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TCAS: a system for preventing midair collisions

January 1, 1989
  |
Journal Article
Author:
William H. Harman III
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 437-458.
Topic:
air traffic control
R&D area:
R&D group:

Summary

To reduce the possibility of midair collisions, the Federal Aviation Administration has developed the Traffic Alert and Collision Avoidance System, or TCAS. This airborne system senses the presence of nearby aircraft by interrogating the transponders carried by these aircraft. When TCAS senses that a nearby aircraft is a possible collision threat, TCAS issues a traffic advisory to the pilot, indicating the presence and location of the other aircraft. If the encounter becomes hazardous, TCAS issues a maneuver advisory.
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Summary

To reduce the possibility of midair collisions, the Federal Aviation Administration has developed the Traffic Alert and Collision Avoidance System, or TCAS. This airborne system senses the presence of nearby aircraft by interrogating the transponders carried by these aircraft. When TCAS senses that a nearby aircraft is a possible collision...

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TCAS: a system for preventing midair collisions

Using aircraft radar tracks to estimate winds aloft

January 1, 1989
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Journal Article
Author:
Walter M. Hollister
…
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 555-565.
Topic:
aviation weather
R&D area:
R&D group:

Summary

In air traffic control, the wind is a critical factor because it affects, among other important variables, the amount of time an aircraft will take to reach its destination. The authors have developed a method for estimating winds aloft in which the radar tracks of aircraft are used; i.e., data beyond what are already available to terminal air traffic control are not required. The method, which has been implemented at Lincoln Laboratory, gives a useful estimate of wind fields.
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Summary

In air traffic control, the wind is a critical factor because it affects, among other important variables, the amount of time an aircraft will take to reach its destination. The authors have developed a method for estimating winds aloft in which the radar tracks of aircraft are used; i.e., data...

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Using aircraft radar tracks to estimate winds aloft

The mode S beacon radar system

January 1, 1989
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Journal Article
Author:
Vincent A. Orlando
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 345-362.
Topic:
air traffic control
R&D area:
R&D group:

Summary

Air traffic controllers rely on primary and secondary radars to locate and identify aircraft. Secondary, or beacon, radars require aircraft to carry devices called transponders that enhance surveillance echoes and provide data links. Airports currently use a secondary-radar system known as the Air Traffic Control Radar Beacon System (ATCRBS). However, ATCRBS has limitations in dense-traffic conditions, and the system's air-to-ground data link is limited. In response to these shortcomings, Lincoln Laboratory has developed the Mode Select Beacon System (referred to as Mode S), a next-generation system that extensive laboratory and field testing has validated. In addition to significant surveillance improvements, Mode S provides the general-purpose ground-air-ground data link necessary to support the future automation of air traffic control (ATC). The Federal Aviation Administration (FAA) is currently installing the system with initial operation scheduled for 1991.
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Summary

Air traffic controllers rely on primary and secondary radars to locate and identify aircraft. Secondary, or beacon, radars require aircraft to carry devices called transponders that enhance surveillance echoes and provide data links. Airports currently use a secondary-radar system known as the Air Traffic Control Radar Beacon System (ATCRBS). However...

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The mode S beacon radar system

Wind shear detection with pencil-beam radars

January 1, 1989
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Journal Article
Author:
Mark W. Merritt
…
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 483-510.
Topic:
aviation weather
R&D area:
R&D group:

Summary

Abrupt changes in the winds near the ground pose serious hazards to aircraft during approach or departure operations. Doppler weather radars can measure regions of winds and precipitation around airports, and automatically provide air traffic controllers and pilots with important warnings of hazardous weather events. Lincoln Laboratory, as one of several organizations under contract to the Federal Aviation Administration, has been instrumental in the design and development of radar systems and automated weather-hazard recognition techniques for this application. The Terminal Doppler Weather Radar (TDWR) system uses automatic computer algorithms to ident* hazardous weather signatures. TDWR detects and warns aviation users about low-altitude wind shear hazards caused by microbursts and gust fronts. It also provides advance warning of the arrival of wind shifts at the airport complex. Extensive weather radar observations, obtained from a Lincoln-built transportable testbed radar system operated at several sites, have validated the TDWR system. As a result, the Federal Aviation Administration has issued a procurement contract for the installation of 47 TDWR radar systems around the country.
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Summary

Abrupt changes in the winds near the ground pose serious hazards to aircraft during approach or departure operations. Doppler weather radars can measure regions of winds and precipitation around airports, and automatically provide air traffic controllers and pilots with important warnings of hazardous weather events. Lincoln Laboratory, as one of...

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Wind shear detection with pencil-beam radars

Wind shear detection with airport surveillance radars

January 1, 1989
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Journal Article
Author:
Mark E. Weber
…
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 511-526.
Topic:
radar
R&D area:
R&D group:

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.
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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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Wind shear detection with airport surveillance radars

Review of neural networks for speech recognition

January 1, 1989
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Conference Paper
Author:
Richard P. Lippmann
Published in:
Neural Comput., Vol. 1, 1989, pp. 1-38.
Topic:
speaker recognition
R&D area:
R&D group:

Summary

The performance of current speech recognition systems is far below that of humans. Neural nets offer the potential of providing massive parallelism, adaptation, and new algorithmic approaches to problems in speech recognition. Initial studies have demonstrated that multi-layer networks with time delays can provide excellent discrimination between small sets of pre-segmented difficult-to-discriminate words, consonants, and vowels. Performance for these small vocabularies has often exceeded that of more conventional approaches. Physiological front ends have provided improved recognition accuracy in noise and a cochlea filter-bank that could be used in these front ends has been implemented using micro-power analog VLSI techniques. Techniques have been developed to scale networks up in size to handle larger vocabularies, to reduce training time, and to train nets with recurrent connections. Multilayer perceptron classifiers are being integrated into conventional continuous-speech recognizers. Neural net architectures have been developed to perform the computations required by vector quantizers, static pattern classifiers, and the Viterbi decoding algorithm. Further work is necessary for large-vocabulary continuous-speech problems, to develop training algorithms that progressively build internal word models, and to develop compact VLSI neural net hardware.
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Summary

The performance of current speech recognition systems is far below that of humans. Neural nets offer the potential of providing massive parallelism, adaptation, and new algorithmic approaches to problems in speech recognition. Initial studies have demonstrated that multi-layer networks with time delays can provide excellent discrimination between small sets of...

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Review of neural networks for speech recognition

Observability of microbursts using Doppler weather radar and surface anemometers during 1987 in Denver, CO

December 29, 1988
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Project Report
Author:
John T. DiStefano
Published in:
MIT Lincoln Laboratory Report ATC-161
Topic:
wind shear
R&D area:
R&D group:

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.
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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 using Doppler weather radar and surface anemometers during 1987 in Denver, CO

Observability of microbursts with Doppler weather radar during 1986 in Huntsville, AL

December 29, 1988
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Project Report
Author:
David A. Clark
Published in:
MIT Lincoln Laboratory Report ATC-160
Topic:
wind shear
R&D area:
R&D group:

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.
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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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Observability of microbursts with Doppler weather radar during 1986 in Huntsville, AL

Miss distance analysis for command guided missiles

December 1, 1988
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Journal Article
Author:
Joel Alpert
Published in:
J. Guid. Control Dyn., Vol. 11, No. 6, November-December 1988, pp. 481-487.
Topic:
missile defense
R&D area:
R&D group:

Summary

A concise theoretical technique is presented for estimating the minimum miss distance capability of command guided missile systems using synthetic proportional navigation. The effect of the parameter values on the system capability is shown to be a function of range-to-intercept; the technique enables the system designer and analyst to quantify system performance and to develop a systematic understanding of the performance limitations of command guidance systems at each intercept range. New analytical equations based upon adjoint theory are developed for statistical miss distance caused by target maneuver, range-dependent, servo, glint and atmosphere noises for command guided systems. An optimal total system time constant is derived which yields the minimum statistical miss distance. Realistic constraints on the minimum achievable system time constant are considered. The equations derived for the optimal total system time constant are valuable to the system designer for minimizing miss distance over the ranges of system parameters and limitations, and intercept conditions.
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Summary

A concise theoretical technique is presented for estimating the minimum miss distance capability of command guided missile systems using synthetic proportional navigation. The effect of the parameter values on the system capability is shown to be a function of range-to-intercept; the technique enables the system designer and analyst to quantify...

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Miss distance analysis for command guided missiles

TDWR Scan Strategy Requirements

November 3, 1988
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Project Report
Author:
Steven D. Campbell
…
Published in:
MIT Lincoln Laboratory Report ATC-144
Topic:
radar
R&D area:
R&D group:

Summary

This report describes the requirements for the wan s+rategy to be employed M the
Terminal Doppler Weather Radar (TDWR). The report in divided into three main sections:
rationale, example scan strategy and requirements. The rationale for the TDWR scanstrategy
is presented in terms of 1) detection of meteorological phenomena, and 2) minimization of
range and velocity folding effects. Next, an example is provided based on an experimental scan
strategy used in Denver during the summer of 1987. Finally, the requirements for the TDWR
scan strategy are presented based on the preceding discussion. Also, an appendix is included describing the proposed criteria for switching between scan modes.
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Summary

This report describes the requirements for the wan s+rategy to be employed M the
Terminal Doppler Weather Radar (TDWR). The report in divided into three main sections:
rationale, example scan strategy and requirements. The rationale for the TDWR scanstrategy
is presented in terms of 1) detection of meteorological phenomena, and...

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TDWR Scan Strategy Requirements
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