Publications
Machine intelligent gust front algorithm for the Terminal Doppler Weather Radar (TDWR) and Integrated Terminal Weather System (ITWS)
November 13, 1996
Conference Paper
Published in:
Workshop on Wind Shear and Wind Shear Alert Systems, 13-15 November, 1996.
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Summary
Thunderstorms often generate gust fronts that can have significant impact on airport operations. Unanticipated changes in wind speed and direction are of concern from an air traffic safety viewpoint (hazardous wind shear) as well as from an airport planning point of view (runway configuration). Automated gust front detection is viewed by FAA and the air traffic community as an important component of current and future hazardous weather detection systems including the Terminal Doppler Weather Radar (TDWR), ASR-9 with Weather Systems Processor (ASR-9 WSP), and the Integrated Terminal Weather Systems (ITWS) for which TDWR is a principal sensor. In cooperation with the FAA, Lincoln Laboratory has successfully developed and tested a real-time Machine Intelligent Gust Front Algorithm (MIGFA) for use with Doppler weather radars. This algorithm resulted from the successful fusion of two complementing technologies developed at Lincoln Laboratory: computer vision/machine intelligence techniques originally developed for automated target recognition, and automated product-oriented weather radar data processing. Using these techniques, a version of MIGFA designed for use with TDWR has demonstrated substantial improvement over the existing TDWR gust front algorithm, detecting more and greater extents of gust fronts with fewer false alarms. MIGFA is slated to eventually replace the existing TDWR gust front algorithm and will be used as the gust front algorithm for the planned ITWS and ASR-9 WSP systems. A brief overview of techniques used by MIGFA to identify and track gust fronts will bre presented in this paper. More details, along with recent detection performance results, can be obtained from prior publications. However, detection and tracking of a gust front is only part of the task. Once the location of a gust front has been determined, the associated wind shear estimate and wind shift forecast must be computed. Several issues arises. For example, a gust front can be tens of kilometers in length, with outflow strength and contrasting environmental winds varying considerably along its length. Where along the front should the wind shear analysis be performed? Also, for airport planning purposes, air traffic controllers and managers need to plan runway configuration based on winds that may change suddenly when a gust front moves over the airport. Depending on the nature of the gust front, some of these winds are relatively transient while others are more persistent. How should the wind shift advisory produced by the algorithm take this into account? MIGFA uses a consensus derived from a variety of estimation techniques as a robust means of generating wind shear and wind shift estimates for detected gust fronts. These techniques, and some of their limitations, are discussed. Results of comparisons of MIGFA-generated wind shear and wind shift reports against observations are also presented. The paper concludes by outlining planned enhancements to incorporate additional information available under ITWS that should further improve the quality of MIGFA's wind shear and wind shift forecasts.
Summary
Thunderstorms often generate gust fronts that can have significant impact on airport operations. Unanticipated changes in wind speed and direction are of concern from an air traffic safety viewpoint (hazardous wind shear) as well as from an airport planning point of view (runway configuration). Automated gust front detection is viewed...
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The Terminal Weather Information for Pilots program
November 13, 1996
Conference Paper
Published in:
Workshop on Wind Shear and Wind Shear Alert Systems,. Oklahoma City, 13-15 November, 1996.
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Summary
The Federal Aviation Administration (FAA) is currently sponsoring programs such as the Terminal Doppler Weather Radar (TDWR) and the Integrated Terminal Weather System (ITWS) which will significantly improve the aviation weather information in the terminal area. Given the great increase in the quantity and quality of this information, it would be highly desirable to provide this data 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 potential weather hazards and reduce air traffic controller workload. The Terminal Weather Information for Pilots (TWLP) program was created to address these needs. This paper will describe the philosophy behind the product, the format of the TWIP messages. and the system design. An interesting weather case from the operational demonstration currently underway will be shown, and plans for the national deployment of the TWIP capability at all TDWR-based airports will be discussed.
Summary
The Federal Aviation Administration (FAA) is currently sponsoring programs such as the Terminal Doppler Weather Radar (TDWR) and the Integrated Terminal Weather System (ITWS) which will significantly improve the aviation weather information in the terminal area. Given the great increase in the quantity and quality of this information, it would...
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A 16-element subarray for hybrid-circuit tile-approach spatial power combining
November 1, 1996
Journal Article
Published in:
IEEE Trans. Microw. Theory Tech., Vol. 44, No. 11, November 1996, pp. 2093-8.
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Summary
Three designs for a 4-by-4 are described for use in a spatial power-combined transmitter. The subarrays are constructed using a hybrid-circuit, tile-approach architecture and are composed of 16 cavity-backed, proximity-coupled microstrip antennas, each fed by a 0.5 watt amplifier. Both linearly and circularly polarized subarrays have been constructed for operation over a 10% band centered at 10 GHz. The linearly polarized subarray showed the following peak performance: EIRP greater than 27 dBW, effective transmitter power greater than 5 watts, dc-RF efficiency greater than 20%, and excellent graceful degradation performance.
Summary
Three designs for a 4-by-4 are described for use in a spatial power-combined transmitter. The subarrays are constructed using a hybrid-circuit, tile-approach architecture and are composed of 16 cavity-backed, proximity-coupled microstrip antennas, each fed by a 0.5 watt amplifier. Both linearly and circularly polarized subarrays have been constructed for operation...
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Automatic English-to-Korean text translation of telegraphic messages in a limited domain
August 5, 1996
Conference Paper
Published in:
Proc. Int. Conf. on Computational Linguistics, 5-9 August 1996, pp. 705-710.
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Summary
This paper describes our work-in-progress in automatic English-to-Korean text; translation. This work is an initial step toward the ultimate goal of text and speech translation for enhanced multilingual and multinational operations. For this purpose, we have adopted an interlingual approach with natural language understanding (TINA) and generation (GENESIS) modules at the core. We tackle the ambiguity problem by incorporating syntactic and semantic categories in the analysis grammar. Our system is capable of producing accurate translation of complex sentences (38 words) and sentence fragments as well as average length (12 words) grammatical sentences. Two types of system evaluation have been carried out: one for grammar coverage and the other for overall performance. For system robustness, integration of two subsystems is under way: (i) a rule-based part-of-speech tagger to handle unknown words/constructions, and (ii) a word-for-word translator to handle other system failures.
Summary
This paper describes our work-in-progress in automatic English-to-Korean text; translation. This work is an initial step toward the ultimate goal of text and speech translation for enhanced multilingual and multinational operations. For this purpose, we have adopted an interlingual approach with natural language understanding (TINA) and generation (GENESIS) modules at...
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Experimental comparison of the radiation efficiency for conventional and cavity backed microstrip antennas
July 21, 1996
Journal Article
Published in:
IEEE Antennas and Propagation Society Intl Symp., 21-26 July 1996.
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Summary
The radiation efficiency of conventional microstrip antennas generally decreases when the substrate thickness or permittivity is increased because of loss to surface waves. However, constructing a metal cavity around the microstrip antenna prevents the surface wave propagation. Thus, the cavity backed microstrip antenna has been predicted to have increased radiation efficiency. In this paper, we compare conventional and cavity backed microstrip patch antennas on substrates with an electrical thickness of 0.067 ho and dielectric constants of ~r=2.94, 6.15, and 10.2. As one would expect, the radiation efficiency of the conventional patch decreases with increasing dielectric constant, but the efficiency remains relatively constant for the cavity backed patch. In this work, three different methods are used to measure the radiation efficiencies: a far field gain comparison, a Wheeler cap method and an input admittance method.
Summary
The radiation efficiency of conventional microstrip antennas generally decreases when the substrate thickness or permittivity is increased because of loss to surface waves. However, constructing a metal cavity around the microstrip antenna prevents the surface wave propagation. Thus, the cavity backed microstrip antenna has been predicted to have increased radiation...
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The COBEL model as part of a terminal-area ceiling & visibility (C&V) nowcast system: a progress report
July 18, 1996
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-241
Summary
The Federal Aviation Administration (FAA) Integrated Terminal Weather System (ITWS) is supporting the development of products aimed at providing automated guidance to the air traffic managers for the anticipation of changes in ceiling and visibility (C&V) conditions and wake vortex behavior in the terminal area. Fine-resolution, one-dimensional (column) numerical models are being considered to provide information on the evolution of the local fine-scale structure of the lower atmosphere over the terminal area. The Code Brouillard Eau Liquids (COBEL) column model is being investigated for potential use within the ITWS. This one-dimensional numerical model has been developed for the short-term prediction of fog events in the north of France. This report describes initial progress in adapting the COBEL model to a wider range of meteorological conditions. A parameterization of surface frost deposition was implemented and a slight error in the computation of stability in a saturated atmosphere was corrected. Tests suggest that these modifications represent important features of the newest version of the COBEL model. Other significant modifications to the COBEL model were performed. Pressure tendencies and vertical motion (vertical advection) were implemented as additional external forcings to the column model. Sensitivity tests show that these forcings play important roles in determining the onset, evolution and dissipation of low stratiform clouds. Some further applications of the model are briefly discussed and future development efforts are suggested.
Summary
The Federal Aviation Administration (FAA) Integrated Terminal Weather System (ITWS) is supporting the development of products aimed at providing automated guidance to the air traffic managers for the anticipation of changes in ceiling and visibility (C&V) conditions and wake vortex behavior in the terminal area. Fine-resolution, one-dimensional (column) numerical models...
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Assessment of the delay aversion benefits of the Airport Surveillence Radar (ASR) Weather Systems Processor (WSP)
July 2, 1996
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-249
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Summary
The Weather Systems Processor (WSP) modification to existing Airport Surveillance Radars (ASR-9) significantly enhances the functionality of the radar with respect to hazardous weather detection and tracking. Dedicated alphanumeric and color graphic displays alert controllers to hazardous wind shear conditions on the runways or final approach/initial departure flight corridors, show current location and anticipated movement of thunderstorm cells, and provide short-term forecasts of operationally significant wind shifts. Operational tests of a prototype WSP and related terminal area hazardous weather detection systems (the Terminal Doppler Weather Radar (TDWR) and the Integrated Terminal Weather System (ITWS)) have shown that, in addition to reducing the risk of aircraft accidents associated with wind shear encounters on landing or takeoff, the information provided by these systems is a significant aid in terminal air traffic management during adverse weather. The resulting efficiency enhancements reduce delay and associated costs. This report assesses the magnitude of the delay aversion benefits that will be realized through national deployment of the WSP. These are quantified both in terms of aircraft delay-hour reductions and corresponding dollar benefits. The analysis indicates that these benefits will total approximately $18M per year given year 2000 expected traffic counts at the 34 planned WSP airports. This exceeds, in equivalent dollar value, the safety benefits realized through WSP deployment by a factor of approximately five.
Summary
The Weather Systems Processor (WSP) modification to existing Airport Surveillance Radars (ASR-9) significantly enhances the functionality of the radar with respect to hazardous weather detection and tracking. Dedicated alphanumeric and color graphic displays alert controllers to hazardous wind shear conditions on the runways or final approach/initial departure flight corridors, show...
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The Marine Stratus Initiative at San Francisco International Airport
June 25, 1996
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-252
Summary
San Francisco International Airport is one of the busiest airports in the United States and one of the highest delay airports in terms of total aircraft delay hours and number of imposed air traffic delay programs. As with most airports, weather is the primary cause of aircraft delay. In particular, the local airspace is prone to regular occurrences of low cloud ceiling conditions due to intrusion of marine air from the eastern Pacific Ocean from May through September. Typically, this layer of stratus clouds forms in the San Francisco Bay area overnight and dissipates during the middle to late morning. The timing of the stratus cloud dissipation is such that it frequently poses a threat to the morning arrival push of air traffic into San Francisco. Weather forecasters at the Central Weather Service Unit (CWSU) at the Oakland AirRoute Traffic Control Center are responsible for providing a forecast whether or not the cloudiness will impact morning traffic operations. This information is used for decision making by the Traffic Management Unit at Oakland Center in order to optimally match arriving traffic demand to available airport capacity. As part of the FAA's Integrated Terminal Weather System, the Weather Sensing Group at MIT Lincoln Laboratory has begun an effort entitled the "Marine Stratus Initiative." Its objective is to provide improved weather information and forecast guidance to the Oakland CWSU, which is responsible for providing weather forecasts to air traffic managers. During 1995, the main focus of the project was the design and implementation of a data acquisition, communication, and display infrastructure that provides forecasters with new sources of weather data and information. These initial capabilities were tested during an operational demonstration in August and September. As the project continues, the intent is to improve these new data sources and develop an automated or semi-automated algorithm that will process raw information to provide weather forecasters with numerical guidance to assist them in the forecast process. A description of airport operations at San Francisco and the impact of marine stratus are presented. An explanation is given of the marine stratus phenomenology and the primary factors contributing to cloud dissipation. This conceptual model of the dissipation process is used to define system requirements. A description of the hardware, communications, and display subsystems is provided. An overview of the 1995 demonstration, including user comments, is presented, as well as future plans for meeting the longer-term objectives of the project.
Summary
San Francisco International Airport is one of the busiest airports in the United States and one of the highest delay airports in terms of total aircraft delay hours and number of imposed air traffic delay programs. As with most airports, weather is the primary cause of aircraft delay. In particular...
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Air Force planetary defense system: initial field test results
June 1, 1996
Conference Paper
Published in:
Proc. of the Fifth Int. Conf. on Space '96: Engineering, Construction, and Operations in Space V, 1-6 June 1996, pp. 46-53.
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Summary
Over the past several years, the Air Force has been developing new devices and technology for the detection and tracking of earth orbiting satellites. This technology has been targeted to provide an upgraded capability for an operational space surveillance system called GEODSS. Currently, a number of GEODSS systems are deployed around the world as part of the world-wide space surveillance system operated by the US Air Force. Each GEODSS site is currently equipped with 1-meter class telescopes and EBSICON detector systems which represent 1970's technology. The Air Force is now in the process of upgrading the GEODSS system to achieve the performance offered by state of the art detector systems. Under Air Force sponsorship, Lincoln Laboratory has developed a new generation of sensitive, large format, frame transfer CCD focal planes for GEODSS. These focal planes have been installed in a new generation of cameras and are currently undergoing testing at the Lincoln Laboratory Experimental Test Site (ETS). When equipped with the new focal plane and camera technology, the modest sized GEODSS telescopes have considerable capability to conduct large coverage, sensitive searches for earth crossing asteroids. Theoretical analysis has indicated that the CCD equipped GEODSS telescope will be capable of achieving a limiting magnitude of 22, over a 2 sq/deg field of view, with about 100 seconds of integration. This is comparable to the sensitivity of considerably larger telescopes equipped with current cameras. In addition to the high sensitivity, the CCD is configured for frame transfer operations which are well suited to asteroid search operations. This paper will present the results of the initial system tests conducted at the ETS and will discuss how this technology fits into a concept of operations for a planetary defense system based on the Air Force developed technology.
Summary
Over the past several years, the Air Force has been developing new devices and technology for the detection and tracking of earth orbiting satellites. This technology has been targeted to provide an upgraded capability for an operational space surveillance system called GEODSS. Currently, a number of GEODSS systems are deployed...
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Six-sector antenna for the GPS-squitter en-route ground station
May 31, 1996
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-248
Summary
Summary: A six-sector antenna for a pole-mounted GPS-Squitter en-route ground station was designed, built, and tested. The fan beam of each of the six sectors of the antenna covers a 60- degree azimuthal sector. Together, the six uniformly-spaced, contiguous 60-degree sectors cover the complete 360 degrees of azimuth at the two Mode S frequencies, 1030 and 1090 MHz. When equipped with its receivers, the antenna achieves a maximum operational squitter reception range in excess of 200nmi. Physically, the antenna consists of six vertical 12-element linear arrays spaced uniformly round the circumference of an imaginary vertical circular cylinder and lying parallel to its axis. Six reflectors in the form of parabolic cylinders are mounted behind the linear arrays, one per array, to define the six separate sector beams. The complete radome-enclosed assembly is a cylinder eight feet tall and 23 inches in diameter. It weighs 250 pounds.
Summary
Summary: A six-sector antenna for a pole-mounted GPS-Squitter en-route ground station was designed, built, and tested. The fan beam of each of the six sectors of the antenna covers a 60- degree azimuthal sector. Together, the six uniformly-spaced, contiguous 60-degree sectors cover the complete 360 degrees of azimuth at the...
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