Publications
Applications of column models for terminal weather nowcasts
January 15, 1995
Conference Paper
Published in:
Sixth Conf. on Aviation Weather Systems, 15-20 January 1995, pp. 66-71.
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Summary
The Planetary Boundary Layer (PBL) is that part of the atmosphere, which is directly influenced by the presence of the earth's surface, and which responds to surface forcing with a time-scale of an hour or less. The Residual Layer (RL) is the portion of the lower atmosphere, which was part of the PBL within the past several hours, and which has become separated from the influence of short-term surface forcing, usually by the formation of a cooler layer at the surface. In the mid-latitudes, the height of the combined PBL and RL is usually 1-2 kilometers. A column model is a one-dimensional prognostic model for the state of a single column of the atmosphere, with special attention to the processes in the lowest few kilometers. It is designed to diagnose and nowcast the vertical structure of the PBL. Important information for ITWS1 nowcast products are the vertical profiles of horizontal wind velocity, temperature, humidity, and turbulent kinetic energy (TKE) in the lowest few kilometers (Sankey, 1994). Traditionally, operational meteorologists have obtained estimates of these quantities by balloon soundings, a measurement process that is not well-suited for continuous updates. We are investigating the possibility of developing an operational column model to obtain this vertical structure information for use in the ITWS. Our approach involves using a combination of sensing technology and analysis techniques that have proven successful in several research programs. Column models are designed to mimic the processes by which the surface forces the processes in the low atmosphere at times when local radiation is a dominant factor. Fluxes are measures of the net rates of these transport processes. The widely used Oregon State University column model (OSUlDPBL) parameterizes the fluxes by gradient transfer techniques (Troen and Mahr!, 1986). This model has provided dependable service in several field experiments, providing information with a vertical resolution of tens of meters. It is not designed to provide a fine-scale description of the stable nocturnal PBL. The French model COB EL has been developed to forecast the occurrence of radiation fog, and therefore concentrates on modeling the stable nocturnal PBL (Bergot and Guedalia, 1994). It uses a prognostic equation to estimate TKE in the stable boundary layer and parameterizes the fluxes in tern1s of the TKE (Duynkerke, 1991). A discussion of the potential uses of the column model in the ITWS is followed by the considerations that motivate the design of an operational column model. The prototype design is described. We conclude with the results of a preliminary evaluation using STORMFEST data (STORM Project Office, 1992) and a discussion of plans for a more comprehensive evaluation.
Summary
The Planetary Boundary Layer (PBL) is that part of the atmosphere, which is directly influenced by the presence of the earth's surface, and which responds to surface forcing with a time-scale of an hour or less. The Residual Layer (RL) is the portion of the lower atmosphere, which was part...
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ITWS gridded winds product
January 15, 1995
Conference Paper
Published in:
Proc. Sixth Conf. on Aviation Weather Systems, 15-20 January 1995, pp. 384-389.
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Summary
The Terminal Winds analysis technique was developed to take advantage of the Doppler information available in the terminal area. This technique, Optimal Estimation (OE), uses a minimum error variance technique (least squares) and is closely related to both the state-of-the-art operational non-Doppler winds analysis technique, Optimal Interpolation (OI) (Gandin, 1963) (Daly, 1991), and standard multiple Doppler techniques (Armijo, 1969). This technique was evaluated on data collected in 1992-1993 in Orlando FL, and demonstrated in real time in the Orlando testbed during the summer of 1993 and in the Memphis testbed during the summer of 1994.
Summary
The Terminal Winds analysis technique was developed to take advantage of the Doppler information available in the terminal area. This technique, Optimal Estimation (OE), uses a minimum error variance technique (least squares) and is closely related to both the state-of-the-art operational non-Doppler winds analysis technique, Optimal Interpolation (OI) (Gandin, 1963)...
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Machine intelligent gust front detection for the Integrated Terminal Weather System (ITWS)
January 15, 1995
Conference Paper
Published in:
Sixth Conf. on Aviation Weather Systems, 15-20 January 1995, pp. 378-383.
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Summary
The Integrated Terminal Weather System (ITWS), currently in development by the FAA, will produce a fully-automated integrated terminal weather information system to improve the safety, efficiency and capacity of terminal area aviation operations. The ITWS will acquire data from FAA and National Weather Service sensors as well as from aircraft in flight in the terminal area. The ITWS will provide products to Air Traffic personnel that are immediately usable without further meteorological interpretation. These products include current terminal area weather and short-term (0-30 minute) predictions of significant weather phenomena. The Terminal Doppler Weather Radar (TDWR) will serve as a principle sensor providing data to a number of the ITWS algorithms. One component of the ITWS will be an algorithm for detecting gust fronts and wind shifts. A gust front is the leading edge of a cold air outflow from a thunderstorm. The outflow, which is deflected at the ground, may propagate many miles ahead of the generating thunderstorm, and may persist as an outflow boundary long after the original storm has dissipated. Gust fronts can have a significant impact on air terminal operations since they often produce pronounced changes in wind speed and direction, forcing a change in active runway configuration and rerouting of aircraft within in the terminal airspace. In addition, wind shear, turbulence, and cross-winds along the frontal boundary pose significant safety hazards to departing and landing aircraft. Reliable detection and forecasting of gust fronts and wind shifts will both improve air safety and reduce costly delays. Lincoln Laboratory has developed an Initial Operational Capability (IOC) Machine Intelligent Gust Front Algorithm (MIGFA) for the ITWS which currently utilizes TDWR and LL WAS or ASOS anemometer data and makes use of new techniques of knowledge-based signal processing originally developed in the context of automatic target recognition [Verly, 1989]. Extensions to the IOC to incorporate additional sensor or product data available under the ITWS (e.g., NEXRAD, terminal winds) are currently under development. MIGFA was first developed for the Airport Surveillance Radar with Wind Shear Processor (ASR-9 WSP). Its design and performance have been documented in previous reports by the authors [Delanoy 1993a]. This paper focuses on the design of the more recently developed TDWR MIGFA and its extension and adaptation to the ITWS (a more detailed description of the TDWR MIGFA can be found in Troxel [1994]). An overview of the signal processing techniques used for detection and tracking is presented, as well as a brief discussion of the wind analysis methods used to arrive at the wind shift and wind shear estimates. Quantitative performance analyses using data collected during recent field testing in Orlando, FL and Memphis, TN are presented. Test results show that MIGFA substantially outperforms the gust front detection algorithm used in current TDWR systems [Hermes, 1993] (MIGFA is currently under consideration as an upgrade option for TDWR).
Summary
The Integrated Terminal Weather System (ITWS), currently in development by the FAA, will produce a fully-automated integrated terminal weather information system to improve the safety, efficiency and capacity of terminal area aviation operations. The ITWS will acquire data from FAA and National Weather Service sensors as well as from aircraft...
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Measuring the economic value of aviation meteorological products
January 15, 1995
Conference Paper
Published in:
9th Conf. on Applied Climatology, 15-20 January 1995.
Summary
The aviation system is one of the principal users of weather information. Assessing the benefits of weather information to aviation is important in a number of contexts: 1. Detemining the priority of investments in aviation weather information vis a vis other options for transportation and/or weather system investments, 2. Determinins priorities for research, implementation, facility staffing and information distribution, 3. The allocation of roles and responsibilities between various government agencies and private industry for various functions, and 4. Use in forecasting to set thresholds (see, e.g., [Felton, 1991], [Andrews, 1993], and [Liljas and Murphy, 1994]) With reduced government funding in a variety of areas related to aviation weather and with cost pressures on the users of the weather information (especially the air carriers), the importance of carefully performed benefits assessment has increased significantly in the past decade and is expected to become even more important in the near future. Our discussion will focus on safety and delay reduction. In the case of safety, we will consider in some depth the case of the deloyment of wind shear detection systems, while delay reduction will focus on results from recent studies of improved information on airport weather. In each case, we will also identify issues related to other benefits assessments in these areas.
Summary
The aviation system is one of the principal users of weather information. Assessing the benefits of weather information to aviation is important in a number of contexts: 1. Detemining the priority of investments in aviation weather information vis a vis other options for transportation and/or weather system investments, 2. Determinins...
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Overview of 1994 Memphis Wake Vortex testing program
January 15, 1995
Conference Paper
Published in:
Proc. Sixth Conf. on Aviation Weather Systems, 15-20 January 1995, pp. 515-520.
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Summary
Significant restrictions currently exist in the air traffic control system due to wake vortex considerations. Eliminating or reducing these restrictions would yield increased capacity, decreased delays and significant cost savings (Evans & Welch, 1991). These improvements would be especially desirable at high traffic airports which cannot expand (e.g., Boston, JFK, LaGuardia, Newark, Washington National, O'Hare, etc.). However, scientific uncertainty about wake vortex behavior under various weather conditions is a major concern. The current wake vortex restrictions me normally very conservative but could be insufficient under certain transient atmospheric conditions. A successful adaptive wake vortex advisory system must be able to 1) monitor for unsafe conditions, 2) predict wake vortex behavior over 2&30 minutes in the future and 3) provide an interface to air traffic controllers. Operational implementation of such a system will involve synergism between the Wake Vortex (WV), Integrated Terminal Weather System (ITWS) and Terminal Air Traffic Control Automation (TATCA) programs. The Wake Vortex program is a new effort at Lincoln Laboratory sponsored by NASA Langley Research Center in cooperation with the FAA. The joint NASA/FAA/Lincoln program seeks to aid in resolving wake vortex behavior issues as a function of the weather environment with a series of field measurements. The field measurements will include obtaining aircraft, meteorological and wake vortex data in an operational airport environment. The data collected will support efforts at NASA and elsewhere to validate wake vortex behavior models, aircraft/vortex interaction and atmospheric diagnosis/prognosis methods. The first of these field measurements is scheduled for the fall of 1994 at the Memphis International Airport.
Summary
Significant restrictions currently exist in the air traffic control system due to wake vortex considerations. Eliminating or reducing these restrictions would yield increased capacity, decreased delays and significant cost savings (Evans & Welch, 1991). These improvements would be especially desirable at high traffic airports which cannot expand (e.g., Boston, JFK...
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The ITWS Runway Wind Nowcast Product
January 15, 1995
Conference Paper
Published in:
Sixth Conf. on Aviation Weather Systems, 15-20 January 1995, pp. 390-395.
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Summary
The Runway Wind Nowcast Product will support the ITWS objective by providing short term (up to 30 minutes) forecasts of the tailwind and crosswind components of the horizontal wind over each runway at an ITWS airport. These forecasts will enable FAA users to better anticipate wind shifts impacting runway usage and trajectories of approaching and departing air traffic. They may also support future ITWS products such ceiling and visibility nowcasts. Our initial development efforts, which are reported here, have been directed toward Orlando International Airport (MCO) as the product request originated there. However, in the near future we plan to expand the scope to include other ITWS airports including Memphis. The Runway Wind Nowcast Product is being developed to help Air Traffic Control (ATC) personnel answer the following question: Do we need to change runways? That would become necessary if tailwinds or crosswinds exceed usage thresholds. At most US airports, with dry runways, tailwinds much be less than five knots and crosswinds must be less than 15 knots. Other, lower thresholds apply if the runways are wet. However, these thresholds are subject to local modifications. For example, the MCO tailwind threshold for dry runways is 7 knots. The decision faced by ATC personnel seems, at first, to be clear cut: if the tailwind or crosswind exceeds nominal thresholds, use of that runway must be discontinued. The problem (at least at MCO) is that most threshold crossings are very brief. So, it may be better to temporarily hold traffic than to switch runways. Reliable (i.e., accurate and precise) short term forecasts will help ATC personnel make better hold-or-switch decisions.
Summary
The Runway Wind Nowcast Product will support the ITWS objective by providing short term (up to 30 minutes) forecasts of the tailwind and crosswind components of the horizontal wind over each runway at an ITWS airport. These forecasts will enable FAA users to better anticipate wind shifts impacting runway usage...
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The Terminal Weather Information for Pilots (TWIP) program
January 11, 1995
Conference Paper
Published in:
Proc. Sixth Conf. on Aviation Weather Systems, 15-20 January 1995, pp. 107-112.
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Summary
The Federal Aviation Administration (F.A.A.) is currently embarking on programs, such as the Integrated Terminal Weather System (ITWS) and Terminal Doppler Weather Radar (TDWR), that will significantly improve the aviation weather information in the terminal area. Given the great increase in the quantity and quality of terminal weather information, it would be highly desirable to provide this information directly to pilots rather than having to rely on voice communications. Providing terminal weather information automatically via data link would both enhance pilot awareness of weather hazards and reduce air traffic controller workload. This paper will describe current work in the area of providing direct pilot access to terminal weather information via existing data link capabilities, such as ACARS (Addressing, Communications and Reporting System). During the summer of 1994, the ITWS testbed systems at Orlando, FL and Memphis, TN provided real–time terminal weather information to pilots in the form of text and character graphics–based products via the ACARS VHF data link. This effort follows an earlier successful demonstration during the summer of 1993 at Orlando (Campbell, 1994). Two types of Terminal Weather lnformation for Pilots (TWIP) messages are generated: a text-only message and a character graphics map. In order to ensure their operational utility, these products were developed in consultation with an ad hoc pilot user group. The TWIP Text Message is intended for typical ACARS cockpit displays, which are roughly 20 characters wide by 10 lines high. The TWIP Character Graphics Depiction is intended for the cockpit printers available on some aircraft that are at least 40 characters wide. Both products are intended to provide strategic information to pilots about terminal weather conditions to aid flight planning and improve situational awareness of potential hazards.
Summary
The Federal Aviation Administration (F.A.A.) is currently embarking on programs, such as the Integrated Terminal Weather System (ITWS) and Terminal Doppler Weather Radar (TDWR), that will significantly improve the aviation weather information in the terminal area. Given the great increase in the quantity and quality of terminal weather information, it...
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Optimum time-varying FIR filter designs for the Airport Surveillance Radar wind shear processor
December 28, 1994
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-191
Summary
We have developed new design algorithms for finite impulse response (FIR) filters that compensate for arbitrary input spacing and that allow for arbitrary group delay specification. The potential of these new designs to work with the ASR-9 staggered pulse spacing is examined in the context of the ASR-9 wind-shear processor (WSP). Benefits derived from the new designs include an improved (optimal) stopband design, an increased yield in pulse samples for moments estimation, and the retention of pulse-stagger phase information, which can be used for velocity dealiasing. These improvements are demonstrated using simulated and test-bed data, the latter acquired during 1991/1992 Orlando operations. Filter utilization, in the context of a pre-existing adaptive selection scheme (1) and the Orlando (FL) clutter environment, is examined using the new filters, and areas for improvement are identified.
Summary
We have developed new design algorithms for finite impulse response (FIR) filters that compensate for arbitrary input spacing and that allow for arbitrary group delay specification. The potential of these new designs to work with the ASR-9 staggered pulse spacing is examined in the context of the ASR-9 wind-shear processor...
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Safety analysis of the Traffic Information Service
November 22, 1994
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-226
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Summary
Traffic Information Service (TIS) is a Mode S data link application being developed for use by general aviation (GA) pilots. Its purpose is to provide a low-cost means of assisting the pilot in visual acquisition of nearby aircraft. The service provides two functions: traffic alerting and threat assessment. These functions are also performed by the Traffic Alert and Collision Avoidance System (TCAS). The purpose of this report is to evaluate the effectiveness and safety of TIS in relation to that of TCAS I. The analysis begins with a conceptual review of Andrews' statistical model of visual acquisition. Next, the surveillance systems and threat-detection logic of TIS and TCAS I are reviewed. Results of a Monte Carlo simulation that modeled the threat-assessment performance of TCAS I and TIS are also presented. The analysis supports the conclusion that, because of the high degree of similarity between TIS and TCAS I, TIS is a safe and effective means of assisting the pilot in visual acquisition of air traffic.
Summary
Traffic Information Service (TIS) is a Mode S data link application being developed for use by general aviation (GA) pilots. Its purpose is to provide a low-cost means of assisting the pilot in visual acquisition of nearby aircraft. The service provides two functions: traffic alerting and threat assessment. These functions...
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Obtaining low sidelobes using non-linear FM pulse compression
November 4, 1994
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-223
Summary
Airport Surveillance Radar (ASR) manufacturers are proposing the use of non-linear FM pulse compression in their all solid state radars. However there is concern that the use of pulse compression will limit the radar's performance. High range sidelobes can cause poor performance in both target and weather detection. The theory of nonlinear FM pulse compression is derived along with a method of minimizing the sidelobes using a minimum mean square error (MMSE) technique. The results of a computer program using the MMSE technique show that very low sidelobe levels of more than 100 dB down may be achieved. These very low sidelobes are affected by filter misalignment, target Doppler, and by transmitter phase errors or stability. Curves are presented demonstrating these effects. We also show how filter misalignment can be corrected by receiver filtering. The methods presented here are general enough to be used to assess the performance of proposed non-linear FM waveform radars.
Summary
Airport Surveillance Radar (ASR) manufacturers are proposing the use of non-linear FM pulse compression in their all solid state radars. However there is concern that the use of pulse compression will limit the radar's performance. High range sidelobes can cause poor performance in both target and weather detection. The theory...
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