Publications
Study of Network Expansion LLWAS (LLWAS-NE) fault identification and system warning optimization through joint use of LLWAS-NE and TDWR data
January 10, 1999
Conference Paper
Published in:
8th Conf. on Aviation, Range, and Aerospace Meteorology (ARAM), 10-15 January 1999.
Summary
Low level wind shear has been identified as an aviation hazard which has caused or contributed to a significant number of aircraft accidents (Soffer, 1990). To protect aircraft from hazardous wind shear, the Federal Aviation Administration (FAA) developed a system called the Low Level Wind Shear Alert System (LLWAS), containing a collection of anemometers as well as data processing logic (Wilson and Gramzow, 1991). The LLWAS has undergone several advancements in both design and algorithmic computation. The latest deployment, known as the Network Expansion Low Level Wind Shear Alert System (LLWAS-NE), consists of additional sensors to the original LLWAS network, providing better coverage of the airfield. In addition, the LLWAS-NE is capable of providing runway-oriented wind shear and microburst alerts with loss and gain values. The alerts from LLWAS-NE will be integrated with those from the Terminal Doppler Weather Radar (TDWR) and the Integrated Terminal Weather System (ITWS) at locations where all systems are available (Cole, 1992; Cole and Todd, 1994). An analysis was undertaken at Orlando (MCO) and Dallas/Ft. Worth (DFW) International Airports to assess the accuracy of wind shear alerts produced by LLWAS-NE and the TDWR/LLWASNE integration algorithm. Identifying improvements that can be made to either system is important, as LLWAS-NE alert information is anticipated to be integrated with ITWS in an ITWS/LLWAS-NE integration algorithm. As currently specified, the ITWS/LLWAS-NE integration algorithm will work the same as the TDWR/LLWAS-NE version. The ITWS/LLWAS-NE algorithm is an area where additional work is necessary to ascertain if the integration parameters should be modified to account for performance differences between the ITWS and TDWR algorithms. We suggest that ongoing assessment of the LLWAS-NE should use both LLWAS-NE data and TDWR base data, when possible. Comparing both data sets also will facilitate optimization of LLWAS-NE parameters used in the computation of the alerts.
Summary
Low level wind shear has been identified as an aviation hazard which has caused or contributed to a significant number of aircraft accidents (Soffer, 1990). To protect aircraft from hazardous wind shear, the Federal Aviation Administration (FAA) developed a system called the Low Level Wind Shear Alert System (LLWAS), containing...
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The benefits of using NEXRAD vertically integrated liquid water as an aviation weather product
January 10, 1999
Conference Paper
Published in:
8th Conf. on Aviation, Range, and Aerospace Meteorology (ARAM), 10-15 January 1999.
Summary
Over the past five years in which the Integrated Terminal Weather System (ITWS) testbed prototypes have been operational, there have been regular discrepancies noticed between the ASR–9 six–level precipitation product and the NEXRAD six–level maximum composite reflectivity product. (1. The NEXRAD composite product used in this study is the NEXRAD maximum composite reflectivity product which both the FAA and the ITWS use for weather data.). At the three prototypes in Memphis, Orlando and Dallas, staff have recognized that in certain situations the NEXRAD composite reflectivity product, which is the ITWS 100 and 200 nm long–range product, can be as much as three Video Integrator and Processor (VIP) levels higher than the ASR–9 precipitation product. This situation has caused some confusion for users of the ITWS system and concern on the part of system safety monitors. The confusion occurs because the two products do not agree with each other. Rhoda and Pawlak (1998) show that more aircraft will deviate around cells of ASR–9 VIP level 4 or greater than will penetrate them. There is also an aviation rule–of–thumb that pilots and air traffic specialists use which states cells of VIP level 3 or greater should be avoided if possible. This rule is a good guide but cannot be applied to the NEXRAD composite product. While the NEXRAD composite may show a cell with an intensity of level 3 or 4, the cell may contain very little of the higher–intensity precipitation while the bulk of the cell contains only level 2. This problem is magnified in the winter months when bright–band effects contaminate the radar data. Clutter [especially anomalous propagation (AP)] contamination of the composite reflectivity product is also a concern (especially when the AP is adjacent to actual weather returns). Differences between the two products will become more apparent with the fielding of the new ITWS situation display which has the capability of displaying both NEXRAD composite reflectivity and ASR–9 data side by side. In this study, we compare the NEXRAD composite reflectivity product with data from both the ASR–9 weather channel and an ASR–9 mosaic product as well as a Vertically Integrated Liquid water (VIL) product generated from NEXRAD base data.
Summary
Over the past five years in which the Integrated Terminal Weather System (ITWS) testbed prototypes have been operational, there have been regular discrepancies noticed between the ASR–9 six–level precipitation product and the NEXRAD six–level maximum composite reflectivity product. (1. The NEXRAD composite product used in this study is the NEXRAD...
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Thunderstorm induced gravity waves as a potential hazard to commercial aircraft
January 10, 1999
Conference Paper
Published in:
8th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 10-15 January 1999.
Summary
Under certain atmospheric conditions, thunderstorm development can induce a phenomenon known as gravity waves (i.e., buoyancy or density waves). These waves are characterized by alternating regions of convergence and divergence over a relatively short distance. Such aerodynamic shear can become hazardous to air traffic if the shear contained within the waves surpasses the threshold for air traffic safety. Gravity waves are particularly hazardous because they develop in seemingly benign weather surrounding the parent thunderstorm and in many cases are not associated with any visual storm feature. Several cases have been studied in which commercial aircraft have encountered gravity waves and have been adversely affected by their encounters. The purpose of this study is to show how gravity waves can have a detrimental effect on aircraft in flight, how gravity waves can be detected, and that need for a detection algorithm exists. With the development of the National Weather Service's Next Generation Radar (WSR–88D NEXRAD) and the Federal Aviation Administration's Terminal Doppler Weather Radar (TDWR), the ability to detect gravity waves exists near many of America's major airports. Since gravity waves are a low–level phenomenon (generally below 2 km), their presence should be of interest to aircraft in the takeoff and landing stages of flight. During operations at Lincoln Laboratory's Integrated Terminal Weather System (ITWS) prototype field site in Dallas, there have been at least two incidents in which commercial aircraft experienced wind shear of at least 40 knots on takeoff, possibly caused by single or multiple gravity wave bands. This study will look at 57 cases of gravity wave formation within the terminal areas of Dallas–Ft. Worth International, Memphis International, and Orlando International airports. Statistics will be compiled to determine the frequency and severity of the gravity waves as well as their duration. The study will include Pilot Reports (PIREPS) from a few of these cases in which aircraft experienced wind shear due to suspected encounters with gravity waves. It is the hope of the author that this study will lead to the development of a detection algorithm that will increase the safety of America's commercial air traffic.
Summary
Under certain atmospheric conditions, thunderstorm development can induce a phenomenon known as gravity waves (i.e., buoyancy or density waves). These waves are characterized by alternating regions of convergence and divergence over a relatively short distance. Such aerodynamic shear can become hazardous to air traffic if the shear contained within the...
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The Terminal Convective Weather Forecast demonstration at the DFW International Airport
January 10, 1999
Conference Paper
Published in:
8th Conf. on Aviation, Range, and Aerospace Meteorology (ARAM), 10-15 January 1999.
Summary
The FAA Convective Weather Product Development Team (PDT) is tasked with developing products for convective weather forecasts for aviation users. The overall product development is a collaborative effort between scientists from MIT Lincoln Laboratory (MIT/LL), the National Center for Atmospheric Research (NCAR), and the National Severe Storms Laboratory (NSSL). As part of the PDT, MIT/LL is being funded to develop algorithms for accurately forecasting the location of strong precipitation in and around airport terminal areas. We began by consulting with air traffic personnel and commercial airline dispatchers to determine the needs of aviation users. Users indicated that convective weather, particularly line storms, caused the most consistent problems for managing air traffic. These storms are by far the major cause of aircraft delays and diversions. MIT/LL has already developed the Integrated Terminal Weather System (ITWS) which combines a variety of near-airport sensors to provide a wide range of current weather information to aviation users. Raytheon is currently building the production ITWS system which will be deployed at 45 major airports by 2003. The initial capability ITWS already provides some convective weather predictive capabilities in the form of storm motion vectors and "Storm Extrapolated Positions" (SEP; leading edge of storm at 10 and 20 minutes). But ITWS users indicated a desire for enhanced forecasts which showed the full spatial extent of the weather, how the weather would change (grow or decay) and extended forecast time periods to at least out one hour. Our approach is to develop an algorithm which may be added as a future product improvement to the ITWS system. Previous attempts at producing forecasts have focused on convective initiation and building from short-term (20-30 min) cell forecasts. Our "reverse time" approach of attacking longer time scale (60 min) features first is an outgrowth of addressing user needs and the discovery of improved tracking techniques for large scale precipitation features. The "Growth and Decay Tracker" developed by MIT/LL (Wolfson et.al., 1999) allows us to generate accurate short and long term forecasts of large scale precipitation features. This paper details the Terminal Convective Weather Forecast (TCWF) demonstration ongoing at Dallas/Ft. Worth International Airport (DFW) and discusses the underlying algorithm being developed.
Summary
The FAA Convective Weather Product Development Team (PDT) is tasked with developing products for convective weather forecasts for aviation users. The overall product development is a collaborative effort between scientists from MIT Lincoln Laboratory (MIT/LL), the National Center for Atmospheric Research (NCAR), and the National Severe Storms Laboratory (NSSL). As...
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Development of improved TCAS II surveillance and interference limiting functions
January 1, 1999
Journal Article
Published in:
Air Traffic Control Q., Vol. 7, No. 1, 1999, pp. 19-46.
Summary
This paper describes the development and validation of improved TCAS II intruder surveillance tracking and interference limiting algorithms. Improvements in interference limiting were prompted by the FAA Spectrum Management Office and by international aviation administrations in order to further reduce interference to ground-based air traffic control surveillance by TCAS II. Improvements in surveillance tracking were prompted by aircarrier pilot organizations in order to increase the level of traffic situational awareness offered by the TCAS II display. The new algorithms are included in a proposed new version of TCAS II MOPS DO-185A which is commonly referred to as Change 7.0. TCAS II change 7.0 units will be introduced into the US airspace beginning as early as 1999 as part of a program to implement improvements in both TCAS II surveillance and collision avoidance.
Summary
This paper describes the development and validation of improved TCAS II intruder surveillance tracking and interference limiting algorithms. Improvements in interference limiting were prompted by the FAA Spectrum Management Office and by international aviation administrations in order to further reduce interference to ground-based air traffic control surveillance by TCAS II...
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TCAS II use of ADS-B surveillance data through hybrid surveillance
January 1, 1999
Journal Article
Published in:
Air Traffic Control Q., Vol. 7, No. 2, 1999, pp. 109-121.
Summary
This paper describes a technique that enables TCAS II to use passive surveillance data obtained via extended squitter, an implementation of automatic dependent surveillance broadcast (ADS-B). The technique, known as hybrid surveillance, is based upon the use of TCAS active surveillance to perform validation of the reported ADS-B position at track acquisition. Aircraft that pass initial validation are maintained on passive surveillance until they become a near threat. At that time, TCAS begins regular active surveillance and thus uses its current surveillance techniques for traffic and resolution advisories. In this way, TCAS is able to use passive extended squitter data while retaining its role as an independent monitor. Simulation results show that the use of passive information for non-threatening aircraft results in a significant decrease in TCAS interrogation rate. This enables TCAS to delay or avoid the range reduction that is now required in order for TCAS to remain within its interference budget in high traffic density airspace. Maintaining TCAS operating range in high density air-space enhances TCAS ability to support situational awareness for the flight crew.
Summary
This paper describes a technique that enables TCAS II to use passive surveillance data obtained via extended squitter, an implementation of automatic dependent surveillance broadcast (ADS-B). The technique, known as hybrid surveillance, is based upon the use of TCAS active surveillance to perform validation of the reported ADS-B position at...
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Total global lightning inferred from Schumann resonance measurements
December 27, 1998
Journal Article
Published in:
J. Geophys. Res., Vol. 103, No. D24, 27 December 1998, pp. 31,775-31,779.
Summary
Radiation with frequencies of 5-30 Hz is ducted between Earth's surface and ionosphere with little attenuation; at the lowest frequencies, waves travel several times around the Earth before losing most of their energy. Much of this radiation is produced by lightning. Here we assume that all of this radiation is produced by lightning, and attempt to invert the observed and electric and magnetic fields to infer global lightning activity. We show 10 days of inversions. For these 10 days, the inferred average rate of vertical charge transfer squared is only 1.7 105 (ten to the fifth) (Ckm)2/s Other studies suggest that the root mean square moment change of a flash is about 166 Coulomb kilometers. If we naively assume that each of these flashes is composed of four equally sized strokes, then we conclude that our entire observed signal could be produced by only 22 flashes per second.
Summary
Radiation with frequencies of 5-30 Hz is ducted between Earth's surface and ionosphere with little attenuation; at the lowest frequencies, waves travel several times around the Earth before losing most of their energy. Much of this radiation is produced by lightning. Here we assume that all of this radiation is...
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En route ATM decision support tool computer-human interface requirements development
December 1, 1998
Conference Paper
Published in:
2nd USA/Europe Air Traffic Management R&D Seminar, 1-4 December 1998.
Summary
MIT Lincoln Laboratory (MIT/LL) is supporting the FAA-sponsored effort to specify Computer Human Interface (CHI) requirements for the En Route Air Traffic Management Decision Support Tools (ERATMDST) program. The ERATMDST CHI specification is the FAA's vehicle to ensure an operationally suitable user interface is provided for the DSTs (such as conflict probe) to support free flight. The initial draft of the ERATMDST CHI requirements was published in September 1998 and defines an initial CHI which incorporates elements of the NASA CTAS and the MITRE URET prototypes, an Operational Display and Input Development (ODID) display philosophy, and an outline of the end-state CHI. The information will be presented with a consistent, usable look and feel modeled on the advanced human-centered CHI developed by Eurocontrol. This paper describes a CHI Requirements Engineering Model (CREM) and presents preliminary test results of ODID-like display elements in the ERATMDST CHI with controller-in- the-loop simulations presented in terms of workload and response times.
Summary
MIT Lincoln Laboratory (MIT/LL) is supporting the FAA-sponsored effort to specify Computer Human Interface (CHI) requirements for the En Route Air Traffic Management Decision Support Tools (ERATMDST) program. The ERATMDST CHI specification is the FAA's vehicle to ensure an operationally suitable user interface is provided for the DSTs (such as...
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Airbus 320 performance during ATC-directed breakouts on final approach
November 20, 1998
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-265
Summary
An evaluation of Airbus 320 (A320) performance during ATC-directed breakouts was conducted in a two-part study during 1995. Phase 1 tested the combined effect of proposed ATC phraseology, pilot situational awareness training, and an A320-specific breakout procedure on performance. Pilot training included a briefing and viewing a videotape, but no simulator practice. Turn performance statistics from the Precision Runway Monitor Demonstration Program were used as the test criteria. Pilot preferences regarding procedures and the training material were also elicited. Three conclusions were: (1) breakout performance given the tested combination of pilot training and proposed ATC phraseology did meet the test criteria; (2) breakout performance given existing procedures did not meet the test criteria; and (3) the tested breakout procedure should be refined because it conflicted with other cockpit procedures and increased the transition time to a positive climb rate. Based on the results of this study, it is recommended that a combination of pilot situational awareness training, A320 breakout procedure, and modified ATC breakout phraseology equivalent to that tested in Phase 2 be employed for simultaneous parallel approach operations in instrument meteorological conditions.
Summary
An evaluation of Airbus 320 (A320) performance during ATC-directed breakouts was conducted in a two-part study during 1995. Phase 1 tested the combined effect of proposed ATC phraseology, pilot situational awareness training, and an A320-specific breakout procedure on performance. Pilot training included a briefing and viewing a videotape, but no...
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Techniques for improved reception of 1090 MHz ADS-B signals
October 31, 1998
Conference Paper
Published in:
17th DASC: Proc. of the 17th. Digital Avionics Systems Conf., 31 October - 7 November 1998, Vol. 2, pp. G25-1 - G25-9.
Summary
The recent development of ADS-B (Automatic Dependent Surveillance-Broadcast) is based on the use of the Mode S transponders now carried by all air carrier and commuter aircraft. ADS-B aircraft broadcast aircraft positions, identity, and other information via semi-random Mode S transponder squitters. Other aircraft or ground facilities receive the squitters and the associated position and status. Squitter reception includes the detection of the Mode S 1090 MHz waveform preamble, declaration of the bit and confidence values, error detection, and (if necessary) error correction. The current techniques for squitter reception are based upon methods developed for use in Mode S narrow-beam interrogators and for ACAS. In both of these applications, the rate of Mode NC fruit that is stronger than the Mode S waveform is relatively low, nominally less than 4,000 fruit per second. Extended squitter applications now include long range (up to 100 nmi) air-air surveillance in support of free flight. This type of surveillance is sometimes referred to as Cockpit Display of Traffic Information (CDTI). In high density environments, it is possible to operate with fruit rates of 40,000 fruit per second and higher. Operation of extended squitter in very high ModeNC fruit environments has led to the need to re-evaluate squitter reception techniques to determine if improved performance is achievable. The purpose of this paper is to provide a summary of work in progress to investigate improved squitter reception techniques. Elements of improved squitter reception being investigated include (1) the use of amplitude to improve bit and confidence declaration accuracy, (2) more capable error correction algorithms, and (3) more selective preamble detection approaches.
Summary
The recent development of ADS-B (Automatic Dependent Surveillance-Broadcast) is based on the use of the Mode S transponders now carried by all air carrier and commuter aircraft. ADS-B aircraft broadcast aircraft positions, identity, and other information via semi-random Mode S transponder squitters. Other aircraft or ground facilities receive the squitters...
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