Publications
Observations of non-traditional wind shear events at the Dallas/Fort Worth International Airport
February 28, 2003
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-308
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Summary
During the past 20 years there has been great success in understanding and detecting microbursts. These "traditional" wind shear events are most prominent in the summer and are characterized by a two-dimensional, divergent outflow associated with precipitation loading from a thunderstorm downdraft or evaporative cooling from high-based rain clouds. Analysis of wind shear loss alerts at the Dallas/Fort Worth International Airport (DFW) from August 1999 through July 2002 reveals that a significant number of the wind shear events were generated by "non-traditional" mechanisms. The "non-traditional" wind shear mechanisms, linear divergence, divergence behind gust fronts, and gravity waves, accounted for one half of the alert events in the period studied. Radar-based algorithms have shown considerable skill in detecting wind shear events. However, the algorithms were developed to identifl features common to the "traditional" events. If the algorithms were modified to detect "non-traditional" wind shear, the corresponding increase in false detections could be unacceptable. Therefore, in this report a new radar-based algorithm is proposed that detects linear divergence, divergence behind gust fronts, and gravity waves for output on the Integrated Terminal Weather System by identifying the radar signatures that are common to these features.
Summary
During the past 20 years there has been great success in understanding and detecting microbursts. These "traditional" wind shear events are most prominent in the summer and are characterized by a two-dimensional, divergent outflow associated with precipitation loading from a thunderstorm downdraft or evaporative cooling from high-based rain clouds. Analysis...
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An evaluation of the Medium-Intensity Airport Weather System (MIAWS) products at the Memphis, TN and Jackson, MS International Airports
May 13, 2002
Conference Paper
Published in:
10th Conf. on Aviation, Range, and Aerospace Meteorology (13th Conf. on Applied Climatology), 13-16 May 2002, pp. J118-J122.
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Summary
The FAA is procuring aviation weather systems, which are designed to enhance safety/capacity and reduce delays at U.S. airports. The two most widely publicized systems currently being installed are the Integrated Terminal Weather System (ITWS) at airports equipped with a Terminal Doppler Weather Radar (TDWR) and the Weather System Processor (WSP) at those terminal areas covered by an Airport Surveillance Radar, Model 9 (ASR-9). At airports not slated to receive either an ITWS or WSP, an emerging system coined the Medium Intensity Airport Weather System (MIAWS) will be installed. Currently, either an ASR-7 or 8 provides terminal aircraft surveillance at these airports. Unfortunately, these platforms do not output calibrated precipitation intensity or storm motion information. Quantitative six-level weather reflectivity data will be available once the digitally enhanced ASR-11 radar system is operational at MIAWS supported sites. The Low Level Wind Shear Alert System - Relocation/Sustainment (LLWAS-RS) anemometer network will provide MIAWS with surface-based winds and wind shear alerts. The rationale for MIAWS evolved from the ITWS and WSP prototype testing. The premise is that the calibrated reflectivity and velocity data from state-of-the-art radar platforms can be utilized to produce a suite of current and forecasted storm positions to aid air traffic control decision making. The forecasted location is a critical issue if the storms are moving rapidly. This can lead to a scenario where the weather conditions deteriorate significantly within a matter of minutes. Once implemented, MIAWS will be an essential component of the National Airspace System by providing this evolving technology to airports whose traffic counts are not sufficient to warrant either an ITWS or WSP, but where commercial carriers could reap the benefits of a high-quality weather radar system. The FAA has contracted the Massachusetts Institute of Technology Lincoln Laboratory (MIT/LL) to undertake a proof-of-concept evaluation of MIAWS. To this end, MIT/LL installed two prototype systems at the Jackson, MS (JAN) and Memphis, TN (MEM) International Airports. The system at MEM is used solely for product evaluation and refinement, while the FAA is operationally evaluating the JAN MIAWS. The focus of this report is a preliminary assessment of the capabilities and limitations of MIAWS in its current implementation, i.e. precipitation based solely on NEXRAD data. Potential enhancements to the NEXRAD product data and MIAWS algorithms will also be discussed.
Summary
The FAA is procuring aviation weather systems, which are designed to enhance safety/capacity and reduce delays at U.S. airports. The two most widely publicized systems currently being installed are the Integrated Terminal Weather System (ITWS) at airports equipped with a Terminal Doppler Weather Radar (TDWR) and the Weather System Processor...
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Designing a terminal area bird detection and monitoring system based on ASR-9 data
August 27, 2001
Conference Paper
Published in:
3rd Joint Annual Meeting Bird Strike Committee, 27-30 August 2001.
Summary
Conflicts between birds and commercial aircraft are a noteworthy problem at both large and small airports [Cleary, 1999]. The risk factor for United States airports continues to increase due to the steady rise in take-off/landings and bird populations. There is a significant bird strike problem in the terminal area as shown by the incidents reported in the National Bird Strike Database [Cleary and Dolbeer, 1999]. The focus of bird strike mitigation in the past has centered primarily on wildlife management techniques. Recently, an Avian Hazard Advisory System (AHAS) has been developed to reduce the risks of bird strikes to military operations [Kelly, 1999]. This system uses a mosaic of data obtained from the Next Generation Weather Radar (NEXRAD). This sensor serves as an excellent tool for enroute bird advisories due to the radar coverage provided across the majority of the United States. However, its utility in the airport terminal environment is limited due to the slow update rate and the fact that the distance of most NEXRADs from the airport results in beam heights that are too high to detect low-altitude birds over the airport. The Federal Aviation Administration (FAA) operates two radar systems – the Terminal Doppler Weather Radar (TDWR), and the Airport Surveillance Radar (ASR-9) -- that could be used to help monitor bird activity at an airport in order to: 1. Provide continuously updated information on locations and approximate numbers of birds in flocks roosting or feeding on or near an airfield; 2. Generate real-time warnings of bird activity for dissemination to pilots of landing or departing aircraft by air traffic controllers or by direct data link. The TDWR provides wind shear warnings in the terminal area to enhance safety, while the ASR-9’s primary function is air traffic control. Both of these systems have been shown to detect biological echoes as well. Characteristics of the two radar systems have been examined and compared to determine capabilities for bird detection. Amongst other favorable factors, the high update rate and on-airport locale makes the ASR-9 a highly desirable platform for a bird detection and warning system for the terminal area. Data from an ASR-9 at Austin TX (AUS) equipped with a Weather Systems Processor (WSP) have been analyzed to assess the ASR-9's capability to detect and monitor bird activity. The WSP add-on provides a variety of radar base data products similar to those that would be available on all ASR-9s as part of an ASR-9 Service Life Extension Program (SLEP) currently underway. The Austin airport area is subject to large flocks of wintering migratory birds as well as a resident population of bats in close proximity to the airport. Radar data, visual observations and bird strike information during periods of active bird/bat movements have been collected for this study. An automated processing algorithm called the Terminal Avian Hazard Advisory System (TAHAS) is being developed to detect and track roosting and migratory birds using ASR-9 data. A key challenge will be the ability to discriminate biological from non-biological targets based on variables such as vertical continuity, variance or spectral width, and horizontal velocity distribution.
Summary
Conflicts between birds and commercial aircraft are a noteworthy problem at both large and small airports [Cleary, 1999]. The risk factor for United States airports continues to increase due to the steady rise in take-off/landings and bird populations. There is a significant bird strike problem in the terminal area as...
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Commercial aircraft encounters with thunderstorms in the Memphis terminal airspace
September 11, 2000
Conference Paper
Published in:
Proc. Ninth Conf. on Aviation, Range, and Aerospace Meteorology, 11-15 September 2000, pp. 37-42.
Summary
Thunderstorms are dynamic obstacles to the flow of air traffic. Aircraft routing in the presence of thunderstorms is as dynamic as the position and intensity of the storms. The question of where pilots will and will not fly is relevant to the decisions made by human air traffic managers as well as to the development of automated decision aid tools. In order to accurately anticipate which routes will be useable one needs to be able to 1) forecast the relevant weather variables, and 2) convert those weather variables into a quantitative probability that pilots will request deviations from the nominal route. The Convective Weather Integrated Product Team at the FAA is improving the accuracy and lead time of forecasts of thunderstorm products. This paper provides an update on our examination of the issue of probability of deviation. In our recent examination of 63 hours of weather and flight track data from the DFW airspace (Rhoda and Pawlak, 1999a,b) we combined several weather variables (measurements, not forecasts) to correctly predict pilot deviation and penetration behavior for 70-85% of the encounters between thunderstorms and aircraft arriving at DW and Dallas Love (DAL) airports. We also found that pilots were more likely to penetrate strong precipitation when they: 1) were near the arrival airport, 2) were following another aircraft, 3) were flying after dark, 4) had been delayed in the air by 15+ minutes upstream of the DFW airspace. We did not find any statistically significant difference between the percentages of thunderstorm penetrations by various airlines. We also found that persistent penetration of storms near the airport is sometimes abruptly interrupted presumably by wind shear alerts from air traffic controllers or cautionary pilot reports from the penetrating aircraft. When the arrivals cease, aircraft on the final approach course may turn suddenly to the left or right to avoid the weather that caused the interruption. Aircraft that abort the approach sometimes fly through very intense precipitation-sometimes through downdrafts that are causing microburst outflows at the surface. The work described in this paper applies the methodology from the DFW study to data collected in the Memphis Terminal Radar Approach Control (TRACON). The methodology is described briefly here and in more detail in (Rhoda and Pawlak, 1999b). We developed several probability of deviation classifiers using a portion of the Memphis data and tested them on the remaining data to determine if it is possible to predict whether pilots will penetrate or deviate around the storms. We also tested the classifiers that were developed in the DNV study on the MEM data and vice versa. We repeated the DFW hypothesis tests for various dichotomies of encounters: near/far, leading/following, light/dark, delayed/undelayed.
Summary
Thunderstorms are dynamic obstacles to the flow of air traffic. Aircraft routing in the presence of thunderstorms is as dynamic as the position and intensity of the storms. The question of where pilots will and will not fly is relevant to the decisions made by human air traffic managers as...
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Analysis of the Integrated Terminal Weather System (ITWS) 5-nm product suite
September 11, 2000
Conference Paper
Published in:
Ninth Conf. on Aviation, Range, and Aerospace Meteorology, 11-15 September 2000, pp.137-140.
Summary
Currently, the prototype Integrated Terminal Weather System (ITWS) displays six-level precipitation data generated from the Airport Surveillance Radar (ASR-9) and the Next Generation Weather Radar (NEXRAD). The ASR-9 data are updated every 30 seconds and provide a 0.5 nm spatial resolution to a distance of 60 nm (Weber, 1986). Since the ASR-9 is a fan beam radar, the data represent the average precipitation within the vertical column. As reported by Isaminger, et al., (1999), this sensor can significantly underestimate the precipitation intensity and areal coverage due to precipitation processing limitations and hardware failures. In particular, storms located near the sensor can be underestimated or missed entirely (Crow& et al., 1999). The NEXRAD data are updated every 5-6 minutes with a spatial resolution of 0.5 nm (2.2 nm) and a coverage region of 100 nm (200 nm). The maximum reflectivity value in the vertical column at each grid point is used to create the product. This sensor can overestimate the precipitation intensity near the surface due to bright band contamination and the composite technique (Crowe and Miller, 1999). The update rate can also become an issue if the storms are moving rapidly or developing quickly. In order to confront these issues, the specified ITWS product suite will include six-level precipitation derived from the Terminal Doppler Weather Radar (TDWR). The data from this sensor will be depicted in a high-resolution window (5-nm) around the airport. The TDWR one-minute update rate will provide timely information on rapidly moving or developing storm cells. In many regards, the data will be complimentary to that provided by the ASR-9 and NEXRAD. In others, the weather levels could vary significantly. This report will focus on a discussion of the 5-nm product capabilities and limitations based on an analysis of data collected in Memphis (MEM) and New York City (NYC). A discussion of key product enhancements will serve to illustrate the modifications required to improve this product suite. Finally, a list of recommendations will be presented to assist in product development.
Summary
Currently, the prototype Integrated Terminal Weather System (ITWS) displays six-level precipitation data generated from the Airport Surveillance Radar (ASR-9) and the Next Generation Weather Radar (NEXRAD). The ASR-9 data are updated every 30 seconds and provide a 0.5 nm spatial resolution to a distance of 60 nm (Weber, 1986). Since...
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ITWS and ITWS/LLWAS-NE runway alert performance at Dallas-Ft. Worth and Orlando
September 11, 2000
Conference Paper
Published in:
Ninth Conf. on Aviation, Range, and Aerospace Meteorology, 11-15 September 2000, pp. 590-595.
Summary
The Integrated Terminal Weather System (ITWS) provides runway-orientated wind shear and microburst alerts to enhance the safety of flight operations at major U.S. airports. The alerts are reported as either losses or gains of airspeed, representing performance decreasing or performance increasing wind shears. The performance of ITWS as a stand-alone system has been thoroughly documented in previous research. During the 1994 ITWS Demonstration and Validation testing, the probability of detection (POD) and probability of false alarm (PFA) at Memphis (MEM) and Orlando (MCO) for all loss events were > 90 and < 5 percent, respectively, based on single-Doppler truth. The Low-Level Windshear Alert System-Network Expansion (LLWAS-NE) also generates runway alerts in the same format as ITWS. LLWAS-NE is not subject to viewing angle problems such as those experienced by single-Doppler radar. However, false alarms caused by LLWAS-NE sensor failures at some Terminal Doppler Weather Radar (TDWR) sites have reduced user confidence in the system. At those ITWS sites with an LLWAS-NE, the ITWS alerts derived from TDWR data will be integrated with LLWAS-NE alerts, hopefully to improve the performance. The ITWS integration algorithm is identical to the TDWR version, with the exception of a few adaptable parameter changes. The ITWS/LLWAS-NE parameters were modified slightly to account for ITWS and TDWR algorithm performance differences. In this paper, the performance of a stand-alone ITWS and the ITWS/LLWAS-NE integration algorithm at the MCO and Dallas-Ft. Worth (DFW) demonstration sites will be discussed. This assessment is considered unique since the radar and anemometer data were combined to create the runway truth. The focus of this research is to identify the shortcomings of both systems in order to recommend modifications that will improve the integration algorithm performance.
Summary
The Integrated Terminal Weather System (ITWS) provides runway-orientated wind shear and microburst alerts to enhance the safety of flight operations at major U.S. airports. The alerts are reported as either losses or gains of airspeed, representing performance decreasing or performance increasing wind shears. The performance of ITWS as a stand-alone...
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An evaluation of the ASR-9 weather channel based on observations from the ITWS prototypes
September 23, 1999
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-270
Summary
The Federal Aviation Administration's (FAA) Airport Surveillance Radar (ASR-9) is a high-scan-rate system which provides a "critical" function in terms of air traffic control (ATC). In addition to its primary role of air traffic surveillance, the system also generates precipitation data for display on air traffic specialists' radar scopes and for use by automated systems such as the Integrated Terminal Weather System (ITWS) and Weather Systems Processor (WSP). Air traffic managers use these data to provide optimum routes for aircraft operating in and near the Terminal Radar Approach Control (TRACON) airspace. The primary advantage of the ASR-9 - as an aviation weather radar - over either the Terminal Doppler Weather Radar (TDWR) or the Next Generation Weather Radar (NEXRAD) is the rapid update rate, i.e., 30 seconds, which provides air traffic managers with a more accurate representation of weather echo location within the sensor's domain. This is far superior toeither the TDWR or NEXRAD, which takes from 2.5 to 6 minutes to create a volume scan, depending on the scan strategy. The sensor is also quite reliable, with limited down time. An analysis of ASR-9 data from the ITWS prototypes has uncovered a number of problems, which impact the quality of the precipitation data. The data quality issues discussed are overly aggressive ground clutter suppression, polarization mode issues, hardware failures associated with high beandlow beam switching, attenuatiodsignal depolarization, beam-filling losses, bright- band contamination, distant weather contamination, calibration issues, and radadantenna failures. The recommendations to address the ASR-9 data quality issues can be grouped into three categories: "Variable Site Parameter (VSP)" adjustments, hardware component maintenance checks, and automated flagging of data quality problems. The report includes discussion of the frequency and characteristics of each degradation, presenting both hardware and non- hardware related problems, and concludes with proposed solutions to the problems and recommendations designed to improve the overall utility of the ASR-9 precipitation data.
Summary
The Federal Aviation Administration's (FAA) Airport Surveillance Radar (ASR-9) is a high-scan-rate system which provides a "critical" function in terms of air traffic control (ATC). In addition to its primary role of air traffic surveillance, the system also generates precipitation data for display on air traffic specialists' radar scopes and...
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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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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 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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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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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 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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Performance characteristics of an algorithm used to remove anomolous propagation from the NEXRAD data
September 12, 1997
Conference Paper
Published in:
28th Conf. on Radar Meteorology, 7-12 September 1997, pp. 317-319.
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Summary
An important limitation of precipitation sensors is contamination from ground clutter targets under conditions of anomalous propagation (AP). This problem can be mitigated significantly by high-pass clutter filters such as used by the Terminal Doppler Weather Radar (TDWR) and Next Generation Weather Radar (NEXRAD) systems....MIT Lincoln Laboratory (MIT/LL) has developed and tested an algorithm that removes AP from the NEXRAD reflectivity data. In this paper, we will first provide a brief description of the algorithm. Next we will present the truthing methodology used to identify AP. Then, we will show the algorithm performance results and failure mechanisms with this initial version. Finally, we consider refinements to improve the algorithm's performance.
Summary
An important limitation of precipitation sensors is contamination from ground clutter targets under conditions of anomalous propagation (AP). This problem can be mitigated significantly by high-pass clutter filters such as used by the Terminal Doppler Weather Radar (TDWR) and Next Generation Weather Radar (NEXRAD) systems....MIT Lincoln Laboratory (MIT/LL) has developed...
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