Publications
Measuring the economic value of aviation meteorological products
January 15, 1995
Conference Paper
Published in:
9th Conf. on Applied Climatology, 15-20 January 1995.
Summary
The aviation system is one of the principal users of weather information. Assessing the benefits of weather information to aviation is important in a number of contexts: 1. Detemining the priority of investments in aviation weather information vis a vis other options for transportation and/or weather system investments, 2. Determinins priorities for research, implementation, facility staffing and information distribution, 3. The allocation of roles and responsibilities between various government agencies and private industry for various functions, and 4. Use in forecasting to set thresholds (see, e.g., [Felton, 1991], [Andrews, 1993], and [Liljas and Murphy, 1994]) With reduced government funding in a variety of areas related to aviation weather and with cost pressures on the users of the weather information (especially the air carriers), the importance of carefully performed benefits assessment has increased significantly in the past decade and is expected to become even more important in the near future. Our discussion will focus on safety and delay reduction. In the case of safety, we will consider in some depth the case of the deloyment of wind shear detection systems, while delay reduction will focus on results from recent studies of improved information on airport weather. In each case, we will also identify issues related to other benefits assessments in these areas.
Summary
The aviation system is one of the principal users of weather information. Assessing the benefits of weather information to aviation is important in a number of contexts: 1. Detemining the priority of investments in aviation weather information vis a vis other options for transportation and/or weather system investments, 2. Determinins...
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Overview of 1994 Memphis Wake Vortex testing program
January 15, 1995
Conference Paper
Published in:
Proc. Sixth Conf. on Aviation Weather Systems, 15-20 January 1995, pp. 515-520.
Summary
Significant restrictions currently exist in the air traffic control system due to wake vortex considerations. Eliminating or reducing these restrictions would yield increased capacity, decreased delays and significant cost savings (Evans & Welch, 1991). These improvements would be especially desirable at high traffic airports which cannot expand (e.g., Boston, JFK, LaGuardia, Newark, Washington National, O'Hare, etc.). However, scientific uncertainty about wake vortex behavior under various weather conditions is a major concern. The current wake vortex restrictions me normally very conservative but could be insufficient under certain transient atmospheric conditions. A successful adaptive wake vortex advisory system must be able to 1) monitor for unsafe conditions, 2) predict wake vortex behavior over 2&30 minutes in the future and 3) provide an interface to air traffic controllers. Operational implementation of such a system will involve synergism between the Wake Vortex (WV), Integrated Terminal Weather System (ITWS) and Terminal Air Traffic Control Automation (TATCA) programs. The Wake Vortex program is a new effort at Lincoln Laboratory sponsored by NASA Langley Research Center in cooperation with the FAA. The joint NASA/FAA/Lincoln program seeks to aid in resolving wake vortex behavior issues as a function of the weather environment with a series of field measurements. The field measurements will include obtaining aircraft, meteorological and wake vortex data in an operational airport environment. The data collected will support efforts at NASA and elsewhere to validate wake vortex behavior models, aircraft/vortex interaction and atmospheric diagnosis/prognosis methods. The first of these field measurements is scheduled for the fall of 1994 at the Memphis International Airport.
Summary
Significant restrictions currently exist in the air traffic control system due to wake vortex considerations. Eliminating or reducing these restrictions would yield increased capacity, decreased delays and significant cost savings (Evans & Welch, 1991). These improvements would be especially desirable at high traffic airports which cannot expand (e.g., Boston, JFK...
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The ITWS Runway Wind Nowcast Product
January 15, 1995
Conference Paper
Published in:
Sixth Conf. on Aviation Weather Systems, 15-20 January 1995, pp. 390-395.
Summary
The Runway Wind Nowcast Product will support the ITWS objective by providing short term (up to 30 minutes) forecasts of the tailwind and crosswind components of the horizontal wind over each runway at an ITWS airport. These forecasts will enable FAA users to better anticipate wind shifts impacting runway usage and trajectories of approaching and departing air traffic. They may also support future ITWS products such ceiling and visibility nowcasts. Our initial development efforts, which are reported here, have been directed toward Orlando International Airport (MCO) as the product request originated there. However, in the near future we plan to expand the scope to include other ITWS airports including Memphis. The Runway Wind Nowcast Product is being developed to help Air Traffic Control (ATC) personnel answer the following question: Do we need to change runways? That would become necessary if tailwinds or crosswinds exceed usage thresholds. At most US airports, with dry runways, tailwinds much be less than five knots and crosswinds must be less than 15 knots. Other, lower thresholds apply if the runways are wet. However, these thresholds are subject to local modifications. For example, the MCO tailwind threshold for dry runways is 7 knots. The decision faced by ATC personnel seems, at first, to be clear cut: if the tailwind or crosswind exceeds nominal thresholds, use of that runway must be discontinued. The problem (at least at MCO) is that most threshold crossings are very brief. So, it may be better to temporarily hold traffic than to switch runways. Reliable (i.e., accurate and precise) short term forecasts will help ATC personnel make better hold-or-switch decisions.
Summary
The Runway Wind Nowcast Product will support the ITWS objective by providing short term (up to 30 minutes) forecasts of the tailwind and crosswind components of the horizontal wind over each runway at an ITWS airport. These forecasts will enable FAA users to better anticipate wind shifts impacting runway usage...
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The Terminal Weather Information for Pilots (TWIP) program
January 11, 1995
Conference Paper
Published in:
Proc. Sixth Conf. on Aviation Weather Systems, 15-20 January 1995, pp. 107-112.
Summary
The Federal Aviation Administration (F.A.A.) is currently embarking on programs, such as the Integrated Terminal Weather System (ITWS) and Terminal Doppler Weather Radar (TDWR), that will significantly improve the aviation weather information in the terminal area. Given the great increase in the quantity and quality of terminal weather information, it would be highly desirable to provide this information directly to pilots rather than having to rely on voice communications. Providing terminal weather information automatically via data link would both enhance pilot awareness of weather hazards and reduce air traffic controller workload. This paper will describe current work in the area of providing direct pilot access to terminal weather information via existing data link capabilities, such as ACARS (Addressing, Communications and Reporting System). During the summer of 1994, the ITWS testbed systems at Orlando, FL and Memphis, TN provided real–time terminal weather information to pilots in the form of text and character graphics–based products via the ACARS VHF data link. This effort follows an earlier successful demonstration during the summer of 1993 at Orlando (Campbell, 1994). Two types of Terminal Weather lnformation for Pilots (TWIP) messages are generated: a text-only message and a character graphics map. In order to ensure their operational utility, these products were developed in consultation with an ad hoc pilot user group. The TWIP Text Message is intended for typical ACARS cockpit displays, which are roughly 20 characters wide by 10 lines high. The TWIP Character Graphics Depiction is intended for the cockpit printers available on some aircraft that are at least 40 characters wide. Both products are intended to provide strategic information to pilots about terminal weather conditions to aid flight planning and improve situational awareness of potential hazards.
Summary
The Federal Aviation Administration (F.A.A.) is currently embarking on programs, such as the Integrated Terminal Weather System (ITWS) and Terminal Doppler Weather Radar (TDWR), that will significantly improve the aviation weather information in the terminal area. Given the great increase in the quantity and quality of terminal weather information, it...
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Robust text-independent speaker identification using Gaussian mixture speaker models
January 1, 1995
Journal Article
Published in:
IEEE Trans. Speech Audio Process., Vol. 3, No. 1, January 1995, pp. 72-83.
Topic:
R&D area:
Summary
This paper introduces and motivates the use of Gaussian mixture models (GMM) for robust text-independent speaker identification. The individual Gaussian components of a GMM are shown to represent some general speaker-dependent spectral shapes that are effective for modeling speaker identify. The focus of this work is on applications which require high identification rates using short utterance from unconstrained conversational speech and robustness to degradations produced by transmission over a telephone channel. A complete experimental evaluation of the Gaussian mixture speaker model is conducted on a 49 speaker, conversational telephone speech database. The experiments examine algorithmic issues (initializations, variance limiting, model order selection), spectral variability robustness techniques, large population performance, and comparisons to other speaker modeling techniques (uni-modal Gaussian, VQ codebook, tied Gaussian mixture, and radial basis functions). The Gaussian mixture speaker model attains 96.8% identification accuracy using 5 second clean speech utterances and 80.8% accuracy using 15 second telephone speech utterances with a 49 speaker population and is shown to outperform the other speaker modeling techniques on an identical 16 speaker telephone speech task.
Summary
This paper introduces and motivates the use of Gaussian mixture models (GMM) for robust text-independent speaker identification. The individual Gaussian components of a GMM are shown to represent some general speaker-dependent spectral shapes that are effective for modeling speaker identify. The focus of this work is on applications which require...
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Sinusoidal coding
January 1, 1995
Book Chapter
Published in:
Chapter 4 in Speech Coding and Synthesis, Elsevier Science Publishers, 1995, pp. 121-173.
Topic:
R&D area:
Summary
This chapter summarizes the sinewave-based pitch extractor, and the high-order all-pole modelling techniques that provided the basis for the multirate Sinusoidal Transform Coder and its application to multi-speaker conferencing.
Summary
This chapter summarizes the sinewave-based pitch extractor, and the high-order all-pole modelling techniques that provided the basis for the multirate Sinusoidal Transform Coder and its application to multi-speaker conferencing.
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Speaker identification and verification using Gaussian mixture speaker models
January 1, 1995
Conference Paper
Published in:
Speech Commun., Vol. 17, 1995, pp. 91-108.
Topic:
R&D area:
Summary
This paper presents high performance speaker identification and verification systems based on Gaussian mixture speaker models: robust, statistically based representations of speaker identification. The identification system is a maximum likelihood classifier and the verification system is a likelihood ratio hypothesis tester using background speaker normalization. The systems are evaluated on four publically available speech databases: TIMIT, NTIMIT, Switchboard and YOHO. The different levels of degradation and variabilities found in these databases allow the examination of system performance for different task domains. Constraints on the speech range from vocabulary-dependent to extemporaneous and speech quality varies from near-ideal, clean speech to noisy, telephone speech. Closed set identification accuracies on the 630 speaker TIMIT and NTIMIT databases were 99.5% and 60.7% respectively. On a 113 speaker population from the Switchboard database the identification accuracy was 82.8%. Global threshold equal error rates of 0.24%, 7.19%, 5.15% and 0.51% were obtained in verification experiments on the TIMIT, NTIMIT, Switchboard and YOHO databases, respectively.
Summary
This paper presents high performance speaker identification and verification systems based on Gaussian mixture speaker models: robust, statistically based representations of speaker identification. The identification system is a maximum likelihood classifier and the verification system is a likelihood ratio hypothesis tester using background speaker normalization. The systems are evaluated on...
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Optimum time-varying FIR filter designs for the Airport Surveillance Radar wind shear processor
December 28, 1994
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-191
Summary
We have developed new design algorithms for finite impulse response (FIR) filters that compensate for arbitrary input spacing and that allow for arbitrary group delay specification. The potential of these new designs to work with the ASR-9 staggered pulse spacing is examined in the context of the ASR-9 wind-shear processor (WSP). Benefits derived from the new designs include an improved (optimal) stopband design, an increased yield in pulse samples for moments estimation, and the retention of pulse-stagger phase information, which can be used for velocity dealiasing. These improvements are demonstrated using simulated and test-bed data, the latter acquired during 1991/1992 Orlando operations. Filter utilization, in the context of a pre-existing adaptive selection scheme (1) and the Orlando (FL) clutter environment, is examined using the new filters, and areas for improvement are identified.
Summary
We have developed new design algorithms for finite impulse response (FIR) filters that compensate for arbitrary input spacing and that allow for arbitrary group delay specification. The potential of these new designs to work with the ASR-9 staggered pulse spacing is examined in the context of the ASR-9 wind-shear processor...
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Safety analysis of the Traffic Information Service
November 22, 1994
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-226
Summary
Traffic Information Service (TIS) is a Mode S data link application being developed for use by general aviation (GA) pilots. Its purpose is to provide a low-cost means of assisting the pilot in visual acquisition of nearby aircraft. The service provides two functions: traffic alerting and threat assessment. These functions are also performed by the Traffic Alert and Collision Avoidance System (TCAS). The purpose of this report is to evaluate the effectiveness and safety of TIS in relation to that of TCAS I. The analysis begins with a conceptual review of Andrews' statistical model of visual acquisition. Next, the surveillance systems and threat-detection logic of TIS and TCAS I are reviewed. Results of a Monte Carlo simulation that modeled the threat-assessment performance of TCAS I and TIS are also presented. The analysis supports the conclusion that, because of the high degree of similarity between TIS and TCAS I, TIS is a safe and effective means of assisting the pilot in visual acquisition of air traffic.
Summary
Traffic Information Service (TIS) is a Mode S data link application being developed for use by general aviation (GA) pilots. Its purpose is to provide a low-cost means of assisting the pilot in visual acquisition of nearby aircraft. The service provides two functions: traffic alerting and threat assessment. These functions...
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Obtaining low sidelobes using non-linear FM pulse compression
November 4, 1994
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-223
Summary
Airport Surveillance Radar (ASR) manufacturers are proposing the use of non-linear FM pulse compression in their all solid state radars. However there is concern that the use of pulse compression will limit the radar's performance. High range sidelobes can cause poor performance in both target and weather detection. The theory of nonlinear FM pulse compression is derived along with a method of minimizing the sidelobes using a minimum mean square error (MMSE) technique. The results of a computer program using the MMSE technique show that very low sidelobe levels of more than 100 dB down may be achieved. These very low sidelobes are affected by filter misalignment, target Doppler, and by transmitter phase errors or stability. Curves are presented demonstrating these effects. We also show how filter misalignment can be corrected by receiver filtering. The methods presented here are general enough to be used to assess the performance of proposed non-linear FM waveform radars.
Summary
Airport Surveillance Radar (ASR) manufacturers are proposing the use of non-linear FM pulse compression in their all solid state radars. However there is concern that the use of pulse compression will limit the radar's performance. High range sidelobes can cause poor performance in both target and weather detection. The theory...
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