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Evaluation of TDWR range-velocity ambiguity mitigation techniques
April 4, 2003
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-310
Summary
Range and velocity ambiguities pose significant data quality challenges for the Terminal Doppler Weather Radar (TDWR). For typical pulse repetition frequencies (PRFs) of 1-2 kHz, the radar is subject to both range-ambiguous precipitation returns and velocity aliasing. Experience shows that these are a major contributor to failures of the system's wind shear detection algorithms. Here we evaluate the degree of mitigation offered by existing phase diversity methods to these problems. Using optimized processing techniques, we analyze the performance of two particular phase codes that are best suited for application to TDWRs- random and SZ(8/64) [Sachidananda and Zrnic', [1999]- in the protection of weak-trip power, velocity, and spectral width estimates. Results from both simulated and real weather data indicate that the SZ(8/64) code generally outperforms the random code, except for protection of 1st trip from 5th trip interference. However, the SZ code estimates require a priori knowledge of out-of-trip spectral widths for censoring. This information cannot be provided adequately by a separate scan with a Pulse Repetition Frequency (PRF) low enough to unambiguously cover the entire range of detectable weather, because then the upper limit of measurable spectral width is only about 2 m/s . For this reason we conclude that SZ phase codes are not appropriate for TDWR use. For velocity ambiguity resolution, the random phase code could be transmitted at two PRFs on alternating dwells. Assuming the velocity changes little between two consecutive dwells, a Chinese remainder type of approach can be used to dealias the velocities. Strong ground clutter at close range, however, disables this scheme for gates at the beginning of the 2nd trip of the higher PRF. We offer an alternative scheme for range-velocity ambiguity mitigation: Multistaggered Pulse Processing (MSPP). Yielding excellent velocity dealiasing capabilities, the MSPP method should also provide protection from patchy, small-scale out-of-trip weather. To obtain maximum performance in both range and velocity dealiasing, we suggest that information from the initial low-PRF scan be used to decide the best waveform to transmit in the following scan-random phase code with alternating-dwell PRFs or MSPP. Such an adaptive approach presages future developments in weather radar, for example electronically scanned arrays allow selective probing of relevant weather events.
Summary
Range and velocity ambiguities pose significant data quality challenges for the Terminal Doppler Weather Radar (TDWR). For typical pulse repetition frequencies (PRFs) of 1-2 kHz, the radar is subject to both range-ambiguous precipitation returns and velocity aliasing. Experience shows that these are a major contributor to failures of the system's...
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Automated forecasting of road conditions and recommended road treatments for winter storms
February 9, 2003
Conference Paper
Published in:
19th Int. Conf. of Interactive Information Processing Systems for Meteorology, Oceanography and Hydrology, 9-13-February 2003.
Summary
Over the past decade there have been significant improvements in the availability, volume, and quality of the sensors and technology utilized to both capture the current state of the atmosphere and generate weather forecasts. New radar systems, automated surface observing systems, satellites and advanced numerical models have all contributed to these advances. However, the practical application of this new technology for transportation decision makers has been primarily limited to aviation. Surface transportation operators, like air traffic operators, require tailored weather products and alerts and guidance on recommended remedial action (e.g. applying chemicals or adjusting traffic flow). Recognizing this deficiency, the FHWA (Federal Highway Administration) has been working to define the weather related needs and operational requirements of the surface transportation community since October 1999. A primary focus of the FHWA baseline user needs and requirements has been winter road maintenance personnel (Pisano, 2001). A key finding of the requirements process was that state DOTs (Departments of Transportation) were in need of a weather forecast system that provided them both an integrated view of their weather, road and crew operations and advanced guidance on what course of action might be required to keep traffic flowing safely. As a result, the FHWA funded a small project (~$900K/year) involving a consortium of national laboratories to aggressively research and develop a prototype integrated Maintenance Decision Support System (MDSS). The prototype MDSS uses state-of-the-art weather and road condition forecast technology and integrates it with FHWA anti-icing guidelines to provide guidance to State DOTs in planning and managing winter storm events (Mahoney, 2003). The overall flow of the MDSS is shown in Figure 1. Basic meteorological data and advanced models are ingested into the Road Weather Forecast System (RWFS). The RWFS, developed by the National Center for Atmospheric Research (NCAR), dynamically weights the ingested model and station data to produce ambient weather forecasts (temperature, precipitation, wind, etc.). More details on the RWFS system can be found in (Myers, 2002). Next, the RCTM (Road Condition Treatment Module) ingests the forecasted weather conditions from the RWFS, calculates the predicted road conditions (snow depth, pavement temperature), Once a treatment plan has been determined, the recommendations are presented in map and table form through the MDSS display. The display also allows users to examine specific road and weather parameters, and to override the algorithm recommended treatments with a user-specified plan. A brief test of the MDSS system was performed in Minnesota during the spring of 2002. Further refinements were made and an initial version of the MDSS was released by the FHWA in September 2002. While this basic system is not yet complete, it does ingest all the necessary weather data and produce an integrated view of the road conditions and recommended treatments. This paper details the RCTM algorithm and its’ components, including the current and potential capabilities of the system.
Summary
Over the past decade there have been significant improvements in the availability, volume, and quality of the sensors and technology utilized to both capture the current state of the atmosphere and generate weather forecasts. New radar systems, automated surface observing systems, satellites and advanced numerical models have all contributed to...
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An analysis of the impacts of wake vortex restrictions at LGA
September 16, 2002
Project Report
Published in:
Project Report ATC-305, MIT Lincoln Laboratory
Summary
Wake vortex restrictions at New York's La Guardia airport cause a significant reduction in capacity when aircraft land on runway 22 and depart on runway 31. This report presents an analysis of the annual delay cost at LGA associated with the wake vortex restrictions. We find that the delay due to these restrictions exceeds 4000 hours annually, and that these restrictions cause a significant workload increase to controllers at both La Guardia and the New York TRACON. If traffic levels were to increase 10% from their February 2001 levels, the corresponding increase in delay due to the wake vortex restrictions would rise from 30 hours a day to over 400 hours a day in this runway configuration. It is also found that for a meaningful increase in passenger capacity in this runway configuration to be as demand grows, restrictions must be reduced from their current levels. If the percentage of heavy/757's doubled at LGA, there would be no increase in passenger capacity while daily delays in this runway configuration due to current wake vortex separation standards would increase by 250 hours.
Summary
Wake vortex restrictions at New York's La Guardia airport cause a significant reduction in capacity when aircraft land on runway 22 and depart on runway 31. This report presents an analysis of the annual delay cost at LGA associated with the wake vortex restrictions. We find that the delay due...
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An analysis of the impacts of wake vortex restrictions at LGA
September 16, 2002
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-305
Summary
Wake vortex restrictions at New York's La Guardia airport cause a significant reduction in capacity when aircraft land on runway 22 and depart on runway 31. This report presents an analysis of the annual delay cost at LGA associated with the wake vortex restrictions. We find that the delay due to these restrictions exceeds 4000 hours annually, and that these restrictions cause a significant workload increase to controllers at both La Guardia and the New York TRACON. If traffic levels were to increase 10% from their February 2001 levels, the corresponding increase in delay due to the wake vortex restrictions would rise from 30 hours a day to over 400 hours a day in this runway configuration. It is also found that for a meaningful increase in passenger capacity in this runway configuration to be as demand grows, restrictions must be reduced from their current levels. If the percentage of heavy/757's doubled at LGA, there would be no increase in passenger capacity while daily delays in this runway configuration due to current wake vortex separation standards would increase by 250 hours.
Summary
Wake vortex restrictions at New York's La Guardia airport cause a significant reduction in capacity when aircraft land on runway 22 and depart on runway 31. This report presents an analysis of the annual delay cost at LGA associated with the wake vortex restrictions. We find that the delay due...
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Forecasting convective weather using multi-scale detectors and weather Classification - enhancements to the MIT Lincoln Laboratory Terminal Weather Forecast
May 13, 2002
Conference Paper
Published in:
10th Conf. on Aviation, Range, and Aerospace Meteorology, 13-16 May 2002, pp. 132-135.
Summary
Over the past decade the United States has seen drastic increases in air traffic delays resulting in enormous economic loses. Analysis shows that more then 50% of air traffic delays are due to convective weather. In response the FAA has assembled scientific and engineering teams from MIT Lincoln Laboratory, NCAR. NSSL, FSL and several universities to develop convective weather forecast systems to aid air traffic managers in delay reduction. A user-needs study conducted by Lincoln Laboratory identified that a major source of air traffic delay was due to line thunderstorms (Forman et al., 1999). Recognizing that the line storm envelope motion was distinct from the local cell motion was the impetus for developing the Growth and Decay Storm Tracker' (Wolfson et al., 1999). The algorithm produces forecasts by extracting large-scale features from two dimensional precipitation images. These images are tracked, using either correlation techniques (Terminal Convective Weather Forecast or TCWF) or centroid techniques (National Convective Weather Forecast or NCWF). In TCWF, the track vector field is used to advect the current precipitation images formed to produce a series of forecasts into minute increments up to 60 minutes. The TCWF forecasts are highly skilled for large scale persistent line storms. However, detailed performance analysis of the algorithm has shown that in cases dominated by airmass storms, the algorithm occasionally performed poorly (Theriault et al., 2001). In this paper we describe the sources of error discovered in the TCWF algorithm during the Memphis 2000 performance evaluation, and describe recent enhancements designed to address these problems.
Summary
Over the past decade the United States has seen drastic increases in air traffic delays resulting in enormous economic loses. Analysis shows that more then 50% of air traffic delays are due to convective weather. In response the FAA has assembled scientific and engineering teams from MIT Lincoln Laboratory, NCAR...
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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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TCWF algorithm assessment - Memphis 2000
July 9, 2001
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-297
Summary
This report describes a formal Assessment of the Terminal Convective Weather Forecast (TCWF) algorithm, developed under the FAA Aviation Weather Research Program by MIT Lincoln Laboratory as part of the Convective Weather Product Development Team (PDT). TCWF is proposed as a Pre-Planned Product Improvement (P3I) enhancement to the operational ITWS currently scheduled for deployment at major airports in 2002. The TCWF Assessment in Memphis, TN ran from 24 March to 30 September 2000. The performance of TCWF was excellent on the large scale, organized storm systems it was designed to predict, and the software was extremely stable during the Assessment. Small changes to the algorithm parameters were made as a result of the 2000 testing. The TCWF performance can be improved on airmass storms and on forecasting new growth and subsequent decay of large-scale storms. These are active areas of research for future ITWS P3I builds.
Summary
This report describes a formal Assessment of the Terminal Convective Weather Forecast (TCWF) algorithm, developed under the FAA Aviation Weather Research Program by MIT Lincoln Laboratory as part of the Convective Weather Product Development Team (PDT). TCWF is proposed as a Pre-Planned Product Improvement (P3I) enhancement to the operational ITWS...
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Delay causality and reduction at the New York City airports using terminal weather information systems
February 16, 2001
Project Report
Published in:
Project Report ATC-291, MIT Lincoln Laboratory
Summary
Adverse weather accounts for the bulk of the aviation delays at the major New York City airports. In this report, we quantify: 1. Aviation delay reduction with an Integrated Terminal Weather System (ITWS) that incorporates the 30-60 minute predictions of convective storms generated by the Terminal Convective Weather Forecast (TCWF) algorithm, 2. Principal causes of aviation delays with the ITWS in operation, and 3. The extent to which the current delays are "avoidable". We find that improved decision making by the New York FAA users of ITWS provides an annual delay reduction of over 49,000 hours per year with a monetary value of over $150,000,000 per year. Convective weather was found to be the leading contributor to delays at Newark International Airport (EWR) between September 1998 and August 2000. It was found that 40% of the arrival delay in this study occurred in association with delay days characterized by convective weather both within and at considerable distances from the New York terminal area. Of the remaining delay, 27% occurred on days characterized by low ceiling/visibility conditions, while 16% occurred on fair weather days with high surface winds. We also concluded that many of the delays which occur with the current ITWS, over $1,500,000 in one case, could be avoided if the ITWS were extended to provide: 1. Predictions of thunderstorm decay, and 2. Predictions of the onset and ending of capacity limiting events such as low ceilings or high surface winds. These delay causality results are very important for studies of the effectiveness of changes made to the U.S. aviation system to reduce delays at airports such as Newark as well as for prioritizing FAA research and development expenditures.
Summary
Adverse weather accounts for the bulk of the aviation delays at the major New York City airports. In this report, we quantify: 1. Aviation delay reduction with an Integrated Terminal Weather System (ITWS) that incorporates the 30-60 minute predictions of convective storms generated by the Terminal Convective Weather Forecast (TCWF)...
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Positive charge in the stratiform cloud of a mesoscale convective system
January 16, 2001
Journal Article
Published in:
J. Geophys. Res., Vol. 106, No. D1, 16 January 2001, pp. 1157-1163.
Summary
A balloon sounding of electric field in the trailing stratiform cloud of a bow echo mesoscale convective system reveals only two substantial in-cloud positive charge regions. These charge regions are located at altitudes of 5.1-5.6 km and 6.4-6.8 km, above the level of 0 degree C at 4.2 km. The two positive charge regions are the likely sources of six positive cloud-to-ground flashes with large peak currents (>32 kA) that occurred within 60 km of the balloon during its flight. The amount of charge transferred by three of these positive flashes that made Q bursts is calculated in the range of 97-196 C. Flashes of this sort are known to produce sprites and elves in the mesosphere. The positive charge regions in this stratiform cloud are substantially lower than the 10-km altitude commonly assumed for the positive charge in many sprite modeling studies.
Summary
A balloon sounding of electric field in the trailing stratiform cloud of a bow echo mesoscale convective system reveals only two substantial in-cloud positive charge regions. These charge regions are located at altitudes of 5.1-5.6 km and 6.4-6.8 km, above the level of 0 degree C at 4.2 km. The...
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Sprites, elves, and glow discharge tubes
January 1, 2001
Journal Article
Published in:
Phys. Today, Vol. 54, No. 11, November 2001, pp. 41-47.
Summary
In the 1920's, the Scottish physicist C.T.R. Wilson predicted the existence of brief flashes of light above large thunderstorms. Almost 70 years later, Bernard Vonnegut of SUNY Albany realized that evidence for Wilson's then-unconfirmed predictions might appear in video imagery of Earth's upper atmosphere recorded by space-shuttle astronauts. He encouraged NASA's William Boeck and Otha Vaughan to look for evidence. Their search was successful. At the 1990 fall meeting of the American Geophysical Union, Boeck and Vaughan presented evidence for upper-atmosphere flashes. Evidence of a different nature came from the University of Minnesota's John Winckler and his colleagues, who had serendipitously observed a flash in moonless night-time skies over Minnesota in 1989. These early findings inspired two independent field programs to target the new phenomenon. In the summer of 1993, Walter Lyons of FMA Research set up detectors on Yucca Ridge in the foothills of the Rocky Mountains. That same summer, Davis Sentman of the University of Alaska Fairbanks (UAF) sought to record the flashes from an aircraft flying over the Great Plains. Within a day of each other, the two research teams had documented what turned out to be a common phenomenon in the mesosphere. In doing so, they initiated not only a new kind of continental-scale field experiment but also—and more important—a new interdisciplinary area of research.
Summary
In the 1920's, the Scottish physicist C.T.R. Wilson predicted the existence of brief flashes of light above large thunderstorms. Almost 70 years later, Bernard Vonnegut of SUNY Albany realized that evidence for Wilson's then-unconfirmed predictions might appear in video imagery of Earth's upper atmosphere recorded by space-shuttle astronauts. He encouraged...
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