Publications
Mode-S data link
June 1, 1993
Journal Article
Published in:
J. of ATC, June 1993, pp. 34-37.
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Summary
Mode-S is an enhancement of the ATCRBS secondary surveillance radar (SSR) system which adds selective interrogation of individual aircraft, monopulse processing of the replies and a digital data link between the ground station and the aircraft. These features result in greatly improved surveillance accuracy, virtual elimination of synchronous garble of the replies from closely spaced aircraft, and provide a high capacity digital communication link for a wide variety of ground/air/ground messages.
Summary
Mode-S is an enhancement of the ATCRBS secondary surveillance radar (SSR) system which adds selective interrogation of individual aircraft, monopulse processing of the replies and a digital data link between the ground station and the aircraft. These features result in greatly improved surveillance accuracy, virtual elimination of synchronous garble of...
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LNKnet: Neural network, machine-learning, and statistical software for pattern classification
June 1, 1993
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 6, No. 2, Summer/Fall 1993, pp. 249-268.
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Pattern-classification and clustering algorithms are key components of modern information processing systems used to perform tasks such as speech and image recognition, printed-character recognition, medical diagnosis, fault detection, process control, and financial decision making. To simplify the task of applying these types of algorithms in new application areas, we have developed LNKnet-a software package that provides access to more than 20 pattern-classification, clustering, and feature-selection algorithms. Included are the most important algorithms from the fields of neural networks, statistics, machine learning, and artificial intelligence. The algorithms can be trained and tested on separate data or tested with automatic cross-validation. LNKnet runs under the UNM operating system and access to the different algorithms is provided through a graphical point-and-click user interface. Graphical outputs include two-dimensional (2-D) scatter and decision-region plots and 1-D plots of data histograms, classifier outputs, and error rates during training. Parameters of trained classifiers are stored in files from which the parameters can be translated into source-code subroutines (written in the C programming language) that can then be embedded in a user application program. Lincoln Laboratory and other research laboratories have used LNKnet successfully for many diverse applications.
Summary
Pattern-classification and clustering algorithms are key components of modern information processing systems used to perform tasks such as speech and image recognition, printed-character recognition, medical diagnosis, fault detection, process control, and financial decision making. To simplify the task of applying these types of algorithms in new application areas, we have...
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ATCRBS Reply Environment at Memphis International Airport
May 28, 1993
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-198
Summary
This report demonstrates, through data and analysis, how the airport environment can affect ATCRBS surveillance. The Lincoln Laboratory ATCRBS Monopulse Processing Subsystem was used to collect reply data at Memphis International Airport during March 1991. These data show a correlation between aircraft density, potential reflectors, and ATCRBS reply integrity. The number of replies has been shown to be directly related to multipath from reflecting surface, including taxiing aircraft. Additionally, it is shown that conditions can exist during which not all of the replies from ATCRBS equipped aircraft can be processed when forming target report measurements. Finally, it is shown that the bunching of replies in both time and space can introduce reply decoder overloading.
Summary
This report demonstrates, through data and analysis, how the airport environment can affect ATCRBS surveillance. The Lincoln Laboratory ATCRBS Monopulse Processing Subsystem was used to collect reply data at Memphis International Airport during March 1991. These data show a correlation between aircraft density, potential reflectors, and ATCRBS reply integrity. The...
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A shear-based microburst detection algorithm for the Integrated Terminal Weather System (ITWS)
May 24, 1993
Conference Paper
Published in:
26th Int. Conf. on Radar Meteorology, 24-28 May 1993, pp. 667-669.
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Summary
This paper explains the initial design of the ITWS microburst detection algorithm and illustrates some early results. The final section concentrates on the plans for algorithm testing and the planned enhancements to its capabilities.
Summary
This paper explains the initial design of the ITWS microburst detection algorithm and illustrates some early results. The final section concentrates on the plans for algorithm testing and the planned enhancements to its capabilities.
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A machine intelligent gust front algorithm for Doppler weather radars
May 24, 1993
Conference Paper
Published in:
26th Int. Conf. on Radar Meteorology, 24-28 May 1993, pp. 654-656.
Summary
Gust fronts generated by thunderstorms can seriously affect the safety and efficiency of airport operations. Lincoln Laboratory, under contract with the Federal Aviation Administration (FAA), has had a significant role in the development of two Doppler radar systems that are capable of detecting low altitude wind shears, including gust fronts, in the airport terminal control area. These systems are the latest generation Airport Surveillance Radar, enhanced with a Wind Shear Processor (ASR-98 WSP) and the Terminal Doppler Weather Radar (TDWR).
Summary
Gust fronts generated by thunderstorms can seriously affect the safety and efficiency of airport operations. Lincoln Laboratory, under contract with the Federal Aviation Administration (FAA), has had a significant role in the development of two Doppler radar systems that are capable of detecting low altitude wind shears, including gust fronts...
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Clutter filter design for multiple-PRT signals
May 24, 1993
Conference Paper
Published in:
Proc. 26th Int. Conf. on Radar Meteorology, 24-28 May 1993, pp. 235-237.
Summary
The trade-off of range vs. velocity ambiguity is fundamental and operationally significant for many S- and C-band pulsed Doppler weather radars. Transmission schemes using multiple pulse repetition times (PRTs) (i.e., nonuniform pulse spacing) offer the potential for extending the unambiguous measurement range by resolving intervals of velocity ambiguity. Unfortunately, multiple PRT methods can be problematic with low-elevation scanning when ground clutter removal is required. We have constructed both Chebyshev and mean-squared error (MSE) desing algorithms (Choroboy, 1993) that deal with design in the complex domain; the MSE algorithms are described below.
Summary
The trade-off of range vs. velocity ambiguity is fundamental and operationally significant for many S- and C-band pulsed Doppler weather radars. Transmission schemes using multiple pulse repetition times (PRTs) (i.e., nonuniform pulse spacing) offer the potential for extending the unambiguous measurement range by resolving intervals of velocity ambiguity. Unfortunately, multiple...
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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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