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Terminal Doppler weather radar/low-level wind shear alert system integration algorithm specification, version 1.1
February 24, 1992
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-187
Summary
There will be a number of airports that receive both a Terminal Doppler Weather Radar (TDWR) windshear detection system and a phase III Low-Level Wind Shear Alert System (LLWAS). At those airports, the two systems will need to he combined into a single windshear detection system. This report specifies the algorithm to be used to integrate the two subsystems. The algorithm takes in the alphanumeric runway alert messages generated by each subsystem and joins them into integrated alert messages. The design goals of this windshear detection system are (1) to maintain the probability of detection for hazardous events while reducing the number of false alerts and microburst overwarnings and 2) to increase the accuracy of the loss/gain estimates. The first design goal is accomplished by issuing an integrated alert for an operational runway whenever either subsystem issues a 'strong' alert for that runway; by canceling a 'weak' windshear alert on an operational runway if only one subsystem is making the declaration; and by reducing a 'weak' microburst alert on an operational runway to a 'strong' windshear alert if only one subsystem is making the declaration. The second design goal is accomplished by using the average of the two loss/gain values, when appropriate. TDWR, windshear, LLWAS, algorithm specification.
Summary
There will be a number of airports that receive both a Terminal Doppler Weather Radar (TDWR) windshear detection system and a phase III Low-Level Wind Shear Alert System (LLWAS). At those airports, the two systems will need to he combined into a single windshear detection system. This report specifies the...
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Microburst divergence detection for Terminal Doppler Weather Radar (TDWR)
September 25, 1991
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-181
Summary
The Terminal Doppler Weather Radar (TDWR) microburst surface divergence detection algorithm has been under development and evaluation at Lincoln Laboratory since 1983. The TDWR program is sponsored by the Federal Aviation Administration (FAA), and the algorithm described in this report is a primary algorithm component of the TDWR system. The divergence algorithm processes radar velocity measurements taken near the earth's surface to identify the strong divergent outflow characteristic of microburst wind shear hazards. The algorithm uses a complex set of pattern matching and validation test criteria to locate microburst outflow signatures and to filter out false alarms from various data contamination sources. The divergence algorithm is primarily responsible for the detection of most microbursts, although the complete TDWR microburst algorithm consists of more than a dozen distinct algorithmic components. The divergence algorithm has demonstrated a very high probability of detection (POD) for strong microburst outflows, and its performance (as well as that of the complete microburst detection algorithm) was first formally assessed in the operational test and evaluation of the TDWR in Denver, CO (1988). Subsequent evaluations were performed in Kansas City, KS (1989) and Orlando, FL (1990). These evaluations have provid
Summary
The Terminal Doppler Weather Radar (TDWR) microburst surface divergence detection algorithm has been under development and evaluation at Lincoln Laboratory since 1983. The TDWR program is sponsored by the Federal Aviation Administration (FAA), and the algorithm described in this report is a primary algorithm component of the TDWR system. The...
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The 1990 Airport Surveillance Radar Wind Shear Processor (ASR-WSP) operational test at Orlando International Airport
July 17, 1991
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-178
Summary
Lincoln Laboratory, under sponsorship from the Federal Aviation Administration (FAA), is conducting a program to evaluate the capability of the newest Airport Surveillance Radars (ASR-9) to detect hazardous weather phenomena -- in particular, low-altitude wind shear created by thunderstorm-generated microbursts and gust fronts. The ASR-9 could provide coverage at airports not slated for a dedicated Terminal Doppler Weather Radar (TDWR) and could augment the TDWR at high-priority (high traffic volume, severe weather) facilities by providing a more rapid update of wind shear products, a better viewing angle for some runways, and redundancy in the event of a TDWR failure. An operational evaluation of a testbed ASR Wind Shear Processor (ASR-WSP) was conducted at the Orlando International Airport in Orlando, FL during August and September 1990. The ASR-WSP operational system issued five distinct products to Air Traffic Control: microburst detections, gust front detections, gust front movement predictions, precipitation reflectivity and storm motion. This document describes the operational system, the operational products, and the algorithms employed. An assessment of system performance is provided as one step in evaluating the operational utility of the ASR-WSP.
Summary
Lincoln Laboratory, under sponsorship from the Federal Aviation Administration (FAA), is conducting a program to evaluate the capability of the newest Airport Surveillance Radars (ASR-9) to detect hazardous weather phenomena -- in particular, low-altitude wind shear created by thunderstorm-generated microbursts and gust fronts. The ASR-9 could provide coverage at airports...
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High resolution microburst outflow vertical profile data from Huntsville, Alabama, and Denver, Colorado
April 10, 1991
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-163
Summary
The purpose of this report is to present detailed data on microburst outflows recorded by the TDWR testbed radar (FL-2) in Huntsville, Alabama (1986) and Denver, Colorado (1987-88). Whenever possible, a microburst detected within 10 km of the radar was scanned in a vertical direction (RHI) at 1 to 2 degree azimuthal intervals about the center of divergence. The vertical profile of the outflow is pertinent to the detection capability and siting strategy of a single Doppler radar observing the microburst from a horizontal viewing angle. Additionally, outflow features are important in assessing the hazard associated with microbursts as well as the capability of other wind shear detection (LLWAS or ASR). Of particular interest is the variability of outflows depths from case to case and site to site. If the depth across the maximum velocity differential is shallow, an outflow might go undetected or underestimated by a radar, the beam ot which was not viewing the axis of peak divergence. Previous research projects in Denver reported the highest winds in a microburst typically occur near the surface with an average outflow depth (1/2 peak velocity) ranging between 500 and 600 meters: however, the vertical resolution of these data was fairly crude due to the scan strategies utilized. This report provides detailed high resolution microburst outflow vertical profile data pertinent to TDWR system studies based on RHI and closely spaced PPI scans. The median observed outflow depth in Huntsville was 200 meters shallower than in Denver while the median height of the maximum velocity varied from 100 meters AGL in Huntsville to 200 meters AGL in Denver. For those Denver events presented here, we recommend that the TDWR microburst detection scan extend to at least 200 meters AGL and 100 meters if there is adequate clutter suppression.
Summary
The purpose of this report is to present detailed data on microburst outflows recorded by the TDWR testbed radar (FL-2) in Huntsville, Alabama (1986) and Denver, Colorado (1987-88). Whenever possible, a microburst detected within 10 km of the radar was scanned in a vertical direction (RHI) at 1 to 2...
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Terminal Doppler Weather Radar operational test and evaluation Orlando 1990
April 9, 1991
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-179
Summary
Lincoln Laboratory conducted an evaluation for hte Federal Aviation Administration (FAA) Terminal Doppler Weather Radar (TDWR) system in Orlando, Florida during the cummer of 1990. In previous years, evaluations have been conducted at airports in Kansas City, MO (1989) and Denver, CO (1988). Since the testing at the Kansas City International Airport, the radar was modified to operate in C-band, which is the intended frequency band for the production TDWR systems. The objectives of the 1990 evaluation period were to evaluate TDWR system performance in detecting low-altitude wind shear, specifically microbursts and gust fronts, at the Orlando International Airport and in the surrounding area; to refine the system's wind shear detection capabilities; and to evaluate elements of the system developed by the contractor, which were new for this C-band system and therefore not available for evaluation in previous years. Some performance comparisons are made among results from the vastly different weather environments of Denver, Kansas City, and Orlando. The report discusses and presents statistics for the performance of the system in detecting and predicting microbursts and gust fronts. A significant use of the prediction capability is its potential use for air traffic control (ATC) personnel to plan aitport operations when hazardous weather is predicted. Issues such as low-velocity ground clutter (from tree leaves, road traffic, and dense urban areas) that affect prediction performance are discussed, along with possible software modifications to account for them. FInally, the ATC personnel and pilots who took part in the evaluation provide the users' perspectives on the usefulness of the system's capabilities.
Summary
Lincoln Laboratory conducted an evaluation for hte Federal Aviation Administration (FAA) Terminal Doppler Weather Radar (TDWR) system in Orlando, Florida during the cummer of 1990. In previous years, evaluations have been conducted at airports in Kansas City, MO (1989) and Denver, CO (1988). Since the testing at the Kansas City...
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A study of dry microburst detection with airport surveillance radars
November 29, 1990
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-176
Summary
This report evaluates the capability of Airport Surveillance Radars (ASRs) for the detection of low altitude wind shear associated with the outflows of dry microbursts. It describes results of simulations of dry microburst observations by an ASR. These simulations incorporated weather and clutter data collected by the FL-2 pencil-beam Doppler weather radar at Denver Stapleton Airport in 1988 and 1989 and clutter data collected by the FL-3 ASR-9 emulation radar at Hunstville, Alabama. The impact of signal strength, overhanging precipitation, and ground clutter on both observability and algorithmic performance are assessed. Principal results of study are the following: 1. Overhanging precipitation and weak signal strength do not, by themselves, prohibit detection of dry outflows; however, occurence of false alarms and biases in velocity estimates indicate that improvements in the dual beam estimator that was evaluated would be required for reliable detection of these events. 2. Ground clutter tends to obscure dry outflow in regions where the difference between median effective clutter reflectivity and weather reflectivity exceeds 17-20 dB. A method for predicting the percentage of missed microburst detections due to ground clutter is used to estimate overall microburst detection probabilities for a "dry" environment such as Denver. Using measured clutter from an experimental ASR in Hunstville, AL, overall microburst detection probability is 83 percent. Using simulated Denver clutter, overall detection probability is 91 percent.
Summary
This report evaluates the capability of Airport Surveillance Radars (ASRs) for the detection of low altitude wind shear associated with the outflows of dry microbursts. It describes results of simulations of dry microburst observations by an ASR. These simulations incorporated weather and clutter data collected by the FL-2 pencil-beam Doppler...
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A comparison of anemometer and Doppler radar winds during wind shear events
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 356-361.
Summary
The Federal Aviation Administration (FAA) currently uses the anemometer-based Low Level Wind Shear Alert System (LLWAS) as the primary method of wind shear detection at major U.S. airports. With the upcoming deployment of the Terminal Doppler Weather Radar (TDWR) system, potential methods for integrating the two systems are being investigated. By integrating, advantages of both sensor systems can be utilized. Advantages of the LLWAS ground sensor network include true wind direction measurements, a high measurement frequency, a lack of sensitivity to clear air reflectivity, and few false alarms from radar point targets such as planes, birds, etc. Advantages of the radar include complete scan coverage of the region of concern, the ability to predict events, fewer terrain problems such as sheltering which can reduce the wind speed readings, and almost no false alarms due to non-hazardous wind shear such as thermals. The objectives of this study are to gain a clearer understanding of the basic relationship between the wind information provided by these two very different sensing systems, and to determine the impact this relationship may have on integration of the two operational systems. A proposed mathematical technique for "correcting" LLWAS winds where needed to better match radar winds is evaluated for cases of microburst (divergent) and gust front (convergent) wind shear.
Summary
The Federal Aviation Administration (FAA) currently uses the anemometer-based Low Level Wind Shear Alert System (LLWAS) as the primary method of wind shear detection at major U.S. airports. With the upcoming deployment of the Terminal Doppler Weather Radar (TDWR) system, potential methods for integrating the two systems are being investigated...
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Understanding and predicting microbursts
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 340-351.
Summary
Wind shear is a major cause of aircarrier accidents in the United States, and most of these accidents have been caused by one particular form of wind shear called a microburst (Zorpette, 1986). Microbursts have been defined as small scale, low-altitude, intense downdrafts which impact the surface and cause strong divergent outflows of wind. We know they are associated with thunderstorms and are usually but not always accompanied by heavy rainfall at the ground. However, a number of meteorologically distinct phenomena associated with thunderstorms can give rise to strong downdrafts and high surface winds. Most microburst research has focused on the main precipitation driven downdraft of thunderstorms, both with and without significant surface rainfall. But other downdraft types such as the dynamically driven downdrafts at low altitude associated with "vortices" at the leading edge of expanding thunderstorm outflows and with "roll clouds" have also been associated with the microburst problem. In this paper, I discuss these two primary forms of low altitude downdraft phenomena in thunderstorms. This differentiation is essential to discovering exactly what atmospheric conditions lead to the development of the most hazardous microbursts. A physically based predictive model for thunderstorm downdraft strength is presented which shows that the radar reflectivity of a storm alone cannot be used as a hazard index; information about the static stability of the atmosphere is also essential. I then show that the downdrafts associated with the gust front around a cold outflow from a small isolated thunderstorm, a microburst, are inherently stronger at low altitudes than those found in more straight-line gust fronts. Finally, I reexamine the most recent fatal U.S. microburst accident, the crash of Delta 191 at Dallas/Ft. Worth in 1985, and show that both types of low altitude downdrafts were encountered as part of the "microburst", although the downdrafts came from different storms.
Summary
Wind shear is a major cause of aircarrier accidents in the United States, and most of these accidents have been caused by one particular form of wind shear called a microburst (Zorpette, 1986). Microbursts have been defined as small scale, low-altitude, intense downdrafts which impact the surface and cause strong...
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Divergence detection in wind fields estimated by an airport surveillance radar
October 15, 1990
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-172
Summary
This report assesses a technique for automatic detection of hazardous divergence in velocity fields estimated by an Airport Surveillance Radar (SAR). We evaluate a least-squares approach to radial divergence estimation through a performance analysis based on simulated data. That approach is compared to an existing decision-based radial shear finding method used for the Terminal Doppler Weather Radar (TDWR). Empirical results derived by the application of two techniques to data collected at ASR testbeds in Huntsville, Alabama and in Kansas City, Missouri are presented. Results indicate that a simple, least-squares divergence estimator combined with time association logic to increase temporal continuity of algorithm output is an equally effective means of detecting divergent wind shear in velocity fields estimated from ASR signals.
Summary
This report assesses a technique for automatic detection of hazardous divergence in velocity fields estimated by an Airport Surveillance Radar (SAR). We evaluate a least-squares approach to radial divergence estimation through a performance analysis based on simulated data. That approach is compared to an existing decision-based radial shear finding method...
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Results of the Kansas City 1989 Terminal Doppler Weather Radar (TDWR) operational evaluation testing
August 17, 1990
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-171
Summary
The Lincoln Laboratory Terminal Doppler Weather Radar (TDWR) testbed was used to carry out an experimental and operational hazardous weather product evaluation program for the Federal Aviation Administration (FAA) at the Kansas City International (KCI) Airport during the summer of 1989. The objective of the program was to test and refine previously tested techniques for the automatic detection of low-altitude wind shear phenomena (specifically microbursts and gust fronts) and heavy precipitation in a midwest weather environment, as well as to assess possible new products such as storm movement predictions. A successful operational evaluation of the TDWR products took place at the KCI tower and terminal radar control room (TRACON) from 15 July to 15 August 1989 and from 15 to 30 September 1989. Several supervisor and controller display refinements that had been determined from the 1988 operational evaluation at Denver were assessed as effective. The system was successful in terms of aircraft at KCI avoiding wind shear encounters during the operational period, and it was assessed as "very good" in usefulness for continuing operation by the KCI air traffic control (ATC) personnel.
Summary
The Lincoln Laboratory Terminal Doppler Weather Radar (TDWR) testbed was used to carry out an experimental and operational hazardous weather product evaluation program for the Federal Aviation Administration (FAA) at the Kansas City International (KCI) Airport during the summer of 1989. The objective of the program was to test and...
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