Publications
Coherent processing across multi-PRI waveforms
May 24, 1993
Conference Paper
Published in:
Proc. 26th Int. Conf. on Radar Meteorology, 24-28 May 1993, pp. 232-234.
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Summary
Meteorological Doppler radars have typically utilized constant pulse-repetition intervals (PRI) to facilitate clutter filtering and estimation of weather echo spectral moments via pulse-pair or periodogram-based algorithms. Utilization of variable PRIs to support resolution of velocity ambiguities has been discussed, for example by Banjanin and Zrnic, but not implemented owing to difficulties associated with clutter filter design. Recent work by Chornoboy presents design algorithms for time-varying finite impulse response (FIR) filters that achieve Chebyshev or mean-squared error (MSE) optimality when processing multi-PRI waveforms. This paper is a follow-on to that work, treating techniques for post-clutter filter processing (e.g. periodogram estimation) that are appropriate for such waveforms. Our approach involves a least-squares fitting of the signal - sampled at a nonuniform rate - to a weighted sum of uniformly spaces sinusoids. The sinusoids or "basis functions" are chosen to span a Nyquist interval consistent with the longest PRI in the transmitted waveform, and need not be centered at zero Doppler. Determination of the sinusoid weightings - effectively a discrete Fourier transformation (DFT) - and the associated residual between the harmonic fit and the data area accomplished via multiplications of the signal vector with precomputed matrices. The resulting spectrum estimate can be used directly for weather echo moment calculations, or can be inverse-Fourier transformed using conventional techniques to generate a time-domain signal representation. This work has been motivated by a specific application - estimation of weather spectrum moments for a Wind Shear Processor (WSP) modification to the Federal Aviation Administration's Airport Surveillance Radar (ASR-9). Our approach supports candidate low-altitude radial wind estimation algorithms that operate on frequency-domain signal representations and require that the radar's block-stagger PRI and the possibility of velocity ambiguities be accounted for in generating the spectrum estimates. In principle, however, these processing techniques are also applicable to weather radar systems such as WSR-88D and Terminal Doppler Weather Radar (TDWR) where range and Doppler ambiguities are an operational concern.
Summary
Meteorological Doppler radars have typically utilized constant pulse-repetition intervals (PRI) to facilitate clutter filtering and estimation of weather echo spectral moments via pulse-pair or periodogram-based algorithms. Utilization of variable PRIs to support resolution of velocity ambiguities has been discussed, for example by Banjanin and Zrnic, but not implemented owing to...
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Dual-Doppler measurements of microburst outflow strength asymmetry
May 24, 1993
Conference Paper
Published in:
26th Int. Conf. on Radar Meteorology, 24-28 May 1993, pp. 664-666.
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Summary
The Federal Aviation Administration (FAA) has been sponsoring Lincoln Laboratory in its effort to develop and test weather detection algorithms for the Terminal Doppler Weather Radar (TDWR). An automated microburst detection algorithm operates on the TDWR radial velocity data and, based on the shear and velocity difference along the radial, outputs regions which are hazards to aviation. This algorithm has been operating since 1987 in Denver, Kansas City, and Orlando and is part of the operational TDWR being deployed across the country. One issue which continues to cause concern for automated windshear detection is microburst asymmetry. Asymmetry, or aspect angle dependence, in microbursts refers to outflows which have a divergent surface outflow strength or extent that varies depending on the viewing angle of the radar. The TDWR is a single-Doppler radar, therefore, an asymmetric microburst may be underestimated or go undetected if the radar is viewing the event from an aspect angle where the strength of the outflow is weak. Past work by Wilson et al., Eilts, and Hallowell has indicated that some microbursts are highly asymmetric. Strength asymmetries (maximum/minimum strength over all viewing angles) from these past studies ranged from 1.3 to as high as 6.0. Hallowell using Denver data examined 27 Denver microbursts (96 observations) and found strength asymmetries from 1.3 to 3.8 with a median of 1.9. However, this previous work has been limited in scope to Denver and Oklahoma (plains) microbursts, and may have used assumptions about the data which introduce false or apparent asymmetry.
Summary
The Federal Aviation Administration (FAA) has been sponsoring Lincoln Laboratory in its effort to develop and test weather detection algorithms for the Terminal Doppler Weather Radar (TDWR). An automated microburst detection algorithm operates on the TDWR radial velocity data and, based on the shear and velocity difference along the radial...
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Estimating a windshear hazard index from ground-based terminal Doppler radar
May 24, 1993
Conference Paper
Published in:
26th Int. Conf. on Radar Meteorology, 24-28 May 1993, pp. 670-672.
Summary
In the past decade, a great deal of effort has been invested in developing ground based wind shear detection systems for major U.S. airports. However, there has been a lack of research in developing a quantitative relationship between the wind shear hazards detected by ground based systems and the actual hazard experienced by an aircraft flying through the affected air space. To date, the main thrust of the verification efforts for ground-based systems has been to ensure that the system accurately detect and report the presence of the meteorological phenomena that cause potentially important hazardous windshear. There is a subtle, but potentially important difference between detecting the presence or a microburst and detecting the presence of an aviation hazard. With this in mind, it would seem prudent to rigorously determine what correlation exists between the wind shear warnings that are generated from ground systems and the performance impact on aircraft flying through the impacted airspace. The operational demonstration of the testbed Terminal Doppler Weather Radar (TDWR) in Orlando, Florida along with the testing of airborne Doppler radar systems created a unique opportunity to compare extensively the ground based windshear reports with in-situ aircraft measurements. This paper presents the results from 69 microburst penetrations flown in 1990 and 1991 by the University of North Dakota (UND), the National Aeronautics and Space Administration (NASA) Langley Research Center, and Rockwell Collins under surveillance of the Lincoln-operated TDWR testbed radar. The primary goal of the research was to determine the relative accuracy of several methods designed to generate a numerical microburst hazard index, called the F factor, from ground-based Doppler radar data. It is hope that this work will provide both a qualitative and quantitative basis for the discussion and assessment of microburst hazard reporting for ground-based microburst detection systems. The Integrated Airborne Wind Shear Program is a joint NASA/FAA program with the objective to provide the technology base that will permit low altitude windshear risk reduction through airborne detection, warning, and avoidance. Additionally, the program aims to demonstrate the practicality and utility of real-time assimilation and synthesis of ground-derived windshear data to support executive level cockpit warning and crew-centered information display. Lincoln Laboratory joined this effort and provided the weather radar ground support and some of the post-flight data analysis for NASA's microburst penetration flights in Orlando, Florida.
Summary
In the past decade, a great deal of effort has been invested in developing ground based wind shear detection systems for major U.S. airports. However, there has been a lack of research in developing a quantitative relationship between the wind shear hazards detected by ground based systems and the actual...
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Quantifying airport terminal area weather surveillance requirements
May 24, 1993
Conference Paper
Published in:
26th Int. Conf. on Radar Meteorology, 24-28 May 1993, pp. 47-49.
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Summary
The Federal Aviation Administration (FAA) Terminal Area Surveillance System (TASS) research, engineering, and development program was initiated in part to address future weather sensing needs in the terminal area. By the early 21st century, planned systems such as the Terminal Doppler Weather Radar (TDWR) and Airport Surveillance Radar-9 (ASR-9) will be well into their designed life cycles. Any new terminal weather surveillance system should be designed to address existing deficiencies. Key unmet weather sensing needs include detections of: true 3-dimensional winds (vs. radial component), winds in the absence of precipitation, wake vortices, total lightning, hail, icing conditions, clear air turbulence, hazardous weather cells (with adequate time and space resolution), cloud cover and cloud bases (including layers), fog, and visibility (Runway Visual Range), as well as predictions of: the atmospheric conditions mentioned above, wind shifts, microbursts, tornadoes, and snow/rainfall rates (Evans 1991a, McCarthy 1991). In this paper, we investigate the premise that hazardous weather cells are not currently being measured with adequate time and space resolution in the terminal area. Since a new surveillance system should be based on knowledge of storm dynamics, we have performed a preliminary study of update rate (using rapid scan radar to detect rapidly developing thunderstorms and precursors to the low altitude hazards such as microbursts that they produce. Other aspects of a future radar system such as multi-parameter techniques required to discriminate between ice and water phase precipitation, etc. are not considered.
Summary
The Federal Aviation Administration (FAA) Terminal Area Surveillance System (TASS) research, engineering, and development program was initiated in part to address future weather sensing needs in the terminal area. By the early 21st century, planned systems such as the Terminal Doppler Weather Radar (TDWR) and Airport Surveillance Radar-9 (ASR-9) will...
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Preliminary results of the weather testing component of the Terminal Doppler Weather Radar operational test and evaluation
May 24, 1993
Conference Paper
Published in:
Proc. 26th Int. Conf. on Radar Meteorology, 24-28 May 1993, pp. 29-34.
Summary
The Terminal Doppler Weather Radar (TDWR) system which has been developed by Raytheon Co. for the Federal Aviation Administration (FAA), provides automatic detection of microbursts and low-altitude wind shear. Microburst- and gust front-induced wind shear can result in a sudden, large change in airspeed which can have disastrous effect on aircraft performance. during take off or landing. The second major function of TDWR is to improve air traffic management through forecasts of wind shifts, precipitation and other weather hazards. The TDWR system generates Doppler velocity, reflectivity, and spectrum width data. The base data are automatically dealiased and clutter is removed through filtering and mapping. Precipitation and windshear products, such as microbursts and gust fronts, are displayed as graphic products on the Geographic Situation Display which is intended for use by Air Traffic Control supervisors. Alphanumeric messages indicating the various windshear alerts and derived airspeed losses and gains are sent to a flat panel ribbon display which is used by the controllers in the control tower. The TDWR proof-of-concept and operational feasibility have been demonstrated in a number of FAA-sponsored tests and evaluations conducted by Massachusetts Institute of Technology's Lincoln Laboratory (MIT/LL) in Memphis, TN (1985); Huntsville, AL (1986); Denver, CO (1987, 1988); Kansas City, MO (1989, and Orlando, FL (1990-1992). In order to verify that the TDWR meets FAA operational suitability and effectiveness requirements, an Operational Test & Evaluations (OT&E) was conducted at the Oklahoma City site during the period from 24 August to 30 October 1992. The testing addressed National Airspace System (NAS)-SS-1000 requirements, weather detection performance, safety, operational system performance, maintenance, instruction books, Remote Maintenance Monitoring System (RMMS), system adaptable parameters, bullgear wear, and limited Air Traffic (AT) suitability. The TDWR OT&E Integration and Operational testing was conducted using a variety of methods dependent on the area being tested. This paper discusses primarily the weather detection performance testing. A rough analysis was performed on the algorithm output and the base data to determine the performance of the TDWR in detecting wind shear phenomena. Final results will be available after additional testing, which is scheduled for Spring of 1993, and post analysis in conducted.
Summary
The Terminal Doppler Weather Radar (TDWR) system which has been developed by Raytheon Co. for the Federal Aviation Administration (FAA), provides automatic detection of microbursts and low-altitude wind shear. Microburst- and gust front-induced wind shear can result in a sudden, large change in airspeed which can have disastrous effect on...
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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.
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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.
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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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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.
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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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