Publications
The physical origin of the land-ocean contrast in lightning activity
January 1, 2002
Journal Article
Published in:
Comptes Rendus Physique, Vol. 3, No. 10, 2002, pp. 1277-1292.
Summary
New tests and older ideas are explored to understand the origin of the pronounced contrast in lightning between land and sea. The behavior of islands as miniature continents with variable area supports the traditional thermal hypothesis over the aerosol hypothesis for lightning control. The substantial land-ocean contrast in updraft strength is supported globally by TRMM (Tropical Rainfall Measuring Mission) radar comparisons of mixed phase radar reflectivity. The land-ocean updraft contrast is grossly inconsistent with the land ocean contrast in CAPE (Convective Available Potential Energy), from the standpoint of parcel theory. This inconsistency is resolved by the scaling of buoyant parcel size with cloud base height, as suggested by earlier investigators. Strongly electrified continental convection is then favored by a larger surface Bowen ratio, and by larger, more strongly buoyant boundary layer parcels which more efficiently transform CAPE to kinetic energy of the updraft in the moist stage of conditional instability.
Summary
New tests and older ideas are explored to understand the origin of the pronounced contrast in lightning between land and sea. The behavior of islands as miniature continents with variable area supports the traditional thermal hypothesis over the aerosol hypothesis for lightning control. The substantial land-ocean contrast in updraft strength...
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Analysis of delay causality at Newark International Airport
December 3, 2001
Conference Paper
Published in:
4th USA/Europe Air Traffic Management R&D Seminar, 3-7 December 2001.
Topic:
R&D area:
Summary
Determining causes of aviation delay is essential for formulating and evaluating approaches to reduce air traffic delays. An analysis was conducted of large weather-related delays at Newark International Airport (EWR), which, located in the heart of the congested northeast corridor of the United States, is an airport with a significant number of delays. Convective weather and reduced ceiling and visibility were found to be the leading contributors to large delays at EWR between September 1998 and August 2001. It was found that 41% of the cumulative arrival delay (delay relative to schedule) on days in this period averaging more than 15 minutes of delay per arrival occurred on days characterized by convective weather either within or at considerable distances from the New York terminal area. Of the remaining delays, 28% occurred on days characterized by low ceiling/visibility conditions, while 14% occurred on fair weather days with high surface winds, and 2% were caused by distant non-convective storms. Known causes other than weather accounted for 9% of the delays, and causes were unknown for 6%. When delay types (airborne, gate, taxi -out etc.) were categorized by the type of weather causing the delay, it was found that: (1) departure delays (gate + taxi-out) were much larger than arrival delays for thunderstorms in the NY terminal area and (2) taxi-out delays were the dominant type when delays were caused by distant convective weather. The fraction of total delay time explained by pre-planned Ground Delay Programs (GDP) rose sharply during 2000, accounting for over 40% of total the arrival delay that year, and then decreased slightly in 2001. On days with thunderstorms in the NY TRACON, arrival and departure delays were significantly higher during the year (2000) that GDPs were used most frequently.
Summary
Determining causes of aviation delay is essential for formulating and evaluating approaches to reduce air traffic delays. An analysis was conducted of large weather-related delays at Newark International Airport (EWR), which, located in the heart of the congested northeast corridor of the United States, is an airport with a significant...
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Tactical convective weather decision support to complement "strategic" traffic flow management for convective weather
November 4, 2001
Conference Paper
Published in:
46th Annual Air Traffic Control Association Conf. Proc., 4-8 November 2001, pp. 98-102.
Summary
Delay increases during the months of the year characterized by thunderstorms have been the principal cause of the dramatic delay growth in the US aviation system over the past 3 years, as shown in Figure 1. In 2000, the key new initiative for reducing these convective weather delays was "strategic" traffic flow management (TFM) through the Collaborative Convective Forecast Product (CCFP), the Strategic Planning Team, and Collaborative Routing (CR). This "strategic" approach has been quite successful in improving operations. However, in congested airspace, the inability to accurately forecast convective weather impacts requires a complementary tactical weather decision support capability. This paper describes terminal and enroute weather prediction systems plus traffic flow management and automation decision support tools to complement the strategic approach.
Summary
Delay increases during the months of the year characterized by thunderstorms have been the principal cause of the dramatic delay growth in the US aviation system over the past 3 years, as shown in Figure 1. In 2000, the key new initiative for reducing these convective weather delays was "strategic"...
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ASR-8/TDX-2000 performance analysis: evaluation of multiple-time-around-detection (MTAD) algorithm and final report
October 1, 2001
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-300
Summary
This report documents the analysis of and subsequent improvements to the performance of the ASR-8/TDX-2000 digitizer equipment combination. Working at the FAA's Palm Springs, CA and Williams (Mesa, AZ) ASR-8 facilities, data was methodically collected and analyzed to isolate the causes of reported correlated radar-only tracks that were being dropped or were never initiated. These problems were subsequently fixed via hard and soft parameter changes in the TDX-2000. A significant study was also undertaken in conjunction with the Sensis Corporation to improve the TDX-2000's capability to reject returns from multiple-time-around detections. The details of that algorithm modification and the results of follow-on testing and analysis are described. Final conclusions on the status of the project are also included.
Summary
This report documents the analysis of and subsequent improvements to the performance of the ASR-8/TDX-2000 digitizer equipment combination. Working at the FAA's Palm Springs, CA and Williams (Mesa, AZ) ASR-8 facilities, data was methodically collected and analyzed to isolate the causes of reported correlated radar-only tracks that were being dropped...
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Surveillance performance requirements for runway incursion prevention systems
September 26, 2001
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-301
Summary
In response to concerns over the number of runway incursions and runway conflicts at U.S. airports, the FAA is sponsoring research and development of safety systems for the airport surface. Two types of safety systems are being actively pursued, a tower cab alerting system and a runway status light system. The tower cab alerting system, called the Airport Movement Area Safety System (AMASS) is currently undergoing initial operational evaluation at several major airports. It provides aural and visual alerts to the tower cab to warn the controllers of potential traffic conflicts. The runway status light system is currently in the development phase, with initial operational suitability demonstrations planned at Dallas/Fort Worth International Airport during FY2003. Intended to offer protection in time-critical conflict scenarios where there is not enough time to warn the aircrews indirectly via the tower cab, the runway status light system provides visual indication of runway status directly to the cockpit; runway entrance lights warn pilots not to enter a runway on which there is approaching high-speed traffic; takeoff-hold lights warn pilots not to start takeoff if a conflict could occur. Both systems operate automatically, requiring no controller inputs. Activation commands for alerts and lights are generated by the systems' safety logic, which in turn receives airport traffic inputs from a surface surveillance and target tracking system. Accurate traffic representation is essential to meet system requirements, which include high conflict detection rate, prompt and accurate alerting and light activation, low nuisance and false alarm rates, and negligible interference with normal operations. This report analyzes the effect of the two fundamental surveillance performance parameters-position accuracy and surveillance update rate - on the performance of three different surface safety systems. The first two are the above-mentioned tower cab alerting and runway status light systems. The third system is a hypothetical cockpit alerting system that delivers alerts directly to the cockpit rather than to the tower cab. The surveillance accuracy and update rate requirements of these three systems are analyzed for three of the most common runway conflict scenarios, using realistic parameter values for aircraft motion. The scenarios are 1) a runway incursion by a taxiing aircraft in front of a departure or arrival, 2) a departure on an occupied runway, and 3) an arrival on an occupied runway. Runway status lights are especially effective at preventing incursions and accidents between takeoff or arrival aircraft and intersection taxi aircraft. Tower cab alerts are effective at alerting controllers to aircraft crossing or on a runway during an arrival. Runway status information provided directly to the cockpit will be required for the case where a previous arrival or a taxi aircraft fails to exit the runway as anticipated shortly before the arrival crossed the threshold. (not complete)
Summary
In response to concerns over the number of runway incursions and runway conflicts at U.S. airports, the FAA is sponsoring research and development of safety systems for the airport surface. Two types of safety systems are being actively pursued, a tower cab alerting system and a runway status light system...
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Designing a terminal area bird detection and monitoring system based on ASR-9 data
August 27, 2001
Conference Paper
Published in:
3rd Joint Annual Meeting Bird Strike Committee, 27-30 August 2001.
Summary
Conflicts between birds and commercial aircraft are a noteworthy problem at both large and small airports [Cleary, 1999]. The risk factor for United States airports continues to increase due to the steady rise in take-off/landings and bird populations. There is a significant bird strike problem in the terminal area as shown by the incidents reported in the National Bird Strike Database [Cleary and Dolbeer, 1999]. The focus of bird strike mitigation in the past has centered primarily on wildlife management techniques. Recently, an Avian Hazard Advisory System (AHAS) has been developed to reduce the risks of bird strikes to military operations [Kelly, 1999]. This system uses a mosaic of data obtained from the Next Generation Weather Radar (NEXRAD). This sensor serves as an excellent tool for enroute bird advisories due to the radar coverage provided across the majority of the United States. However, its utility in the airport terminal environment is limited due to the slow update rate and the fact that the distance of most NEXRADs from the airport results in beam heights that are too high to detect low-altitude birds over the airport. The Federal Aviation Administration (FAA) operates two radar systems – the Terminal Doppler Weather Radar (TDWR), and the Airport Surveillance Radar (ASR-9) -- that could be used to help monitor bird activity at an airport in order to: 1. Provide continuously updated information on locations and approximate numbers of birds in flocks roosting or feeding on or near an airfield; 2. Generate real-time warnings of bird activity for dissemination to pilots of landing or departing aircraft by air traffic controllers or by direct data link. The TDWR provides wind shear warnings in the terminal area to enhance safety, while the ASR-9’s primary function is air traffic control. Both of these systems have been shown to detect biological echoes as well. Characteristics of the two radar systems have been examined and compared to determine capabilities for bird detection. Amongst other favorable factors, the high update rate and on-airport locale makes the ASR-9 a highly desirable platform for a bird detection and warning system for the terminal area. Data from an ASR-9 at Austin TX (AUS) equipped with a Weather Systems Processor (WSP) have been analyzed to assess the ASR-9's capability to detect and monitor bird activity. The WSP add-on provides a variety of radar base data products similar to those that would be available on all ASR-9s as part of an ASR-9 Service Life Extension Program (SLEP) currently underway. The Austin airport area is subject to large flocks of wintering migratory birds as well as a resident population of bats in close proximity to the airport. Radar data, visual observations and bird strike information during periods of active bird/bat movements have been collected for this study. An automated processing algorithm called the Terminal Avian Hazard Advisory System (TAHAS) is being developed to detect and track roosting and migratory birds using ASR-9 data. A key challenge will be the ability to discriminate biological from non-biological targets based on variables such as vertical continuity, variance or spectral width, and horizontal velocity distribution.
Summary
Conflicts between birds and commercial aircraft are a noteworthy problem at both large and small airports [Cleary, 1999]. The risk factor for United States airports continues to increase due to the steady rise in take-off/landings and bird populations. There is a significant bird strike problem in the terminal area as...
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Assessing delay benefits of the Final Approach Spacing Tool (FAST)
August 6, 2001
Conference Paper
Published in:
AIAA Guidance, Navigation and control Conf., Vol. 3, 6-9 August 2001, pp. 1851-1859.
Topic:
R&D area:
Summary
Air traffic delay grows each year. NASA is developing the Final Approach Spacing Tool (FAST) to help reduce airport arrival delays. FAST is intended to increase throughput and reduce delays. Analysis and field trials have suggested that FAST can help controllers increase arrival throughput on busy runways by several aircraft per hour. Published simulation studies have predicted that delay reductions from such throughput increases would save several hundred million dollars annually. However, these predictions disagree on delay savings for some airports and omit other airports of interest. Their predicted delay savings for some airports are higher than actual reported delays for those airports. They do not consider hazardous weather disruptions to arrival routes, and they do not address downstream delays caused by schedule disruption. This paper focuses on simple statistical and analytical measures of delay to resolve these problems. It develops a rule for ranking benefits and compares delay reduction predictions against actual reported delays. It relates delay to ceiling and visibility and thunderstorms. It examines the correlation of delay between airports and estimates the impact of downstream delay on FAST benefits.
Summary
Air traffic delay grows each year. NASA is developing the Final Approach Spacing Tool (FAST) to help reduce airport arrival delays. FAST is intended to increase throughput and reduce delays. Analysis and field trials have suggested that FAST can help controllers increase arrival throughput on busy runways by several aircraft...
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Evaluation of Eta model forecasts as a backup weather source for CTAS
August 6, 2001
Conference Paper
Published in:
AIAA Guidance, Navigation and Control Conf.: a collection of Technical Papers, Vol. 3, 6-9 August 2001, pp. 1837-1842.
Topic:
R&D area:
Summary
Knowledge of present and future winds and temperature is important for air traffic operations in general, but is crucial for Decision Support Tools (DSTs) that rely heavily on accurately predicting trajectories of aircraft. One such tool is the Center-TRACON Automation System (CTAS) developed by NASA Ames Research Center. The Rapid Update Cycle (RUC) system is presently the principal source of weather information for CTAS. RUC provides weather updates on an hourly basis on a nationwide grid with horizontal resolution of 40 km and vertical resolution of 25 mb in pressure. However, a recent study of RUC data availability showed that the NWS and NOAA servers are subject to frequent service interruptions. Over a 210 day period (4/19/00-11/11/00), the availability of two NOAA and one NWS RUC server was monitored automatically. It was found that 60 days (29%) had periods of one hour or more where at least one server was out, with the longest outage lasting 13 hours on 9/21/00. In addition, there were 9 days (4%) for which all three servers were simultaneously unavailable, with the longest outage lasting 6 hours on 5/7/00. Moreover, even longer outages have been experienced with the RUC servers over the past several years. RUC forecasts are provided for up to 12 hours, but these are not currently used in CTAS as back up sources (except that the 1 or 2 hour forecasts are used for the current winds to compensate for transmission delays in obtaining the RUC data). Since RUC outages have been experienced for longer than 12 hours, it is therefore necessary to back RUC up with another weather source providing long-range forecasts. This paper examines the use of the Eta model forecasts as a back-up weather sources for CTAS. A specific output of the Eta km model, namely Grid 104, was selected for evaluation because its horizontal and vertical resolution, spatial extent and output parameters match most closely those of RUC. While RUC forecasts for a maximum of 12 hours into the future, Eta does so for up to 60 hours. In the event that a RUC outage would occur, Eta data could be substituted. If Eta data also became unavailable, the last issued forecasts could allow CTAS to continue to function properly for up to 60 hours. The approach used for evaluating the suitability of the Eta model and RUC forecasts was to compare them with the RUC analysis output or 0 hour forecast file, at the forecast time. Not surprisingly, it was found that the RUC model forecasts had lower wind magnitude errors out to 12 hours (the limit of the RUC forecasts) than the Eta model had. Hosever, the wind magnitude error for the Eta model grew only from 9 ft/s at 12 hours (comparable with RUC) to 11 ft/s at 48 hours. We therefore conclude that RUC forecasts should be used for outages up to 12 hours and Eta model forecasts should be used for outages up to 60 hours.
Summary
Knowledge of present and future winds and temperature is important for air traffic operations in general, but is crucial for Decision Support Tools (DSTs) that rely heavily on accurately predicting trajectories of aircraft. One such tool is the Center-TRACON Automation System (CTAS) developed by NASA Ames Research Center. The Rapid...
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Radar-based analysis of the efficiency of runway use
August 6, 2001
Conference Paper
Published in:
AIAA Guidance, Navigation & Control Conference, Montreal, Quebec, 6-9 August, 2001, pp. 1-17.
Summary
The air transportation system faces a challenge in accommodating growing air traffic despite an inability to build new runways at most major airports. One approach to alleviating congestion is to find ways of using each available runway to the maximum extent possible without violating safety standards. Some decision support tools, such as the Final Approach Spacing Tool (FAST) that is a part of the Center TRACON Automation System (CTAS), are specifically targeted toward achieving greater runway throughput by reducing the average landing time interval (LTI) between arrivals at a given runway. In order to understand the potential benefits of such innovations, techniques for detecting spacing inefficiencies and estimating potential throughput improvements are needed. This paper demonstrates techniques for analyzing radar data from actual airport operations and using it to validate, calibrate, and extend analyzes of the FAST benefits mechanisms. The emphasis is upon robust statistical measures that can be produced through automated analysis of radar data, thus enabling large amounts of data to be analyzed.
Summary
The air transportation system faces a challenge in accommodating growing air traffic despite an inability to build new runways at most major airports. One approach to alleviating congestion is to find ways of using each available runway to the maximum extent possible without violating safety standards. Some decision support tools...
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The design and implementation of the new center/TRACON automation system (CTAS) weather distribution system
August 6, 2001
Conference Paper
Published in:
AIAA Guidance, Navigation and Control Conf.: a collection of Technical Papers, Vol. 3, 6-9 August 2001, pp. 1818-1836.
Topic:
R&D area:
Summary
The National Aeronautics and Space Administration (NASA), working with the Federal Aviation Administration (FAA), is developing a suite of decision support tools, called the Center/TRACON Automation System (CTAS). CTAS tools such as the Traffic Management Advisor (TMA) and Final Approach Spacing Tool (FAST) are designed to increase the efficiency of the air traffic flow into and through Terminal airspace. A core capability of CTAS is the Trajectory Synthesis (TS) software for accurately predicting an aircraft's trajectory. In order to compute these trajectories, TS needs an efficient access mechanism for obtaining the most up-to-date and accurate winds. The current CTAS weather access mechanism suffers from several major drawbacks. First, the mechanism can only handle a winds at a single resolution (presently 40-80 km). This prevents CTAS from taking advantage of high resolution wind from sources such as the Integrated Terminal Weather System (ITWS). Second, the present weather access mechanism is memory intensive and does not extend well to higher grid resolutions. This potentially limits CTAS in taking advantage of improvements in wind resolution from sources such as the Rapid Update Cycle (RUC). Third, the present method is processing intensive and limits the ability of CTAS to handle higher traffic loads. This potentially could impact the ability of new tools such as Direct-To and Multi-Center TMA (McTMA) to deal with increased traffic loads associated with adjacent Centers. In response to these challenges, M.I.T. Lincoln Laboratory has developed a new CTAS weather distribution (WxDist) system. There are two key elements to the new approach. First, the single wind grid is replaced with a set of nested grids for the TRACON, Center and Adjacent Center airspaces. Each and the grids are updated independently of each other. The second key element is replacement of the present interpolation scheme with a nearest-neighbor value approach. Previous studies have shown that this nearest-neighbor method does not degrade trajectory accuracy for the grid sizes under consideration. The new software design replaces the current implementation, known as the Weather Data Processing Daemon (WDPD), with a new approach. The Weather Server (WxServer) sends the weather grids to a Weather Client (WxClient) residing on each CTAS workstation running TS or PGUI (Planview Graphical User Interface) processes. The present point-to-point weather file distribution is replaced in the new scheme with a reliable multi-cast mechanism. This new distribution mechanism combined with data compression techniques greatly reduces network traffic compared to the present method. Other new processes combine RUC and ITWS data in a fail-soft manner to generate the multiple grids. The nearest-neighbor access method also substantially speeds up weather access. In combination with other improvements, the winds access speed is more than doubled over the original implementation.
Summary
The National Aeronautics and Space Administration (NASA), working with the Federal Aviation Administration (FAA), is developing a suite of decision support tools, called the Center/TRACON Automation System (CTAS). CTAS tools such as the Traffic Management Advisor (TMA) and Final Approach Spacing Tool (FAST) are designed to increase the efficiency of...
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