Publications
Bioinspired resource management for multiple-sensor target tracking systems
March 7, 2011
Conference Paper
Published in:
2011 IEEE Aerospace Conf., 5-12 March 2011.
Summary
We present an algorithm, inspired by self-organization and stigmergy observed in biological swarms, for managing multiple sensors tracking large numbers of targets. We devise a decentralized architecture wherein autonomous sensors manage their own data collection resources and task themselves. Sensors cannot communicate with each other directly; however, a global track file, which is continuously broadcast, allows the sensors to infer their contributions to the global estimation of target states. Sensors can transmit their data (either as raw measurements or some compressed format) only to a central processor where their data are combined to update the global track file. We outline information-theoretic rules for the general multiple-sensor Bayesian target tracking problem. We provide specific formulas for problems dominated by additive white Gaussiannoise. Using Cramer-Rao lower bounds as surrogates for error covariances, we illustrate, using numerical scenarious involving ballistic targets, that the bioinspired algorithm is highly scalable and peforms very well for large numbers of targets.
Summary
We present an algorithm, inspired by self-organization and stigmergy observed in biological swarms, for managing multiple sensors tracking large numbers of targets. We devise a decentralized architecture wherein autonomous sensors manage their own data collection resources and task themselves. Sensors cannot communicate with each other directly; however, a global track...
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Measurement of the absolute Raman scattering cross sections of sulfur and the standoff Raman detection of a 6-mm-thick sulfur specimen at 1500m
March 1, 2011
Journal Article
Published in:
J. Raman Spectr., Vol. 42, No. 3, March 2011, pp. 461-464.
Summary
The absolute Raman scattering cross sections (σRS) for the 471, 217, and 153 cm−1 modes of sulfur were measured as 6.0 ± 1.2 × 10−27, 7.7 ± 1.6 × 10−27, and 1.2 ± 0.24 × 10−26 cm2 at 815, 799, and 794 nm, respectively, using a 785-nm pump laser. The corresponding values of σRS at 1120, 1089, and 1081 nm were determined to be 1.5 ± 0.3 × 10−27, 1.2 ± 0.24 × 10−27, and 1.2 ± 0.24 × 10−27 cm2 using a 1064-nm laser. A temperature-controlled, small-cavity (2.125 mm diameter) blackbody source was used to calibrate the signal output of the Raman spectrometers for these measurements. Standoff Raman detection of a 6-mm-thick sulfur specimen located at 1500 m from the pump laser and the Raman spectrometer was made using a 1.4-W, CW, 785-nm pump laser.
Summary
The absolute Raman scattering cross sections (σRS) for the 471, 217, and 153 cm−1 modes of sulfur were measured as 6.0 ± 1.2 × 10−27, 7.7 ± 1.6 × 10−27, and 1.2 ± 0.24 × 10−26 cm2 at 815, 799, and 794 nm, respectively, using a 785-nm pump laser. The...
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Work-function-tuned TiN metal gate FDSOI transistors for subthreshold operation
February 1, 2011
Journal Article
Published in:
IEEE Trans. Electron Devices, Vol. 58, No. 2, February 2011, pp. 419-426.
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Summary
The effective work function of a reactively sputtered TiN metal gate is shown to be tunable from 4.30 to 4.65 eV. The effective work function decreases with nitrogen flow during reactive sputter deposition. Nitrogen annealing increases the effective work function and reduces Dit. Thinner TiN improves the variation in effective work function and reduces gate dielectric charge. Doping of the polysilicon above the TiN metal gate with B or P has negligible effect on the effective work function. The work-function-tuned TiN is integrated into ultralow-power fully depleted silicon-on-insulator CMOS transistors optimized for subthreshold operation at 0.3 V. The following performance metrics are achieved: 64-80-mV/dec subthreshold swing, PMOS/NMOS on-current ratio near 1, 71% reduction inCgd, and 55% reduction in Vt variation when compared with conventional transistors, although significant short-channel effects are observed.
Summary
The effective work function of a reactively sputtered TiN metal gate is shown to be tunable from 4.30 to 4.65 eV. The effective work function decreases with nitrogen flow during reactive sputter deposition. Nitrogen annealing increases the effective work function and reduces Dit. Thinner TiN improves the variation in effective...
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Partially-controlled Markov decision processes for collision avoidance systems
January 28, 2011
Conference Paper
Published in:
ICAART 2011, Proc. of the 2rd Int. Conf. on Agents and Artificial Intelligence, 28-30 January 2011, pp. 61-70.
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Summary
Deciding when and how to avoid collision in stochastic environments requires accounting for the likelihood and relative costs of future sequences of outcomes in response to different sequences of actions. Prior work has investigated formulating the problem as a Markov decision process, discretizing the state space, and solving for the optimal strategy using dynamic programming. Experiments have shown that such an approach can be very effective, but scaling to higher-dimensional problems can be challenging due to the exponential growth of the discrete state space. This paper presents an approach that can greatly reduce the complexity of computing the optimal strategy in problems where only some of the dimensions of the problem are controllable. The approach is demonstrated on an airborne collision avoidance problem where the system must recommend maneuvers to an imperfect pilot.
Summary
Deciding when and how to avoid collision in stochastic environments requires accounting for the likelihood and relative costs of future sequences of outcomes in response to different sequences of actions. Prior work has investigated formulating the problem as a Markov decision process, discretizing the state space, and solving for the...
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Collaborative Decision Making (CDM) Weather Evaluation Tool (WET) operational bridging for convective weather: demonstrations and implementation plans
January 25, 2011
Conference Paper
Published in:
2nd Aviation, Range and Aerospace Meteorology Special Symp. on Weather-Air Traffic Management Integration, 22-27 January 2011.
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Summary
The purpose of this manuscript is twofold. First, it provides a review of the activities of the Weather Evaluation Team (WET), which is part of a joint Industry and Federal Aviation Administration (FAA) effort called Collaborative Decision Making (CDM). Over ten years ago, the predecessor to the WET, the Weather Action Group (WAG), developed a process that involved industry and government participants in the production of the Collaborative Convective Forecast Product (CCFP). The CCFP was developed in response to the need of industry and government Air Traffic Managers to have a common forecast of convective information used in their decision making processes. In light of the concepts introduced by the Next Generation Air Transportation System (NextGen), the CCFP could be viewed as one predecessor to the Single Authoritative Source. During the period 2008 through 2010, the WET worked on a task to increase the amount of detail as well as extend its forecast time period. At the same time, new automated convective forecasts were developed and introduced to both the WET and Traffic Flow Management (TFM) community. The manuscript includes a description of how the WET has strived to integrate both Human-in-the-Loop (HITL) and fully automated products, including the Localized Aviation Model Output Statistics (MOS) Product (LAMP)/CCFP Hybrid (LCH), the Aviation Impact Guidance for Convective Weather, the Corridor Integrated Weather System (CIWS) and the Consolidated Storm Prediction for Aviation (CoSPA). The second purpose of this manuscript is to introduce the new concept called Operational Bridging. The WET first discussed Operational Bridging at the 2010 Friends and Partners of Aviation Weather (FPAW) Vision Meeting in July, 2010. Foundational materials such as a Concept of Operations (CONOPS) and a demonstration plan are now being developed by the WET. Operational Bridging is first described from within a meteorology-centric view of the CCFP forecast process. Not only does this allow the new concept to be further defined, it also lays out a transition path for the current CCFP. Operational Bridging is next described from the broader conceptual perspective of Air Traffic Management (ATM)/Weather Integration, and two key areas are explored: 1) the role of the CDM weather community in the area of automated probabilistic and deterministic convective weather forecast information and 2) the integration of probabilistic forecast information into both strategic and deterministic (tactical) ATM decision making process.
Summary
The purpose of this manuscript is twofold. First, it provides a review of the activities of the Weather Evaluation Team (WET), which is part of a joint Industry and Federal Aviation Administration (FAA) effort called Collaborative Decision Making (CDM). Over ten years ago, the predecessor to the WET, the Weather...
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Modeling convective weather avoidance of arrivals in the terminal airspace
January 25, 2011
Conference Paper
Published in:
2nd Aviation, Range, and Aerospace Meteorology Special Symp. on Weather-Air Traffic Management Integration, 22-27 January 2011.
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Summary
For several years the NASA sponsored Convective Weather Avoidance Model (CWAM) has been under development at Lincoln Lab to correlate pilot behavior with observable weather parameters available from convective weather systems. To date, the current CWAM has focused primarily on the enroute airspace used by aircraft at cruise altitude. At these altitudes there is a strong correlation between the observable echo tops from the Corridor Integrated Weather System (CIWS) and the probability that a pilot will deviate around weather. The CWAM has lead to the development of a Weather Avoidance Field (WAF) that combines the echo tops and vertically integrated liquid (VIL) into a probabilistic forecast of the likelihood of pilot deviation. In recent years the WAF has become widely acceptance as a reliable indicator of the impact of convective weather on air traffic operations. This paper will explore the adaptation of the CWAM into the terminal airspace with a focus on the weather impact on arrival decision making. A database of convective weather impacts on several major terminals from 2009 has been collected and identification of the impact on arriving aircraft has begun. Past studies of terminal weather impact have identified aircraft that penetrated severe weather or made clear deviations around convective cells within the terminal. This study will expand the definition of an impact to identify pilot decision making occurring outside of the terminal with regard to the expected weather impact upon arrival in the terminal. Examples include rerouting to an alternate corner post, holding in enroute airspace, or diverting to an alternate airport when weather is expected along the planned terminal trajectory. These types of terminal weather avoidance decisions can often be made many miles outside of the terminal. The enroute CWAM uses spatial filters applied to the echo tops and VIL to obtain the best correlation between the weather and pilot behavior. This paper will evaluate the current CWAM filters and identify alternate spatial filters or additional weather products that may best correlate pilot decision making in the terminal. Ultimately the goal of this work is provide ATC managers and automated decision supports tools with a weather avoidance field for effective management of convective weather in terminal airspace.
Summary
For several years the NASA sponsored Convective Weather Avoidance Model (CWAM) has been under development at Lincoln Lab to correlate pilot behavior with observable weather parameters available from convective weather systems. To date, the current CWAM has focused primarily on the enroute airspace used by aircraft at cruise altitude. At...
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Observations of a 25 January 2010 gravity wave in the New York City metropolitan area and its impact on air traffic
January 24, 2011
Conference Paper
Published in:
2nd Aviation, Range and Aerospace Meteorology Special Symp. on Weather-Air Traffic Management Integration, 22-27 January 2011.
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Summary
A strong low pressure system moved through the Northeast United States on 25 January 2010. As the day progressed, a north-south line of convection formed ahead of an approaching cold front and intensified very rapidly as it passed over the four major New York City airports. Exceptionally strong winds and low-level shears occurred throughout the terminal areas and forced arriving aircraft to divert to alternate airports, hold in the air and on the ground, or abort the landing approach. Analysis shows that a narrow but intense squall line developed as a result of a gravity wave or buoyancy wave and caused vertical shear of the horizontal winds from the surface up through cruise flight levels throughout all of the Terminal Radar Approach Control airspace. Air traffic control planning procedures are examined because the extent and severity of the weather was underestimated; consequently, air traffic managers over-delivered aircraft which lead to excessive airborne holding in regions of known turbulence. Although not available to the operational aviation community at the time, evidence is also shown that the NOAA Earth System Research Laboratory experimental High-Resolution Rapid Refresh (HRRR) model forecasted the event. HRRR supplemental output fields could have provided the spatial and temporal resolution necessary for Managers to plan and execute an orderly reduction in air traffic demand, which, in-turn, would have improved safety and significantly reduced passenger delays. A framework for incorporating HRRR data into Air Traffic Management (ATM) Decision Support Tools and specific ATM Collaborative Decision Making guidance is offered.
Summary
A strong low pressure system moved through the Northeast United States on 25 January 2010. As the day progressed, a north-south line of convection formed ahead of an approaching cold front and intensified very rapidly as it passed over the four major New York City airports. Exceptionally strong winds and...
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Use of a high-resolution deterministic weather forecast for strategic air traffic management decision support
January 14, 2011
Conference Paper
Published in:
91st American Meteorological Society Annual Meeting, 22-27 January 2011.
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Summary
One of the most significant air traffic challenges is managing the National Airspace System (NAS) in a manner that optimizes efficiency and mitigates avoidable delay, while maintaining safety, when convective weather is present. To do this, aviation planners seek to develop strategic air traffic management (ATM) plans and initiatives that anticipate weather constraints 2-8 hours in the future and identify options and alternatives for efficient operations during the off-nominal NAS conditions. In support of strategic planning, traffic managers currently conduct bi-hourly Strategic Planning Telcons (SPTs) and devise weather impact mitigations plans using the human-generated Collaborative Convective Forecast Product (CCFP). However, most operational decision-makers agree that the quasi-deterministic CCFP "polygons" (accompanied by a "low/high" forecast confidence rating) lack the granularity and temporal resolution to adequately support efficient strategic ATM plans and decisions. Moreover, traffic managers also assert that probabilistic forecasts of convective weather likelihood, while helpful in highlighting regions of possible airspace disruptions, generally lack the ability to resolve specific weather characteristics pertinent to strategic planning. MIT Lincoln Laboratory, NCAR Research Applications Laboratory, and NOAA Earth Systems Research Laboratory (ESRL) have collaborated to develop a high-resolution, rapidly updating 0-8 hour deterministic precipitation and echo tops forecast, known as CoSPA, to aid operational decision-makers in developing strategic plans for weather impact mitigation. In the summer of 2010, a comprehensive field study was conducted to assess potential benefits and the operational performance of CoSPA in the context of strategic ATM planning. The data were gathered by simultaneous real-time observations of I5 FAA and airline operations facilities during 15 convective weather impact days affecting the Northern Plains, Great Lakes, and East Coast regions of the NAS. CoSPA field evaluation results will be presented to demonstrate the various ways aviation planners have utilized the increased spatial and temporal resolution of CoSPA - the ability of CoSPA to resolve storm structure and refine forecasts with high update rates - to make more detailed assessments of potential weather impacts and to determine the subsequent need for airspace management initiatives. Results will also be presented that highlight CoSPA enhancement needs, primarily related to forecast uncertainty, that would improve the operational effectiveness of CoSPA-derived weather impact mitigation plans. Finally, opportunities to translate CoSPA deterministic forecasts into integrated weather-ATM decision support for specific strategic planning tasks will be discussed
Summary
One of the most significant air traffic challenges is managing the National Airspace System (NAS) in a manner that optimizes efficiency and mitigates avoidable delay, while maintaining safety, when convective weather is present. To do this, aviation planners seek to develop strategic air traffic management (ATM) plans and initiatives that...
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Aircraft collision avoidance using Monte Carlo real-time belief space search
January 13, 2011
Journal Article
Published in:
J. Intell. Robot. Syst., Vol. 64, No. 2, 2011, pp. 277-98.
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Summary
The aircraft collision avoidance problem can be formulated using a decision-theoretic planning framework where the optimal behavior requires balancing the competing objectives of avoiding collision and adhering to a flight plan. Due to noise in the sensor measurements and the stochasticity of intruder state trajectories, a natural representation of the problem is as a partially-observable Markov decision process (POMDP), where the underlying state of the system is Markovian and the observations depend probabilistically on the state. Many algorithms for finding approximate solutions to POMDPs exist in the literature, but they typically require discretization of the state and observation spaces. This paper investigates the introduction of a sample-based representation of state uncertainty to an existing algorithm called Real-Time Belief Space Search (RTBSS), which leverages branch-and-bound pruning to make searching the belief space for the optimal action more efficient. The resulting algorithm, called Monte Carlo Real-Time Belief Space Search (MC-RTBSS), is demonstrated on encounter scenarios in simulation using a beacon-based surveillance system and a probabilistic intruder model derived from recorded radar data.
Summary
The aircraft collision avoidance problem can be formulated using a decision-theoretic planning framework where the optimal behavior requires balancing the competing objectives of avoiding collision and adhering to a flight plan. Due to noise in the sensor measurements and the stochasticity of intruder state trajectories, a natural representation of the...
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Robust airborne collision avoidance through dynamic programming
January 3, 2011
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-371
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Summary
The Traffic Alert and Collision Avoidance System (TCAS) uses an on-board beacon radar to monitor the local air traffic and logic to determine when to alert pilots to potential conflict. The current TCAS logic was the result of many years of development and involved the careful engineering of many heuristic rules specified in pseudocode. Unfortunately, due to the complexity of the logic, it is difficult to revise the pseudocode to accommodate the evolution of the airspace and the introduction of new technologies and procedures. This report summarizes recent advances in computational techniques for automatically deriving the optimal logic with respect to a probabilistic model and a set of performance metrics. Simulations demonstrate how this new approach results in logic that significantly outperforms TCAS according to the standard safety and operational performance metrics.
Summary
The Traffic Alert and Collision Avoidance System (TCAS) uses an on-board beacon radar to monitor the local air traffic and logic to determine when to alert pilots to potential conflict. The current TCAS logic was the result of many years of development and involved the careful engineering of many heuristic...
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