Publications
The Experimental Integrated Switched Network - a system-level network test facility
October 31, 1983
Conference Paper
Published in:
Proc. 1983 IEEE Military Communications Conf., MILCOM, 31 October-2 November 1983.
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Summary
An Experimental Integrated Switched Network (EISN) has been developed to provide a system-level testbed for the evaluation of advanced communications networking techniques, including survivable network routing algorithms using a mix of transmission media, for application in the Defense Switched Network (DSN). EISN includes five CONUS sites linked by a wideband demand-assigned satellite channel and by dialed-up terrestrial trunks for alternate satellite/terrestrial routing experiments. Experiments to date have validated techniques for integration of circuit-switched terrestrial systems with the demand-assigned satellite system, and for the establishment of alternate routes over satellite and terrestrial paths. Currently, candidate routing algorithms for application in the DSN are being implemented and tested using external routing/controller processors attached to digital circuit switches at EISN sites. In addition, EISN is also being used to support data communication experiments using DoD standard data protocols in a combined satellite/terrestrial network environment. Work is ongoing both in system experiments and in testbed developments to include additional capabilities. This paper represents a description and status report on both the testbed and the experimental efforts.
Summary
An Experimental Integrated Switched Network (EISN) has been developed to provide a system-level testbed for the evaluation of advanced communications networking techniques, including survivable network routing algorithms using a mix of transmission media, for application in the Defense Switched Network (DSN). EISN includes five CONUS sites linked by a wideband...
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Airborne Intelligence Display (AID) phase I software description
October 24, 1983
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-123
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The Airborne Intelligent Display is a microprocessor-based display capable of serving as a cockpit data terminal in a variety of FAA developmental applications. A prototype of this display was developed by Lincoln Laboratory during 1979-1980 in order to evaluate and demonstrate the use of the data link between Mode S ground sensor and Mode S transponder-equipped aircraft. The AID served as a data link interface allowing the pilot to see, respond to, and initiate communications from a ground sensor. Later, when Lincoln began testing the Traffic Alert and Collision Avoidance System (TCAS), the AID became the TCAS display device, showing position estimates for TCAS-tracked aircraft. More recently, a redesign effort, focused principally on software, was begun to extend the AID design so that it could be more quickly adapted to a variety of FAA developmental programs. This document describes the redesigned Airborne Intelligent Display, with special emphasis on software design.
Summary
The Airborne Intelligent Display is a microprocessor-based display capable of serving as a cockpit data terminal in a variety of FAA developmental applications. A prototype of this display was developed by Lincoln Laboratory during 1979-1980 in order to evaluate and demonstrate the use of the data link between Mode S...
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Ground clutter cancellation for the NEXRAD system
October 19, 1983
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-122
Summary
Returns from the ground and associated obstacles surroudning a NEXRAD weather radar (i.e., ground clutter) will contaminate the estimates of weather echo spectral features (e.g., reflectivity, mean velocity, and spectral width). The ground clutter returns are particularly large at low elevation angles and close range (e.g., within 40 km). Additionally, the pulse repetition frequency (PRF) values necessary to obtain the desired weather Doppler features result in ground clutter contamination at ranges that are multiples of the unambiguous range interval (e.g., 115-175 km for a typical NEXRAD). Fortunately, the groung clutter power spectrum is localized around zero velocity so that one can reduce its effect by appropriate Doppler signal processing. Automatic reduction of clutter contamination is essential if NEXRAD is to achieve the desired automatic weather product generation capability. The results of an analytical/experimental study oreinted toward development of a clutter cancellation specification and assiciated quality assurance tests for the NEXRAD system are described.
Summary
Returns from the ground and associated obstacles surroudning a NEXRAD weather radar (i.e., ground clutter) will contaminate the estimates of weather echo spectral features (e.g., reflectivity, mean velocity, and spectral width). The ground clutter returns are particularly large at low elevation angles and close range (e.g., within 40 km). Additionally...
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A traffic alert and collision avoidance system for general aviation
October 1, 1983
Conference Paper
Published in:
IEEE/AIAA 5th Digital Avionics Systems Conf., Seattle, WA, 31 October - 3 November 1983, pp. 20.
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One component of the Federal Aviation Administration approach to independent aircraft separation assurance is known as the Traffic Alert and Collision Avoidance System I (TCAS I), which employs passive or active techniques for the detection of nearby transponder-equipped aircraft. This paper gives the results of a study conducted by Lincoln Laboratory of simple techniques for the passive and active detection of transponders. Filter criteria that may be used to restrict passive detections to potentially threatening aircraft are described and evaluated. These techniques and criteria were used in a candidate passive detector whose performance was evaluated in flight against targets of opportunity. A candidate low-power active interrogator was also evaluated through link calculations and airborne measurements. The results indicate that a low-power active interrogator can provide more reliable detection of nearby aircraft and a lower false alert rate than any of the simple passive techniques considered. The active technique generates insignificant levels of interference and, unlike a passive system, also provides protection in regions where there are no ground interrogators.
Summary
One component of the Federal Aviation Administration approach to independent aircraft separation assurance is known as the Traffic Alert and Collision Avoidance System I (TCAS I), which employs passive or active techniques for the detection of nearby transponder-equipped aircraft. This paper gives the results of a study conducted by Lincoln...
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An experimental GPS navigation receiver for general aviation: design and measured performance
September 27, 1983
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-121
Summary
This report describes work performed by MIT Lincoln Laboratory between 1 October 1979 and 1 March 1983, to evaluate the use of the Global Positioning System (GPS) for low-cost civil air navigation. The report describes a GPS Test and Evaluation System developed jointly by MIT Lincoln Laboratory, Stanford Telecommunications, Inc., and Intermetrics, Inc., using techniques that could lead to low-cost commercial avionics. System performance results obtained in the laboratory and during flight tests are provided which demonstrate compliance with current and future navigation accuracy requirements for enroute, terminal, and non-precision flight paths. The report also includes functional specifications for a low-cost GPS navigation system for civil aircraft. The GPS Test and Evaluation system design was based on two important features: 1) automatic tracking of all visible satellites (rather than a minimum set of four) and 2) a dual-channel GPS C/A code receiver. Tracking all visible satellites allows the system to maintain continuous navigation when a satellite sets or is momentarily masked during aircraft maneuvers. The dual-channel receiver dedicates one channel to pseudo-range measurements, and the other channel to acquiring new satellites as they become visible. These two features, validated by flight test, allow the system to provide continuous navigation updates during critical aircraft maneuvers, such as non-precision approaches, and during satellite constellation changes.
Summary
This report describes work performed by MIT Lincoln Laboratory between 1 October 1979 and 1 March 1983, to evaluate the use of the Global Positioning System (GPS) for low-cost civil air navigation. The report describes a GPS Test and Evaluation System developed jointly by MIT Lincoln Laboratory, Stanford Telecommunications, Inc...
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Doppler radar observations of an Oklahoma downburst
September 23, 1983
Conference Paper
Published in:
21st Conf., on Radar Meteorology, 19-23 September 1983, pp. 590-595.
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"Downbursts", first discovered by Dr. T. T. Fujita, are small intense downdrafts at very low altitudes which impact the surface and cause a divergent outflow of wind. They can occur under a variety of meteorological conditions as was demonstrated during the JAWS 1982 field experiment which took place in the vicinity of Stapleton airport in Denver, CO. Many downbursts were detected but most of them were of the type now being called "dry" or "cumulus" or "virga" downbursts. A distinction must be made between these and the "wet" or "thunderstorm" downbursts which are the subject of this study. The two phenomena are very different. They are easy to distinguish: the former come from benign looking cumulus clouds and fall through a very deep and dry subcloud layer and the latter are associated with thunderstorms. Thunderstorm downbursts have been detected throughout the Great Plains and the Midwest, on the east coast, and in Florida, while the virga downbursts have been detected mainly over the high plains east of the Rockies. The word "downburst" was first introduced by Fujita (1976) after the investigation of a plane crash at JFK airport, to describe the situation in which a thunderstorm downdraft becomes hazardous to the operation of jet aircraft on take-off or landing. At first, Fujita (1979) thought that the downburst and the well known thunderstorm downdraft were essentially the same but that, in the same way a funnel cloud aloft is not called a tornado, a mid-level downdraft in a thunderstorm would not be called a downburst. The concept was later refined when it was decided that the downburst must induce "an outburst of damaging winds on or near the ground" (Fujita and Wakimoto, 1981) where "damaging winds" refers to winds that can be estimated on the F-scale (for which there minimum threshold is 18 m/s). These damaging winds can be either straight or curved but they must be highly divergent (Fujita, 1981). Thus, even in its most recent and more meteorological definition, the term downburst is meant to signify a potential human hazard. Whether of not it also signifies a dynamically distinct phenomenon in thunderstorms is a matter of some debate and one which will be investigated in the current work.
Summary
"Downbursts", first discovered by Dr. T. T. Fujita, are small intense downdrafts at very low altitudes which impact the surface and cause a divergent outflow of wind. They can occur under a variety of meteorological conditions as was demonstrated during the JAWS 1982 field experiment which took place in the...
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Mode S Beacon System: Functional Description (Revision C)
July 15, 1983
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-42,C
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This document provides a functional description of the Mode S Beacon Systme, a combined secondary surveillance radar (beacon) and ground-air-ground data link system capable of providing the aircraft surveillance and communications necessary to support ATC automation in future traffic environments. Mode S is capable of common-channel interoperation with the current ATC beacon system, and may be implemented at low user cost over an extended transition period. Mode S will provide the surveillance and communication performance required by the ATC automation, the reliable communications needed to support data link services, and the capability of operating with a terminal or enroute, radar digitizer-equipped, ATC surveillance radar. The material contained in this document updates and expands the information presented in "Mode S Beacon System: Functional Description", DOT/FAA/RD-82/52, 27 October 1982.
Summary
This document provides a functional description of the Mode S Beacon Systme, a combined secondary surveillance radar (beacon) and ground-air-ground data link system capable of providing the aircraft surveillance and communications necessary to support ATC automation in future traffic environments. Mode S is capable of common-channel interoperation with the current...
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Short-term prediction of high reflectivity contours for aviation safety
June 9, 1983
Conference Paper
Published in:
Proc. Ninth Conf. Aerospace and Aeronautical Meteorology, 6-9 June 1983, pp. 118-122.
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Airspace utilization and safety could benefit significantly from accurate, real-time, short-term predictions of hazardous weather regions (e.g., 5-30 minutes). For some hazards, such as heavy turbulence, the detection process itself is in an immature stage. No universally accepted algorithm exists for indicating the regions of current turbulence - let alone predicting it. For other hazards, such as hail and more particularly for heavy rain, the detection process is in a more mature state. In fact heavy rain may be unambiguously associated with high dBZ (reflectivity), if no ice phases are present. Hail is also associated with high reflectivities. We have therefore chosen to place our initial emphasis on the prediction of reflectivity contours in the context of ATC (air traffic control) operations. For all or our prediction techniques, we begin by collecting fixed dBZ-level contours on a fixed-elevation scan by fixed-elevation scan basis, and then combining these elevation cell slices into volume cells as is done in the algorithm of Bjerkaas and Forsyth (1980). To these volume cells we attach translations vectors to make the desired prediction: at this time no provision is made for the growth or decay of reflectivity cells. We generate our translation vectors using each of several algorithms which have already been described elsewhere. Firstly, we use the centroid-tracking approach of Bjerkaas and Forsyth (1980). This is the current tracker of choice in the NEXRAD (Next Generation Weather Radar) program. Secondly, we use tracking vectors of clusters of volume cells, as described ny Crane (1979): much of this work was performed under the sponsorship of the Federal Aviation Administration (FAA). Thirdly, we generate translation vectors by cross-correlating low-altitude (0-4 cm) CAPPIs (constant-altitude plan position indicators): this correlation is done either for the entire storm, or for 30 km by 30 km segments of the storm. This approach has been motivated by the work of Rinehart and Garvey (1978), although we generally use a CAPPI of liquid water content. Fourthly, we use as a prediction the current, composite reflectivity map - our so-called status-quo prediction.
Summary
Airspace utilization and safety could benefit significantly from accurate, real-time, short-term predictions of hazardous weather regions (e.g., 5-30 minutes). For some hazards, such as heavy turbulence, the detection process itself is in an immature stage. No universally accepted algorithm exists for indicating the regions of current turbulence - let alone...
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Traffic Alert and Collision Avoidance System (TCAS): a functional overview of minimum TCAS II
April 8, 1983
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-119
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The Traffic Alert and Collision Avoidance System (TCAS) is a beanon-based airborne collision avoidance system that is able to operate in all airspace without reliance on ground equipment. The TCAS concept encompasses a range of capabilities that include TCAS I, a low-cost, limited-perofrmance version, and TCAS II, which is intended to provide a comprehensive level of separation assurance in all current and predicted airspace environments through the end of this century. This document provides a functional overview of the TCAS II including operating features, a description of the avionics package, and examples of surveillance data obtained with experimental TCAS equipment.
Summary
The Traffic Alert and Collision Avoidance System (TCAS) is a beanon-based airborne collision avoidance system that is able to operate in all airspace without reliance on ground equipment. The TCAS concept encompasses a range of capabilities that include TCAS I, a low-cost, limited-perofrmance version, and TCAS II, which is intended...
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Traffic Alert and Collision Avoidance System (TCAS): a functional overview of active TCAS I
April 8, 1983
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-118
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Summary
The Traffic Alert and Collision Avoidance System (TCAS) is a beacon-based airborne collision avoidance system that is able to operate in all airspace without reliance on ground equipment. The TCAS concept encompasses a range of capabilities that include TCAS I, a low-cost, limited-performance version, and TCAS II, which is intended to provide a comprehensive level of separation assurance in all current and predicted airspace enviornments through the end of this century. This document provides a functional overview of a TCAS I equipped with a low power active transponder detector. It includes a definition of TCAS I functions, calculated and measured surveillance performance for a low power interrogator and an implementation approach that incorporates the TCAS I functions in a Mode S transponder.
Summary
The Traffic Alert and Collision Avoidance System (TCAS) is a beacon-based airborne collision avoidance system that is able to operate in all airspace without reliance on ground equipment. The TCAS concept encompasses a range of capabilities that include TCAS I, a low-cost, limited-performance version, and TCAS II, which is intended...
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