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Wind shear detection with airport surveillance radars
January 1, 1989
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 511-526.
Summary
Airport surveillance radars (ASR) utilize a broad, cosecant-squared elevation beam pattern, rapid azimuthal antenna scanning, and coherent pulsed-Doppler processing to detect and track approaching and departing aircraft. These radars, because of location, rapid scan rate, and direct air traffic control (ATC) data link, can also provide flight controllers with timely information on weather conditions that are hazardous to aircraft. With an added processing channel, an upgraded ASR can automatically detect regions of low-altitude wind shear. This upgrade can provide wind shear warnings at airports where low traffic volume or infrequent thunderstorm activity precludes the deployment of a dedicated Terminal Doppler Weather Radar (TDWR). Field measurements and analysis conducted by Lincoln Laboratory indicate that the principal technical challenges for low-altitude wind shear detection with an ASR-groundclutter suppression, estimation of near-surface radial velocity, and automatic wind shear hazard recognition--can be successfully met for microbursts accompanied by rain at the surface.
Summary
Airport surveillance radars (ASR) utilize a broad, cosecant-squared elevation beam pattern, rapid azimuthal antenna scanning, and coherent pulsed-Doppler processing to detect and track approaching and departing aircraft. These radars, because of location, rapid scan rate, and direct air traffic control (ATC) data link, can also provide flight controllers with timely...
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Observability of microbursts using Doppler weather radar and surface anemometers during 1987 in Denver, CO
December 29, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-161
Summary
This report focuses on the observability of microbursts using pulse Doppler weather radars and surface anemometers respectively by an experienced meterologist. The data used for this study were collected in the Denver, Colorado area during the FAA Terminal Doppler Weather Radar (TDWR) measurement program in 1987. The methods used for declaring a microburst from both Doppler radar and surface anemometer data are described. The main objective of this report is to compare the 1987 radar observed microbursts (which impacted the area covered by a surface anemometer system) with the surface mesonet observed microbursts. Of the 66 microbursts for which radar and mesonet data were available, 4 were not observed by the radar and 1 was not observed by the mesonet. All four microbursts not observed by the radar were classified as "dry" events with low surface reflectivities and with three of the four being relatively weak (peak velocity differences < 20 m/s) shear events. Possible reasons as to why these microbursts were not observed are discussed in detail. The strongest event exceeded 20 m/s (differential velocity) for two minutes and appears to have been missed due to a combination of very low reflectivity and a very shallow depth overflow.
Summary
This report focuses on the observability of microbursts using pulse Doppler weather radars and surface anemometers respectively by an experienced meterologist. The data used for this study were collected in the Denver, Colorado area during the FAA Terminal Doppler Weather Radar (TDWR) measurement program in 1987. The methods used for...
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Observability of microbursts with Doppler weather radar during 1986 in Huntsville, AL
December 29, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-160
Summary
Thhis report investigates the observability of low-level wind shear events using Doppler weather radar through a comparison of radar and surface wind sensor data. The data was collected during 1986 in the Huntsville, AL area as part of the FAA Terminal Doppler Weather Radar (TDWR) development program. Radar data were collected by both an S-band radar (FL-2) and C-band radar (UND). Surface data were collected by a network of 77 weather sensors covering an area of enarly 1000 square km centered approximately 15 km to the northwest of the FL-2 radar site. The UND site was located at the approximate center of the surface sensor network. A list of 131 microbursts which impacted the surface sensor network is presented. Particular emphasis is on the 107 events for which both radar data and surface data where available. Of these events, 14 were not observed by the surface network, while two events were not identified as microbursts by radar. Possible explanations of these missed microburst identifications are presented. The first case was an instance of the radar viewing a weak, asymmetric event from an unfavorable viewing angle. The second case describes an extremely shallow microburst outflow occurring at a heigh too low to be observed by the lowest elevation scan of the radar. In each of these cases, the featured microburst was very weak and, although a microburst-strength differential velocity was not observable by radar, in both instances the divergent wind pattern associated with the event was clearly evident in the radar velocity data field. All microbursts which exhibited a differential velocoity of in excess of 13 m/s were identified by radar. No microbursts went unobserved as the result of insufficient signal return.
Summary
Thhis report investigates the observability of low-level wind shear events using Doppler weather radar through a comparison of radar and surface wind sensor data. The data was collected during 1986 in the Huntsville, AL area as part of the FAA Terminal Doppler Weather Radar (TDWR) development program. Radar data were...
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Low-altitude wind shear detection with airport surveillance radars: evaluation of 1987 field measurements
August 31, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-159
Summary
A field measurement program is being conducted to investigate the capabilities of airport surveillance radars (ASR) to detect low altitude wind shear (LAWS). This capability would require minor RF signal path modifications in existing ASRs and the addition of a signal processing channel to measure the radial velocity of precipitation wind tracers and automatically detect regions of hazardous velocity shear. A modified ASR-8 has been deployed in Huntsville, Alabama and is operated during periods of nearby thunderstorm activity. Data from approximately 30 "wet" (i.e., high radar reflectivity) microbursts during 1987 have been evaluated through comparison with simultaneous measurements from a collocated pencil beam weather radar. In this report, we describe the 1987 field experiment and utilize the resulting data to illustrate problems and potential prcoessing approaches for LAWS detection with airport surveillance radars. Techniques are described for estimation of low altitude wind fields in the presence of interference such as ground clutter or weather aloft and for automatic detection of microburst wind shear from the resulting radial velocity fields. Evaluation of these techniques using case studies and statistical scoring of the automatic detection algorithm indicates that a suitability modified ASR could detect wet microbursts within 16 km of the radar with a detection probability in excess of 0.90 and a corresponding false alarm probability of less than 0.10. These favorable results indicate the need for careful consideration of implementation issues and the potential operational role of wind measurements from an ASR.
Summary
A field measurement program is being conducted to investigate the capabilities of airport surveillance radars (ASR) to detect low altitude wind shear (LAWS). This capability would require minor RF signal path modifications in existing ASRs and the addition of a signal processing channel to measure the radial velocity of precipitation...
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Characteristics of microbursts in the continental United States
January 1, 1988
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 1, No. 1, Spring 1988, pp. 49-74.
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 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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A comparison of PAM-II and FLOWS mesonet data during COHMEX
December 23, 1987
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-154
Summary
Surface weather stations are being used in the Terminal Doppler Weather Radar program to assess the radar detectibility of wind shear and to help gain an understanding of microburst forcing mechanisms. During 1986, surface station networks operated by Lincoln Laboratory (FLOWS) and the National Center for Atmonspheric Research (PAM-II) were deployed in the Huntsville, AL area. A preliminary assessment of the overall performance of PAM-II and FLOWS networks suggests that they performed with comparable accuracy for those meterological characteristics most important to the detection of microbursts. While differences and discrepancies were noted, especially in the network total precipitation amounts, none would preclude treating PAM-II and FLOWS data together as if they were generated by a single network. We condlcue that the data can be directly combined for microburst detection analyses.
Summary
Surface weather stations are being used in the Terminal Doppler Weather Radar program to assess the radar detectibility of wind shear and to help gain an understanding of microburst forcing mechanisms. During 1986, surface station networks operated by Lincoln Laboratory (FLOWS) and the National Center for Atmonspheric Research (PAM-II) were...
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Automated detection of microburst windshear for terminal doppler weather radar
October 28, 1987
Conference Paper
Published in:
SPIE, Vol. 846, Digital Image Processing and Visual Communications Technolody in Meteorology, 27-28 October 1987, pp. 61-68.
Summary
An image analysis method is presented for use in detecting strong windshear events, called microbursts, in Doppler weather radar images. This technique has been developed for use in a completely automated surveil-lance system being procured by the Federal Aviation Administration (FAA) for the protection of airport terminal areas. The detection system must distill the rapidly evolving radar imagery into brief textual warning messages in real time, with high reliability.
Summary
An image analysis method is presented for use in detecting strong windshear events, called microbursts, in Doppler weather radar images. This technique has been developed for use in a completely automated surveil-lance system being procured by the Federal Aviation Administration (FAA) for the protection of airport terminal areas. The detection...
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Study of microburst detection performance during 1985 in Memphis, TN
August 5, 1987
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-142
Summary
This report focuses on the detectability of microbursts using pulse Doppler weather radars and surface anemometers. The data used for this study were collected in the Memphis, TN area during the FLOWS project of 1985. The methods used for declaring a microburst from both Doppler radar and surface anemometer data are described. The main objective of this report was to identify the results that were generated by comparing the 1985 radar detected microbursts (which impacted the surface anemometer system) wit the surface mesonet detected microbursts. In so doing, the issue of missed microburst detections, for which there occurred two (both by the radar), is identified. Possible reasons as to why there two microbursts were not detected are discussed in detail.
Summary
This report focuses on the detectability of microbursts using pulse Doppler weather radars and surface anemometers. The data used for this study were collected in the Memphis, TN area during the FLOWS project of 1985. The methods used for declaring a microburst from both Doppler radar and surface anemometer data...
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Preliminary Memphis FAA/Lincoln Laboratory operational weather studies results
April 22, 1987
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-141
Summary
During 1984 and 1985 M.I.T. Lincoln Laboratory, under the sponsorship of the Federal Aviation Administration (FAA) conducted a measurement program in the Memphis, Tennessee, area to study low-level wind shear events and other weather phenomena that are potentially hazardous to aircraft operations, with particular emphasis on those issues related to the Terminal Doppler Weather Radar (TDWR). The principal sensor for the measurement program was the S-band FAA-Lincoln Laboratory Testbed Doppler Weather Radar (FL2) which incorporates many of the functional features of the TDWR. Both FL2 and a C-band Doppler Weather Radar operated by the University of North Dakota (UND) obtained reflectivity, mean velocity and spectrum width measurements with a radar geometry and scan sequences to facilitate determining the surface outflow features of microbursts at the anticipated TDWR ranges. A 30-station network of automatic weather stations (mesonet) collected I-min averages of temperature, humidity, pressure, wind speed and direction, and total rainfall, plus the peak wind speed during each minute; this system operated from about March through November 1984 and 1985. Finally, the UND Citation aircraft operated two 3-week periods during 1985, collecting thermodynamical, kinematical and microphysical data within and around selected storms in the area as well as providing in situ truth for locations and intensity of turbulence. This report describes the principal initial results from the Memphis operations, stressing the results from 1985 when the FL2 radar was fully operational. These results are compared to those from previous studies of wind-shear programs, e.g., NIMROD near Chicago, JAWS and CLAWS near Denver. During 1985, 102 microbursts were identified in real time along with 81 gust fronts. One of the dominant results is that most microbursts in the mid-south are wet; that is, they are accompanied by significant rainfall. This is in contrast, for example, to the results from Denver where more than half of all microbursts have little or no appreciable rain reaching the ground. Aside from this major difference, microbursts near Memphis were similar to those found elsewhere in the country in terms of wind shear magnitude. The report also gives more representative results from the aircraft operations and discusses the effectiveness of the ground-clutter filters used on the FL2 radar.
Summary
During 1984 and 1985 M.I.T. Lincoln Laboratory, under the sponsorship of the Federal Aviation Administration (FAA) conducted a measurement program in the Memphis, Tennessee, area to study low-level wind shear events and other weather phenomena that are potentially hazardous to aircraft operations, with particular emphasis on those issues related to...
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Correcting wind speed measurements for site obstructions
January 16, 1987
Conference Paper
Published in:
Sixth Symp. Meteorological Observations and Instrumentation, 12-16 January 1987, pp. 358-363.
Summary
The FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) Project is developing methods for automatically detecting and warning against aviation weather hazards, such as low-altitude wind shear, in airport terminal areas using NEXRAD-like Doppler weather radars. Currently, the FAA uses the Low Level Wind Shear Alert System (LLWAS), an anemometer array situated within and around an airport terminal area, for real-time detection of wind shear events. Even with the installation of Terminal Doppler Weather Radars (TDWRs) at some airports, the LLWAS systems there could still play an important role in the accurate detection of wind shear events, and at airports without TDWRs, the LLWAS will remain the primary detection system. The slowing or obstruction of wind by local obstacles is a well know n problem to those wishing to make accurate wind speed measurements. Anemometers should always be located where there will be, as nearly as passible, an unobstructed wind flow free from turbulent eddies in all directions. Because of the fairly precise required sensor configuration of the anemometers in an LLWAS system, it can occasionally be difficult or impossible to find sites with good exposure in all directions. The FLOWS project is interested in the unobstructed wind speed measurements for two main reasons. First, when analyzing a snapshot of the wind field over a mesonet (or LLWAS) for horizontal wind shear and/or for comparison with Doppler radar data, use of the measured, uncorrected winds would reveal spurious patterns of divergence or vorticity that depend little on time but greatly on the prevailing wind direction and that would, in some cases, obscure the true wind shear pattern. Second, when using surface wind measurements to estimate winds aloft that might be encountered by an aircraft on take-off or landing, an· appropriate power law can be accurately used if the original surface wind speed measurements are representative of the unobstructed flow.
Summary
The FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) Project is developing methods for automatically detecting and warning against aviation weather hazards, such as low-altitude wind shear, in airport terminal areas using NEXRAD-like Doppler weather radars. Currently, the FAA uses the Low Level Wind Shear Alert System (LLWAS), an anemometer array situated...
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