Publications
Terminal Doppler Weather Radar operational test and evaluation Orlando 1990
April 9, 1991
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-179
Summary
Lincoln Laboratory conducted an evaluation for hte Federal Aviation Administration (FAA) Terminal Doppler Weather Radar (TDWR) system in Orlando, Florida during the cummer of 1990. In previous years, evaluations have been conducted at airports in Kansas City, MO (1989) and Denver, CO (1988). Since the testing at the Kansas City International Airport, the radar was modified to operate in C-band, which is the intended frequency band for the production TDWR systems. The objectives of the 1990 evaluation period were to evaluate TDWR system performance in detecting low-altitude wind shear, specifically microbursts and gust fronts, at the Orlando International Airport and in the surrounding area; to refine the system's wind shear detection capabilities; and to evaluate elements of the system developed by the contractor, which were new for this C-band system and therefore not available for evaluation in previous years. Some performance comparisons are made among results from the vastly different weather environments of Denver, Kansas City, and Orlando. The report discusses and presents statistics for the performance of the system in detecting and predicting microbursts and gust fronts. A significant use of the prediction capability is its potential use for air traffic control (ATC) personnel to plan aitport operations when hazardous weather is predicted. Issues such as low-velocity ground clutter (from tree leaves, road traffic, and dense urban areas) that affect prediction performance are discussed, along with possible software modifications to account for them. FInally, the ATC personnel and pilots who took part in the evaluation provide the users' perspectives on the usefulness of the system's capabilities.
Summary
Lincoln Laboratory conducted an evaluation for hte Federal Aviation Administration (FAA) Terminal Doppler Weather Radar (TDWR) system in Orlando, Florida during the cummer of 1990. In previous years, evaluations have been conducted at airports in Kansas City, MO (1989) and Denver, CO (1988). Since the testing at the Kansas City...
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Dynamic suppression of interface-state dark current in buried-channel CCDs
February 1, 1991
Journal Article
Published in:
IEEE Trans. Electron. Devices, Vol. 38, No. 2, February 1991, pp. 285-290.
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Summary
It is shown that the time dependence of the carrier generation rate at a depleted surface can be exploited to completely suppress interface-state dark current in buried-channel charge-coupled devices (CCDs). When a surface is switched from an inverted to a depleted state, the generation current recovers with a time constant which is strongly temperature dependent and varies from a few milliseconds at room temperature to nearly 3 h at -80 degrees C. This property can be applied to three- and four-phase CCDs by exchanging charge packets between adjacent phases within a cell at a rate that ensures that each phase remains out of inversion for time that is short in comparison to the recovery time. Measurements of this effect have been made on a CCD imager over the temperature range from -40 degrees C to +22 degrees C, and the results agree well with theory.
Summary
It is shown that the time dependence of the carrier generation rate at a depleted surface can be exploited to completely suppress interface-state dark current in buried-channel charge-coupled devices (CCDs). When a surface is switched from an inverted to a depleted state, the generation current recovers with a time constant...
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Peak-to-rms reduction of speech based on a sinusoidal model
February 1, 1991
Journal Article
Published in:
IEEE Trans. Signal Process., Vol. 39, No. 2, February 1991, pp. 273-288.
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Summary
In a number of applications, a speech waveform is processed using phase dispersion and amplitude compression to reduce its peak-to-rms ratio so as to increase loudness and intelligibility while minimizing perceived distortion. In this paper, a sinusoidal-based analysis/synthesis system is used to apply a radar design solution to the problem of dispersing the phase of a speech waveform. Unlike conventional methods of phase dispersion, this solution technique adapts dynamically to the pitch and spectral characteristics of the speech, while maintaining the original spectral envelope. The solution can also be used to drive the sine-wave amplitude modification for amplitude compression, and is coupled to the desired shaping of the speech spectrum. The new dispersion solution, when integrated with amplitude compression, results in a significant reduction in the peak-to-rms ratio of the speech waveform with acceptable loss in quality. Application of a real-time prototype sine-wave preprocessor to AM radio broadcasting is described.
Summary
In a number of applications, a speech waveform is processed using phase dispersion and amplitude compression to reduce its peak-to-rms ratio so as to increase loudness and intelligibility while minimizing perceived distortion. In this paper, a sinusoidal-based analysis/synthesis system is used to apply a radar design solution to the problem...
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Clutter suppression for Doppler weather radars with multirate sampling schemes
December 11, 1990
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-149
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Summary
Reliable weather parameter estimates are required of radars such as the Terminal Doppler Weather Radar (TDWR) - a Federal Aviation Administration project - which will automatically detect hazaradous weather phenomena in the vicinity of an airport. Velocity and range aliasing will degrade the quality of these estimates, as will contamination by ground clutter. For radars which operate at short ranges and at low elevation angles, as the TDWR will to detect windshears at the airport surface, clutter contamination is an especiallly severe problem. Multirate pulse trains - pulse trains containing multiple intersample spacings - can extend both the unambiguous velocity and range of a Pulsed Doppler Radar beyond those afforded by pulse trains with a constant intersample spacing; but the usual properties of conventional clutter filter architectures change radically when applied to data collected with a multirate sampling scheme. A brief introduction to the systems and weather considerations fo Doppler Weather Radars is provided and the Pulse-Pair spectral moment estimators are presented. This introduction is followed by a discussion of frequency domain clutter rejection tecniques for Batch PRT (Pulse Repetition Time) sequences - blocks of equispaced samples with the PRT alternating from block to block. The main topic of the report is clutter suppression for Staggered PRT sequences in which the PRT alternates from pulse to pulse. The Staggered PRT scheme has the advantage over the Batch PRT scheme of spatial coherency for estimates of the radar return signal's autocorrelation function at the lags corresponding to the two PRT's. A time-varying filter architecture with multiple transfer functions is presented and analyzed, and its interaction with the Pulse-Pair estimators is explored. Three design techniques for Staggered PRT filters are described and assessed in the context of clutter suppression. The final section of the report summarizes the results for the Batch and Staggered PRT schemes and provides suggestions for further research.
Summary
Reliable weather parameter estimates are required of radars such as the Terminal Doppler Weather Radar (TDWR) - a Federal Aviation Administration project - which will automatically detect hazaradous weather phenomena in the vicinity of an airport. Velocity and range aliasing will degrade the quality of these estimates, as will contamination...
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Characteristics of thunderstorm-generated low altitude wind shear: a survey based on nationwide Terminal Doppler Weather Radar testbed measurements
December 1, 1990
Conference Paper
Published in:
Proc. 29th IEEE Conf. on Decision and Control, 5-7 December 1990, Vol. 2, pp. 682-688.
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Summary
The characteristics of microbursts and gust fronts, two forms of aviation-hazardous low altitude wind shear, are presented. Data were collected with a prototype terminal Doppler weather radar and a network of surface weather stations in Memphis, Huntsville, Denver, Kansas City, and Orlando. Regional differences and features that could be exploited in detection systems such as the associated reflectivity, surface wind shear, and temperature change are emphasized.
Summary
The characteristics of microbursts and gust fronts, two forms of aviation-hazardous low altitude wind shear, are presented. Data were collected with a prototype terminal Doppler weather radar and a network of surface weather stations in Memphis, Huntsville, Denver, Kansas City, and Orlando. Regional differences and features that could be exploited...
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A study of dry microburst detection with airport surveillance radars
November 29, 1990
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-176
Summary
This report evaluates the capability of Airport Surveillance Radars (ASRs) for the detection of low altitude wind shear associated with the outflows of dry microbursts. It describes results of simulations of dry microburst observations by an ASR. These simulations incorporated weather and clutter data collected by the FL-2 pencil-beam Doppler weather radar at Denver Stapleton Airport in 1988 and 1989 and clutter data collected by the FL-3 ASR-9 emulation radar at Hunstville, Alabama. The impact of signal strength, overhanging precipitation, and ground clutter on both observability and algorithmic performance are assessed. Principal results of study are the following: 1. Overhanging precipitation and weak signal strength do not, by themselves, prohibit detection of dry outflows; however, occurence of false alarms and biases in velocity estimates indicate that improvements in the dual beam estimator that was evaluated would be required for reliable detection of these events. 2. Ground clutter tends to obscure dry outflow in regions where the difference between median effective clutter reflectivity and weather reflectivity exceeds 17-20 dB. A method for predicting the percentage of missed microburst detections due to ground clutter is used to estimate overall microburst detection probabilities for a "dry" environment such as Denver. Using measured clutter from an experimental ASR in Hunstville, AL, overall microburst detection probability is 83 percent. Using simulated Denver clutter, overall detection probability is 91 percent.
Summary
This report evaluates the capability of Airport Surveillance Radars (ASRs) for the detection of low altitude wind shear associated with the outflows of dry microbursts. It describes results of simulations of dry microburst observations by an ASR. These simulations incorporated weather and clutter data collected by the FL-2 pencil-beam Doppler...
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Automated flight strip management system functional description
November 19, 1990
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-174
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This document gives a high level functional overview of an automated flight strip management system. The current manual flight strip system at Boston's Logan Airport is reviewed and described in detail for both the Tower Cab and TRACON with emphasis on the information flow as an aircraft progresses through the system. The interfaces between the ATC elements, as they related to flight data, are explained. Finally, the system requirements are described including specific requirements for Tower Cab positions.
Summary
This document gives a high level functional overview of an automated flight strip management system. The current manual flight strip system at Boston's Logan Airport is reviewed and described in detail for both the Tower Cab and TRACON with emphasis on the information flow as an aircraft progresses through the...
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A prototype microburst prediction product for the terminal doppler weather radar
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 393-396.
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Summary
This paper describes a prototype microburst prediction product for the Terminal Doppler Weather Radar (TDWR). The prediction product was evaluated for microbursts observed during the spring and summer of 1989 at Kansas City. Results are presented demonstrating reliable prediction of high reflectivity microbursts of at least 15 m/s outflow intensity from single-Doppler radar data. The ability of the algorithm to predict microbursts approximately five minutes prior to the onset of surface outflow could be used to improve air traffic control (ATC) planning and to improve hazard warning time to pilots. In particular, this product could allow aircraft to avoid an impending microburst hazard, rather than penetrating it. The present TDWR microburst recognition algorithm uses features aloft such as reflectivity cores and convergence to recognize microburst precursors. The algorithm uses precursors to make a microburst declaration while the surface outflow is still weak, thereby improving the hazard warning time (Campbell, 1989). The microburst prediction product is an extension of the algorithm to predict microbursts from these precursor signatures. The prototype prediction product is tuned to predict the high reflectivity microburst typical of humid regions of the United States. The paper begins by reviewing conceptual models for microburst development and comparing them to the observed characteristics of Kansas City microbursts. The prototype prediction product is then described, and performance statistics are presented. Finally, failure mechanisms and future work are discussed.
Summary
This paper describes a prototype microburst prediction product for the Terminal Doppler Weather Radar (TDWR). The prediction product was evaluated for microbursts observed during the spring and summer of 1989 at Kansas City. Results are presented demonstrating reliable prediction of high reflectivity microbursts of at least 15 m/s outflow intensity...
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A comparison of anemometer and Doppler radar winds during wind shear events
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 356-361.
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The Federal Aviation Administration (FAA) currently uses the anemometer-based Low Level Wind Shear Alert System (LLWAS) as the primary method of wind shear detection at major U.S. airports. With the upcoming deployment of the Terminal Doppler Weather Radar (TDWR) system, potential methods for integrating the two systems are being investigated. By integrating, advantages of both sensor systems can be utilized. Advantages of the LLWAS ground sensor network include true wind direction measurements, a high measurement frequency, a lack of sensitivity to clear air reflectivity, and few false alarms from radar point targets such as planes, birds, etc. Advantages of the radar include complete scan coverage of the region of concern, the ability to predict events, fewer terrain problems such as sheltering which can reduce the wind speed readings, and almost no false alarms due to non-hazardous wind shear such as thermals. The objectives of this study are to gain a clearer understanding of the basic relationship between the wind information provided by these two very different sensing systems, and to determine the impact this relationship may have on integration of the two operational systems. A proposed mathematical technique for "correcting" LLWAS winds where needed to better match radar winds is evaluated for cases of microburst (divergent) and gust front (convergent) wind shear.
Summary
The Federal Aviation Administration (FAA) currently uses the anemometer-based Low Level Wind Shear Alert System (LLWAS) as the primary method of wind shear detection at major U.S. airports. With the upcoming deployment of the Terminal Doppler Weather Radar (TDWR) system, potential methods for integrating the two systems are being investigated...
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A case study of the Claycomo, Missouri microburst on July 30, 1989
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 388-392.
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The Terminal Doppler Weather Radar (TDWR) testbed collected thunderstorm measurements in the Kansas City area from March 27 through October 6, 1989. Of the 393 microbursts detected by the radar, 21 were classified as severe, with a differential velocity > 24 m/s. None of the severe events impacted terminal operations at Kansas City International Airport (KCI). Nevertheless, there were 42 microbursts within 3 nautical miles of the airport.
Summary
The Terminal Doppler Weather Radar (TDWR) testbed collected thunderstorm measurements in the Kansas City area from March 27 through October 6, 1989. Of the 393 microbursts detected by the radar, 21 were classified as severe, with a differential velocity > 24 m/s. None of the severe events impacted terminal operations...
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