Publications
An airborne traffic situation display system
June 23, 1971
Technical Report
Published in:
MIT Lincoln Laboratory Report TN-1971-19
Summary
An airborne traffic situation display system which could be used as an adjunct to the evolving National Airspace System/Automatic Radar Control Terminal System (NAS/ARTS) is described. In the proposed system, a contemporary realization of an old concept, the NAS/ARTS data are broadcast. A small digital computer in an aircraft then selects from the message stream the data on its own aircraft, nearby aircraft, and a local map. These data, plus aircraft heading data from a directional gyro, are used to generate a situation display that can be aircraft-centered and heading-oriented.
Summary
An airborne traffic situation display system which could be used as an adjunct to the evolving National Airspace System/Automatic Radar Control Terminal System (NAS/ARTS) is described. In the proposed system, a contemporary realization of an old concept, the NAS/ARTS data are broadcast. A small digital computer in an aircraft then...
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Propagation phenomena affecting satellite communications systems operating in the centimeter and millimeter wavelength bands
February 1, 1971
Journal Article
Published in:
Proc. IEEE, Vol. 59, No. 2, February 1971, pp. 173-188.
Summary
The theories describing the effects of the troposphere on satellite communication systems operating in the microwave region are reviewed. The results of computations based upon the theories and atmospheric models are presented and compared with available experimental data. From the model computations it is seen that rain causes the major propagation problems for the frequency bands allocated to or proposed for allocation to the satellite communications service. Two effects are dominant: attenuation due to rainfall along the line-of-sight and interference between two systems operating at the same frequency and beyond each other's radio horizon due to rain scatter. The methods for calculating the magnitude of the effects of rain given the spatial distribution of rainfall intensity are available. The statistical data required for the prediction of the spatial distribution of rainfall intensity are not available.
Summary
The theories describing the effects of the troposphere on satellite communication systems operating in the microwave region are reviewed. The results of computations based upon the theories and atmospheric models are presented and compared with available experimental data. From the model computations it is seen that rain causes the major...
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Radar meteorological applications of automatic film reading
January 1, 1971
Conference Paper
Published in:
Opt. Eng., Vol. 9, No. 2, January 1971, 090246.
Summary
The data recording of storm information as detected by a weather radar has been customarily made on photographic film. Research radars and an occasional U. S. Weather Bureau radar are fitted with scope cameras to record the radar plan position indicator (PPI) display. Over the past 15 years a large sample of weather radar data has been accumulated in this fashion. The photographic technique provides an easy, quick, and inexpensive way to record weather radar data. The major drawback of this technique is data reduction. Information on storm shape, size, and intensity is normally extracted from the photographic images by hand. This means that only the most interesting aspects of individual storms are analyzed and the vast majority of the collected radar data is not analyzed. A vast amount of climatological information could be obtained from the existing store of weather radar data if an automatic technique of data retrieval were available. The first part of this report describes the use of a computer-controlled programmable film reader to process weather radar PPI photographs to obtain digital maps of rainfall intensity for use in climatological studies.
Summary
The data recording of storm information as detected by a weather radar has been customarily made on photographic film. Research radars and an occasional U. S. Weather Bureau radar are fitted with scope cameras to record the radar plan position indicator (PPI) display. Over the past 15 years a large...
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A cockpit situation display of selected NAS/ARTS data
December 15, 1970
Technical Report
Published in:
MIT Lincoln Laboratory Report TN-1970-39
Summary
By the mid-1970's, the evolving NAS/ARTS ground environment will provide the air traffic controllers with high quality computer-processed traffic situation displays. We believe it would be useful, particularly in busy terminal areas, to display some of this data in the cockpit. Systems with this objective have been constructed and flight tested at least 3 times during the past 25 years, but these earlier systems could not benefit from: 1) a source of computer-processed data of the quality to be available from NAS/ARTS; 2) aircraft altitude information; 3) contemporary digital data link techniques; and 4) airborne equipment capable of automatically selecting and displaying only information relevant to a particular airplane. It is believed that an effective cockpit display would permit pilots, under IFR conditions, to retain some of the station-keeping and navigation functions they perform during VFR conditions and thereby improve the efficiency of terminal area operation. The goals of the proposed program are: a) to evaluate the effectiveness of this class of system in reducing pilot and controller work loads, and b) to determine its potential for expediting traffic flow in busy terminal areas. A simulated cockpit display has been developed and experienced pilots and controllers who have "flown" it have endorsed enthusiastically the desirability of evaluating this class of system in an operational environment.
Summary
By the mid-1970's, the evolving NAS/ARTS ground environment will provide the air traffic controllers with high quality computer-processed traffic situation displays. We believe it would be useful, particularly in busy terminal areas, to display some of this data in the cockpit. Systems with this objective have been constructed and flight...
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Measurement of clear air turbulence in the lower stratosphere using the Millstone Hill L-Band Radar
November 1, 1970
Conference Paper
Published in:
14th Conf. on Radar Meteorology, 17-20 November 1970, pp. 101-106.
Summary
Radar measurements of thin turbulent layers in the clear atmosphere have been extensively reported in the literature and have recently been summarized by Hardy and Katz (1969). The majority of the thin turbulent layer detections reported have been for layers in the lower troposphere. Using the high power radar facilities at Wallops Island, Atlas, et al (1966) have detected layers at heights up to the tropopause. In this paper, layer detections at heights above the tropopause are discussed. The detection of layers in the lower 10 km of the stratosphere is made possible by using a radar system which has approximately 10 dB more sensitivity than the Wallops Island radars for the detection of turbulent layers. The program of radar measurements of thin turbulent layers was undertaken to provide basic information about the structure of scattering layers in the upper troposphere and lower stratosphere for use in the prediction of troposcatter field strengths. The radar measurements were accompanied by radiosonde soundings. For a limited series of measurements, a U-2 aircraft was also used to probe for turbulent layers.
Summary
Radar measurements of thin turbulent layers in the clear atmosphere have been extensively reported in the literature and have recently been summarized by Hardy and Katz (1969). The majority of the thin turbulent layer detections reported have been for layers in the lower troposphere. Using the high power radar facilities...
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A comparison between monostatic and bistatic scattering from rain and thin turbulent layers
October 6, 1970
Technical Report
Published in:
MIT Lincoln Laboratory Report TN-1970-29
Summary
Simultaneous measurements were made of the backscatter cross section and the bistatic scattering cross section of rain and thin turbulent layers. The radar measurements were made at a frequency of 1.3 GHz using the Millstone Hill Radar. The bistatic scattering measurements were made using CW transmission at 7.7 GHz with a 145-km separation between transmitter and receiver. The receive station was the Westford Communication Terminal with a 60-foot antenna. The transmitter was van-mounted and used either a 6-foot antenna or a standard gain horn. Stable frequency sources were used to allow Doppler shift measurements on the bistatic scattering link. The measurements were made by fixing the pointing angles of the transmit antenna and scanning both the receive antenna and the radar to investigate the dependence of the scattered signals both on scattering angle and on the location of the scatterers. The measurements of the scattering cross section of the thin turbulent layers were made in the near forward direction, the measurements of rain at a large number of scattering angles. System sensitivities allowed the measurement of scattering from turbulent layers at a 10-km height with a thickness, Cn^2 product of 10^-13 N^2 m^1/3 and from rain with a 0.1 mm/hr. rate. Comparisons between the radar and bistatic measurements were in good agreement with the appropriate scattering theories.
Summary
Simultaneous measurements were made of the backscatter cross section and the bistatic scattering cross section of rain and thin turbulent layers. The radar measurements were made at a frequency of 1.3 GHz using the Millstone Hill Radar. The bistatic scattering measurements were made using CW transmission at 7.7 GHz with...
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Air Traffic Control quarterly technical summary, May 1970
May 15, 1970
Technical Report
Published in:
MIT Lincoln Laboratory Report ATC-QTS-05-70
Summary
This is the first report in the Quarterly Technical Summary series covering the Air Traffic Control activities at Lincoln Laboratory. The previous work on ATC was included in the General Research Quarterly Technical Summary. Because the allowable effort on ATC is comparatively small, it has been focused on only one facet of the problem; namely, on the data acquisition and communications task. The new group has started to make significant progress in several study aspects of the problem and has also obtained experimental L-band multipath data from an experimental airground test system. When additional support is received, the program will be expanded to include over-all system design studies and the investigation of radar improvements and multilateration systems, both ground- and satellite-based.
Summary
This is the first report in the Quarterly Technical Summary series covering the Air Traffic Control activities at Lincoln Laboratory. The previous work on ATC was included in the General Research Quarterly Technical Summary. Because the allowable effort on ATC is comparatively small, it has been focused on only one...
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Monostatic and bistatic scattering from thin turbulent layers in the atmosphere
September 18, 1968
Technical Report
Published in:
MIT Lincoln Laboratory Report TN-1968-34
Summary
Measurements were made of the scattering properties of thin turbulent layers at and above the tropopause. The Millstone Hill L-band radar was used to measure the backscatter cross section per unit volume of these layers as a function of time and space. An X-band forward scatter link was set up between Wallops Island, Virginia and Westford, Massachusetts to observe scattering from these layers. Although the radar could not provide observations of the common volume of the forward scatter link, for days where no clouds were observed in the vicinity of the tropopause, the radar observations of layers near the tropopause showed horizontal uniformity of height and backscatter cross section, and the radiosonde data taken near the radar and near the common volume showed similar wind and temperature structure near the tropopause, the signal strength on the forward scatter link and its dependence on scattering angle behaved in accordance with the prediction of turbulent scattering theory using the radar data as an input. The radar observations have shown that on each day measurements were made, layers were detected near and above the tropopause. Turbulent layers in the stratosphere have been detected at heights up to 22 km. These layers provide one of the mechanisms for weak, long-distance troposcatter propagation.
Summary
Measurements were made of the scattering properties of thin turbulent layers at and above the tropopause. The Millstone Hill L-band radar was used to measure the backscatter cross section per unit volume of these layers as a function of time and space. An X-band forward scatter link was set up...
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Simultaneous radar and radiometer measurements of rain shower structure
September 18, 1968
Technical Report
Published in:
MIT Lincoln Laboratory Report TN-1968-33
Summary
Simultaneous measurements of the backscatter cross section per unit volume and the sky temperature were made for limited volumes of rain showers using an L-band radar and an X-band radiometer. The object of the measurements was to provide data to validate the method used to compute attenuation and sky temperature given weather radar data as an input and to investigate the spatial changes in rainfall intensity and in the attenuation cross section per unit volume. The sky temperature was calculated using the radiative transfer equation and the distribution of attenuation cross section per unit volume estimated from the weather radar data. An empirical relationship between attenuation and backscatter cross sections was used based upon the results of a large number of Mie theory computations using measured raindrop size distributions. The results of the comparisons between calculated and measured sky temperature show good agreement. The discrepancies between the measured and calculated values are due to the difference in the antenna beamwidths for the two systems (0.6° for the L-band radar, 0.07° for the X-band radiometer). From these discrepancies the spatial distances over which the attenuation cross section can change significantly can be estimated. The results show that for the rain showers investigated, the attenuation cross section per unit volume can change an order of magnitude in 400 meters and the integrated attenuation along a horizontal line-of-sight can change an order of magnitude for a 1. 5km horizontal translation of the path.
Summary
Simultaneous measurements of the backscatter cross section per unit volume and the sky temperature were made for limited volumes of rain showers using an L-band radar and an X-band radiometer. The object of the measurements was to provide data to validate the method used to compute attenuation and sky temperature...
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Rain attenuation at millimeter wavelengths
January 1, 1968
Conference Paper
Published in:
IEEE Int. Convention Digest, 1968, p. 65.
Summary
The major propagation problem confronting the use of millimeter waves for line-of-sight communication links operating through the atmosphere is hydrometeor scattering. Rain, hail, sleet, snow, and fog all can cause severe attenuation at millimeter wave frequencies. The severest problem is that of attenuation by rain. Attenuations in excess of 1 db/km are computed for frequencies in excess of 45 GHz (6.7 mm) and rain rates in excess of 0.1"/hr (2.5 mm/hr). Light rain of this intensity occurs on the average of 80 hrs/year in the New York area and is generally wide spread, completely covering typical line-of-sight ground link distances. This means that for a ground link of 50 km extent the attenuation would exceed 50 db 0.9 percent of the time for frequencies above 45 GHz.
Summary
The major propagation problem confronting the use of millimeter waves for line-of-sight communication links operating through the atmosphere is hydrometeor scattering. Rain, hail, sleet, snow, and fog all can cause severe attenuation at millimeter wave frequencies. The severest problem is that of attenuation by rain. Attenuations in excess of 1...
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