Publications
1995 wake vortex program at Memphis, TN
January 5, 1996
Conference Paper
Published in:
AIAA 34th Aerospace Sciences Meeting and Exhibit, 15-18 January 1996.
Summary
This paper describes wake vortex field measurements conducted during August, 1995 at Memphis, TN. The objective of this effort was to record wake vortex behavior for varying atmospheric conditions and aircraft types. Wake vortex behavior was observed using a mobile CW coherent lidar. This lidar features a number of improvements over previous systems, including the first-ever demonstration of an automatic wake vortex detection and tracking algorithm. An extensive meteorological data collection system was deployed in support of the wake vortex measurements, including a 150-ft instrumented tower, wind profiler/RASS (radio acoustic sounding system), sonar and balloon soundings. Aircraft flight plan and beacon data were automatically collected to determine aircraft flight number, type, speed, and descent rate. Additional data was received from airlines in postprocessing to determine aircraft weight and model. Preliminary results from the field measurement program are presented illustrating differences in wake vortex behavior depending on atmospheric conditions and aircraft type.
Summary
This paper describes wake vortex field measurements conducted during August, 1995 at Memphis, TN. The objective of this effort was to record wake vortex behavior for varying atmospheric conditions and aircraft types. Wake vortex behavior was observed using a mobile CW coherent lidar. This lidar features a number of improvements...
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Selected abstracts on aviation weather hazard research
January 2, 1996
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-242
Summary
This paper consists of bibliographic information and abstracts for literature on the topics of weather-related aviation hazards. These abstracts were selected from reports written for the ASR-9, ITWS, TDWR programs, sponsored by the Federal Aviation Administration (FAA), and the Wake Vortex program, sponsored by NASA Langley Research Center. All research was performed by MIT Lincoln Laboratory; some research was performed in collaboration with other organizations. These abstracts were compiled to allow participants in the ASR-9 program to conduct research related to their design, development, and production effort. The abstracts and bibliographic information were retrieved from several commercial databases (INSPEC, Ei Compendex*Plus, Aerospace Database, and NTIS) through an open literature search at the Lincoln Laboratory library. Sufficient information is included for readers to obtain documents of interest to them, but documents will not be provided directly by Lincoln Laboratory.
Summary
This paper consists of bibliographic information and abstracts for literature on the topics of weather-related aviation hazards. These abstracts were selected from reports written for the ASR-9, ITWS, TDWR programs, sponsored by the Federal Aviation Administration (FAA), and the Wake Vortex program, sponsored by NASA Langley Research Center. All research...
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Comparison of four approaches to automatic language identification of telephone speech
January 1, 1996
Journal Article
Published in:
IEEE Trans. Speech Audio Process., Vol. 4, No. 1, January 1996, pp. 31-44.
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Summary
We have compared the performance of four approaches for automatic language identification of speech utterances: Gaussian mixture model (GMM) classification; single-language phone recognition followed by language-dependent, interpolated n-gram language modeling (PRLM); parallel PRLM, which uses multiple single-language phone recognizers, each trained in a different language; and language dependent parallel phone recognition (PPR). These approaches which space a wide range of training requirements and levels of recognition complexity, were evaluated with the Oregon Graduate Institute Multi-Language Telephone Speech Corpus. Systems containing phone recognizers performed better than the simpler GMM classifier. The top-performing system was parallel PRLM, which exhibited an error rate of 2% for 45-s utterances and 5% for 10-s utterances in two-language, closed-set, forced-choice classification. The error rate for 11-language, closed-set, forced-choice classification was 11% for 45-s utterances and 21% for 10-s utterances.
Summary
We have compared the performance of four approaches for automatic language identification of speech utterances: Gaussian mixture model (GMM) classification; single-language phone recognition followed by language-dependent, interpolated n-gram language modeling (PRLM); parallel PRLM, which uses multiple single-language phone recognizers, each trained in a different language; and language dependent parallel phone...
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Initial evaluation of terminal-area atmospheric vertical structure prediction algorithms using Fall 1994 ITWS/Wake Vortex Programs' meteorological data
November 6, 1995
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-237
Summary
A Dynamic Atmospheric Vertical Structure Nowcast System (DAVS-NS) is being developed that will add value to the Integrated Terminal Weather System (ITWS) by providing current and short-term forecasts of the vertical atmospheric structure focused at specific sites within the terminal domain. Operational applications of these estimates of the atmospheric vertical structure include predicting changes in airport operation rates due to ceiling and visibility (C&V) changes and in predicting wake vortex behavior. The core of this system would be a one-dimensional boundary layer column model. This report summarizes the evaluation of a modified Oregon State University (OSU) column model using data collected during the fall 1994 combined National Aeronautics and Space Administration (NASA) wake vortex project and the ITWS site operations at Memphis International Airport (MEM). Further efforts are necessary to develop and test an operational DAVS-NS prototype. The accuracy typically seen in column model predictions of the vertical temperature structure will limit errors in wake vortex dissipation rates to within a factor of two. Given the current working hypothesis for the San Francisco stratus burn-off phenomenon that rests largely on warming of the marine boundary layer by surface heat flux, the OSU model will also appear to be well suited for addressing this particular problem.
Summary
A Dynamic Atmospheric Vertical Structure Nowcast System (DAVS-NS) is being developed that will add value to the Integrated Terminal Weather System (ITWS) by providing current and short-term forecasts of the vertical atmospheric structure focused at specific sites within the terminal domain. Operational applications of these estimates of the atmospheric vertical...
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A human factors approach to the development and evaluation of the Graphical Weather Service
November 5, 1995
Conference Paper
Published in:
14th AIAA/IEEE Digital Avionics Systems Conf., 5-9 November 1995, pp. 264-269.
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Summary
With the sponsorship of the Federal Aviation Administration, MIT Lincoln Laboratory is developing the Graphical Weather Service (GWS), a data link application that provides near-real-time ground-based weather information to pilots. Through the use of GWS, the pilot will be able to access both graphical and text weather information for any location in the contiguous United States. In-cockpit access to near-real-time weather information may substantially affect the situational awareness and subsequent decision making of pilots. In developing and evaluating this service, a human factors approach has been taken. This paper is an overview of the human factors activities performed in the development and evaluation of GWS.
Summary
With the sponsorship of the Federal Aviation Administration, MIT Lincoln Laboratory is developing the Graphical Weather Service (GWS), a data link application that provides near-real-time ground-based weather information to pilots. Through the use of GWS, the pilot will be able to access both graphical and text weather information for any...
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A subband approach to time-scale expansion of complex acoustic signals
November 1, 1995
Journal Article
Published in:
IEEE Trans. Speech Audio Process., Vol. 3, No. 6, November 1995, pp. 515-519.
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Summary
A new approach to time-scale expansion of short-duration complex acoustic signals is introduced. Using a subband signal representation, channel phases are selected to preserve a desired time-scaled temporal envelope. The phase representation is derived from locations of events that occur within filter bank outputs. A frame-based generalization of the method imposes phase consistency across consecutive synthesis frames. The method is applied to synthetic and actual complex acoustic signals consisting of closely spaced rapidly damped sine wave. Time-frequency resolution limitations are discussed.
Summary
A new approach to time-scale expansion of short-duration complex acoustic signals is introduced. Using a subband signal representation, channel phases are selected to preserve a desired time-scaled temporal envelope. The phase representation is derived from locations of events that occur within filter bank outputs. A frame-based generalization of the method...
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Description of radar correlation and interpolation algorithms for the ASR-9 Processor Augmentation Card (9-PAC)
October 27, 1995
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-236
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Summary
MIT Lincoln Laboratory, under sponsorship from the Federal Aviation Adminstration (FAA), is conducting a program to replace/upgrade the existing ASR-9 array signal processor (ASP) and associated algorithms to improve performance and future maintainability. The ASR-9 processor augmentation card (9-PAC) replaces the ASP four-board set with a single card containing three TMS320c40 processors and 32 Megabytes of memory. The resulting increase in both processing speed and memory size allows more sophisticated beacon and radar processing algorithms to be implemented. The majority of the improvement to the radar correlation and interpolation (C&I) function lies in the area of geocensoring and adaptive thresholding, where the larger memory capacity of the 9-PAC allows more detailed maps to be maintained. A dynamic road map mechanism has been implemented to reduce the need for manual tuning of the system when the radars are first installed or when new road construction occurs. The map is twice the resolution of the original geocensormap, resulting in a decrease in total area desensitized to radar-only targets. In addition, the new geocensor mechanism makes use of target amplitude information, allowing aircraft with amplitudes significantly greater than the road traffic returns at a particular cell to pass through uncensored. The adaptive thresholding cell geometry has been modified so that adaptive map cells now overlap one another, eliminating the false target breakthrough that occurs in the present system when regions of false alarms due to birds or weather transition from one cell to the next. The entire C & I function has been recorded in a high-level language (ANSI-C), allowing it to be easily ported between platforms and better facilitating off-line analysis.
Summary
MIT Lincoln Laboratory, under sponsorship from the Federal Aviation Adminstration (FAA), is conducting a program to replace/upgrade the existing ASR-9 array signal processor (ASP) and associated algorithms to improve performance and future maintainability. The ASR-9 processor augmentation card (9-PAC) replaces the ASP four-board set with a single card containing three...
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Time-scale modification with inconsistent constraints
October 15, 1995
Conference Paper
Published in:
Proc. 1995 Workshop on Applications of Signal Processing to Audio Acoustics, 15-18 October 1995.
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Summary
A set theoretic estimation approach is introduced for timescale modification of complex acoustic signals. The method determines a signal that meets, in a least-squared error sense, desired temporal and spectral envelope constraints that are inconsistent. These constraints are generalized within the set theoretic framework to include other signal characteristics such as instantaneous frequency and group delay. The approach can enhance acoustic signals consisting of closely-spaced sequential time components, and is applicable to biological, underwater, and music sound processing.
Summary
A set theoretic estimation approach is introduced for timescale modification of complex acoustic signals. The method determines a signal that meets, in a least-squared error sense, desired temporal and spectral envelope constraints that are inconsistent. These constraints are generalized within the set theoretic framework to include other signal characteristics such...
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GPS-squitter automatic dependent surveillance broadcast: flight testing in the Gulf of Mexico
October 13, 1995
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-235
Summary
During November - December 1994, MIT Lincoln Laboratory conducted a field evaluation of the air surveillance capabilities of GPS-Squitter in the Gulf of Mexico. Three squitter ground stations were located in the vincinity of Morgan City, Louisiana, for this evaluation: two were located on offshore oil platforms, and the third was located at an onshore heliport. Surveillance coverage tests were flown over the Gulf with three test aircraft - two helicopters and one Cessna 421 fixed wing aircraft. The helicopters flew at altitudes ranging from 100 to 2000 feet above sea level and the Cessna flew at 7500 and 20,000 feet. Extended squitter messages broadcast by each of the test aircraft provided aircraft position and identification. This report documents results of these texts and compares measured coverage to predicted coverage from the ground stations. Based on the good agreement between predicted and measured performance, a description of a possible operational system is included that would provide surveillance of the entire Gulf region serviced by oil platform helicopters. The report concludes that GPS Squitter is a near-term option for providing accurate, real time surveillance of aircraft operating in the offshore airspace in the Gulf of Mexico.
Summary
During November - December 1994, MIT Lincoln Laboratory conducted a field evaluation of the air surveillance capabilities of GPS-Squitter in the Gulf of Mexico. Three squitter ground stations were located in the vincinity of Morgan City, Louisiana, for this evaluation: two were located on offshore oil platforms, and the third...
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Runway status light system demonstration at Logan Airport
October 12, 1995
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-206
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Summary
The Runway Status Light System (RSLS), developed under the FAA's Airport Surface Traffic Automation (ASTA) program, is intended to help reduce the incidence of runway incursions and airport surface accidents. It will do so by providing a preventive, back-up system of automatically controlled lights on the airport surface that inform pilots when runways are unsafe for entry or takeoff, and by providing controllers with enhanced surface radar displays. This report documents a proof-of-concept evaluation of the RSLS at Boston's Logan Airport. It details the methods used to provide the necessary surface surveillance and safety logic to allow a computer to operate the runway status lights and associated controller displays without human assistance. The system was installed and tested off-line at Boston's Logan Airport using an inexpensive commercial marine radar as a primary surveillance source. The system operated live and in real time but the runway status lights were not physically installed. They were displayed on a scale model of Logan Airport located in a demonstration room that had a good view of the airport. This allowed visual comparison between the actual aircraft and the resulting lights and displays. In addition to providing a convincing demonstration of the system, real-timing viewing of the aircraft movement was an important aid in the development of the surveillance processing and safety logic software. Surveillance performance and runway status light operational performance were evaluated quantitatively. The probability of tracking an aircraft in movement areas with line-of-sight coverage was better than 98%. The false track rate was about four per hour, and the surveillance jitter was about 1 meter rms. From an operational point of view, had there been real lights on the field, it appears that they would have provided the intended safety back-up with little impact on airport capacity or controller and pilot workload, Only once in 15 minutes would the pilot population have observed a light in an incorrect state for more than four seconds. From the point of view of a specific cockpit crew, only once in 36 operations would a runway status light have been seen in an incorrect state for more than four seconds, and, furthermore, only once in 50 operations would light illuminations have interfered with normal, safe traffic flow. These are encouraging results for a system in an early demonstration phase because significant improvement is possible in all of these performance measures. Specific suggestions for improvement are included in this document.
Summary
The Runway Status Light System (RSLS), developed under the FAA's Airport Surface Traffic Automation (ASTA) program, is intended to help reduce the incidence of runway incursions and airport surface accidents. It will do so by providing a preventive, back-up system of automatically controlled lights on the airport surface that inform...
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