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Using features aloft to improve timeliness of TDWR hazard warnings
February 7, 1989
Conference Paper
Published in:
Third Int. Conf. on the Aviation Weather System, 30 January - 3 February 1989, pp. 184-189.
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Summary
The Terminal Doppler Weather Radar (TDWR) has an operational requirement to provide a one minute advance warning for aircraft encountering a hazardous wind shear. This paper describes the use of features aloft in the prototype TDWR microburst recognition algorithm to improve the timeliness of microburst hazard warnings. The use of features aloft allows the algorithm to make a microburst declaration while the surface outflow is still weak, thereby increasing the hazard warning time. In addition, current work indicates that these signatures can also be used to predict the onset of surface outflow for high-reflectivity events. An initial version of the microburst recognition algorithm using surface velocity data only was described by Merritt (1987). Initial work on the use of features aloft to increase the reliability and timeliness of microburst alarms was described in Campbell, 1988. This work was motivated by the desire to emulate the ability of human experts to use features aloft to enhance the timeliness of microburst warnings (McCarthy & Wilson, 1986). This research was further influences by the conceptual models for the evolution of low, medium and high reflectivity microburst events in the Denver area proposed by Roberts and Wilson (1986), and by studies of features aloft associated with microbursts in the Southeast (Isaminger, 1987). The current TDWR microburst recognition algorithm is described in Campbell and Merritt, 1988. The present paper presents results demonstrating the ability of the prototype algorithm to recognize features aloft for microburst events observed at Huntsville, AL and Denver, CO. It is shown that the ability to recognize features aloft improved the hazard warning time for these events. Initial results for microburst prediction are also presented.
Summary
The Terminal Doppler Weather Radar (TDWR) has an operational requirement to provide a one minute advance warning for aircraft encountering a hazardous wind shear. This paper describes the use of features aloft in the prototype TDWR microburst recognition algorithm to improve the timeliness of microburst hazard warnings. The use of...
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Gust front detection algorithm for the Terminal Doppler Weather Radar: part 2, performance assessment
February 3, 1989
Conference Paper
Published in:
Third Int. Conf. on the Aviation Weather System, 30 January - 3 February 1989, pp. 398-402.
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Summary
During the summer of 1988, the Terminal Doppler Weather Radar (TDWR) Operational Test and Evaluation (OT&E) was conducted near Denver, CO. One of the objectives of this test was to assess the performance of the Gust Front Detection and Wind Shift Algorithms (Gust Front Algorithm) to be used in the TDWR system. This paper presents an overview of the Gust Front Algorithm system from data collection to products displays and discusses the performance of the algorithm during the 1988 OT&E. Data editing, product generation, ground truth and scoring issues are addressed. Scoring results for the various products are presented and problems identified during the OT&E are discussed. The design of the Gust Front Algorithm is discussed in the companion paper (Part 1 Current Status) numbered 1.6 in this preprint volume. The Gust Front Algorithm serves two functions: warning and planning. Warnings are provided in alphanumeric messages on a "Ribbon Display Terminal", Wind shear warnings are issued when a gust front impacts the runways or within 3 miles of the ends of the runways. The planning function consists of alerting an Air Traffic Control Supervisor when a change in wind speed and/or direction due to a gust front at the airport will occur within 20 minutes. This planning information is displayed on a Geographic Situation Usplay (GSD).
Summary
During the summer of 1988, the Terminal Doppler Weather Radar (TDWR) Operational Test and Evaluation (OT&E) was conducted near Denver, CO. One of the objectives of this test was to assess the performance of the Gust Front Detection and Wind Shift Algorithms (Gust Front Algorithm) to be used in the...
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The FAA Terminal Doppler Weather (TDWR) Program
February 3, 1989
Conference Paper
Published in:
Proc. Third Int. Conf. on the Aviation Weather Systems, 30 January - 3 February 1989, pp. 414-419.
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Summary
The Federal Aviation Administration (FAA) initiated the Terminal Doppler Weather Radar (TDWR) program in the mid-1980s in response to overwhelming scientific evidence that low-altitude wind shear had caused a number of major air-carrier accidents. The program is designed to develop a reliable automated system for detecting low-altitude wind shear in the terminal area and providing warnings that will help pilots successfully avoid it on approach and departure. Wind shear has caused more U.S. air-carrier fatalities than any other weather hazard. A 1983 National Research Council (NRC) study (National Research Council, 1983) identified low-altitude wind shear as the cause of 27 aircraft accidents and incidents between 1964 and 1982. A total of 488 people died in seven of these accidents, 112 of them in the 1975 crash of Eastern Flight 66 at New York and 153 in the crash of Pan American Flight 759 at New Orleans in 1982. Since the NRC study was completed, the National Transportation Safety Board (NTSB) has investigated at least three more wind-shear incidents. One of these, the crash of Delta Flight 191 at Dallas/Fort Worth on August 2, 1985, took another 137 lives. Wind shear is not a serious hazard for aircraft enroute between airports at normal cruising altitudes, but low-level wind shear in the terminal area can be deadly for an aircraft on approach or departure. The most hazardous form of wind shear is the microburst, an outflow of air from a small-scale but powerful downward gush of cold, heavy air that can occur beneath a thunderstorm or rain shower or even in rain-free air under a harmless-looking cumulus cloud. As this downdraft reaches the earth's surface, it spreads out horizontally, like a stream of water sprayed straight down on a concrete driveway from a garden hose. An aircraft that flies through a microburst at low altitude first encounters a strong headwind, then a downdraft, and finally a tailwind that produces a sharp reduction in airspeed and a sudden loss of lift. This deadly sequence of events caused the fatal crash at Dallas/Fort Worth in 1985, as well as a number of other serious air-carrier accidents. Wind shear can also be associated with gust fronts, warm and cold fronts, and strong winds near the ground. It is important for pilots to be trained in recovery techniques to use if they are caught in wind shear. But a sudden windspeed change of at least 40 to 50 knots, which is not uncommon in microbursts, presents a serious hazard to jet airliners, and some microbursts simply are non-survivable. The only sure way to survive wind shear in the terminal area is to avoid it. However, flight crews do not have adequate information available today to predict or detect wind shear. The primary goal of the IDWR program is to provide pilots with an objective, quantitative assessment of the wind-shear hazard. The TDWR system also will improve operational efficiency and reduce delays in the terminal area by providing air traffic control supervisors with timely warnings of impending wind shifts resulting from gust fronts.
Summary
The Federal Aviation Administration (FAA) initiated the Terminal Doppler Weather Radar (TDWR) program in the mid-1980s in response to overwhelming scientific evidence that low-altitude wind shear had caused a number of major air-carrier accidents. The program is designed to develop a reliable automated system for detecting low-altitude wind shear in...
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Weather sensing with airport surveillance radars
February 3, 1989
Conference Paper
Published in:
Proc. Third Int. Conf. on the Aviation Weather System, 30 January - 3 February 1989, pp. 68-74.
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Modern airport surveillance radars (ASR) are coherent, pulsed-Doppler radars used for detection and tracking of aircraft in terminal area air space. The Federal Aviation Agency (FAA is procuring over 100 next-generation ASR-9 radars for major US. airports while relocating existing ASR-8s to secondary terminals. Thus within the next five years, almost every U.S. airport that supports commercial operations will be equipped with one of these sensitive, highly stable S-band radars. In view of their on- or near-airport location, rapid scan rate and direct data link to air traffic control personnel, it has been recognized that ASRs can also provide flight controllers with timely information on weather conditions that are hazardous to aircraft. An ASR's transmitted frequency, power, pulse-to-pulse stability and receiver sensitivity are well suited for weather sensing. Conversely, its broad elevation beamwidth, rapid antenna scan rate and non-uniform pulse transmission sequence introduce significant complications for the quantitative interpretation of echoes returned from weather. This paper reviews principal results of a four-year, FAA-sponsored program to evaluate the capabilities and limitations of ASRs for measuring storm severity.
Summary
Modern airport surveillance radars (ASR) are coherent, pulsed-Doppler radars used for detection and tracking of aircraft in terminal area air space. The Federal Aviation Agency (FAA is procuring over 100 next-generation ASR-9 radars for major US. airports while relocating existing ASR-8s to secondary terminals. Thus within the next five years...
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Electrical characteristics of microburst-producing storms in Denver
January 1, 1989
Conference Paper
Published in:
Proc. 24th Conf. on Radar Meteorology, 27-31 March 1989, pp. 89-92.
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Summary
Coordinated Doppler radar and electrical measurements of thunderstorm microbursts were initiated by Lincoln Laboratory and the MIT Weather Radar group in Huntsville, AL in 1987. These measurements were intended to identify electrical precursors to aviation hazards at ground level and to study the relationship between the state of cloud convective development and the prevalent lightning type. The results of the Huntsville Study (Williams and Orville, 1988; Williamd et al., 1988) showed pronounced peaks in intracloud lightning activity and radar reflectivity above the melting level 5-10 minutes prior to maximum outflow velocities at the surface. A similar behavior has been reported by Goodman et al. (1988) for a thunderstorm observed in COHMEX in the same region. These observations support a prominent role for ice, both in promoting the intracloud lightning aloft and in subsequently driving the outflow by virtue of the melting process. All Huntsville cases studied were 'wet' microbursts with maximum low level reflectivity factors greater than 50 dBZ. The parent storms were deep (H>11km) and electrically active (flash rate greater than or equal to 1min^-1). Recent microburst studies in Denver (Hjelmfelt, 1987); Biron and isaminger, 1989) have identified, in addition to a majority of 'wet' microbursts, substantial numbers of dry microburst-producing storms (Z<10^3 mm^6/m^3) with elevated cloud bases and modest radar cloud tops. The present studies were aimed at determining to what extent the electrical manifestations observed in Huntsville were prevalent in Denver. This paper presents some preliminary results for the Denver measurements from the summer of 1988.
Summary
Coordinated Doppler radar and electrical measurements of thunderstorm microbursts were initiated by Lincoln Laboratory and the MIT Weather Radar group in Huntsville, AL in 1987. These measurements were intended to identify electrical precursors to aviation hazards at ground level and to study the relationship between the state of cloud convective...
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Multipath modeling for simulating the performance of the Microwave Landing System
January 1, 1989
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 459-474.
Summary
The Microwave Landing System (MLS) will be deployed throughout the world in the 1990s to provide precision guidance to aircraft for approach and landing at airports. At Lincoln Laboratory, we have developed a computer-based simulation that models the performance of MLS and takes into account the multipath effects of buildings, the surrounding terrain, and other aircraft in the vicinity. The simulation has provided useful information about the effects of multipath on MLS performance.
Summary
The Microwave Landing System (MLS) will be deployed throughout the world in the 1990s to provide precision guidance to aircraft for approach and landing at airports. At Lincoln Laboratory, we have developed a computer-based simulation that models the performance of MLS and takes into account the multipath effects of buildings...
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Using aircraft radar tracks to estimate winds aloft
January 1, 1989
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 555-565.
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In air traffic control, the wind is a critical factor because it affects, among other important variables, the amount of time an aircraft will take to reach its destination. The authors have developed a method for estimating winds aloft in which the radar tracks of aircraft are used; i.e., data beyond what are already available to terminal air traffic control are not required. The method, which has been implemented at Lincoln Laboratory, gives a useful estimate of wind fields.
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In air traffic control, the wind is a critical factor because it affects, among other important variables, the amount of time an aircraft will take to reach its destination. The authors have developed a method for estimating winds aloft in which the radar tracks of aircraft are used; i.e., data...
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Wind shear detection with pencil-beam radars
January 1, 1989
Journal Article
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Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 483-510.
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Abrupt changes in the winds near the ground pose serious hazards to aircraft during approach or departure operations. Doppler weather radars can measure regions of winds and precipitation around airports, and automatically provide air traffic controllers and pilots with important warnings of hazardous weather events. Lincoln Laboratory, as one of several organizations under contract to the Federal Aviation Administration, has been instrumental in the design and development of radar systems and automated weather-hazard recognition techniques for this application. The Terminal Doppler Weather Radar (TDWR) system uses automatic computer algorithms to ident* hazardous weather signatures. TDWR detects and warns aviation users about low-altitude wind shear hazards caused by microbursts and gust fronts. It also provides advance warning of the arrival of wind shifts at the airport complex. Extensive weather radar observations, obtained from a Lincoln-built transportable testbed radar system operated at several sites, have validated the TDWR system. As a result, the Federal Aviation Administration has issued a procurement contract for the installation of 47 TDWR radar systems around the country.
Summary
Abrupt changes in the winds near the ground pose serious hazards to aircraft during approach or departure operations. Doppler weather radars can measure regions of winds and precipitation around airports, and automatically provide air traffic controllers and pilots with important warnings of hazardous weather events. Lincoln Laboratory, as one of...
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Characteristics of microbursts observed in the Continental U.S.
February 26, 1988
Conference Paper
Published in:
15th Conf. on Severe Local Storms, 22-26 February 1988, pp. 372-379.
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The topic of microbursts is explored in this paper through a historical perspective and review of the studies that have been performed since Fujita (1976) first introduced the concept. Taken as a whole, this body of work actually defines microbursts, and begins to take some of the initial steps toward their understanding. However, a number of dynamically distinct phenomena that give rise to strong surface outflows are being referred to as microbursts. The recent emphasis within the scientific and aviation communities on understanding microbursts makes it particularly important to categorize these various phenomena according to their meteorological nature and true aviation hazard potential. This paper takes some of the first steps toward this categorization, and emphasizes some of the differences in storms that can be expected in different climatological regimes.
Summary
The topic of microbursts is explored in this paper through a historical perspective and review of the studies that have been performed since Fujita (1976) first introduced the concept. Taken as a whole, this body of work actually defines microbursts, and begins to take some of the initial steps toward...
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Characteristics of microbursts in the continental United States
January 1, 1988
Journal Article
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Lincoln Laboratory Journal, Vol. 1, No. 1, Spring 1988, pp. 49-74.
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Microbursts - powerful downdrafts generally associated with thunderstorms that occur in hot, humid weather - have caused a number of aircraft crashes. To prevent future accidents, air traffic controllers must be able to detect, and predict, microburst events. All microbursts are not alike, however; several distinct weather patterns can produce microbursts. Thus a categorization of the different types of microbursts is an essential part of understanding these hazardous phenomena Using this categorization, the relative hazard to aviation of the various types of microbursts can be assessed.
Summary
Microbursts - powerful downdrafts generally associated with thunderstorms that occur in hot, humid weather - have caused a number of aircraft crashes. To prevent future accidents, air traffic controllers must be able to detect, and predict, microburst events. All microbursts are not alike, however; several distinct weather patterns can produce...
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