Publications
Tagged As
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.
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...
READ MORE
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.
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...
READ MORE
Advanced trigger development
November 1, 2007
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 17, No. 1, November 2007, pp. 29-62.
Topic:
R&D area:
Summary
The deadliest form of a biological attack is aerosolized agents dispersed into the atmosphere. Early detection of aerosolized biological agents is important for defense against these agents. Because of the wide range of possible attack scenarios and attack responses, there is also a wide range of detector requirements. This article focuses on real-time, single-particle, optically based bio-agent trigger detectors--the first responder to an aerosol attack--and how to engineer these detectors to achieve optimal detection performance.
Summary
The deadliest form of a biological attack is aerosolized agents dispersed into the atmosphere. Early detection of aerosolized biological agents is important for defense against these agents. Because of the wide range of possible attack scenarios and attack responses, there is also a wide range of detector requirements. This article...
READ MORE
Measurement of aerosol-particle trajectories using a structured laser beam
June 1, 2007
Journal Article
Published in:
Appl. Opt., Vol. 46, No. 16, 1 June 2007, pp. 3150-3155.
Summary
What is believed to be a new concept for the measurement of micrometer-sized particle trajectories in an inlet air stream is introduced. The technique uses a light source and a mask to generate a spatial pattern of light within a volume in space. Particles traverse the illumination volume and elastically scatter light to a photodetector where the signal is recorded in time. The detected scattering waveform is decoded to find the particle trajectory. A design is presented for the structured laser beam, and the accuracy of the technique in determining particle position is demonstrated. It is also demonstrated that the structured laser beam can be used to measure and then correct for the spatially dependent instrument-response function of an optical-scattering-based particle-sizing system for aerosols.
Summary
What is believed to be a new concept for the measurement of micrometer-sized particle trajectories in an inlet air stream is introduced. The technique uses a light source and a mask to generate a spatial pattern of light within a volume in space. Particles traverse the illumination volume and elastically...
READ MORE
SiGe IC-based mm-wave imager
May 27, 2007
Conference Paper
Published in:
2007 IEEE Int. Symp. on Circuits and Systems, 27-30 May 2007, pp. 1975-1978.
Summary
Millimeter-wave radiation and detection offers the possibility of detecting concealed weapons. Passive imaging measures the mm-wave radiation emitted from target objects. A passive mm-wave imager and the designs affecting the overall system performance are discussed. With low power receiver architecture and SiGe ICs, a focal plane based full staring array is feasible and can provide a high thermal resolution, ~1.1K at >10Hz frame rate.
Summary
Millimeter-wave radiation and detection offers the possibility of detecting concealed weapons. Passive imaging measures the mm-wave radiation emitted from target objects. A passive mm-wave imager and the designs affecting the overall system performance are discussed. With low power receiver architecture and SiGe ICs, a focal plane based full staring array...
READ MORE
Laser-induced fluorescence-cued, laser induced- breakdown spectroscopy biological-agent detection
December 1, 2006
Journal Article
Published in:
Appl. Opt., Vol. 45, No. 34, 1 December 2006, pp. 8806-8814.
Topic:
R&D area:
Summary
Methods for accurately characterizing aerosols are required for detecting biological warfare agents. Currently, fluorescence-based biological agent sensors provide adequate detection sensitivity but suffer from high false-alarm rates. Combining single-particle fluorescence analysis with laser-induced breakdown spectroscopy (LIBS) provides additional discrimination and potentially reduces false-alarm rates. A transportable UV laser-induced fluorescence-cued LIBS test bed has been developed and used to evaluate the utility of LIBS for biological-agent detection. Analysis of these data indicates that LIBS adds discrimination capability to fluorescence-based biological-agent detectors. However, the data also show that LIBS signatures of biological agent simulants are affected by washing. This may limit the specificity of LIBS and narrow the scope of its applicability in biological-agent detection.
Summary
Methods for accurately characterizing aerosols are required for detecting biological warfare agents. Currently, fluorescence-based biological agent sensors provide adequate detection sensitivity but suffer from high false-alarm rates. Combining single-particle fluorescence analysis with laser-induced breakdown spectroscopy (LIBS) provides additional discrimination and potentially reduces false-alarm rates. A transportable UV laser-induced fluorescence-cued LIBS...
READ MORE
MIGFA: the Machine Intelligent Gust Front Algorithm for NEXRAD
October 24, 2005
Conference Paper
Published in:
32nd Conf. on Radar Meteorology, 24-29 October 2005.
Summary
Over a decade ago the FAA identified a need to detect and forecast movement of wind shear hazards such as gust fronts that impact the terminal air space. The Machine Intelligent Gust Front Algorithm (MIGFA) was developed to address this need (Delanoy and Troxel, 1993). The MIGFA product provides the position, the forecasted positions, and the strength of each wind shear detection to support air traffic control safety and planning functions. MIGFA will realize a new capability for NEXRAD but was originated for use with the FAA's Airport Surveillance Radar Model 9 (ASR-9) Weather Systems Processor (WSP) as described in Troxel and Pughe (2002). Subsequently, a second version was developed for the FAA's Terminal Doppler Weather Radar (TDWR) and is a component of the FAA's Integrated Terminal Weather System (ITWS). Most of the larger U.S. airports have ITWS installations. The ASR-9s are associated with medium-sized airports. MIGFA in NEXRAD is intended to further expand MIGFA support of air traffic control functions. There are significant algorithmic differences between the ASR-9 WSP and TDWR versions of MIGFA, primarily because of the different beam types of the two radars. Physically, the TDWR's pencil beam allows for good vertical resolution in a spatial volume of data. The ASR-9's vertical fan beam results in poor vertical resolution. Nonetheless, a key tenet in developing these two versions of MIGFA was to use the same core image processing analysis techniques (Morgan and Troxel, 2002) central to the MIGFA functionality. This same core is also central to MIGFA in NEXRAD. The Massachusetts Institute of Technology's Lincoln Laboratory (LL) has been tasked by the FAA to transfer MIGFA technology to NEXRAD. The goal is to enable a NEXRAD MIGFA capability at airports within about 70 km of any NEXRAD. LL has been developing NEXRAD algorithms to address the FAA's weather systems' needs since the Open Radar Product Generator (ORPG) was fielded in 2001. FAA sponsored, LL-developed NEXRAD algorithms generate the following products: the Data Quality Assurance (DQA), the High Resolution VIL (HRVIL), and the High Resolution Enhanced Echo Tops (HREET) (Smalley et al., 2003). These algorithms have proven useful to non-FAA users of NEXRAD products such as the National Weather Service (NWS) and the Department of Defense (DoD). Similarly, the NWS and DoD are developing plans to use MIGFA. MIGFA is slated to be included in the ORPG Build 9 baseline that is scheduled to be released in the Spring of 2007. In the following sections, we will discuss the salient features of MIGFA; the tuning of MIGFA to NEXRAD data; a comparison of detection performance of the TDWR and NEXRAD MIGFA versions; and some examples of MIGFA in operation.
Summary
Over a decade ago the FAA identified a need to detect and forecast movement of wind shear hazards such as gust fronts that impact the terminal air space. The Machine Intelligent Gust Front Algorithm (MIGFA) was developed to address this need (Delanoy and Troxel, 1993). The MIGFA product provides the...
READ MORE
Enhanced detection and classification of buried mines with an UWB multistatic GPR
July 3, 2005
Conference Paper
Published in:
IEEE Antennas and Propagation Society Int. Symp. 2005 Digest, Vol. 3B, 3-8 July 2005, pp. 88-91.
Topic:
R&D group:
Summary
In this paper we present a resonance-based classification technique for the identification of plastic-cased antipersonnel (AP) land mines buried in lossy and dispersive soils under rough surfaces by a stepped-frequency ultra-wideband (UWB) downward-looking ground penetrating radar (GPR) with an array of receivers. For this application the multistatic ground probing sensor is positioned just above the ground surface and operates from UHF to C-Band frequencies. Novel physics-based models based on the finite difference frequency domain (FDFD) technique simulate the characteristic resonating multi-aspect target frequency responses for several realistic buried land mine detection scenarios. Matched filter detection results are presented which assess the GPR's performance in identifying a simulated mine buried under a rough surface at varying depths in dry sand and a dispersive clay loam soil from other false targets such as buried rocks.
Summary
In this paper we present a resonance-based classification technique for the identification of plastic-cased antipersonnel (AP) land mines buried in lossy and dispersive soils under rough surfaces by a stepped-frequency ultra-wideband (UWB) downward-looking ground penetrating radar (GPR) with an array of receivers. For this application the multistatic ground probing sensor...
READ MORE
Advanced terminal weather products demonstration in New York
October 4, 2004
Conference Paper
Published in:
Proc. 11th Conf. on Aviation, Range and Aerospace Meteorology, 4-8 October 2004.
Summary
Weather continues to be a significant source of delay for aircraft destined to and departing from the New York metropolitan area, with weather delays through the first half of 2004 reaching levels not seen since 2000. In Allan et al. (2001), it was shown that total arrival delays on days with low ceiling and visibility at Newark Airport (EWR) averaged 210 hours, increasing to an average of 280 hours on days with thunderstorms impacting EWR operations. An analysis of Ground Delay Programs (GDPs) due to weather in the National Airspace System was performed for 2002-20031. Low ceilings, thunderstorms, snow, and wind were all shown to be significant sources of delay (Figure 1). These same weather conditions that lead to GDPs often also lead to holding and long departure delays. In 1998, demonstration of a prototype Integrated Terminal Weather System (ITWS) began in the New York area, helping significantly reduce terminal delays from convection, high surface winds, and vertical wind shear (Allan et al., 2001). In 2002, a new demonstration system, the Corridor Integrated Weather System (CIWS), was introduced at New York Center (ZNY) to help mitigate convective weather delays in the enroute airspace. Substantial benefits were realized from this system and are documented in Robinson et al. (2004). While systems such as ITWS and CIWS have helped significantly with convective weather, much has been learned during the field-testing of these systems about areas where existing research and technology could be leveraged to reduce weather delay in areas that have not been addressed previously. This paper will discuss four experimental products that recently have been or will be fielded in the NY area and how they are expected to benefit the aviation system. Enhancements to the Terminal Convective Weather Forecast (TCWF) address delays in convective weather, snowstorms, and steady rain. The newly fielded Route Availability Planning Tool (RAPT) addresses departure delays in convective weather. The Ceiling and Visibility (C&V) Diagnosis and Prediction Product will address delay due to low ceiling and visibility. The Path-Based Shear Detection (PSD) tool is expected to help both to reduce delays on days with high winds and to indicate regions of potential low altitude turbulence.
Summary
Weather continues to be a significant source of delay for aircraft destined to and departing from the New York metropolitan area, with weather delays through the first half of 2004 reaching levels not seen since 2000. In Allan et al. (2001), it was shown that total arrival delays on days...
READ MORE
Commercial aviation encounters with severe low altitude turbulence
October 4, 2004
Conference Paper
Published in:
11th Conf. on Aviation, Range and Aerospace Meteorology, 4-8 October 2004.
Summary
Turbulence encounters continue to be one of the largest sources of personal injury in both commercial and general aviation. A significant percentage of these encounters occur without warning, at low altitudes, and have been observed to occur outside of the strong reflectivity storm cores where pilots typically anticipate severe wind shear and/or turbulence. In this paper, statistics illustrating the altitude distributions of specific turbulence encounters are presented. These results suggest that a significant percentage of the moderate and greater turbulence encounters occur at low altitudes. One particularly dangerous form of low altitude turbulence, often associated with convective storms, is the buoyancy wave (BW). Observational evidence of commercial airline encounters with these phenomena indicates that they can cause an impairment of aircraft control that results in significant attitude and altitude fluctuations. Over the past two years several serious aircraft incidents involving low altitude turbulence have been reported. In our investigation of the meteorological conditions surrounding these incidents, there are strong indications that buoyancy waves played a major role in initiating the turbulence. While encounters with this type of buoyancy wave-induced turbulence can be as severe as microburst wind shear encounters, they are typically not detected by current wind shear detection systems. However, these phenomena do have detectable signatures. We suggest two modifications to existing wind shear detection systems that would make it possible to detect these potentially dangerous phenomena.
Summary
Turbulence encounters continue to be one of the largest sources of personal injury in both commercial and general aviation. A significant percentage of these encounters occur without warning, at low altitudes, and have been observed to occur outside of the strong reflectivity storm cores where pilots typically anticipate severe wind...
READ MORE