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Comparisons of long-term Schumann resonance records in Europe and North America

June 7, 1999
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Conference Paper
Author:
G. Satori
…
Published in:
11th Int. Conf. on Atmos. Electr. 7-11 June 1999, pp. 705-708.
Topic:
electrical engineering
R&D area:
R&D group:

Summary

Two stations at a distance comparable with the wavelength in the Schumann resonance (SR) frequency range, one in Europe (Nagycenk, Hungary) and one in North America (West Greenwich, Rhode Island) have simultaneously monitored the natural vertical electric and horizontal magnetic field components in the frequency range of 3-25 Hz. This is a unique opportunity, as Schumann resonance stations are scarce and even fewer station have records with 5-6 year durations. The main purpose of this paper is to make comparisons in the SR time series measured simultaneously at the two field sites, thereby providing access to global behavior on the seasonal and interannual time scales. The comparative measurements described here point out distinct differences in the nature of convection in South America and in Africa, and reveal new aspects about the behavior of tropical continental convection on the ENS0 time scale.
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Summary

Two stations at a distance comparable with the wavelength in the Schumann resonance (SR) frequency range, one in Europe (Nagycenk, Hungary) and one in North America (West Greenwich, Rhode Island) have simultaneously monitored the natural vertical electric and horizontal magnetic field components in the frequency range of 3-25 Hz. This...

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Comparisons of long-term Schumann resonance records in Europe and North America

Schumann Resonances and the temporal-spatial dynamics of global thunderstorm activity

June 7, 1999
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Conference Paper
Author:
V. Mushtak
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Published in:
11th Int. Conf. on Atmospheric Electricity, 7-11 June 1999, pp. 698-700.
Topic:
weather
R&D area:
R&D group:

Summary

A two-dimensional computational ELF technique has been applied to interpret variations of peak frequencies of Schumann resosnances (SR) observed at the MIT experimental site (West Greenwich, Rhode Island). The spatial-temporal dynamics of global thunderstorm activity has been simulated on the basis of general meteorological data. It is shown that the proposed models provide a reasonable qualitative agreement between computed and observed variations for SR I to IV. Some inverse task diagrams has been constructed as an instrument for distinguishing between day-to-day thunderstorm scenarios.
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Summary

A two-dimensional computational ELF technique has been applied to interpret variations of peak frequencies of Schumann resosnances (SR) observed at the MIT experimental site (West Greenwich, Rhode Island). The spatial-temporal dynamics of global thunderstorm activity has been simulated on the basis of general meteorological data. It is shown that the...

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Schumann Resonances and the temporal-spatial dynamics of global thunderstorm activity

The relationship between the background and transient signals in Schumann resonances

June 7, 1999
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Conference Paper
Author:
Earle R. Williams
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Published in:
Proc. 11th Int. Conf. on Atmospheric Electricity, 7-11 June 1999, pp. 758-761.
Topic:
weather
R&D area:
R&D group:

Summary

Two distinct measures of the Earth's Schumann resonances -- the background and the transients -- are studied through comparisons at the mesoscale and at the continental scale. A rough proportionality is shown between the far more abundant afternoon lightning activity and the larger positive mesoscale discharges that make sprites and simultaneously ring the Earth- ionosphere cavity to levels higher than the integration of all other lightnings.
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Summary

Two distinct measures of the Earth's Schumann resonances -- the background and the transients -- are studied through comparisons at the mesoscale and at the continental scale. A rough proportionality is shown between the far more abundant afternoon lightning activity and the larger positive mesoscale discharges that make sprites and...

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The relationship between the background and transient signals in Schumann resonances

Total lightning activity associated with tornadic storms

June 7, 1999
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Conference Paper
Author:
Steven J. Goodman
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Published in:
11th Int. Conf. on Atmos. Electr., 7-11 June 1999, pp. 515-518.
Topic:
weather
R&D area:
R&D group:

Summary

Severe storms often have high flash rates (in excess of one flash per second) and are dominated by intracloud lightning activity. In addition to the extraordinary flash rates, there is a second distinguishing lightning characteristic of severe storms that seems to be important. When the total lightning history is examined, one finds sudden increases in the lightning rate, which we refer to as lightning "jumps", that precede the occurrence of severe weather by ten or more minutes. These jumps are typically 30-60 flashes/min, and are easily identified as anomalously large derivatives in the flash rate. This relationship is associated with updraft intensification and updraft strength is an important factor in storm severity (through the accumulation of condensate aloft and the stretching of vorticity). In several cases, evidence for diminishment of midlevel rotation and the descent of angular momentum from aloft is present prior to the appearance of the surface tornado. Based on our experience with severe and tornadic storms in Central Florida, we believe the total lightning may augment the more traditional use of NEXRAD radars and storm spotters. However, a more rigorous relation of these jumps to storm kinematics is needed if we are to apply total lightning in a decision tree that leads to improved warning lead times and decreased false alarm rates.
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Summary

Severe storms often have high flash rates (in excess of one flash per second) and are dominated by intracloud lightning activity. In addition to the extraordinary flash rates, there is a second distinguishing lightning characteristic of severe storms that seems to be important. When the total lightning history is examined...

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Total lightning activity associated with tornadic storms

Security implications of adaptive multimedia distribution

June 6, 1999
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Conference Paper
Author:
Thomas M. Parks
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Published in:
Proc. IEEE Int. Conf. on Communications, Multimedia and Wireless, Vol. 3, 6-10 June 1999, pp. 1563-1567.
Topic:
communications
R&D area:
R&D group:

Summary

We discuss the security implications of different techniques used in adaptive audio and video distribution. Several sources of variability in the network make it necessary for applications to adapt. Ideally, each receiver should receive media quality commensurate with the capacity of the path leading to it from each sender. Several different techniques have been proposed to provide such adaptation. We discuss the implications of each technique for confidentiality, authentication, integrity, and anonymity. By coincidence, the techniques with better performance also have better security properties.
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Summary

We discuss the security implications of different techniques used in adaptive audio and video distribution. Several sources of variability in the network make it necessary for applications to adapt. Ideally, each receiver should receive media quality commensurate with the capacity of the path leading to it from each sender. Several...

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Security implications of adaptive multimedia distribution

Rotating a weather map

June 1, 1999
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Journal Article
Author:
Robert D. Grappel
Published in:
Dr. Dobb's J., Vol. 24, No. 6, June 1999, pp. 80-88.
Topic:
aircraft
R&D area:
R&D group:

Summary

Introduction: I was recently part of a project developing a system for aircraft pilots to access the national ground weather-radar database while in flight. This weather-radar graphical database is generated from the outputs of the FAA and National Weather Service network of radars covering the continental United States and is updated every five minutes. Each pixel in the database covers a square measuring two kilometers (about one nautical mile) on a side. The content of each data pixel is a measure of the radar reflectivity measured at that location - radar reflectivity is proportional to the water content in the atmosphere (the precipitation rate). This graphical database is available through several commercial vendors - it's what you see displayed on The Weather Channel or during typical TV weather reports. Our system, on the other hand, provides a low-speed digital datalink connection from an FAA ground computer to an avionics computer/display located in the aircraft cockpit.
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Summary

Introduction: I was recently part of a project developing a system for aircraft pilots to access the national ground weather-radar database while in flight. This weather-radar graphical database is generated from the outputs of the FAA and National Weather Service network of radars covering the continental United States and is...

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Rotating a weather map

A photomixer local oscillator for a 630-GHz heterodyne receiver

June 1, 1999
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Journal Article
Author:
Simon Verghese
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Published in:
IEEE Microw. Guid. Wave Lett., Vol. 9, No. 6, June 1999, pp. 245-7.
Topic:
microelectronics
R&D area:
R&D group:

Summary

A photomixer local oscillator (LO) operating at the 630-GHz difference frequency of two laser diodes was successfully demonstrated with a heterodyne detector based on a niobium superconducting tunnel junction. The low-temperature-grown GaAs photomixer generated 0.20 uW in the input spatial mode of the receiver. Using the photmixer LO, the double-sideband noise temperature of the receiver was 331 K - in good agreement with the 323-K noise temperature obtained when a multiplied Gunn oscillator generating 0.25 uW was substituted for the photomixer.
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Summary

A photomixer local oscillator (LO) operating at the 630-GHz difference frequency of two laser diodes was successfully demonstrated with a heterodyne detector based on a niobium superconducting tunnel junction. The low-temperature-grown GaAs photomixer generated 0.20 uW in the input spatial mode of the receiver. Using the photmixer LO, the double-sideband...

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A photomixer local oscillator for a 630-GHz heterodyne receiver

Review of NYC ITWS during the September 7, 1998 severe weather event

May 26, 1999
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Project Report
Author:
Shawn S. Allan
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Published in:
Project Report ATC-269, MIT Lincoln Laboratory
Topic:
weather
R&D area:
R&D group:

Summary

The New York City Integrated Terminal Weather System (ITWS) prototype became operational for the first time on August 30, 1998. Although this was near the end of the region's convective season, site staff were afforded a unique chance to assess the system's performance during Labor Day weekend on the afternoon of September 7 when a line of severe thunderstorms wreaked havoc over large areas of the Tri-state region. The storm with gusts reported as high as 80 mph, caused fatalities as boats overturned and trees fell on cars. Tornadoes were confirmed over New Jersey and Long Island, with major structural damage occurring in other areas as the result of strong straight-line winds and hail reported as large as 1.75 inches in diameter. Significant airport delays were experienced at the three major New York airports (over 600 flights delayed at least 15 minutes) and several hundred flights were cancelled. This report will assess the performance of ITWS and NEXRAD products during the time severe weather impacted the TRACON area, from about 1700 to 1930 UTC on September 7 (hereafter all times will be given in UTC). It will also discuss the synoptic weather setting and conclude with a section on the operational benefits users derived from ITWS on this day.
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Summary

The New York City Integrated Terminal Weather System (ITWS) prototype became operational for the first time on August 30, 1998. Although this was near the end of the region's convective season, site staff were afforded a unique chance to assess the system's performance during Labor Day weekend on the afternoon...

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Review of NYC ITWS during the September 7, 1998 severe weather event

Lessons learned designing an alternative CHI for en route air traffic control

April 27, 1999
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Conference Paper
Author:
Maria Picardi Kuffner
Published in:
Controller Centered HMI, 27-29 April 1999.
Topic:
air traffic control
R&D area:
R&D group:

Summary

MIT Lincoln Laboratory is supporting the FAA-sponsored effort to design an operationally suitable Computer Human Interface (CHI) for the recently upgraded En Route Air Traffic Control Centers. All centers will soon receive new control consoles with state-of-the-art 20 square (2K by 2K resolution) color displays (currently operating in Seattle as of January 1999). The future CHI is being modeled on Eurocontrol's Operational Display and Input Development (ODID) CHI, as requested by active controllers in the US. The ODID-like CHI, with its minimal information display and color coded guidance, provides increased efficiency and productivity through employment of a modern graphical user interface. Lessons learned during the on-going design process, including research of look and feel issues in conjunction with data analysis from controller-in-the-loop testing of a prototype ODID-like CHI will be discussed. The Laboratory plans to model the alternative ODID-like CHI on the best of the European ODID, Denmark Sweden Interface (DSI) and EATCHIP CHI features, while cognizant of the FAA?s DSR capabilities and limitations to support an improved user interface. Human factors issues need resolution to provide a consistent look and feel across the Free Flight Phase 1 products and platforms, the Center TRACON Automation System (CTAS) and the User Request Evaluation Tool (URET). MIT Lincoln Laboratory has built a CHI Requirements Engineering Model (CREM) to support controller-in-the-loop testing of the ODID-like CHI, validate CHI requirements and determine applicable standards for the design of an integrated CHI. The CREM provides a means to assess various CHI alternatives and the capability to iterate options with controller teams to address user concerns. Lessons learned from the ODID-like CHI specification process will also be shared.
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Summary

MIT Lincoln Laboratory is supporting the FAA-sponsored effort to design an operationally suitable Computer Human Interface (CHI) for the recently upgraded En Route Air Traffic Control Centers. All centers will soon receive new control consoles with state-of-the-art 20 square (2K by 2K resolution) color displays (currently operating in Seattle as...

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Lessons learned designing an alternative CHI for en route air traffic control

Automatic speaker clustering from multi-speaker utterances

March 15, 1999
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Conference Paper
Author:
John J. McLaughlin
…
Published in:
Proc. IEEE Int. Conf. on Acoustics, Speech and Signal Processing, ICASSP, Vol. II, 15-19 March 1999, pp. 817-820.
Topic:
speaker recognition
R&D area:
R&D group:

Summary

Blind clustering of multi-person utterances by speaker is complicated by the fact that each utterance has at least two talkers. In the case of a two-person conversation, one can simply split each conversation into its respective speaker halves, but this introduces error which ultimately hurts clustering. We propose a clustering algorithm which is capable of associating each conversation with two clusters (and therefore two-speakers) obviating the need for splitting. Results are given for two speaker conversations culled from the Switchboard corpus, and comparisons are made to results obtained on single-speaker utterances. We conclude that although the approach is promising, our technique for computing inter-conversation similarities prior to clustering needs improvement.
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Summary

Blind clustering of multi-person utterances by speaker is complicated by the fact that each utterance has at least two talkers. In the case of a two-person conversation, one can simply split each conversation into its respective speaker halves, but this introduces error which ultimately hurts clustering. We propose a clustering...

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Automatic speaker clustering from multi-speaker utterances
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