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A wind forecast algorithm to support Wake Turbulence Mitigation for Departures (WTMD)
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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Summary
Turbulence associated with wake vortices generated by arriving and departing aircraft poses a potential safety risk to other nearby aircraft, and as such this potential risk may apply to aircraft operating on Closely Spaced Parallel Runways (CSPRs). Aircraft separation standards are imposed to mitigate this potential risk. The FAA and NASA are investigating application of wind-dependent procedures for improved departure operations that would safely reduce spacing restrictions to allow increased airport operating capacity. These procedures are referred to collectively as Wake Turbulence Mitigation for Departures (WTMD). An important component of WTMD is a Wind Forecast Algorithm (WFA) developed by MIT Lincoln Laboratory. The algorithm is designed to predict when runway crosswind conditions will remain persistently favorable to preclude transport of aircraft departure wakes into the path of aircraft on parallel runways (Figure 1). The algorithm has two distinct components for predicting the winds at the surface (33 ft) and aloft up to 1000 ft (the altitude by which an alternate form of separation would be applied by Air Traffic Control to aircraft departing the parallel runways, typically 15 degree or greater divergence in aircraft paths). The surface component forecast applies a statistical approach using recent observations of winds from 1-minute ASOS observations. The winds-aloft component relies on the 2 to 4 hour wind forecasts from NCEP's Rapid Update Cycle (RUC) model. The baseline version of the algorithm was developed and tested using data from St. Louis Lambert International Airport (STL). Algorithm performance was evaluated using 1-minute ASOS observations and crosswind component measurements taken from a dedicated Light Detection and Ranging (LIDAR) system. The algorithm was also demonstrated and evaluated at Houston George Bush International Airport (IAH). Use of the WFA is planned for 8 other airports deemed likely to derive significant benefit from WTMD procedures. The operational concept of WTMD for use by Air Traffic Control (ATC) includes additional decision levels beyond the WFA forecast. These include a check for VFR ceiling and visibility conditions, and final enablement by a human controller. More details concerning WTMD can be found in Lang et al. (2005) and Lang et al. (2007). A more complete description of the WFA is given in Robasky and Clark (2008). The early history of WFA development is detailed in Cole and Winkler (2004).
Summary
Turbulence associated with wake vortices generated by arriving and departing aircraft poses a potential safety risk to other nearby aircraft, and as such this potential risk may apply to aircraft operating on Closely Spaced Parallel Runways (CSPRs). Aircraft separation standards are imposed to mitigate this potential risk. The FAA and...
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Comparison of Rapid Update Cycle (RUC) model crosswinds with LIDAR crosswind measurements at St. Louis Lambert International Airport
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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Summary
Turbulence associated with wake vortices generated by arriving and departing aircraft pose a potential safety risk to other nearby aircraft, and as such this potential risk may apply to aircraft operating on Closely Spaced Parallel Runways (CSPRs). To take wake vortex behavior into account, current aircraft departing/landing standards require a safe distance behind the wake generating aircraft at which operations can be conducted. The Federal Aviation Administration (FAA) and National Aeronautics and Space Administration (NASA) have initiated an improved wake avoidance solution, referred to as Wake Turbulence Mitigation for Departures (WTMD). The process is designed to safely increase runway capacity via actively monitoring wind conditions that impact wake behavior (Hallock, et al., 1998; Lang et al., 2005). An important component of WTMD is a Wind Forecast Algorithm (WFA) being developed by MIT Lincoln Laboratory (Cole & Winkler, 2004). The WFA predicts runway crosswinds from the surface up to a height of approximately ~300 m (1000 ft) once per minute and thus forecasts when winds favorable for WTMD will persist long enough for safe procedures for a particular runway (Lang et al., 2007). The algorithm uses 1–4 hr wind forecasts from the Rapid Update Cycle (RUC) model operated by the National Oceanic and Atmospheric Administration/National Centers for Environmental Prediction (NOAA/NCEP) for upper atmospheric wind profiles. Detailed description of the RUC model can be found elsewhere (Benjamin et al., 1994; 2004a; 2004b). Briefly, the RUC model inputs are assimilations of high frequency observations from a suite of meteorological sensors, including Automated Surface Observing System (ASOS), rawinsonde profiles, satellite, airborne sensors from commercial aircraft, etc. The vertical layers of the atmosphere are resolved approximately isentropically. The model is run hourly, producing hourly forecasts out to 24 hours. The coverage of the RUC grid includes the continental United States, southern Canada, northern Mexico, and adjacent coastal waters. Here we evaluate the performance of RUC in predicting crosswinds with reliability sufficient to support WTMD. For RUC validation, in situ wind profile data were obtained from a Light Imaging Detection and Ranging (LIDAR) deployed at St. Louis Lambert International Airport (STL). The focus of this study is to provide a general quantitative characterization of the difference between RUC predictions and LIDAR measurements of the runway crosswinds. Particular attention was given to cases with inaccurate RUC crosswind forecasts, and cases when significant horizontal and vertical shears occur during situations of convective weather or proximity to large scale weather features, e.g., air mass fronts. (In practice, WTMD procedures and existing weather sources in the Control Tower will manage, to an acceptable level of risk, the hazard exposure associated with the extreme wind shift examples presented here.) Also included was examination of performance degradation with longer RUC forecast horizons and coarser horizontal resolutions, which may be relevant with regard to actual operational forecast data availability, or future applications of the operational concept to include arrival operations. A detailed report for this study is also available (Huang et al., 2007).
Summary
Turbulence associated with wake vortices generated by arriving and departing aircraft pose a potential safety risk to other nearby aircraft, and as such this potential risk may apply to aircraft operating on Closely Spaced Parallel Runways (CSPRs). To take wake vortex behavior into account, current aircraft departing/landing standards require a...
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Improving weather radar data quality for aviation weather needs
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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Summary
A fundamental function of any aviation weather system is to provide accurate and timely weather information tailored to the specific air traffic situations for which a system is designed. Weather location and intensity are of prime importance to such systems. Knowledge of the weather provides "nowcasting" functionality in the terminal and en route air spaces. It also is used as input into aviation weather forecasting applications for purposes such as storm tracking, storm growth and decay trends, and convective initiation. Weather radar products are the primary source of the weather location and intensity information used by the aviation weather systems. In the United States, the primary radar sources are the Terminal Doppler Weather Radar (TDWR) and the Weather Surveillance Radar 1988 Doppler (WSR-88D, known as NEXRAD). Additional weather radar products from the Canadian network are used by some of the aviation weather systems. Product quality from all these radars directly impacts the quality of the down stream products created by the aviation weather systems and their utility to air traffic controllers. Four FAA weather systems use some combination of products from the aforementioned radars. They are the Corridor Integrated Weather System (CIWS), the Integrated Terminal Weather System (ITWS), the Weather and Radar Processor (WARP), and the Medium Intensity Airport Weather System (MIAWS). This paper focuses on the improvement of weather radar data quality specific to CIWS. The other mentioned FAA aviation weather systems also benefit either directly or indirectly from the improvements noted in this paper. For CIWS, the legacy data quality practices involve two steps. Step one is the creation of weather radar products of highest possible fidelity. The second step involves creating a mosaic from these products. The mosaic creation process takes advantage of inter-radar product comparisons to interject a further level of improved data quality. The new CIWS data quality plan will use a mounting evidence data quality classifier technique currently being developed. The technique applies a multi-tiered approach to weather radar data quality. Its premise is that no single data quality improvement technique is as effective as a collaboration of many. The evidence will be expanded to include data and products from the radars along with data from additional sensing platforms. The mosaic creation process will correspondingly expand to take advantage of the additional evidence. Section 2 covers data quality of products from the single radar perspective. Section 3 focuses on the use of satellite data as the first additional sensing platform to augment removal of problematic radar contamination. Section 4 describes the data quality procedures associated with creation of mosaics from the single radar products augmented with new satellite masking information. Last, Section 5 discusses future plans for the mounting evidence data quality improvement technique.
Summary
A fundamental function of any aviation weather system is to provide accurate and timely weather information tailored to the specific air traffic situations for which a system is designed. Weather location and intensity are of prime importance to such systems. Knowledge of the weather provides "nowcasting" functionality in the terminal...
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Modeling convective weather avoidance in enroute airspace
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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Summary
It is generally agreed that effective management of convective weather in congested airspace requires decision support tools that translate the weather products and forecasts into forecasts of ATC impacts and then use those ATC impact forecasts to suggest air traffic management strategies. In future trajectory-based operations, it will be necessary to automatically generate flight trajectories through or around convective weather that pilots will find acceptable. A critical first step, needed in both today's air traffic management environment and in the highly automated systems of the future, is a validated model for airspace that pilots will seek to avoid. At the 12th Conference on Aviation, Range and Aerospace Meteorology (Atlanta, 2006), we reported on an initial Convective Weather Avoidance Model (CWAM1) (DeLaura and Evans; 2006). The CWAM1 outputs are three dimensional deterministic and probabilistic weather avoidance fields (WAFs). CWAM1 used Corridor Integrated Weather System (CIWS) VIL and echo top fields and National Lightning Detection Network (NLDN) data to predict aircraft deviations and penetration. CWAM1 was developed using more than 500 aircraft-convective weather encounters in the Indianapolis Air Route Traffic Control Center (ZID ARTCC) airspace. CWAM1 gave the greatest weight to the difference between flight altitude and the 18 dbZ radar echo top with precipitation intensity playing a secondary role. The deviation prediction error rate in CWAM1 was approximately 25%. This paper presents a new model (CWAM2), based on the analysis of trajectories from several ARTCCs [Indianapolis (ZID), Cleveland (ZOB) and meteorological deviation predictors. Additional weather factors that are considered include vertical storm structure (upper level reflectivity and the height of the VIL centroid derived from the NSSL 3D reflectivity mosaic), vertical and horizontal storm growth, the spatial variation in VIL and echo top fields and storm motion.
Summary
It is generally agreed that effective management of convective weather in congested airspace requires decision support tools that translate the weather products and forecasts into forecasts of ATC impacts and then use those ATC impact forecasts to suggest air traffic management strategies. In future trajectory-based operations, it will be necessary...
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Measuring the utilization of available aviation system capacity in convective weather
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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Summary
There is currently great interest in improving the ability to quantitatively assess how well U.S. Air Traffic Control (ATC) services are being provided as new weather-air traffic management (ATM) decision support capabilities are added. One of the three proposed metrics currently under study by the Federal Aviation Administration (FAA) and airlines is resource utilization, which has been defined as "the safe and efficient use of available airport or airspace capacity." Measurement of capacity utilization is particularly difficult during convective weather since storms cause capacity reductions in both en route and terminal airspace. In particular, en route capacity loss results in network congestion that cannot be readily characterized by scalar metrics. This paper proposes the use of (i) models for translating 3-D weather radar data into time-varying estimates of the capacity reductions in affected en route sectors, terminal airspace, and airports, together with (ii) automatically-generated, broad-area ATM strategies that utilize the time-varying estimates of airspace capacity and demand to determine optimal reroute strategies or, when necessary, minimally disruptive ground or airborne delay programs to assess how the available capacity could best been utilized. By comparing actual vs. optimal capacity utilization, one can assess how effective the actual weather-ATM system was at utilizing the available capacity. Examples of applying this methodology to severe convective weather events from 2005 and 2006 will be presented.
Summary
There is currently great interest in improving the ability to quantitatively assess how well U.S. Air Traffic Control (ATC) services are being provided as new weather-air traffic management (ATM) decision support capabilities are added. One of the three proposed metrics currently under study by the Federal Aviation Administration (FAA) and...
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Comparative analysis of terminal wind-shear detection systems
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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Summary
Low-level wind shear, especially a microburst, is very hazardous to aircraft departing or approaching an airport. The danger became especially clear in a series of fatal commercial airliner accidents in the 1970s and 1980s at U.S. airports. In response, the Federal Aviation Agency (FAA) developed and deployed three ground-based low-altitude wind-shear detection systems: the Low Altitude Wind Shear Alert System (LLWAS) (Wilson and Gramzow 1991), the Terminal Doppler Weather Radar (TDWR) (Michelson et al. 1990), and the Airport Surveillance Radar Weather Systems Processor (ASR-9 WSP) (Weber and Stone 1995). Since the deployment of these sensors, commercial aircraft wind-shear accidents have dropped to near zero in the U.S. This dramatic decrease in accidents caused by wind shear appears to confirm the safety benefits provided by these detection systems. In addition, the broad area measurement capability of the TDWR and WSP provides ancillary delay reduction benefits, for example, by forecasting airport wind shifts that may require runway reconfiguration. The current deployment strategy for these various windshear detection systems is justified by an earlier integrated wind-shear systems cost-benefit analysis (Martin Marietta 1994). Since that time, conditions in the national airspace system (NAS) have evolved, such as the installation of onboard predictive wind-shear detection systems in an increasing number of aircraft, improved pilot training for wind-shear hazard identification, avoidance, and recovery, and further integration of observed wind-shear data into terminal weather systems. Given the tight fiscal environment at the FAA in recent years, the cost of maintaining the wind-shear detection systems has also become an issue. All systems require periodic service life extension programs (SLEPs). In light of these developments, the FAA has tasked MIT Lincoln Laboratory to provide an updated cost-benefit study on their terminal wind-shear detection systems. One of the key factors in estimating the benefits of a terminal wind-shear detection system is its performance. Thus, it is necessary to quantify the wind-shear detection probability for each sensor, preferably on an airport-by-airport basis. To consider sensors that are not yet deployed, a model must be developed that takes into account the various effects that factor into the detection probability. We have developed such a model. The focus of this paper is on this model and the results obtained with it.
Summary
Low-level wind shear, especially a microburst, is very hazardous to aircraft departing or approaching an airport. The danger became especially clear in a series of fatal commercial airliner accidents in the 1970s and 1980s at U.S. airports. In response, the Federal Aviation Agency (FAA) developed and deployed three ground-based low-altitude...
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Cloud-to-ground lightning as a proxy for nowcasts of VIL and echo tops
January 20, 2008
Conference Paper
Published in:
13th Conf. on Aviation, Range and Aerospace Meteorology, ARAM, 20-24 January 2008.
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Summary
The primary fields that provide weather situational awareness in the Corridor Integrated Weather System (CIWS) are radar-derived vertically-integrated liquid (VIL) and echo top height (ET). In situations of reduced or non-existent radar coverage, such as over the oceans, in mountainous terrain or during periods of radar outages, the radar VIL and ET fields are severely compromised or even absent. In these situations, the lightning data are often unaffected and fully available to use as a proxy for the radar fields in convective weather nowcasts. The purpose of this study is to develop the capability to utilize cloud-to-ground lightning strike data as a proxy for radar VIL and echo tops (ET) in the CIWS. The datasets used in this study are the National Lightning Detection Network (NLDN) and the 1 km/5min radar VIL and ET mosaics produced at MIT LL. To capture the synoptic variability of the lightning-VIL and lightning-ET relationships over the CIWS domain, atmospheric variables from the NOAA Rapid Update Cycle (RUC) model and the Space-time Mesoscale Analysis System (STMAS) are utilized with the lightning data in a statistical regression framework. Once spatially and temporally coherent regions of VIL and ET derived from the lightning are produced, the potential exists for tracking these regions and providing accurate short-term forecasting of convective hazards.
Summary
The primary fields that provide weather situational awareness in the Corridor Integrated Weather System (CIWS) are radar-derived vertically-integrated liquid (VIL) and echo top height (ET). In situations of reduced or non-existent radar coverage, such as over the oceans, in mountainous terrain or during periods of radar outages, the radar VIL...
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The next-generation multimission U.S. surveillance radar network
November 1, 2007
Journal Article
Published in:
Bull. American Meteorological Society, Vol. 88, No. 11, November 2007, pp. 1739-1751.
Summary
Current U.S. weather and aircraft surveillance radar networks vary in age from 10 to more than 40 years. Ongoing sustainment and upgrade programs can keep these operating in the near to mid-term, but the responsible agencies National Weather Service (NWS), Federal Aviation Administration (FAA), and the Departments of Defense (DoD) and Homeland Security (DHS) recognize that large-scale replacement activities must begin during the next decade. The National Weather Radar Testbed (NWRT) in Norman, Oklahoma, is a multiagency project demonstrating operational weather measurements capability enhancements that could be realized using electronically steered phased-array radars as a replacement for the current Weather Surveillance Radar-1988 Doppler (WSR-88D). FAA support for the NWRT and related efforts address air traffic control (ATC) and homeland defense surveillance missions that could be simultaneously accomplished using the agile-beam capability of a phased array weather radar network. In this paper, we discuss technology issues, operational considerations, and cost trades associated with the concept of replacing current national surveillance radars with a single network of multimission phased array radars (MPAR). We begin by describing the current U.S. national weather and aircraft surveillance radar networks and their technical parameters. The airspace coverage and surveillance capabilities of these existing radars provide a starting point for defining requirements for the next-generation airspace surveillance system. We next describe a conceptual MPAR high-level system design and our initial development and testing of critical subsystems. This work, in turn, has provided a solid basis for estimating MPAR costs for comparison with existing, mechanically scanned operational surveillance radars. To assess the numbers of MPARs that would need to be procured, we present a conceptual MPAR network configuration that duplicates airspace coverage provided by current operational radars. Finally, we discuss how the improved surveillance capabilities of MPAR could be utilized to more effectively meet the weather and aircraft surveillance needs of U.S. civil and military agencies.
Summary
Current U.S. weather and aircraft surveillance radar networks vary in age from 10 to more than 40 years. Ongoing sustainment and upgrade programs can keep these operating in the near to mid-term, but the responsible agencies National Weather Service (NWS), Federal Aviation Administration (FAA), and the Departments of Defense (DoD)...
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Model estimates of traffic reduction in storm impacted en route airspace
September 18, 2007
Conference Paper
Published in:
7th AIAA Aviation Technology, Integration, and Operations (ATIO) Conf., 18-20 September 2007.
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Summary
An understanding of convective weather impacts on en route airspace capacity is a first step toward development of predictive tools to support both tactical and strategic routing decisions in storm-impacted airspace. This study presents a model for traffic reductions in en route sectors that result from convective weather impacts. A model to predict the impact of convective weather on en route traffic, Traffic Normalized Fractional Route Availability (TNFRA), combines Weather Avoidance Fields (WAF) from the Convective Weather Avoidance Model (CWAM) with a model for route usage in air traffic control (ATC) sectors. The model estimates the number of flights that will be able to pass through convective weather in a given sector. Results show that TNFRA provides a relatively unbiased estimate of sector traffic when compared to actual operations during high impact - convective weather events.
Summary
An understanding of convective weather impacts on en route airspace capacity is a first step toward development of predictive tools to support both tactical and strategic routing decisions in storm-impacted airspace. This study presents a model for traffic reductions in en route sectors that result from convective weather impacts. A...
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An approach to verify a model for translating convective weather information to air traffic management impact
September 18, 2007
Conference Paper
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7th AIAA Aviation Technology, Integration, and Operations (ATIO) Conf., 18-20 September 2007.
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Summary
This paper describes a method to determine the accuracy of the Convective Weather Avoidance Model which predicts the likelihood that pilots will deviate away from specific areas of convective activity. Visual inspection with a reduced data set helped refine the algorithms used in the verification and offered some preliminary results of the model's accuracy in today's airspace. This model has some explanatory power in predicting regions of airspace where pilots are willing to deviate or fly through. In some instances, pilots appeared not to make an early decision to deviate around convective weather and continued on course as the region appeared more passable when they reached it. In other instances, pilots skirted the edges of regions where the model expected pilots avoid. This behavior suggests edge areas of those model regions were more passable and the convection in that region was not uniform in intensity.
Summary
This paper describes a method to determine the accuracy of the Convective Weather Avoidance Model which predicts the likelihood that pilots will deviate away from specific areas of convective activity. Visual inspection with a reduced data set helped refine the algorithms used in the verification and offered some preliminary results...
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