Publications
Effects of metering precision and terminal controllability on runway throughput
July 1, 1993
Journal Article
Published in:
Air Traffic Control Q., Vol. 1, No. 3, July 1993, pp. 277-297.
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Summary
In order to efficiently use available runway capacity while avoiding undue congestion within terminal airspace, systems of flow control and en route metering have been implemented. Recent work in automation has attempted to extend traffic flow planning to provide precise scheduling of traffic flow within the terminal area itself (from the metering fixes to the runways). The goal of this more detailed terminal scheduling is more efficient runway utilization. This article addresses an important practical question regarding the degree of precision required from the en route portion of such systems in order to allow the terminal scheduler to achieve its throughput benefits. The answer to this question determines the sophistication and rigidity required of en route automation and addresses the question of whether the success of new terminal automation is contingent upon improvements in en route metering. The method of analysis is mathematical modeling and fast-time computer simulation. A crucial parameter is controllability, which expresses the largest flight delay that the terminal scheduling can impose within the airspace available to it. The analysis reveals that achievable run-way utilization depends upon the type of metering employed, the available controllability within the terminal, and the extent to which controllers can be expected to intervene to handle transient peaks in arrival rates that cannot be handled by the automation. The major conclusion of the study is that in order to fully utilize a runway, the standard deviation of the errors in arrival time at the metering fixes should be kept to about half the terminal controllability. For the airports studied, there seems to be sufficient controllability available to allow a terminal scheduler to operate the runways at essentially full capacity when a metering system, even with modest delivery precision, is operating in the en route area.
Summary
In order to efficiently use available runway capacity while avoiding undue congestion within terminal airspace, systems of flow control and en route metering have been implemented. Recent work in automation has attempted to extend traffic flow planning to provide precise scheduling of traffic flow within the terminal area itself (from...
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Mode-S data link
June 1, 1993
Journal Article
Published in:
J. of ATC, June 1993, pp. 34-37.
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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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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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Adjoint-method retrievals of microburst winds from TDWR data
May 24, 1993
Conference Paper
Published in:
26th Int. Conf. on Radar Meteorology, 24-28 May 1993, pp. 433-434.
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Summary
The simple adjoint (SA) method of Qiu and Xu (1992, henceforth referred to as QX92) was recently upgraded and tested with the Phoenix-II data for retrieving the low-altitude winds from single-Doppler scans (Xu et al. 1993a,b henceforth referred to as XQY93a,b). The major results can be briefly reviewed as follows: (i) Using multiple time-level data with the adjoint formulation makes the retrieval more accurate and less sensitive to the observational error. (ii) Imposing a weak nondivergence constraint can suppress the spurious divergence caused by the data noise and improve the retrieval. (iii) Retrieving the eddy coefficients improves the wind retrieval. (iv) Retrieving the time-man residual term improves the wind retrieval. Although the results in XQY93a,b were encouraging, the Phoenix-II data used in XQY93a,b were collected on non-storm days with chaff dispensed from an aircraft. The real challenge is to test the SA method with storm data. A microburst case is selected for the test in this paper.
Summary
The simple adjoint (SA) method of Qiu and Xu (1992, henceforth referred to as QX92) was recently upgraded and tested with the Phoenix-II data for retrieving the low-altitude winds from single-Doppler scans (Xu et al. 1993a,b henceforth referred to as XQY93a,b). The major results can be briefly reviewed as follows...
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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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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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