Publications
Observability of microbursts using Doppler weather radar and surface anemometers during 1987 in Denver, CO
December 29, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-161
Summary
This report focuses on the observability of microbursts using pulse Doppler weather radars and surface anemometers respectively by an experienced meterologist. The data used for this study were collected in the Denver, Colorado area during the FAA Terminal Doppler Weather Radar (TDWR) measurement program in 1987. The methods used for declaring a microburst from both Doppler radar and surface anemometer data are described. The main objective of this report is to compare the 1987 radar observed microbursts (which impacted the area covered by a surface anemometer system) with the surface mesonet observed microbursts. Of the 66 microbursts for which radar and mesonet data were available, 4 were not observed by the radar and 1 was not observed by the mesonet. All four microbursts not observed by the radar were classified as "dry" events with low surface reflectivities and with three of the four being relatively weak (peak velocity differences < 20 m/s) shear events. Possible reasons as to why these microbursts were not observed are discussed in detail. The strongest event exceeded 20 m/s (differential velocity) for two minutes and appears to have been missed due to a combination of very low reflectivity and a very shallow depth overflow.
Summary
This report focuses on the observability of microbursts using pulse Doppler weather radars and surface anemometers respectively by an experienced meterologist. The data used for this study were collected in the Denver, Colorado area during the FAA Terminal Doppler Weather Radar (TDWR) measurement program in 1987. The methods used for...
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Observability of microbursts with Doppler weather radar during 1986 in Huntsville, AL
December 29, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-160
Summary
Thhis report investigates the observability of low-level wind shear events using Doppler weather radar through a comparison of radar and surface wind sensor data. The data was collected during 1986 in the Huntsville, AL area as part of the FAA Terminal Doppler Weather Radar (TDWR) development program. Radar data were collected by both an S-band radar (FL-2) and C-band radar (UND). Surface data were collected by a network of 77 weather sensors covering an area of enarly 1000 square km centered approximately 15 km to the northwest of the FL-2 radar site. The UND site was located at the approximate center of the surface sensor network. A list of 131 microbursts which impacted the surface sensor network is presented. Particular emphasis is on the 107 events for which both radar data and surface data where available. Of these events, 14 were not observed by the surface network, while two events were not identified as microbursts by radar. Possible explanations of these missed microburst identifications are presented. The first case was an instance of the radar viewing a weak, asymmetric event from an unfavorable viewing angle. The second case describes an extremely shallow microburst outflow occurring at a heigh too low to be observed by the lowest elevation scan of the radar. In each of these cases, the featured microburst was very weak and, although a microburst-strength differential velocity was not observable by radar, in both instances the divergent wind pattern associated with the event was clearly evident in the radar velocity data field. All microbursts which exhibited a differential velocoity of in excess of 13 m/s were identified by radar. No microbursts went unobserved as the result of insufficient signal return.
Summary
Thhis report investigates the observability of low-level wind shear events using Doppler weather radar through a comparison of radar and surface wind sensor data. The data was collected during 1986 in the Huntsville, AL area as part of the FAA Terminal Doppler Weather Radar (TDWR) development program. Radar data were...
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Miss distance analysis for command guided missiles
December 1, 1988
Journal Article
Published in:
J. Guid. Control Dyn., Vol. 11, No. 6, November-December 1988, pp. 481-487.
Summary
A concise theoretical technique is presented for estimating the minimum miss distance capability of command guided missile systems using synthetic proportional navigation. The effect of the parameter values on the system capability is shown to be a function of range-to-intercept; the technique enables the system designer and analyst to quantify system performance and to develop a systematic understanding of the performance limitations of command guidance systems at each intercept range. New analytical equations based upon adjoint theory are developed for statistical miss distance caused by target maneuver, range-dependent, servo, glint and atmosphere noises for command guided systems. An optimal total system time constant is derived which yields the minimum statistical miss distance. Realistic constraints on the minimum achievable system time constant are considered. The equations derived for the optimal total system time constant are valuable to the system designer for minimizing miss distance over the ranges of system parameters and limitations, and intercept conditions.
Summary
A concise theoretical technique is presented for estimating the minimum miss distance capability of command guided missile systems using synthetic proportional navigation. The effect of the parameter values on the system capability is shown to be a function of range-to-intercept; the technique enables the system designer and analyst to quantify...
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TDWR Scan Strategy Requirements
November 3, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-144
Summary
This report describes the requirements for the wan s+rategy to be employed M the
Terminal Doppler Weather Radar (TDWR). The report in divided into three main sections:
rationale, example scan strategy and requirements. The rationale for the TDWR scanstrategy
is presented in terms of 1) detection of meteorological phenomena, and 2) minimization of
range and velocity folding effects. Next, an example is provided based on an experimental scan
strategy used in Denver during the summer of 1987. Finally, the requirements for the TDWR
scan strategy are presented based on the preceding discussion. Also, an appendix is included describing the proposed criteria for switching between scan modes.
Terminal Doppler Weather Radar (TDWR). The report in divided into three main sections:
rationale, example scan strategy and requirements. The rationale for the TDWR scanstrategy
is presented in terms of 1) detection of meteorological phenomena, and 2) minimization of
range and velocity folding effects. Next, an example is provided based on an experimental scan
strategy used in Denver during the summer of 1987. Finally, the requirements for the TDWR
scan strategy are presented based on the preceding discussion. Also, an appendix is included describing the proposed criteria for switching between scan modes.
Summary
This report describes the requirements for the wan s+rategy to be employed M the
Terminal Doppler Weather Radar (TDWR). The report in divided into three main sections:
rationale, example scan strategy and requirements. The rationale for the TDWR scanstrategy
is presented in terms of 1) detection of meteorological phenomena, and...
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A preliminary study of precursors to Huntsville microbursts
October 25, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-153
Summary
Lincoln Laboratory under the sponsorship of the FAA is currently developing automated algorithms for the detection of wind shears such as microbursts and gust fronts. Previous studies have shown that these outflows can be hazardous to an airplance during takeoffs and landings. The ultimate goal of a microburst detection algorithm is the timely warning of potentially hazardous wind shears through the detection of reliable precursors. Research in Colorado and Oklahoma documented the significance of precursors such as descending reflectivity cores, convergence, rotation, and reflectivity notching as indicators that a microburst will occur in the very near future. The overall importance of an individual feature varies between regions. This investiagtion will focus on those precursors which play a dominant role in the formation of wet microbursts in the southern United States. The data analyzed in this report was gathered by the FAA TDWR S-band Doppler radar during 1985 and 1986 in Memphis, Tennessee, and Hunstville, Alabama.
Summary
Lincoln Laboratory under the sponsorship of the FAA is currently developing automated algorithms for the detection of wind shears such as microbursts and gust fronts. Previous studies have shown that these outflows can be hazardous to an airplance during takeoffs and landings. The ultimate goal of a microburst detection algorithm...
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Low-altitude wind shear detection with airport surveillance radars: evaluation of 1987 field measurements
August 31, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-159
Summary
A field measurement program is being conducted to investigate the capabilities of airport surveillance radars (ASR) to detect low altitude wind shear (LAWS). This capability would require minor RF signal path modifications in existing ASRs and the addition of a signal processing channel to measure the radial velocity of precipitation wind tracers and automatically detect regions of hazardous velocity shear. A modified ASR-8 has been deployed in Huntsville, Alabama and is operated during periods of nearby thunderstorm activity. Data from approximately 30 "wet" (i.e., high radar reflectivity) microbursts during 1987 have been evaluated through comparison with simultaneous measurements from a collocated pencil beam weather radar. In this report, we describe the 1987 field experiment and utilize the resulting data to illustrate problems and potential prcoessing approaches for LAWS detection with airport surveillance radars. Techniques are described for estimation of low altitude wind fields in the presence of interference such as ground clutter or weather aloft and for automatic detection of microburst wind shear from the resulting radial velocity fields. Evaluation of these techniques using case studies and statistical scoring of the automatic detection algorithm indicates that a suitability modified ASR could detect wet microbursts within 16 km of the radar with a detection probability in excess of 0.90 and a corresponding false alarm probability of less than 0.10. These favorable results indicate the need for careful consideration of implementation issues and the potential operational role of wind measurements from an ASR.
Summary
A field measurement program is being conducted to investigate the capabilities of airport surveillance radars (ASR) to detect low altitude wind shear (LAWS). This capability would require minor RF signal path modifications in existing ASRs and the addition of a signal processing channel to measure the radial velocity of precipitation...
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Preliminary results of the 1983 Coordinated Aircraft - Doppler weather radar turbulence experiment, volume 1
July 26, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-137-I
Summary
This report presents results of analyses of coordinated radar-aircraft data acquired form the 1983 experiment conducted at Hanscom AFB, Massachusetts. The objective of the experiment is to assess and validate the current NEXRAD algorithms for estimating aircraft turbulence from volume-scanned Doppler weather observations. Estimates of the turbulence severity index epsilon to the 1/3 power (a quantity used by NEXRAD) computed from radar and aircraft data are presented as a time series along each aircraft track. The radar point estimates of turbulence were averaged horizontally and vertically to yield layered Cartesian maps such as are intended for use by real time ATC controllers and pilots. The derived gust velocity (Ude), also used to indicate the intensity of aircraft encountered turbulence, was computed so that comparisons could be made of the turbulence intensity scales inferred from values of epsilon and U sub de. These quantitative comparisons indicate that for the turbulence generally encountered during the flights, both radar and aircraft estimates of epsilon to the 1/3 power significantly overstate the severity of turbulence as reported by the aircraft pilot. The data analysis also shows that radar-based estimates of epsilon to the 1/3 power, often significantly exceeded aircraft based estimates of epsilon to the 1/3 power. In contrast, the quantity Ude underestimates the aircraft reported turbulence intensity on all the flights. The uncertainty as to operationally useful thresholds for radar epsilon to the 1/3 power, aircraft epsilon to the 1/3 power and Ude is discussed as is the use of spectrum width as a turbulence indicator. It should be noted that the turbulence detection flights used in the study were conducted at ranges such that the radar resolution cell cross range extent was typically 1.5 to 3 km. With such resolution cell size extents, the hypothesis of spatially homogeneous turbulence may not hold and/or the assumed relationship of radar measured spectrum width to kinetic dissipation rate may not be fully accurate.
Summary
This report presents results of analyses of coordinated radar-aircraft data acquired form the 1983 experiment conducted at Hanscom AFB, Massachusetts. The objective of the experiment is to assess and validate the current NEXRAD algorithms for estimating aircraft turbulence from volume-scanned Doppler weather observations. Estimates of the turbulence severity index epsilon...
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Airport surface traffic automation study
May 9, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-156
Summary
This report documents a study of requirements for an Airport Surface Traffic Automation (ASTA) system. The objective was to determine the necessary functions, establish the cost and benefits, and outline a modular system design. The highest priority function identified was an improved surface surveillance and communication system. The greatest potential for safety benefits is provided by automatic conflict alert and collision warning for pilots and controllers to prevent runway incursion accidents. Strategic and tactical planning assistance to maximize runway utilization can improve controller productivity while keeping them responsible for final decisions. The report contains a modular design for ASTA and includes specifications for a man-in-the-loop simulation of the system.
Summary
This report documents a study of requirements for an Airport Surface Traffic Automation (ASTA) system. The objective was to determine the necessary functions, establish the cost and benefits, and outline a modular system design. The highest priority function identified was an improved surface surveillance and communication system. The greatest potential...
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TDWR PRF selection criteria
March 15, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-147
Summary
The Terminal Doppler Weather Radar (TDWR) system shall provide high quality Doppler radar data on weather phenomena near high traffic airports. These data shall be used in real time by automated TDWR algorithms to detect weather situations which may be hazardous to the safe operation of aircraft within the vicinity of the airport. One of the major factors which could cause the degradation of the quality of these TDWR data is obscuration by 'distant' storm cells. This obscuration is caused by storms located beyond the range interval being sampled by the radar, yet whose radar echo ambiguously folds within the range interval of interest. These range aliased echoes could trigger false detections by the algorithms, and/or cause actual hazardous situations near the airport to remain undetected. By carefully selecting the pulse repetition frequency (PRF) of the radar, range obscuration from distant storms can be minimized over specified airport regions. This document describes techniques for predicting the obscuration as a function of PRF, and details the criteria which shall be used by the TDWR system to automatically and adaptively select an optimal PRF in order to minimize these obscuration effects. Weather radar, Radar range obscuration, TDWR, Radar range aliasing, Radar pulse, Repetition Frequency (PRF).
Summary
The Terminal Doppler Weather Radar (TDWR) system shall provide high quality Doppler radar data on weather phenomena near high traffic airports. These data shall be used in real time by automated TDWR algorithms to detect weather situations which may be hazardous to the safe operation of aircraft within the vicinity...
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Characteristics of microbursts observed in the Continental U.S.
February 26, 1988
Conference Paper
Published in:
15th Conf. on Severe Local Storms, 22-26 February 1988, pp. 372-379.
Summary
The topic of microbursts is explored in this paper through a historical perspective and review of the studies that have been performed since Fujita (1976) first introduced the concept. Taken as a whole, this body of work actually defines microbursts, and begins to take some of the initial steps toward their understanding. However, a number of dynamically distinct phenomena that give rise to strong surface outflows are being referred to as microbursts. The recent emphasis within the scientific and aviation communities on understanding microbursts makes it particularly important to categorize these various phenomena according to their meteorological nature and true aviation hazard potential. This paper takes some of the first steps toward this categorization, and emphasizes some of the differences in storms that can be expected in different climatological regimes.
Summary
The topic of microbursts is explored in this paper through a historical perspective and review of the studies that have been performed since Fujita (1976) first introduced the concept. Taken as a whole, this body of work actually defines microbursts, and begins to take some of the initial steps toward...
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