Publications
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
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, 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.
Summary
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.
Summary
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
Published in:
AIAA Guidance, Navigation and Control Conf. and Exhibit, 18-21 August 2008.
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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 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.
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 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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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 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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Encounter modeling for sense and avoid deployment
May 5, 2008
Conference Paper
Published in:
2008 Integrated Communications, Navigation, and Surveillence Conf., 5-7 May 2008.
Summary
Integrating unmanned aircraft into civil airspace requires the development and certification of systems for sensing and avoiding other aircraft. Because such systems are typically very complex and a high-level of safety must be maintained, rigorous analysis is required before they can be certified for operational use. As part of the certification process, collision avoidance systems need to be evaluated across millions of randomly generated close encounters that are representative of actual operations. New encounter models are under development that capture changes that have occurred in U.S. airspace since earlier models were developed in the 1980s and 1990s. These models capture the characteristics of small, General Aviation aircraft that may not be receiving Air Traffic Control services as well as typically larger aircraft that are squawking a discrete transponder code. Both models allow dynamic changes in airspeed, vertical rates, and turn rates in a way that was not possible previously. This paper describes the process used to construct the encounter models, how the models may be used in the development of sense-and-avoid systems for unmanned aircraft, and their application in an analysis of an electro-optical system for collision avoidance.
Summary
Integrating unmanned aircraft into civil airspace requires the development and certification of systems for sensing and avoiding other aircraft. Because such systems are typically very complex and a high-level of safety must be maintained, rigorous analysis is required before they can be certified for operational use. As part of the...
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Elementary surveillance (ELS) and enhanced surveillance (EHS) validation via Mode S secondary radar surveillance
April 25, 2008
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-337
Summary
Several applications of the Mode S data link are currently being implemented and equipage requirements have been issued in countries around the world. Elementary surveillance (ELS) and enhanced surveillance (EHS) applications have been mandated in Europe with full equipage of all aircraft in the airspace required by 2009. Exemptions to the ELS requirement include aircraft that will be out of service by 31 December 2009, and aircraft undergoing flight-testing, delivery, or transit into or out of maintenance bases. Transport type aircraft (defined as having a maximum take-off weight in excess of 250 knots) are to be equipped to support ELS and EHS. Exemptions to the requirements for EHS include those listed above for ELS and: a- fighter and training aircraft; b- rotary-wing aircraft; c- existing/older transport type aircraft undergoing avionics upgrades which will then support ELS/EHS; and d- aircraft types granted special exemptions (e.g., B1-B, B2-A, and B-52H bombers). [not complete]
Summary
Several applications of the Mode S data link are currently being implemented and equipage requirements have been issued in countries around the world. Elementary surveillance (ELS) and enhanced surveillance (EHS) applications have been mandated in Europe with full equipage of all aircraft in the airspace required by 2009. Exemptions to...
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The next-generation multimission U.S. surveillance radar network
November 1, 2007
Journal Article
Published in:
Bull. American Meteorological Society, Vol. 88, No. 11, November 2007, pp. 1739-1751.
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Summary
Current U.S. weather and aircraft surveillance radar networks vary in age from 10 to more than 40 years. Ongoing sustainment and upgrade programs can keep these operating in the near to mid-term, but the responsible agencies National Weather Service (NWS), Federal Aviation Administration (FAA), and the Departments of Defense (DoD) and Homeland Security (DHS) recognize that large-scale replacement activities must begin during the next decade. The National Weather Radar Testbed (NWRT) in Norman, Oklahoma, is a multiagency project demonstrating operational weather measurements capability enhancements that could be realized using electronically steered phased-array radars as a replacement for the current Weather Surveillance Radar-1988 Doppler (WSR-88D). FAA support for the NWRT and related efforts address air traffic control (ATC) and homeland defense surveillance missions that could be simultaneously accomplished using the agile-beam capability of a phased array weather radar network. In this paper, we discuss technology issues, operational considerations, and cost trades associated with the concept of replacing current national surveillance radars with a single network of multimission phased array radars (MPAR). We begin by describing the current U.S. national weather and aircraft surveillance radar networks and their technical parameters. The airspace coverage and surveillance capabilities of these existing radars provide a starting point for defining requirements for the next-generation airspace surveillance system. We next describe a conceptual MPAR high-level system design and our initial development and testing of critical subsystems. This work, in turn, has provided a solid basis for estimating MPAR costs for comparison with existing, mechanically scanned operational surveillance radars. To assess the numbers of MPARs that would need to be procured, we present a conceptual MPAR network configuration that duplicates airspace coverage provided by current operational radars. Finally, we discuss how the improved surveillance capabilities of MPAR could be utilized to more effectively meet the weather and aircraft surveillance needs of U.S. civil and military agencies.
Summary
Current U.S. weather and aircraft surveillance radar networks vary in age from 10 to more than 40 years. Ongoing sustainment and upgrade programs can keep these operating in the near to mid-term, but the responsible agencies National Weather Service (NWS), Federal Aviation Administration (FAA), and the Departments of Defense (DoD)...
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Analysis of ground surveillance assets to support Global Hawk airspace access at Beale Air Force Base
August 10, 2007
Project Report
Published in:
Project Report ATC-335, MIT Lincoln Laboratory
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Summary
This study, performed from May 2006 to January 2007 by MIT Lincoln Laboratory, investigated the feasibility of providing ground-sensor-based traffic data directly to Global Hawk operators at Beale AFB. The system concept involves detecting and producing tracks for all cooperative (transponder-equipped) and non-cooperative aircraft from the surface to 18,000 ft MSL, extending from the Beale AFB Class C airspace cylinder northward to the China Military Operations Area (MOA). Data from multiple sensors can be fused together to create a comprehensive air surveillance picture, with the altitudes of non-cooperative targets estimated by fusing returns from all available sensor data. Such a capability, if accepted by the FAA, could mitigate the need for Temporary Flight Restrictions (TFR) to satisfy Certificate of Waiver or Authorization (COA) requirements. There are no existing specifications for ground-sensor-based Unmanned Aerial Systems (UAS) traffic avoidance procedures, nor is it yet known how precisely altitude needs to be estimated. It may be possible to avoid traffic laterally, in which case traffic altitude need not be known accurately. If, however, it is necessary to also avoid traffic vertically, then altitudes will need to be estimated to some (as yet undefined) level of accuracy.
Summary
This study, performed from May 2006 to January 2007 by MIT Lincoln Laboratory, investigated the feasibility of providing ground-sensor-based traffic data directly to Global Hawk operators at Beale AFB. The system concept involves detecting and producing tracks for all cooperative (transponder-equipped) and non-cooperative aircraft from the surface to 18,000 ft...
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Macroscopic workload model for estimating en route sector capacity
July 2, 2007
Conference Paper
Published in:
USA/Europe ATM Seminar, 2-5 July 2007.
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Summary
Under ideal weather conditions, each en route sector in an air traffic management (ATM) system has a certain maximum operational traffic density that its controller team can safely handle with nominal traffic flow. We call this the design capacity of the sector. Bad weather and altered flow often reduce sector capacity by increasing controller workload. We refer to sector capacity that is reduced by such conditions as dynamic capacity. When operational conditions cause workload to exceed the capability of a sector's controllers, air traffic managers can respond either by reducing demand or by increasing design capacity. Reducing demand can increase aircraft operating costs and impose delays. Increasing design capacity is usually accomplished by assigning more control resources to the airspace. This increases the cost of ATM. To ensure full utilization of the dynamic capacity and efficient use of the workforce, it is important to accurately characterize the capacity of each sector. Airspace designers often estimate sector capacity using microscopic workload simulations that model each task imposed by each aircraft. However, the complexities of those detailed models limit their real-time operational use, particularly in situations in which sector volumes or flow directions must adapt to changing conditions. To represent design capacity operationally in the United States, traffic flow managers define an acceptable peak traffic count for each sector based on practical experience. These subjective thresholds-while usable in decision-making-do not always reflect the complexity and geometry of the sectors, nor the direction of the traffic flow. We have developed a general macroscopic workload model to quantify the workload impact of traffic density, sector geometry, flow direction, and air-to-air conflict rates. This model provides an objective basis for estimating design capacity. Unlike simulation models, this analytical approach easily extrapolates to new conditions and allows parameter validation by fitting to observed sector traffic counts. The model quantifies coordination and conflict workload as well as observed relationships between sector volume and controller efficiency. The model can support real-time prediction of changes in design capacity when traffic is diverted from nominal routes. It can be used to estimate residual airspace capacity when weather partially blocks a sector. Its ability to identify dominant manual workload factors can also help define the benefits and effectiveness of alternative concepts for automating labor-intensive tasks.
Summary
Under ideal weather conditions, each en route sector in an air traffic management (ATM) system has a certain maximum operational traffic density that its controller team can safely handle with nominal traffic flow. We call this the design capacity of the sector. Bad weather and altered flow often reduce sector...
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