Publications
Encounter models for unconventional aircraft version 1.0
April 10, 2009
Project Report
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MIT Lincoln Laboratory Report ATC-348
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Summary
Airspace encounter models, covering close encounter situations that may occur after standard separation assurance has been lost, are a critical component in the safety assessment of aviation procedures and collision avoidance systems. Of particular relevance to Unmanned Aircraft Systems (UAS) is the potential for encountering general aviation aircraft that are flying under Visual Flight Rules (VFR) and are not in contact with air traffic control. In response to the need to develop a model of these types of encounters, Lincoln Laboratory undertook an extensive data collection and modeling effort involving more than 96,000 unconventional aircraft tracks. The outcome of this effort was nine individual models encompassing ultralights, gliders, balloons, and airships. The models use Bayesian networks to represent relationships between dynamic variables and to construct random trajectories that are statistically similar to those observed in the data. The intruder trajectories can be used in fast-time Monte Carlo simulations to estimate collision risk. The model described in this report is one of three developed by Lincoln Laboratory. A correlated encounter model has been developed to represent situations in which it is likely that there would b e air traffic control intervention prior to a close enounter. The correlated model applies to encounters involving aircraft receiving Air Traffic Control (ATC) services and with transponders. TAn encounter with an intruder that does not have a transponder is uncorrelated in the sense that it is unlikely that there would be prior intervention by air traffic control. The uncorrelated model described in this report is based on global databases of pilot-submitted track data. This work is a follow-on to an uncorrelated conventional model developed from recorded radar tracks from aircraft using a 1200 transponder code. A byproduct of this encounter modeling effort was the extraction of feature distributions for unconventional aircraft. This provides an extensive collection of unconventional aircraft behavior in the airspace.
Summary
Airspace encounter models, covering close encounter situations that may occur after standard separation assurance has been lost, are a critical component in the safety assessment of aviation procedures and collision avoidance systems. Of particular relevance to Unmanned Aircraft Systems (UAS) is the potential for encountering general aviation aircraft that are...
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Airspace encounter models for conventional and unconventional aircraft
March 25, 2009
Conference Paper
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8th USA/Europe Air Traffic Management Research and Development Sem. (ATM 2009), 25 March 2009.
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Collision avoidance systems play an important role in the future of aviation safety. Before new technologies on board manned or unmanned aircraft are deployed, rigorous analysis using encounter simulations is required to prove system robustness. These simulations rely on models that accurately reflect the geometries and dynamics of aircraft encounters at close range. These types of encounter models have been developed by several organizations since the early 1980s. Lincoln Laboratory's newer encounter models, however, provide a higher-fidelity representation of encounters, are based on substantially more data, leverage a theoretical framework for finding optimal model structures, and reflect recent changes in the airspace. Three categories of encounter model were developed by Lincoln Laboratory. Two of these categories are used for modeling conventional aircraft; one involving encounters with prior air traffic control intervention and one without. The third category of encounter model is for encounters with unconventional aircraft -- such as gliders, skydivers, balloons, and airships -- that typically do not carry transponders. Together, these encounter models are being used to examine the safety and effectiveness of aircraft collision avoidance systems and as a foundation for algorithms for future manned and unmanned systems.
Summary
Collision avoidance systems play an important role in the future of aviation safety. Before new technologies on board manned or unmanned aircraft are deployed, rigorous analysis using encounter simulations is required to prove system robustness. These simulations rely on models that accurately reflect the geometries and dynamics of aircraft encounters...
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A comprehensive aircraft encounter model of the National Airspace System
December 1, 2008
Journal Article
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Lincoln Laboratory Journal, Vol. 17, No. 2, December 2008, pp. 41-54.
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Summary
Collision avoidance systems play an important role in the future of aviation safety. Before new technologies on board manned or unmanned aircraft are deployed, rigorous analysis using encounter simulations is required to prove system robustness. These simulations rely on models that accurately reflect the geometries and dynamics of aircraft encounters at close range. These types of encounter models have been developed by several organizations since the early 1980s. Lincoln Laboratory's newer encounter models, however, provide a higher-fidelity representation of encounters, are based on substantially more radar data, leverage a theoretical framework for finding optimal model structures, and reflect recent changes in the airspace.
Summary
Collision avoidance systems play an important role in the future of aviation safety. Before new technologies on board manned or unmanned aircraft are deployed, rigorous analysis using encounter simulations is required to prove system robustness. These simulations rely on models that accurately reflect the geometries and dynamics of aircraft encounters...
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Automatic dependent surveillance-broadcast in the Gulf of Mexico
December 1, 2008
Journal Article
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Lincoln Laboratory Journal, Vol. 17, No. 2, December 2008, pp. 55-69.
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The Federal Aviation Administration is adopting Automatic Dependent Surveillance-Broadcast (ADS-B) to provide surveillance in the National Airspace System (NAS). Aircraft separation services are currently provided by a system of en route and terminal radars, and the performance of these radars in part dictates the separation distance required between aircraft. ADS-B is designed to provide comparable service in areas where no radar coverage exists. It will eventually be the primary surveillance source in the NAS, if it is proven to provide performance equal to or better than radar.
Summary
The Federal Aviation Administration is adopting Automatic Dependent Surveillance-Broadcast (ADS-B) to provide surveillance in the National Airspace System (NAS). Aircraft separation services are currently provided by a system of en route and terminal radars, and the performance of these radars in part dictates the separation distance required between aircraft. ADS-B...
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Uncorrelated encounter model of the National Airspace System version 1.0
November 14, 2008
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-345
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Summary
Airspace encounter models, covering close encounter situations that may occur after standard separation assurance has been lost, are a critical component in the safety assessment of aviation procedures and collision avoidance systems. Of particular relevance to Unmanned Aircraft Systems (UAS) is the potential for encountering general aviation aircraft that are flying under Visual Flight Rules (VFR) and which may not be in contact with air traffic control. In response to the need to develop a model of these types of encounters, Lincoln Laboratory undertook an extensive radar data collection and modeling effort involving more than 120 sensors across the U.S. This report describes the structure and content of that encounter model. The model is based on the use of Bayesian networks to represent relationships between dynamic variables and to construct random aircraft trajectories that are statistically similar to those observed in the radar data. The result is a framework from which representative intruder trajectories can be generated and used in fast-time Monte Carlo simulations to provide accurate estimates of collision risk. The model described in this report is one of three developed by Lincoln Laboratory. An encounter with an intruder that does not have a transponder, or between two aircraft using a Mode A code of 1200 (VFR), is uncorrelated in the sense that it is unlikely that there would be prior intervention by air traffic control. The uncorrelated model described in this report is based on transponder-equipped aircraft using a 1200 (VFR) Mode A code observed by radars across the U.S. As determined from a comparison against primary-only tracks, in addition to representing VFR-on-VFR encounters, this model is representative of encounters between a cooperative aircraft and conventional noncooperative aircraft similar to those that use a 1200 transponder code. A second uncorrelated model is also being developed for unconventional aircraft that have different flight characteristics than 1200-code aircraft. Finally, a correlated encounter model has been developed to represent situations in which it is likely that there would be air traffic control intervention prior to a close encounter. The correlated model applies to intruders that are using a discrete (non-1200) code. Separate electronic files are available from Lincoln Laboratory that contain the statistical data required to generate and validate encounter trajectories. Details on how to interpret the data file and an example of how to randomly construct trajectories are provided in Appendices A and B, respectively. A Matlab software package is also available to generate random encounter trajectories based on the data tables. A byproduct of the encounter modeling effort was the development of National aircraft track and traffic density databases. Example plots of traffic density data are provided in this report, but the complete track and density databases are not provided in electronic form due to their size and the complexity of processing specific locations, altitudes, and times.
Summary
Airspace encounter models, covering close encounter situations that may occur after standard separation assurance has been lost, are a critical component in the safety assessment of aviation procedures and collision avoidance systems. Of particular relevance to Unmanned Aircraft Systems (UAS) is the potential for encountering general aviation aircraft that are...
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Correlated encounter model for cooperative aircraft in the National Airspace System, version 1.0
October 24, 2008
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-344
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This document describes a new cooperative aircraft encounter model for the National Airspace System (NAS). The model is used to generate random close encounters between transponder-equipped (cooperative) aircraft in fast-time Monte Carlo simulations to evaluate collision avoidance system concepts. An extensive set of radar data from across the United States, including more than 120 sensors and collected over a period of nine months, was used to build the statistical relationships in the model to ensure that the encounters that are generated are representative of actual events in the airspace.
Summary
This document describes a new cooperative aircraft encounter model for the National Airspace System (NAS). The model is used to generate random close encounters between transponder-equipped (cooperative) aircraft in fast-time Monte Carlo simulations to evaluate collision avoidance system concepts. An extensive set of radar data from across the United States...
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A Bayesian approach to aircraft encounter modeling
August 18, 2008
Conference Paper
Published in:
AIAA Guidance, Navigation, and Control Conf., 18-21 August 2008.
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Aircraft encounter models can be used in a variety of analyses, including collision avoidance system safety assessment, sensor design trade studies, and visual acquisition analysis. This paper presents an approach to airspace encounter model construction based on Markov models estimated from radar data. We use Bayesian networks to represent the distribution over initial states and dynamic Bayesian networks to represent transition probabilities. We apply Bayesian statistical techniques to identify the relationships between the variables in the model to best leverage a large volume of raw aircraft track data obtained from more than 130 radars across the United States.
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Aircraft encounter models can be used in a variety of analyses, including collision avoidance system safety assessment, sensor design trade studies, and visual acquisition analysis. This paper presents an approach to airspace encounter model construction based on Markov models estimated from radar data. We use Bayesian networks to represent the...
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Applications of a macroscopic model for en route sector capacity
August 18, 2008
Conference Paper
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AIAA Guidance, Navigation and Control Conf. and Exhibit, 18-21 August 2008.
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Airspace capacity estimates are important both for airspace design and for operational air traffic management. Considerable effort has gone into understanding the complexity factors that reduce sector capacity by increasing controller workload. Yet no analytical means is available for accurately estimating the maximum capacity of an en route sector. The Monitor Alert Parameter (MAP) values that determine the operational traffic limit of en route sectors in the United States account only for workload from inter-sector coordination tasks. We propose a more complete sector capacity model that also accounts for workload from conflict avoidance and recurring tasks. We use mean closing speeds and airspace separation standards to estimate aircraft conflict rates. We estimate the mean controller service times for all three task types by fitting the model against observed peak traffic counts for hundreds of en route airspace volumes in the Northeastern United States. This macroscopic approach provides numerical capacity predictions that closely bound peak observed traffic densities for those airspace volumes. This paper reviews recent efforts to improve the accuracy of the bound by replacing certain global parameters with measured data from individual sectors. It also compares the model capacity with MAP values for sectors in the New York Center. It concludes by illustrating the use of the model to predict the capacity benefits of proposed technological and operational improvements to the air traffic management system.
Summary
Airspace capacity estimates are important both for airspace design and for operational air traffic management. Considerable effort has gone into understanding the complexity factors that reduce sector capacity by increasing controller workload. Yet no analytical means is available for accurately estimating the maximum capacity of an en route sector. The...
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Electro-optical system analysis for sense and avoid
August 18, 2008
Conference Paper
Published in:
AIAA Guidance, Navigation, and Control Conf. and Exhibit, 19-21 August 2008.
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This paper presents a parametric analysis of the sense and avoid capability for an electro- optical system on unmanned aircraft. Our sensor analysis is based on simulated encounters from a new U.S. airspace encounter model that provides a comprehensive distribution of typical visual flight rule (VFR) aircraft behavior and encounter geometries. We assess the exchange between the sensor field-of-view shape and detection range with the probability of intruder detection prior to near miss. This assessment also includes a trade-off analysis between field-of-view azimuth angle and probability of detection with fixed tracking technology (i.e. pixel array sensor and tracking algorithm). Initial results suggest that current standards are suitable for detecting larger aircraft but may not be ideal for small aircraft such as ultralights.
Summary
This paper presents a parametric analysis of the sense and avoid capability for an electro- optical system on unmanned aircraft. Our sensor analysis is based on simulated encounters from a new U.S. airspace encounter model that provides a comprehensive distribution of typical visual flight rule (VFR) aircraft behavior and encounter...
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Hazard alerting using line-of-sight rate
August 18, 2008
Conference Paper
Published in:
AIAA Guidance, Navigation, and Control Conf., 18-21 August 2008.
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This paper presents an analysis of an electro-optical hazard alerting system based on intruder line-of-sight rate. We use a recently-developed airspace encounter model to analyze intruder line-of-sight rate behavior prior to near miss. We look at a simple hazard alerting system that alerts whenever the line-of-sight rate drops below some set threshold. Simulations demonstrate that such an approach, regardless of the chosen threshold, leads to frequent false alerts. We explain how the problem of hazard alerting can also be formulated as a partially observable Markov decision process (POMDP) and show how such an approach significantly decreases the false alert rate.
Summary
This paper presents an analysis of an electro-optical hazard alerting system based on intruder line-of-sight rate. We use a recently-developed airspace encounter model to analyze intruder line-of-sight rate behavior prior to near miss. We look at a simple hazard alerting system that alerts whenever the line-of-sight rate drops below some...
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