Publications
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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Surveillance processing in the Mode S sensor
October 21, 1987
Conference Paper
Published in:
Radar-87, IEE Int. Conf., London, U.K., 19-21 October 1987, pp. 189-194.
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Summary
The principal function of the Mode S sensor (1), an evolutionary upgrade to the current ATCRBS (Air Traffic Control Radar Beacon System) sensor, is the output of one reportper aircraft per antenna scan. This report contains the current aircraft position (range and azimuth), the identity code of its transponder, and the altitude code as supplied by its encoding altimeter. This information is derived from the aircraft transponder replies received at the sensor in response to interrogations transmitted by the sensor. For aircraft equipped with Mode S transponders, a single scheduled interrogation, directed only to that aircraft, elicits a single coding-protected reply containing both identity code and altitude code. For aircraft equipped with ATCRSS transponders, a sequence of interrogations alternately eliclt replies containing un-protected identity code or altitude code from all aircraft in the antenna mainbeam. From this description, it is clear that a Mode S aircraft report can be constructed directly fron the single reply. Surveillance processing, defined as functions that perform scan-to-scan correlation and tracking, are required in general only to predict the next scan position of the aircraft. This information is needed for the proper scheduling of the next interrogation. ATCRBS reports constructed from the aircraft replies, on the other hand, can have a number of deficiencies. The more common such problems are: 1. Either the identity code or altitude code or both can have bits declared either in error or with low confidence by the reply processor due to garbling of overlapping replies. 2. False alarm reports not corresponding to aircraft can be generated from fruit replies (responses to other sensors' interrogations) or reflection replies. 3. Multiple reports for an aircraft can be generited due to incorrect correlation of replies caused by errors in range, azimutn, or code determination. Surveillance processing for ATCRBS aircraft is tasked with correcting these problems prior to report output to the controllers or other users. It does this by correlating raw target reports with, existing track files, and using the information in these files derived from prior scan reports to correct, complete, or reject erroneous reports. This paper presents the major algorithms contained within the Mode S sensor ATCRBS surveillance processing function. It then presents experimental results that demonstrate their effectiveness. Full details of surveillance processing can be obtained by reference to (2) or [3).
Summary
The principal function of the Mode S sensor (1), an evolutionary upgrade to the current ATCRBS (Air Traffic Control Radar Beacon System) sensor, is the output of one reportper aircraft per antenna scan. This report contains the current aircraft position (range and azimuth), the identity code of its transponder, and...
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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
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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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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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Gust front characteristics as detected by Doppler radar
May 1, 1987
Journal Article
Published in:
Mon. Weather Rev., Vol. 115, No. 5, May 1987, pp. 905-918.
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Summary
Gust fronts produce low altitude wind shear that can be hazardous to aircraft operations, especially during takeoff and landing. Radar meteorologists have long been able to identify gust front signatures in Doppler radar data, but in order to use the radar efficiently, automatic detection of such hazards is essential. In a study designed to accumulate statistics on the gust frontal signature in Doppler radar data, nine gust front cases were analyzed. Data were collected on those characteristics thought to be most important in developing rules for automatic gust-front detection such as gust front length and height, maximum and minimum values of reflectivity, velocity and spectrum width, and estimates of radical shear. To provide the reader with a concrete example, photographs of the Doppler radar displays of just two (in the interest of brevity) of the nine gust fronts are presented and discussed, as well as summary data for all cases. For these cases, outflows could be detected most reliably in the velocity field. Line features in the spectrum width and reflectivity fields associated with some of the gust fronts could also be identified, although somewhat less reliably than in a Doppler velocity.
Summary
Gust fronts produce low altitude wind shear that can be hazardous to aircraft operations, especially during takeoff and landing. Radar meteorologists have long been able to identify gust front signatures in Doppler radar data, but in order to use the radar efficiently, automatic detection of such hazards is essential. In...
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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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Spatial and temporal analysis of weather radar reflectivity images
April 9, 1987
Conference Paper
Published in:
Proc. IEEE Int. Conf. on Acoustics, Speech and Signal Processing, ICASSP, 6-9 April 1987, pp. 606-609.
Summary
This paper illustrates the use of a primitive symbolic description of an image to obtain more robust identification of amorphous objects than would be possible with more conventional edge or gradient-based segmentation techniques. An algorithm is described which uses a simple multi-level thresholding operation to form a symbolic representation of weather radar reflectivity images. This representation allows the use of detailed rules for the detection and quantification of the image features. A method is described for using this information to identify significant intensity peaks in an image, and examples of its performance are shown.
Summary
This paper illustrates the use of a primitive symbolic description of an image to obtain more robust identification of amorphous objects than would be possible with more conventional edge or gradient-based segmentation techniques. An algorithm is described which uses a simple multi-level thresholding operation to form a symbolic representation of...
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Recognizing low-altitude wind shear hazards from doppler weather radar: an artificial intelligence approach
March 1, 1987
Journal Article
Published in:
J. Atmos. Oceanic Technol., Vol. 4, No. 1, March 1987, pp. 5-18.
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Summary
This paper describes an artificial intelligence-based approach for automated recognition of wind shear hazards. The design of a prototype system for recognizing low-altitude wind shear events from Doppler radar displays is presented. This system, called WXI, consists of a conventional expert system augmented by a specialized capability for processing radar images. The radar image processing component of the system employs numerical and computer vision techniques to extract features from radar data. The expert system carries out symbolic reasoning on these features using a set of heuristic rules expressing meteorological knowledge about wind shear recognition. Results are provided demonstrating the ability of the system to recognize microburst and gust front wind shear events.
Summary
This paper describes an artificial intelligence-based approach for automated recognition of wind shear hazards. The design of a prototype system for recognizing low-altitude wind shear events from Doppler radar displays is presented. This system, called WXI, consists of a conventional expert system augmented by a specialized capability for processing radar...
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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.
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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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The FLOWS automatic weather station network
January 12, 1987
Conference Paper
Published in:
Proc. Sixth Symp. on Meterological Observations and Instrumentation, 12-16 January 1987, pp. 294-9.
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Summary
Lincoln Laboratory is operating a network of 30 automatic weather stations for the FAA as part of the ongoing FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) Project, which focuses on developing techniques for automated hazardous weather detection in airport terminal areas using NEXRAD-like Doppler weather radars. The stations, designed to measure temperature, relative humidity, barometric pressure, wind speed, wind direction, and precipitation amounts, originally used one of the first commercially available data collection platforms (DCPs) to transmit 5-min averaged data to the GOES satellites. Under FAA sponsorship, Lincoln has procured modern DCPs and has refurbished amd modified the sensors to create a reliable 30 station network capable of transmitting one minute averages of the variables mentioned above, as well as the peak wind speed each minute and some internal diagnostic variables, on a single GOES satellite channel. The complete system is described and some performance results from the FLOWS 1984-1985 Memphis operation are presented.
Summary
Lincoln Laboratory is operating a network of 30 automatic weather stations for the FAA as part of the ongoing FLOWS (FAA-Lincoln Laboratory Operational Weather Studies) Project, which focuses on developing techniques for automated hazardous weather detection in airport terminal areas using NEXRAD-like Doppler weather radars. The stations, designed to measure...
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