Publications
A preliminary study of precursors to Huntsville microbursts
October 25, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-153
Summary
Lincoln Laboratory under the sponsorship of the FAA is currently developing automated algorithms for the detection of wind shears such as microbursts and gust fronts. Previous studies have shown that these outflows can be hazardous to an airplance during takeoffs and landings. The ultimate goal of a microburst detection algorithm is the timely warning of potentially hazardous wind shears through the detection of reliable precursors. Research in Colorado and Oklahoma documented the significance of precursors such as descending reflectivity cores, convergence, rotation, and reflectivity notching as indicators that a microburst will occur in the very near future. The overall importance of an individual feature varies between regions. This investiagtion will focus on those precursors which play a dominant role in the formation of wet microbursts in the southern United States. The data analyzed in this report was gathered by the FAA TDWR S-band Doppler radar during 1985 and 1986 in Memphis, Tennessee, and Hunstville, Alabama.
Summary
Lincoln Laboratory under the sponsorship of the FAA is currently developing automated algorithms for the detection of wind shears such as microbursts and gust fronts. Previous studies have shown that these outflows can be hazardous to an airplance during takeoffs and landings. The ultimate goal of a microburst detection algorithm...
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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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Preliminary results of the 1983 Coordinated Aircraft - Doppler weather radar turbulence experiment, volume 1
July 26, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-137-I
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Summary
This report presents results of analyses of coordinated radar-aircraft data acquired form the 1983 experiment conducted at Hanscom AFB, Massachusetts. The objective of the experiment is to assess and validate the current NEXRAD algorithms for estimating aircraft turbulence from volume-scanned Doppler weather observations. Estimates of the turbulence severity index epsilon to the 1/3 power (a quantity used by NEXRAD) computed from radar and aircraft data are presented as a time series along each aircraft track. The radar point estimates of turbulence were averaged horizontally and vertically to yield layered Cartesian maps such as are intended for use by real time ATC controllers and pilots. The derived gust velocity (Ude), also used to indicate the intensity of aircraft encountered turbulence, was computed so that comparisons could be made of the turbulence intensity scales inferred from values of epsilon and U sub de. These quantitative comparisons indicate that for the turbulence generally encountered during the flights, both radar and aircraft estimates of epsilon to the 1/3 power significantly overstate the severity of turbulence as reported by the aircraft pilot. The data analysis also shows that radar-based estimates of epsilon to the 1/3 power, often significantly exceeded aircraft based estimates of epsilon to the 1/3 power. In contrast, the quantity Ude underestimates the aircraft reported turbulence intensity on all the flights. The uncertainty as to operationally useful thresholds for radar epsilon to the 1/3 power, aircraft epsilon to the 1/3 power and Ude is discussed as is the use of spectrum width as a turbulence indicator. It should be noted that the turbulence detection flights used in the study were conducted at ranges such that the radar resolution cell cross range extent was typically 1.5 to 3 km. With such resolution cell size extents, the hypothesis of spatially homogeneous turbulence may not hold and/or the assumed relationship of radar measured spectrum width to kinetic dissipation rate may not be fully accurate.
Summary
This report presents results of analyses of coordinated radar-aircraft data acquired form the 1983 experiment conducted at Hanscom AFB, Massachusetts. The objective of the experiment is to assess and validate the current NEXRAD algorithms for estimating aircraft turbulence from volume-scanned Doppler weather observations. Estimates of the turbulence severity index epsilon...
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TDWR PRF selection criteria
March 15, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-147
Summary
The Terminal Doppler Weather Radar (TDWR) system shall provide high quality Doppler radar data on weather phenomena near high traffic airports. These data shall be used in real time by automated TDWR algorithms to detect weather situations which may be hazardous to the safe operation of aircraft within the vicinity of the airport. One of the major factors which could cause the degradation of the quality of these TDWR data is obscuration by 'distant' storm cells. This obscuration is caused by storms located beyond the range interval being sampled by the radar, yet whose radar echo ambiguously folds within the range interval of interest. These range aliased echoes could trigger false detections by the algorithms, and/or cause actual hazardous situations near the airport to remain undetected. By carefully selecting the pulse repetition frequency (PRF) of the radar, range obscuration from distant storms can be minimized over specified airport regions. This document describes techniques for predicting the obscuration as a function of PRF, and details the criteria which shall be used by the TDWR system to automatically and adaptively select an optimal PRF in order to minimize these obscuration effects. Weather radar, Radar range obscuration, TDWR, Radar range aliasing, Radar pulse, Repetition Frequency (PRF).
Summary
The Terminal Doppler Weather Radar (TDWR) system shall provide high quality Doppler radar data on weather phenomena near high traffic airports. These data shall be used in real time by automated TDWR algorithms to detect weather situations which may be hazardous to the safe operation of aircraft within the vicinity...
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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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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 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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TDWR clutter residue map generation and usage
January 29, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-148
Summary
The Terminal Doppler Weather Radar (TDWR) system is designed to provide high quality low altitude Doppler radar data near airports. Ground clutter suppression will be a major challenge to supplying such high quality Doppler data. To confront this challenge the FAA has specified stringent clutter suppression requirements in the TDWR technical specifications. These specifications are designed to provide an effective clutter suppression system. In particular, the specifications require an antenna with narrow beam width and low side-lobes to minimize ground target illumination. Also, a high pass frequency filter (with a stop attenuation in excess of 50 dB) is required to reduce stationary clutter. FInally, a clutter reisdue map editing system is used to remove remaining clutter. This report describes the algorithms used to generate and use the clutter residue editing system. The major issues are discussed followed by a description of the algorithms designed to address these issues. Finally, preliminary experimental results using a clutter residue map are presented.
Summary
The Terminal Doppler Weather Radar (TDWR) system is designed to provide high quality low altitude Doppler radar data near airports. Ground clutter suppression will be a major challenge to supplying such high quality Doppler data. To confront this challenge the FAA has specified stringent clutter suppression requirements in the TDWR...
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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.
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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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Ground clutter processing for wind measurements with airport surveillance radars
November 4, 1987
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-143
Summary
Modern airport surveillance radars (ASR) are coherent pulsed-Doppler radars used for detecting and tracking aircraft in terminal area air-space. These radars might serve an additional role by making radial wind measurements in the immediate vicinity of an airport to provide data on low altitude wind shear (LAWS). One factor that will affect their capability in this role is the requirement that intense low-beam ground clutter be filtered from the signals prior to estimation of the reflectivity and radial velocity of weather scatterers. This report describes and analyzes a specific signal processing algorithm for ASR weather parameter measurements. An adaptively selected Finite Impulse Repsonse high-pass filter is used for ground clutter suppression, followed by pulse-pair weather reflectivity and radial velocity estimation. Measurements from a Lincoln Laboratory-developed testbed ASR in Huntsville, Alabama are used to characterize the ground clutter environment under siting ocnditions that are representative of operational ASRs. Temporal fluctuations in ground clutter intensity are analyzed with attention to their impact on the adaptive clutter-filter selection procedure. The performance of the signal processing algorithms is then analyzed using the testbed ASR ground clutter measurements in combination with simulated or real weather signals. We conclude that ground clutter and hte requisite clutter filtering will not severely distort ASR wind shear measurements when the reflectivity factor of the microburst or gust front is approximately 20 dBz or greater. This is typically the case for microbursts ocurring in moist conditions such as prevail over the Eastern United States during summer.
Summary
Modern airport surveillance radars (ASR) are coherent pulsed-Doppler radars used for detecting and tracking aircraft in terminal area air-space. These radars might serve an additional role by making radial wind measurements in the immediate vicinity of an airport to provide data on low altitude wind shear (LAWS). One factor that...
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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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