagation (AP) ground clutter from the ASR-9 precipitation product. This has been identified as a critical component of ITWS due to the frequent occurrence of AP when storms or outflows move over an ASR-9. Editing is accomplished by comparing the raw ASR-9 weather data to composite maps generated by the Next Generation Weather Radar (NEXRAD) and the Terminal Doppler Weather Radar (TDWR). An editing template, containing regions of AP, is created based on the ASR-9 data collected at the middle of the composite volume scan to minimize the difference in update rates. The template is used to edit the ASR-9 scan immediately after the composite map and all subsequent scans until a new composite map is received. This algorithm has been shown to perform quite well, especially if the weather and AP returns are not co-located. During the 1994 Demonstration and Validation Operational Test and Evaluation in Memphis (MEM) and Orlando (MCO), the probability of editing AP (PEAP) in the absence of weather was 0.97 for level 2 and greater returns (Klingle-Wilson, 1995). The probability of editing weather (PEW) for those cases with weather only was quite low, i.e., 0.01. In order to minimize the removal of weather returns in those cases where the AP and weather are located in close proximity, the editing thresholds are quite conservative. This is reflected by the 1994 results which show a PEAP of 0.81 and a PEW of 0.02 for this class of event. Besides the conservative thresholds, another area of concern is the fact that the AP regions can expand or increase in intensity after the AP editing template is created. This rapid variation frequently occurs with convectively generated AP and can cause the performance of the algorithm to decrease with time until a new template is created. In this study, we will examine the algorithm failure mechanisms in detail to identify possible site-adaptable parameter changes that can be used to improve the performance for the mixed weather/AP events. This is especially germane since the parameter set was not re-evaluated after the TDWR composite map was incorporated in 1995. In the critical region over the airport during hazardous weather conditions, this radar updates more frequently than the NEXRAD. Since the parameters were designed to account for the NEXRAD volume update rate, they are probably too conservative for the current algorithm (which uses both composite maps).
Summary
A key product within the Integrated Terminal Weather System (ITWS) Initial Operating Capability (IOC) product suite removes anomalous propagation (AP) ground clutter from the ASR-9 precipitation product. This has been identified as a critical component of ITWS due to the frequent occurrence of AP when storms or outflows move over...
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The growth and decay storm tracker
January 10, 1999
Conference Paper
Published in:
Proc. Eighth Conf. on Aviation, Range, and Aerospace Meteorology, 10-15 Jan. 1999, pp. 58-62.
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An elliptical filter/tracker capable of accounting for systematic growth and delay, designated the Growth and Decay Storm Tracker, has been developed and tested. Its performance depends on the size and shape of the filter, the performance of the cross-correlation tracker, the time interval between successive scans, the forecast lead time, and the type of storm being tracked.
Summary
An elliptical filter/tracker capable of accounting for systematic growth and delay, designated the Growth and Decay Storm Tracker, has been developed and tested. Its performance depends on the size and shape of the filter, the performance of the cross-correlation tracker, the time interval between successive scans, the forecast lead time...
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Study of Network Expansion LLWAS (LLWAS-NE) fault identification and system warning optimization through joint use of LLWAS-NE and TDWR data
January 10, 1999
Conference Paper
Published in:
8th Conf. on Aviation, Range, and Aerospace Meteorology (ARAM), 10-15 January 1999.
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Low level wind shear has been identified as an aviation hazard which has caused or contributed to a significant number of aircraft accidents (Soffer, 1990). To protect aircraft from hazardous wind shear, the Federal Aviation Administration (FAA) developed a system called the Low Level Wind Shear Alert System (LLWAS), containing a collection of anemometers as well as data processing logic (Wilson and Gramzow, 1991). The LLWAS has undergone several advancements in both design and algorithmic computation. The latest deployment, known as the Network Expansion Low Level Wind Shear Alert System (LLWAS-NE), consists of additional sensors to the original LLWAS network, providing better coverage of the airfield. In addition, the LLWAS-NE is capable of providing runway-oriented wind shear and microburst alerts with loss and gain values. The alerts from LLWAS-NE will be integrated with those from the Terminal Doppler Weather Radar (TDWR) and the Integrated Terminal Weather System (ITWS) at locations where all systems are available (Cole, 1992; Cole and Todd, 1994). An analysis was undertaken at Orlando (MCO) and Dallas/Ft. Worth (DFW) International Airports to assess the accuracy of wind shear alerts produced by LLWAS-NE and the TDWR/LLWASNE integration algorithm. Identifying improvements that can be made to either system is important, as LLWAS-NE alert information is anticipated to be integrated with ITWS in an ITWS/LLWAS-NE integration algorithm. As currently specified, the ITWS/LLWAS-NE integration algorithm will work the same as the TDWR/LLWAS-NE version. The ITWS/LLWAS-NE algorithm is an area where additional work is necessary to ascertain if the integration parameters should be modified to account for performance differences between the ITWS and TDWR algorithms. We suggest that ongoing assessment of the LLWAS-NE should use both LLWAS-NE data and TDWR base data, when possible. Comparing both data sets also will facilitate optimization of LLWAS-NE parameters used in the computation of the alerts.
Summary
Low level wind shear has been identified as an aviation hazard which has caused or contributed to a significant number of aircraft accidents (Soffer, 1990). To protect aircraft from hazardous wind shear, the Federal Aviation Administration (FAA) developed a system called the Low Level Wind Shear Alert System (LLWAS), containing...
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The benefits of using NEXRAD vertically integrated liquid water as an aviation weather product
January 10, 1999
Conference Paper
Published in:
8th Conf. on Aviation, Range, and Aerospace Meteorology (ARAM), 10-15 January 1999.
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Summary
Over the past five years in which the Integrated Terminal Weather System (ITWS) testbed prototypes have been operational, there have been regular discrepancies noticed between the ASR–9 six–level precipitation product and the NEXRAD six–level maximum composite reflectivity product. (1. The NEXRAD composite product used in this study is the NEXRAD maximum composite reflectivity product which both the FAA and the ITWS use for weather data.). At the three prototypes in Memphis, Orlando and Dallas, staff have recognized that in certain situations the NEXRAD composite reflectivity product, which is the ITWS 100 and 200 nm long–range product, can be as much as three Video Integrator and Processor (VIP) levels higher than the ASR–9 precipitation product. This situation has caused some confusion for users of the ITWS system and concern on the part of system safety monitors. The confusion occurs because the two products do not agree with each other. Rhoda and Pawlak (1998) show that more aircraft will deviate around cells of ASR–9 VIP level 4 or greater than will penetrate them. There is also an aviation rule–of–thumb that pilots and air traffic specialists use which states cells of VIP level 3 or greater should be avoided if possible. This rule is a good guide but cannot be applied to the NEXRAD composite product. While the NEXRAD composite may show a cell with an intensity of level 3 or 4, the cell may contain very little of the higher–intensity precipitation while the bulk of the cell contains only level 2. This problem is magnified in the winter months when bright–band effects contaminate the radar data. Clutter [especially anomalous propagation (AP)] contamination of the composite reflectivity product is also a concern (especially when the AP is adjacent to actual weather returns). Differences between the two products will become more apparent with the fielding of the new ITWS situation display which has the capability of displaying both NEXRAD composite reflectivity and ASR–9 data side by side. In this study, we compare the NEXRAD composite reflectivity product with data from both the ASR–9 weather channel and an ASR–9 mosaic product as well as a Vertically Integrated Liquid water (VIL) product generated from NEXRAD base data.
Summary
Over the past five years in which the Integrated Terminal Weather System (ITWS) testbed prototypes have been operational, there have been regular discrepancies noticed between the ASR–9 six–level precipitation product and the NEXRAD six–level maximum composite reflectivity product. (1. The NEXRAD composite product used in this study is the NEXRAD...
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Thunderstorm induced gravity waves as a potential hazard to commercial aircraft
January 10, 1999
Conference Paper
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8th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 10-15 January 1999.
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Summary
Under certain atmospheric conditions, thunderstorm development can induce a phenomenon known as gravity waves (i.e., buoyancy or density waves). These waves are characterized by alternating regions of convergence and divergence over a relatively short distance. Such aerodynamic shear can become hazardous to air traffic if the shear contained within the waves surpasses the threshold for air traffic safety. Gravity waves are particularly hazardous because they develop in seemingly benign weather surrounding the parent thunderstorm and in many cases are not associated with any visual storm feature. Several cases have been studied in which commercial aircraft have encountered gravity waves and have been adversely affected by their encounters. The purpose of this study is to show how gravity waves can have a detrimental effect on aircraft in flight, how gravity waves can be detected, and that need for a detection algorithm exists. With the development of the National Weather Service's Next Generation Radar (WSR–88D NEXRAD) and the Federal Aviation Administration's Terminal Doppler Weather Radar (TDWR), the ability to detect gravity waves exists near many of America's major airports. Since gravity waves are a low–level phenomenon (generally below 2 km), their presence should be of interest to aircraft in the takeoff and landing stages of flight. During operations at Lincoln Laboratory's Integrated Terminal Weather System (ITWS) prototype field site in Dallas, there have been at least two incidents in which commercial aircraft experienced wind shear of at least 40 knots on takeoff, possibly caused by single or multiple gravity wave bands. This study will look at 57 cases of gravity wave formation within the terminal areas of Dallas–Ft. Worth International, Memphis International, and Orlando International airports. Statistics will be compiled to determine the frequency and severity of the gravity waves as well as their duration. The study will include Pilot Reports (PIREPS) from a few of these cases in which aircraft experienced wind shear due to suspected encounters with gravity waves. It is the hope of the author that this study will lead to the development of a detection algorithm that will increase the safety of America's commercial air traffic.
Summary
Under certain atmospheric conditions, thunderstorm development can induce a phenomenon known as gravity waves (i.e., buoyancy or density waves). These waves are characterized by alternating regions of convergence and divergence over a relatively short distance. Such aerodynamic shear can become hazardous to air traffic if the shear contained within the...
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