Publications
Real-time multiple single Doppler analysis with NEXRAD data
May 24, 1993
Conference Paper
Published in:
26th Int. Conf. on Radar Meteorology, 24-28 May 1993, pp. 460-462.
Summary
As part of the Aviation Weather Development Program of the Federal Aviation Administration, a high resolution winds analysis system was demonstrated at Orlando International Airport (MCO) in the summer of 1992. The purpose of this demonstration was to illustrate the winds analysis capability possible from operational sensors in the mid '90s. An important part of the design of this system was the development of a procedure for the assimilation of Doppler data from multiple radars. This procedure had to be able to automatically handle regions with missing data from one or more radars, as well as avoid baseline instability. The two operational radars scanning the analysis region were the National Weather Service WSR-88D (NEXRAD) radar located approximately 65 km east and slightly south of MCO, and the MIT prototype Terminal Doppler Weather Radar (TDWR) located 7 km due south of the airport. The base data from these two Doppler radars were the major information component for the analysis system. Our system includes the most recent improvements in the winds analysis portion of the Local Analysis and Prediction System (LAPS) developed by the Forecast Systems Laboratory (McGinely et al., 1991). LAPS is designed to run locally on systems affordable for operational weather offices and takes advantages of all sources of local data at the highest possible resolution. Our implementation for the airport terminal region id called the Terminal-area LAPS (T-LAPS). LAPS formerly had a technique for the assimilation of data from a single Doppler radar. We have modified that technique for the assimilation of data from the two available radars. Our approach, using a Multiple Single Doppler Analysis (MSDA) technique, is more suited for unsupervised operational analysis than traditional Dual Doppler Analysis (DDA), because it is able to handle such problems as incomplete data and baseline instability. We will describe the T-LAPS analysis, with particular attention to our implementation of ASDA, and give some examples from our demonstration.
Summary
As part of the Aviation Weather Development Program of the Federal Aviation Administration, a high resolution winds analysis system was demonstrated at Orlando International Airport (MCO) in the summer of 1992. The purpose of this demonstration was to illustrate the winds analysis capability possible from operational sensors in the mid...
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The Memphis Precision Runway Monitor Program Instrument Landing System final approach study
May 24, 1993
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-194
Summary
This report documents the study of the lateral positions of aircraft on Instrument Landing System (ILS) approaches during the Memphis, Tennessee, Precision Runway Monitor (PRM) demonstration. The PRM is an advanced radar monitoring system that improved the arrival capacity of closely spaced parallel runways in poor weather conditions. The results of this study are used to assist in determining the minimum runway spacing that will he authorized for PRM. The objective of this study was to quantify the lateral character of ILS arrivals and the consequent impact on independent simultaneous ILS arrival to closely spaced parallel runways. The sensitivity of the arriving aircrafts' lateral positions to different variables such as visibility, wind runway, aircraft type, autopilot performance, and localizer beam width was determined. Also, the Memphis arrival data were compared to FAA Technical Center Chicago O'Hare approach data. The analysis was primarily based on surveillance reports of 4,000 ILS arrivals into Memphis International Airport, collected with the PRM AMPS sensor (ATCRBS Monopulse Processing System). A major result of the study was that lateral aircraft positions will not hamper independent arrivals to parallel runways spaced 3,400 feet apart, but will impede operations at 3,000 feet or smaller unless approach modifications are introduced. Lateral deviations were found to be most sensitive to reduced visibility and certain autopilots. Lateral deviations were also found to be somewhat more at Memphis relative to Chicago O'Hare. Recommendations for further data analysis and collection are discussed.
Summary
This report documents the study of the lateral positions of aircraft on Instrument Landing System (ILS) approaches during the Memphis, Tennessee, Precision Runway Monitor (PRM) demonstration. The PRM is an advanced radar monitoring system that improved the arrival capacity of closely spaced parallel runways in poor weather conditions. The results...
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GLONASS performance in 1992: a review
May 1, 1993
Journal Article
Published in:
GPS World, Vol. 4, No. 5, May 1993, pp. 28-39.
Summary
Researchers at MIT's Lincoln Laboratory reviewed GLONASS developments during 1992, focusing on the requirements of civil aviation and the issues related to position estimation. The results show that the overall performance remains substantially the same as observed in 1991.
Summary
Researchers at MIT's Lincoln Laboratory reviewed GLONASS developments during 1992, focusing on the requirements of civil aviation and the issues related to position estimation. The results show that the overall performance remains substantially the same as observed in 1991.
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Optimal mean velocity estimation for Doppler weather radars
May 1, 1993
Journal Article
Published in:
IEEE Trans. Geosci. Remote Sens., Vol. 31, No. 3, May 1993, pp. 575-586.
Summary
Optimal Doppler velocity estimation is explored for a standard Gaussian signal measurement model and thematic maximum likelihood (ML) and Bayes estimation. Because the model considered depends on a vector parameter (velocity, spectrum width (SW), and signal-to-noise ratio (SNR), the exact formulation of an ML or Bayes solution involves a system of coupled equations which cannot be made explicit for any of the parameters. In the past, iterative methods have been suggested for solving the required equations. In addition to being computationally intensive, it is unclear whether an iterative method can be constructed to converge well under general conditions. Simple computational forms are shown to exist when SW and SNR are assumed known. An information theoretic concept is used to propose an adaptive extension of these equations to the general case of SW and SNR unknown. This new idea is developed to the poise of operational application. A Monte Carlo simulations experiment is used to verify that the method can work; the example presented considers the particularly difficult situation of no a priori information for either SW or SNR under the additional constraint of a very small (20 pulse samples) sample size. The improved performance of this new Doppler velocity estimator is documented by comparison with derived optimal bounds and with the performance of the well-known pulse pair (PP) method. Small-sample estimator statistics are presented; and Bayes estimator results, assuming known SW and SNR, are used to provide true performance bounds for comparison. Cramer-Rao (CR) bounds are also derived and shown to be inferior to the Bayes bounds in the small sample case considered.
Summary
Optimal Doppler velocity estimation is explored for a standard Gaussian signal measurement model and thematic maximum likelihood (ML) and Bayes estimation. Because the model considered depends on a vector parameter (velocity, spectrum width (SW), and signal-to-noise ratio (SNR), the exact formulation of an ML or Bayes solution involves a system...
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Automatic language identification using Gaussian mixture and hidden Markov models
April 27, 1993
Conference Paper
Published in:
Proc. IEEE Int. Conf. on Acoustics, Speech and Signal Processing, Vol. 2, Speech Processing, ICASSP, 27-30 April 1993, pp. 399-402.
Topic:
R&D area:
Summary
Ergodic, continuous-observation, hidden Markov models (HMMs) were used to perform automatic language classification and detection of speech messages. State observation probability densities were modeled as tied Gaussian mixtures. The algorithm was evaluated on four multilanguage speech databases: a three language subset of the Spoken Language Library, a three language subset of a five language Rome Laboratory database, the 20 language CCITT database, and the ten language OGI telephone speech database. Generally, performance of a single state HMM (i.e. a static Gaussian mixture classifier) was comparable to the multistate HMMs, indicating that the sequential modeling capabilities of HMMs were not exploited.
Summary
Ergodic, continuous-observation, hidden Markov models (HMMs) were used to perform automatic language classification and detection of speech messages. State observation probability densities were modeled as tied Gaussian mixtures. The algorithm was evaluated on four multilanguage speech databases: a three language subset of the Spoken Language Library, a three language subset...
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Detection of transient signals using the energy operator
April 27, 1993
Conference Paper
Published in:
Proc. IEEE Int. Conf. on Acoustics, Speech and Signal Processing, Vol. 3, ICASSP, 27-30 April 1993, pp. 145-148.
Topic:
R&D area:
Summary
A function of the Teager-Kaiser energy operator is introduced as a method for detecting transient signals in the presence of amplitude-modulated and frequency-modulated tonal interference. This function has excellent time resolution and is robust in the presence of white noise. The output of the detection function is also independent of the interference-to-transient ratio when that ratio is large. It is demonstrated that the detection function can be applied to interference signals with multiple amplitude-modulated and frequency-modulated tonal components.
Summary
A function of the Teager-Kaiser energy operator is introduced as a method for detecting transient signals in the presence of amplitude-modulated and frequency-modulated tonal interference. This function has excellent time resolution and is robust in the presence of white noise. The output of the detection function is also independent of...
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Time-scale modification of complex acoustic signals
April 27, 1993
Conference Paper
Published in:
Proc. IEEE Int. Conf. on Acoustics, Speech and Signal Processing, ICASSP, Vol. 1, Plenary, Special, Audio, Underwater Acoustics, VLSI, Neural Networks, 27-30 April 1993, pp. 213-216.
Topic:
R&D area:
Summary
A new approach is introduced for time-scale modification of short-duration complex acoustic signals to improve their audibility. The technique constrains the modified signal to take on a specified spectral characteristic while imposing a time-scaled version of the original temporal envelope. Both full-band and sub-band representations of the temporal envelope are considered. In the full-band case, the modified signal is obtained by appropriate selection of its Fourier transform phase. In the sub-band case, using locations of maxima in the sub-band temporal envelopes, the phase of each bandpass signal is formed to preserve "events" in the envelope of the composite signal. The approach is applied to synthetic and actual short-duration acoustic signals consisting of closely-spaced and overlapping sequential time components.
Summary
A new approach is introduced for time-scale modification of short-duration complex acoustic signals to improve their audibility. The technique constrains the modified signal to take on a specified spectral characteristic while imposing a time-scaled version of the original temporal envelope. Both full-band and sub-band representations of the temporal envelope are...
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Automated gust front detection using knowledge-based signal processing
April 20, 1993
Conference Paper
Published in:
Proc. 1993 IEEE Natl. Radar Conf., 20-22 April 1993, pp. 150-155.
Summary
For reasons of aviation safety and airport operations efficiency, gust front detection and tracking is an important product of Doppler weather radars developed for use in airport terminal areas. Previous gust front algorithms, which have relied on the detection of one or two conspicuous signatures in Doppler radar imagery, have worked reasonably well in images generated by the high-resolution, pencil-beam Terminal Doppler Weather Radar (TDWR). The latest Airport Surveillance Radar, enhanced with a Wind Shear Processor (ASR-9 WSP), is being developed as a less expensive alternative weather radar. Although gust fronts are visible to human observers in ASR-9 WSP imagery, the lower sensitivity and less reliable Doppler measurements of this radar make automated gust front detection a much more challenging problem. Using machine intelligence and knowledge-based signal processing techniques developed in the context of automatic target recognition, a Machine Intelligent Gust Front Algorithm (MIGFA) has been constructed that is radically different from the previous algorithms. Developed initially for use with ASR-9 WSP data, MIGFA substantially outperforms a state-of-the-art gust front detection algorithm based on earlier approaches. These results also indirectly suggest that MIGFA performance may be nearly as good as human performance. Preliminary results of an operational test period (two months, approximately 15000 scans processed) are presented.
Summary
For reasons of aviation safety and airport operations efficiency, gust front detection and tracking is an important product of Doppler weather radars developed for use in airport terminal areas. Previous gust front algorithms, which have relied on the detection of one or two conspicuous signatures in Doppler radar imagery, have...
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Evaluation of the capacity and delay benefits of terminal air traffic control automation
April 14, 1993
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-192
Summary
This report reviews the benefits that the CTAS component of the FAA Terminal Air Traffic Control Automation program (TATCA) offers to aviation users. In particular, the report evaluates the prospects that exist for increasing arrival capacity during Instrument Meteorological Conditions (IMC) by introducing CTAS functionality into current operations. The impact of anticipated capacity gains on air traffic delays is analyzed. Savings in delay are translated into dollar savings using FAA statistics on the fleet-weighted direct cost of delay to domestic air carriers. Also, the value of passenger time is considered. Economic impacts are estimated and reported on an annualized, nationwide basis. Adopting FAA projections of future traffic growth, estimates of delay and attendant cost savings to air carriers and their passengers are provided for fiscal years 1995-2015. Taking the nominal estimate of a 12% gain in IMC arrival capacity, a nationwide implementation of CTAS would be estimated to save an average of 412,000 hours of air carrier delay annually over this 21-year period, and 273 million gallons of fuel per year. With current fuel and labor costs, this amounts to average direct operating savings to air carriers of $1.5 billion per year, and value to passengers of over $3 billion per year, in constant 1988 dollars. There may be factors outside the scope of this study that restrict the implementation of CTAS to certain sites, or that limit the weather conditions in which CTAS is effective. Methods are discussed in the report for modifying benefits estimates in response to such considerations. However, since development and implementation costs of CTAS are estimated to be a small fraction of the benefits enumerated above, and since the delay savings recur annually, it is concluded that the development of STC automation software such as CTAS is economically justifiable.
Summary
This report reviews the benefits that the CTAS component of the FAA Terminal Air Traffic Control Automation program (TATCA) offers to aviation users. In particular, the report evaluates the prospects that exist for increasing arrival capacity during Instrument Meteorological Conditions (IMC) by introducing CTAS functionality into current operations. The impact...
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ADS-Mode S: Initial System Description
April 2, 1993
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-200
Summary
Dependent Surveillance and the Mode S beacon radar. The result is an integrated concept for seamless surveillance and data link that permita equipped aircraft to participate in ADS or beacon ground environmenta. This offers many possibilities for transition from a beacon to an ADS based environment. The ADS-Mode S concept in baaed on use of the Mode S squitter. The Mode S squitter is a spontaneous, periodic (once per second) 56-bit Mode S broadcast containing the Mode S 24-bit address. This broadcast is provided by all Mode S transponders and in used by the Traffic Alert and Collision Avoidance System (TCAS) to acquire Mode S equipped aircraft. For ADS-Mode S use, this squitter broadcast is extended to 112 bits to provide for the transmission of a 56-bit ABS message field. The ADS squitter is transmitted in addition to the current TCAS squitter in order to maintain compatibility with current TCAS equipment. This paper defines the ADS-Mode S concept, describes its principal surveillance and data link applications and provides estimates of expected performance.
Summary
Dependent Surveillance and the Mode S beacon radar. The result is an integrated concept for seamless surveillance and data link that permita equipped aircraft to participate in ADS or beacon ground environmenta. This offers many possibilities for transition from a beacon to an ADS based environment. The ADS-Mode S concept...
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