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TCAS-II: design and validation of the high-traffic-density surveillance subsystem

February 12, 1985
  |
Project Report
Author:
William H. Harman III
…
Published in:
MIT Lincoln Laboratory Report ATC-126
Topic:
collision avoidance
R&D area:
R&D group:

Summary

Lincoln Laboratory, under FAA sponsorship, is developing an airborne collision avoidance system (TCAS II), concentrating primarily on the air-to-air surveillance subsystem. The surveillance functions required are to detect the presence of nearby transponder equipped aircraft, and then generate a surveillance track on each aircraft, issuing range and altitude reports once per second. The development effort from mid-1981 to the present has focused on the surveillance problems associated with high aircraft density. A number of surveillance techniques to deal with the high density environment have been identified and evaluated mainly through airborne measurements. A TCAS II design was synthesized, and this design was subjected to in-flight testing in the Los Angeles Basin using a Boeing 727. Results indicate that the performance objectives have been met.
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Summary

Lincoln Laboratory, under FAA sponsorship, is developing an airborne collision avoidance system (TCAS II), concentrating primarily on the air-to-air surveillance subsystem. The surveillance functions required are to detect the presence of nearby transponder equipped aircraft, and then generate a surveillance track on each aircraft, issuing range and altitude reports once...

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TCAS-II: design and validation of the high-traffic-density surveillance subsystem

TCAS II ATCRBS surveillance algorithms

January 28, 1985
  |
Project Report
Author:
M. Loren Wood Jr
Published in:
MIT Lincoln Laboratory Report ATC-131
Topic:
surveillance
R&D area:
R&D group:

Summary

The Traffic Alert and Collision Avoidance System (TCAS) has been developed to reduce mid air collisions between transponder equipped aircraft. The TCAS concept encompasses a range of capabilities. TCAS I is a low-cost version which provides traffic advisories only. TCAS II adds vertical resolution advisories and is intended to provide a comprehensive level of separation assurance in all current and predicted airspace environments through the end of this century. Enhanced TCAS II uses more accurate intruder bearing data to allow it to generate horizontal resolution advisories. All three forms of TCAS equipment track aircraft equipped with both the existing Air Traffic Control Radar Beacon System (ATCRBS) transponders and with the new Mode S transponders. A TCAS equipped aircraft makes ATCRBS or Mode S range measurements on nearby aircraft. The ATCRBS or Mode S replies contain the altitude of the aircraft if it has an encoding altimeter. TCAS II uses range rate and altitude rate to decide if a collision is imminent. Therefore the replies from a given aircraft must be tracked and correlated in range and altitude. This report documents surveillance techniques developed by Lincoln Laboratory for use by TCAS II equipment in tracking aircraft equipped with ATCRBS transponders. Specifically, it describes the two tracking algorithms used for ATCRBS replies. One algorithm is for aircraft that report altitude, and the other is for those that do not.
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Summary

The Traffic Alert and Collision Avoidance System (TCAS) has been developed to reduce mid air collisions between transponder equipped aircraft. The TCAS concept encompasses a range of capabilities. TCAS I is a low-cost version which provides traffic advisories only. TCAS II adds vertical resolution advisories and is intended to provide...

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TCAS II ATCRBS surveillance algorithms

A gust front case studies handbook

January 10, 1985
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Project Report
Author:
Diana L. Klingle-Wilson
…
Published in:
MIT Lincoln Laboratory Report ATC-129
Topic:
doppler radar
R&D area:
R&D group:

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 radars efficiently, automatic detection of such hazards is essential. Eight gust front case studies are presented. The data include photographs of the Doppler weather radar displays, thermodynamic and wind measurements from a 440 m high tower, environmental soundings and tables of gust front characteristics. The tabulated characteristics are those thought to be most important in developing rules for automatic gust front detection such as length and height, maximum and minimum values of reflectivity, velocity and spectrum width, and estimates of radial shear. For the cases studied, outflows could be detected most reliably in the velocity field, but useful information also could be gleaned from the spectrum width and reflectivity fields. The signal-to-noise ratio threshold was found to be a major factor in the ability of an observer to discern the gust front signature in the Doppler radar displays. Detection within the spectrum width field required a higher SNR than did the radial velocity field.
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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 radars efficiently, automatic detection of such hazards is essential. Eight...

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A gust front case studies handbook

Air-to-air visual acquisition performance with TCAS II

November 7, 1984
  |
Project Report
Author:
John W. Andrews
Published in:
MIT Lincoln Laboratory Report ATC-130
Topic:
collision avoidance
R&D area:
R&D group:

Summary

The ability of pilots to visually acquire aircraft approaching on collision cources is analyzed using a mathematical model of visual acquisition. The model is calibrated by reference to subject pilot flight test data resulting from testing of the Traffic Alert and Collision Avoidance System (TCAS). Techniques are presented that allow the determination of the probability of visual acquisition for a range of intruder aircraft sizes and closing rates. The effect of visual range (atmospheric visibility) upon visual acquisition performance is analyzed.
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Summary

The ability of pilots to visually acquire aircraft approaching on collision cources is analyzed using a mathematical model of visual acquisition. The model is calibrated by reference to subject pilot flight test data resulting from testing of the Traffic Alert and Collision Avoidance System (TCAS). Techniques are presented that allow...

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Air-to-air visual acquisition performance with TCAS II

An automatic weather station network for low-altitude wind shear investigations

September 18, 1984
  |
Project Report
Author:
Diana L. Klingle-Wilson
…
Published in:
MIT Lincoln Laboratory Report ATC-128
Topic:
weather
R&D area:
R&D group:

Summary

During the summer of 1983 an experimental network of automatic weather stations (a mesonet) was operated in the vicinity of Hanscom Field, northwest of Boston, as part of a larger effort to collect Doppler radar and meteorological data on thunderstorms and other potentially hazardous weather events in this area. This report describes the mesonet system used and presents in detail the data collected on 21-22 July 1983. Conclusions about the limitations and the future use of the mesonet system are also included.
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Summary

During the summer of 1983 an experimental network of automatic weather stations (a mesonet) was operated in the vicinity of Hanscom Field, northwest of Boston, as part of a larger effort to collect Doppler radar and meteorological data on thunderstorms and other potentially hazardous weather events in this area. This...

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An automatic weather station network for low-altitude wind shear investigations

A comparison of storm tracking and extrapolation algorithms

July 31, 1984
  |
Project Report
Author:
John C. Brasunas
Published in:
MIT Lincoln Laboratory Report ATC-124
Topic:
weather
R&D area:
R&D group:

Summary

The FAA requires short-term forecasts of the development and motion of high reflectivity regions to plan for weather avoidance in the en route and terminal areas. Specific needs include choice of air routes and anticipating when to open or close approach/departure gates, descent corridors, and runways. This report compares storm-tracking algorithms for making short-term (0-30 minute) forecasts of high reflectivity areas, to serve these air traffic control needs. The area forecasts are made by moving the key features of the current reflectivity map according to the velocities derived from the storm trackers. The NEXRAD centroid, correlation, and Crane peak-cell trackers are compared against themselves, persistence, and a best-fit extrapolation. Two performance measures are used: (a) overlap of predicted versus actual areas (b) accuracy in flight-path choice. The second method is a new way of scoring the predictor performance and is particularly suited to aviation needs. Five storms are considered, three in Massachusetts and two in Oklahoma. The correlation and peak-cell trackers generally performed well in the Massachusetts storms, close to a best correlation fit extrapolator. The centroid tracker behaves erratically, due to contour merging and splitting. The centroid tracker performed well on compact, Oklahoma storms where the correlation and peak-cell trackers were misled by storm propagation, an effect to be expected when there is high vertical shear of the horizontal wind. It is recommended that either the correlation or centroid tracker be used, depending on the type of storm expected. The centroid tracker would be used on compact storms; the correlation tracker would be used on storms without substantial propagation. The forecasts appear to be skillful in predicting high-reflectivity areas; however, they are less skillful in anticipating flight-paths which do not intersect these areas. Inclusion of forecasts of storm growth and decay will probably be required to improve the performance; anticipating growth and decay will also be important for forecasts of greater than 30 minutes.
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Summary

The FAA requires short-term forecasts of the development and motion of high reflectivity regions to plan for weather avoidance in the en route and terminal areas. Specific needs include choice of air routes and anticipating when to open or close approach/departure gates, descent corridors, and runways. This report compares storm-tracking...

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A comparison of storm tracking and extrapolation algorithms

Rain rate climatologies over marine regions

May 1, 1984
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Project Report
Author:
Andreas K. Goroch
…
Published in:
no published logic to cover case - index 63
Topic:
weather
R&D area:
R&D group:

Summary

A method to relate archived marine meteorological observations to two-minute average rain rates is described. The method is used to produce maps that indicate the frequency of observation of critical rain rates (5, 8, and 15 mm/hr) for the Atlantic, North Pacific and Indian Oceans.
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Summary

A method to relate archived marine meteorological observations to two-minute average rain rates is described. The method is used to produce maps that indicate the frequency of observation of critical rain rates (5, 8, and 15 mm/hr) for the Atlantic, North Pacific and Indian Oceans.

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Rain rate climatologies over marine regions

Fundamentals of mode S parity coding

April 2, 1984
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Project Report
Author:
Jeffrey L. Gertz
Published in:
MIT Lincoln Laboratory Report ATC-117
Topic:
mode S data links
R&D area:
R&D group:

Summary

This report presents the details and basic theory of the coding scheme employed on Mode S uplink and downlink transmissions. Since ATCRBS interference is the main source of error for these signals, a cyclic burst detection code was chosen for Mode S. This code permits simple error detection at the transponder and more complex error correction at the sensor. The theory behind cyclic encoding and decoding as used for Mode S is presented first. Then, since polynomial multiplication and division are required for these processes, circuits for these operations are described. Finally, the last chapter describes the actual implementations specified for encoding and decoding in both the transponder and sensor.
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Summary

This report presents the details and basic theory of the coding scheme employed on Mode S uplink and downlink transmissions. Since ATCRBS interference is the main source of error for these signals, a cyclic burst detection code was chosen for Mode S. This code permits simple error detection at the...

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Fundamentals of mode S parity coding

Adaptive noise cancellation in a fighter cockpit environment

March 19, 1984
  |
Conference Paper
Author:
William A. Harrison
…
Published in:
ICASSP'84, IEEE Int. Conf. on Acoustics, Speech and Signal Processing, 19-21 March 1984.
Topic:
speech
R&D area:
R&D group:

Summary

In this paper we discuss some preliminary results on using Widrow's Adaptive Noise Cancelling (ANC) algorithm to reduce the background noise present in a fighter pilot's speech. With a dominant noise source present and with the pilot wearing an oxygen facemask, we demonstrate that good (>10 dB) cancellation of the additive noise and little speech distortion can be achieved by having the reference microphone attached to the outside of the facemask and by updating the filter coefficients only during silence intervals.
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Summary

In this paper we discuss some preliminary results on using Widrow's Adaptive Noise Cancelling (ANC) algorithm to reduce the background noise present in a fighter pilot's speech. With a dominant noise source present and with the pilot wearing an oxygen facemask, we demonstrate that good (>10 dB) cancellation of the...

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Adaptive noise cancellation in a fighter cockpit environment

A high stability TWTA for ground surveillance applications

March 13, 1984
  |
Conference Paper
Author:
C. E. Hayse
…
Published in:
Proc. 1984 IEEE Natl. Radar Conf., 13-14 March 1984, pp. 110-114.
Topic:
radar
R&D area:
R&D group:

Summary

A high stability, C-band transmitter capable of supporting -68 dBr subclutter visibility over a wide range of pulse widths and duty factors was developed for use in a multimode, battlefield surveillance radar. The transmitter was mode-switched between groups of 1/4, 20 and 65 microsecond radar pulses and long duration (100ms) FSK burst. A key feature was the use of a high speed, interpulse regulator to maintain proper TWT voltage and to limit ripple independent of waveform without the need for excessively large energy storage. Actual measured performance met the 100 mV cathode ripple specification without the use of PKF synchronization, independent of PKI, duty cycle and pulse width and was confirmed via direct evaluation of electrode voltages, serrodyne phase jitter and the radar pulsed-Doppler spectrum.
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Summary

A high stability, C-band transmitter capable of supporting -68 dBr subclutter visibility over a wide range of pulse widths and duty factors was developed for use in a multimode, battlefield surveillance radar. The transmitter was mode-switched between groups of 1/4, 20 and 65 microsecond radar pulses and long duration (100ms)...

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A high stability TWTA for ground surveillance applications
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