Publications
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Clutter rejection in Doppler weather radars used for airport wind shear detection
June 1, 1990
Conference Paper
Published in:
Proc. Second Int. Symp. on Noise & Clutter Rejection in Radars & Imaging Sensors (ISNCR-89), 14-16 November 1989, PP. 275-280.
Summary
Techniques for the suppression of ground and storm clutter to permit the detection of low altitude windshear by pulse Doppler radars are described. Novel features of the system include the use of clutter residue and range aliased weather echo editing maps which edit out the range-azimuth cells on a "data adaptive" basis.
Summary
Techniques for the suppression of ground and storm clutter to permit the detection of low altitude windshear by pulse Doppler radars are described. Novel features of the system include the use of clutter residue and range aliased weather echo editing maps which edit out the range-azimuth cells on a "data...
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Terminal Doppler Weather Radar clutter control
May 10, 1990
Conference Paper
Published in:
Proc. IEEE 1990 Int. Radar Conf., 7-10 May 1990, pp. 12-16.
Summary
The FAA is developing the Terminal Doppler Weather Radar system to automatically detect low altitude wind shear due to microbursts and gust fronts. Detection of this phenomenon presents a significant radar engineering challenge due to the need to observe low reflectivity events in the presence of strong clutter from ground objects and range aliased weather returns. This paper describes a number of unique approaches to clutter recognition which have been validated with the TDWR test bed radar.
Summary
The FAA is developing the Terminal Doppler Weather Radar system to automatically detect low altitude wind shear due to microbursts and gust fronts. Detection of this phenomenon presents a significant radar engineering challenge due to the need to observe low reflectivity events in the presence of strong clutter from ground...
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Development of an automated windshear detection system using doppler weather radar
November 1, 1989
Journal Article
Published in:
Proc. IEEE, Vol. 77, No. 11, November 1989, pp. 1661-1673.
Summary
The US Federal Aviation Administration (FAA) is developing the Terminal Doppler Weather Radar (TDWR) system to determine the location and severity of LAWS (low-altitude windshear) phenomena and other weather hazards (e.g. tornadoes and turbulence) and to provide the pertinent information to real-time air traffic control users. The FAA program for developing and evaluating the TDWR is described, with emphasis on the resolution of key technical issues such as separation of the radar return due to the low-altitude weather phenomena from that caused by various clutter sources and the automatic detection of the phenomena by means of pattern recognition applied to images depicting the weather reflectivity and Doppler shift. These technical issues have been addressed using experimental data obtained using a testbed radar in representative meteorological regimes. The system performance has been assessed using numerous experimental windshear data sets with corresponding 'truth' developed by experienced radar meteorologists from a number of organizations. It is shown that the system provides very reliable detection of strong microbursts in a variety of environments with a gust-front detection capability that supports effective planning of airport runway use.
Summary
The US Federal Aviation Administration (FAA) is developing the Terminal Doppler Weather Radar (TDWR) system to determine the location and severity of LAWS (low-altitude windshear) phenomena and other weather hazards (e.g. tornadoes and turbulence) and to provide the pertinent information to real-time air traffic control users. The FAA program for...
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The relationship between lightning type and convective state of thunderclouds
September 30, 1989
Journal Article
Published in:
J. Geophys. Res., Vol. 94, No. D11, 30 September 1989, pp. 13,213-13,220.
Summary
Thunderstorm case studies and earlier observations are described which illuminate the relationship between cloud vertical development and the prevalence of intracloud (IC) and cloud-to-ground (CG) lightning. A consistent temporal evolution starting with peak IC activity changing to predominant CG activity and concluding with strong outflow (microburst) suggests that ice is responsible for both the electrical (i.e., lightning) and dynamical (i.e., microburst) phenomena. The IC activity is attributed to the updraft-driven accumulation of graupel particles in the central dipole region, and the subsequent CG activity to the descent of ice particles beneath the height of the main negative charge. The subsequent descent and melting of ice particles beneath the height of the 0 degree C isotherm are associated with the acceleration of the downdraft and outflow. The IC lightning precursor can provide a valuable short-term (5-10 min) warning for microburst hazard at ground level.
Summary
Thunderstorm case studies and earlier observations are described which illuminate the relationship between cloud vertical development and the prevalence of intracloud (IC) and cloud-to-ground (CG) lightning. A consistent temporal evolution starting with peak IC activity changing to predominant CG activity and concluding with strong outflow (microburst) suggests that ice is...
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Notes and correspondence - Correcting wind speed measurements for site obstructions
April 1, 1989
Journal Article
Published in:
J. Atmos. Oceanic Technol., Vol. 6. No. 2, April 1989, pp. 343-352.
Summary
The effects of obstructions on winds measured by the 30 station FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) mesonet and the 6 station FAA LLWAS (Low Level Wind Shear Alèrt System) near Memphis, TN in 1985 are analyzed. The slowing of surface winds by anemometer site obstructions is a continuing problem for scientific and operational wind shear measurement system This paper considers an improved version of the technique used by Fujita and Wakimoto for compensating the obstruction effects by the use of mathematical models relating the unobstructed wind speed to the measured wind speed and the observed obstructions at each site. Over eight million wind speed measurements gathered over 197 days (15 February–31 August) were used. The effects of obstructions at a particular site were evidenced by a strong negative correlation between the observed wind speed transmission factors and the obstruction angles as measured from panoramic photographs taken of the horizon around each station. The functional relationship between them was modeled as a decaying exponential plus a constant, and an iterative least squares regression technique was used on data from all of the stations at once in deriving the three parameters of the equation. It was found that the first 8° of obstruction have the greatest blockage effects, and that even a 2° or 3° high isolated clump of trees can have a pronounced effect on the measured wind speeds from that direction. The possibility that the transmission factors are scale dependent and time dependent is explored.
Summary
The effects of obstructions on winds measured by the 30 station FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) mesonet and the 6 station FAA LLWAS (Low Level Wind Shear Alèrt System) near Memphis, TN in 1985 are analyzed. The slowing of surface winds by anemometer site obstructions is a continuing problem...
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The FLOWS automatic weather station network
April 1, 1989
Journal Article
Published in:
J. Atmos. Oceanic Technol., Vol. 6, No. 2, April 1989, pp. 307-326.
Summary
This report describes in detail the FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) automatic weather station network which is being used in the Terminal Doppler Weather Radar program to assess the radar detectability of wind shear and to help gain an understanding of microburst forcing mechanisms. The weather stations are descended from the PROBE stations originally operated by the Bureau of Reclamation. The current instrumentation has been modified slightly but is largely the same as that originally used as is the hardware structure, but the data collection platforms are entirely new. Each station in the 30-station network transmits 1 min averages of temperature, relative humidity, barometric pressure, wind speed, wind direction and precipitation amounts, as well as peak wind speed, on a single GOES satellite channel. Performance results from the first 3 yr (1984-86) of mesonet operations are presented. During June and July 1986 the FLOWS network was collocated with the NCAR PAM-II network near Huntsville, Alabama to measure surface data on microbursts as part of the Cooperative Huntsville Meteorological Experiment (COHMEX). A preliminary assessment of the overall performance of the two networks suggests that they performed with comparable accuracy for those meteorological characteristics most important to the detection of microbursts. While differences and discrepancies were noted, none would preclude treating PAM-II and FLOWS data together as if they were generated by a single network.
Summary
This report describes in detail the FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) automatic weather station network which is being used in the Terminal Doppler Weather Radar program to assess the radar detectability of wind shear and to help gain an understanding of microburst forcing mechanisms. The weather stations are descended...
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Analysis of microburst observability with Doppler radar through comparison of radar and surface wind sensor data
March 27, 1989
Conference Paper
Published in:
24th Conf. on Radar Meteorology, 27-31 March 1989, pp. 171-174.
Summary
As part of the FAA Terminal Weather Doppler Weather Radar (TDWR) measurement program in Huntsville, AL and Denver, CO during 1986 and 1987, respectively, the ability of a single Doppler weather radar to observe microburst outflow signatures (i.e., show identifiable radial velocity patterns) was assessed by comparing radar-observed microbursts with those identified by joint use of both radar and data from a mesoscale network (mesonet) of surface meteorological stations (Clark, 1988; DiStefano, 1988). Observability by radar must be considered together with pattern recognition algorithm performance for observable microbursts (Campbell et al., 1988) in order to fully assess the potential effectiveness of an automated microburst detection system which relies on data from a single Doppler radar. The comparison of radar and surface sensor data presented here investigates the possibility that some outflows may not be observable by radar due to: (1) low SNR (signal-to-noise ratio), (2) very shallow outflows for which the radar beam is scanning too high above the surface, (3) blockage of the beam, and/or (4) asymmetry in the surface outflow causing the radar to significantly underestimate the magnitude of the surface wind shear (Eilts and Doviak, 1987; GAO, 1987). Also addressed is the possibility that microbursts are not observed by the mesonet surface sensors because the spacing between stations is too great, or because the microburst outflow does not reach the surface due to a dense layer of cold air at the surface.
Summary
As part of the FAA Terminal Weather Doppler Weather Radar (TDWR) measurement program in Huntsville, AL and Denver, CO during 1986 and 1987, respectively, the ability of a single Doppler weather radar to observe microburst outflow signatures (i.e., show identifiable radial velocity patterns) was assessed by comparing radar-observed microbursts with...
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Range obscuration mitigation by adaptive PRF selection for the TDWR System
March 27, 1989
Conference Paper
Published in:
24th Conf. on Radar Meteorology, 27-31 March 1989, pp. 175-178.
Summary
The Federal Aviation Administration has recently awarded a contract for the procurement of 47 Terminal Doppler Weather Radar (TDWR) systems to be sited near high traffic airports. These systems will collect and process Doppler radar data that will be used by fully automated algorithms to identify hazardous meteorological wind shear events in real time (eg., microbursts and gust fronts.) This information will the be conveyed to aircraft pilots in order that potentially hazardous takeoffs or landings be averted. In a pulsed Doppler weather radar, one of the most serious causes of data quality degradation is due to range aliased echoes from distant storms [3]. This range contamination can occur in the immediate vicinity of a meteorological hazard, possibly obscure the event, and thus decrease the probability of detecting it. In other instances, range contaminated data can present a radar signature similar to that of a wind shear hazard, and perhaps cause an algorithm to issue a false alarm. In order for the TDWR system to achieve a high probability of detecting meteorological hazards, while maintaining a low probability of false alarms, an effective means of dealing with range contamination is required. An adaptive procedure by which to select the radar's pulse repetition frequency (Pm) has been developed as a primary means by which to minimize range contamination within the operationally significant coverage area of a TDWR system. This procedure will be developed within this paper and a quantitative assessment as to the anticipated effectiveness of this technique in the TDWR system will be provided.
Summary
The Federal Aviation Administration has recently awarded a contract for the procurement of 47 Terminal Doppler Weather Radar (TDWR) systems to be sited near high traffic airports. These systems will collect and process Doppler radar data that will be used by fully automated algorithms to identify hazardous meteorological wind shear...
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Use of features aloft in the TDWR microburst recognition algorithm
March 27, 1989
Conference Paper
Published in:
Proc. 24th Conf. on Radar Meteorology, 27-31 March 1989, pp. 167-170.
Summary
This paper describes the use of features aloft in the Terminal Doppler Weather Radar (TWDR) microburst recognition algorithm. The paper is divided into three sections: algorithm description, scan strategy and recent results. The prototype algorithm recognizes features aloft associated with microbursts, such as descending reflectivity cores and convergence aloft. The algorithm uses these signatures to improve the detection performance and timeliness of microburst hazard warnings. For example, the algorithm can use features aloft to make a microburst declaration while the surface outflow is still weak, thereby increasing the hazard warning time. An important factor in microburst recognition algorithm performance is the scan strategy employed. The TDWR scan strategy is designed for timely detection of microburst surface outflows and features aloft. The rationale for the prototype TDWR scan strategy is presented using Denver's Stapleton airport as an example. Recent results are presented demonstrating the ability of the system to recognize features aloft for microburst events observed during the summer of 1988 at Denver, CO. It is shown that the ability to recognize features aloft improved the probability of detection and hazard warning time for these events.
Summary
This paper describes the use of features aloft in the Terminal Doppler Weather Radar (TWDR) microburst recognition algorithm. The paper is divided into three sections: algorithm description, scan strategy and recent results. The prototype algorithm recognizes features aloft associated with microbursts, such as descending reflectivity cores and convergence aloft. The...
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An analysis of microburst characteristics related to automatic detection from Huntsville, Alabama and Denver, Colorado
March 1, 1989
Conference Paper
Published in:
24th Conf. on Radar Meteorology, 27-31 March 1989, pp. 269-273.
Summary
During 1986 and 1987-8, Lincoln Laboratory, under the sponsorship of the Federal Aviation Administration (FAA), collected Doppler radar measurements in Huntsville, Alabama and Denver, Colorado, respectively. These field programs focused on developing and evaluating an automated wind shear detection system that would provide timely warnings of hazardous low-altitude wind shear events to pilots in the airport terminal area. Two previous projects in Denver (JAWS and CLAWS) documented the ability of a pulsed Doppler radar system to detect wind shear near an airport. In the last two decades, there have been 27 aircraft accidents or incidents at least partially attributed to this phenomenon. According to the National Transportation Safety Board, the most hazardous form of wind shear to aviation is the microburst, first identified by Fujita (1981). A microburst is an outflow of downdraft winds from a convective cloud which exhibits a strong divergent pattern near the surface. The radial velocity differential (delta V) must be greater than or equal to 10 m/s over a distance of 4 km or less to be classified as a microburst. In this paper, microburst measurements from the TDWR testbed are analyzed to characterize and compare the type of outflows in an environment with a typically dry sub-cloud layer (Denver) and a typically moist sub-cloud layer (Huntsville), and to relate these characteristics wo observable radar features being used in the Terminal Doppler Weather Radar (TDWR) system for microburst detection. Section 2 describes the primary radar used in the data collection program. Section 3 contrasts microburst characteristics from the two locales. Evidence is presented which suggests that the reflectivity and intensity of the outflow are important to the performance of the microburst detection algorithm, while the frequency and intensity of features aloft may provide for an earlier declaration of a microburst. In section 4, key microburst characteristics from Huntsville and Denver are summarized in relation to the automatic detection process.
Summary
During 1986 and 1987-8, Lincoln Laboratory, under the sponsorship of the Federal Aviation Administration (FAA), collected Doppler radar measurements in Huntsville, Alabama and Denver, Colorado, respectively. These field programs focused on developing and evaluating an automated wind shear detection system that would provide timely warnings of hazardous low-altitude wind shear...
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