Publications
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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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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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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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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A preliminary assessment of thunderstorm outflow wind measurement with airport surveillance radars
May 15, 1987
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-140
Summary
Modern airport surveillance radars (ASR), situated on or near most major air terminals, feature coherent pulse-Doppler processing, a vertical-fan beam and rapid azimuthal antenna scanning for detection and tracking of aircraft. These radars might serve an additional useful role by making radial wind measurements in the immediate vicinity of an airport so as to provide data on thunderstorm outflow winds. This report presents a preliminary analysis of the capabilities and limitations of ASRs in measuring outflow winds. Principal results are: (10) radar sensitivity is adequate to measure winds associated with weakly reflecting (5-20 dBZ) thunderstorm outflows at ranges less than 20 km provided that appropriate operating parameters are chosen; (2) overhanging precipitation, often moving at a markedly different radial velocity than the outflow, will be a significant source of interference owing to the verrtical-fan antenna pattern. If radar reflectivity is approximately constant with altitude, this interference will limit the maximum range for reliable outflow velocity measurements to about 20 km for an outflow that extends 1000 m above the surface and to 7 km for an outflow that extends only 300 m above the surface; (3) At two example major air terminals (Memphis International and Denver Stapleton) ground clutter suppression of approximately 40 dB, combined with the use of unter-clutter visibility techniques, would result in ad adequate signal-to-interference ratio for thunderstorm outflow velocity measurement over the significant approach/departure corridors. This result applies when the radar reflectivity factor in the outflow is 20 dBZ or greater and the associated winds extend at least 300 m above the surface.
Summary
Modern airport surveillance radars (ASR), situated on or near most major air terminals, feature coherent pulse-Doppler processing, a vertical-fan beam and rapid azimuthal antenna scanning for detection and tracking of aircraft. These radars might serve an additional useful role by making radial wind measurements in the immediate vicinity of an...
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Assessment of ASR-9 weather channel performance: analysis and simulation
July 31, 1986
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-138
Summary
In this report, we use pencil-beam Doppler weather radar data, combined with on-airport ground clutter measurements, to analyze the performance of the six-level weather channel in the next generation airport surveillance radar, the ASR-9. A key tool was a computer procedure that used these data to simulate the output of the ASR-9's weather channel, including effects of the radar's fan-shaped elevation beams, short coherent processing intervals and ground clutter filters. Our initial analysis indicates that: (a) the combination of high-pass Doppler filters and spatial/temporal smoothing should normally prevent ground clutter from having a significant effect on the controllers' weather display; (b) the spatial/temporal smoothing processor will result in weather contours that are statistically stable on a to-scan basis, reinforcing controller confidence in the validity of the data; (c) relative to the coarse resolution imposed by use of the NWS levels, accurate two-dimensional parameterizations of storm reflectivity can be estimated. Our assessment indicates that the ASR-9's weather reflectivity maps should be reliable. The radar will be widely deployed at significant air terminals, and will provide a combination of high update rate and large volumetric coverage not available from other sensors. These attributes should lead the ASR-9 becoming an important component of the Federal Aviation Agency's modernized weather nowcasting system.
Summary
In this report, we use pencil-beam Doppler weather radar data, combined with on-airport ground clutter measurements, to analyze the performance of the six-level weather channel in the next generation airport surveillance radar, the ASR-9. A key tool was a computer procedure that used these data to simulate the output of...
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Evaluation of the ASR-9 weather reflectivity product
June 21, 1985
Conference Paper
Published in:
Proc. Second Int. Conf. on the Aviation Weather System, 19-21 June 1985, pp. 196-202.
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Summary
The ASR-9 is a modern airport surveillance radar (ASR) under procurement by the United States Federal Aviation Agency. The radar operates at S-band, providing range-azimuth position information on aircraft targets within a 111-km radius. A fully-coherent klystron amplifier, large dynamic range and digital signal processing enable high integrity target processing and display under condition of ground clutter, weather, angel clutter, RF interference and ground vehicular traffic. To aid controllers in the identification of hazardous weather conditions, the processor will also generate two- or six-level weather reflectivity contours for display at the terminal radar control center and (potentially) remote sites. In this paper, we present an overview of the ASR-9 and its weather processor, emphasizing those features that raise issues with respect to the utility of the weather reflectivity product in an air-traffic control environment. We then describe a simulation procedure that utilizes pencil-beam Doppler weather radar data and ground clutter measurements to preview the ASR-9 product and assess the effects of the radar's configuration on the weather intensity reports. Examples of the simulated weather reports are used to illustrate" (a) partial beamfilling die to the fan-shaped surveillance antenna pattern; (b) attenuation of low velocity weather by the clutter filters' (c) the effects of the spatial filters used in weather processing.
Summary
The ASR-9 is a modern airport surveillance radar (ASR) under procurement by the United States Federal Aviation Agency. The radar operates at S-band, providing range-azimuth position information on aircraft targets within a 111-km radius. A fully-coherent klystron amplifier, large dynamic range and digital signal processing enable high integrity target processing...
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