Publications
FAA weather surveillance requirements in the context on NEXRAD
November 19, 1982
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-112
Summary
The Federal Aviation Administration (FAA), National Weather Service and Air Force Weather Service are currently engaged in a program to develop a next generation of weather radars (NEXRAD) capable of satisfying (to the greatest extent possible) the common weather information needs of these agencies. This report identifies the unique FAA weather radar surveillance requirements and examines the technical issues that arise in attempting to meet these requirements with the NEXRAD strawman radar sensors and siting. Current air traffic control (ATC) weather data usage and statistics of aviation weather hazards and system efficiency are used to prioritize products needed for ATC. The strawman NEXRAD capability is then reviewed in the context of the identified weather products and factors such as: (1) effects of front end noise and weather return statistics (2) resolution and low altitude coverage constraints (3) the clutter environment associated with various siting options, and (4) data quality required for real time automated display of hazardous weather regions to ATC controllers. It is concluded that significant problems will arise in attempting to simultaneously provide terminal and en route weather surveillance by a single radar as envisioned in the NEXRAD strawman. An analytical/experimental research and development program is described to resolve the identified technical uncertainties in the NEXRAD strawman design for FAA applications. The suggested research and development program includes an operationally oriented interactive data gathering program to evaluate weather products at an ARTCC and TRACON using existing pencil beam S-band radars (e.g., similar to that at MIT) to be followed by similar evaluations in other key geographical areas (e.g., the southeast) using a transportable testbed. Both radar systems would incorporate special features to minimize the likelihood of false targets (e.g., due to obscuration and/or clutter) as well as automated display and short term prediction of hazardous weather regions for use by ATC controllers.
Summary
The Federal Aviation Administration (FAA), National Weather Service and Air Force Weather Service are currently engaged in a program to develop a next generation of weather radars (NEXRAD) capable of satisfying (to the greatest extent possible) the common weather information needs of these agencies. This report identifies the unique FAA...
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Experimental measurements of low angle ground reflection characteristics at L- and C-bands for irregular terrain
November 1, 1982
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-107
Summary
Field measurements of terrain reflection data at L band and C band have been taken during 1980 at several test sites at Hanscom airport, Fort Devens, and Camp Edwards, Massachusetts. These field data are used to (1) characterization of the L band and C band multipath environments, (2) validation of terrain mutlipath propagation models, and (3) assessment of TRSB elevation angle estimation performance with various aperture sizes. Conventional beamsum, maximum likelihood, and maximum entropy angular power spectral estimates have been employed as a means to characterize the multipath environment. The maximum entropy angular power spectral estimate offered highest resolution of the various multipath signals. The L-band field measurement results indicated that the terrain multipath were specular reflections with a high multipath levels. L-band M/D ratios ranging from -5 dB to 1 dB were observed in a variety of terrain conditions. At C band, diffuse ground reflections were evident at some measurement sites, especially at Camp Edwards J2 range site, where small scale terrain roughness was fairly visible. However, these C-band disffuse reflections appeared to be at fairly low levels, e.g., -15 dB to -20dB relative to the direct signal. The C-band peak specular multipath levels of -10dB to -2 dB were slightly lower than those of the L-band for the same terrain geometry. The phenomenon of hte "focusing" ground reflections, i.e., more than one specular ground reflection present at the same time, was observed at both L-band and C-band. For the L-band, this generally occurred in the rolling type of terrain. However, for the C-band, this also happened in the fairly flat terrain at Hanscom airport site.
Summary
Field measurements of terrain reflection data at L band and C band have been taken during 1980 at several test sites at Hanscom airport, Fort Devens, and Camp Edwards, Massachusetts. These field data are used to (1) characterization of the L band and C band multipath environments, (2) validation of...
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L-Band DME multipath environment in the microwave landing system (MLS) approach and landing region
April 13, 1982
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-116
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Summary
The multipath environment in the approach and landing region represents an important factor in the optimization and ultimate performance of the Microwave Landing System (MLS) Precision Distance Measuring Equipment (DME/P). Various types of multipath are assessed in the context of the proposed DME/P implementation error characteristics to ascertain the principal challenges. It is shown (analytically and experimentally) that specular reflections from buildings represent a significant challenge, particularly at low altitudes (e.g., category II decision height and below) where terrain lobing can cause the effective multipath levels to exceed the effective direct signal level. However, the time delay discrimination capabilities of the proposed DME/P should effectively eliminate the bulk of such multipath. Limited S-band (3 GHz) measurements of diffuse reflections from nominally flat terrain indicated very low levels. However, specular reflections from bare, hilly terrain may present problems in some cases.
Summary
The multipath environment in the approach and landing region represents an important factor in the optimization and ultimate performance of the Microwave Landing System (MLS) Precision Distance Measuring Equipment (DME/P). Various types of multipath are assessed in the context of the proposed DME/P implementation error characteristics to ascertain the principal...
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Results of L band multipath measurements at operational United States (U.S.) airports in support of the Microwave Landing System (MLS) Precision Distance Measuring Equipment (DME/P)
July 23, 1981
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-109
Summary
This report presents the results of a short duration L band multipath measurement program at five major U.S. airports (St. Louis, Tulsa, Wright Patterson Air Force Base, Philadelphia and Washington National) and one smaller airport (Quonset, RI) to better quantify the expected multipath environment for the Microwave Landing System (MLS) Precision Distance Measuring Equipment (DME/P). Specific objectives included: (1) Measurements of the principal multipath parameters (amplitude and time delay) with realistic aircraft/ground site locations at runways which had the major DME/multipath sources (large buildings) identified in previous analytical (simulation) studies. (2) Determination of whether significant DME/P multipath sources exist which had not been considered to date and (3) Comparison of the measured results with computer simulation results obtained with simplified airport models (such as have been used for DME/P system design to date). Particular emphasis was placed on the final approach region including the flare and rollout regions since these areas correspond to the most stringent DME/P accuracy requirements and, have not been utilized operationally with the current L band DME. All of the above objectives were achieved although in some cases the experimental data in the flare/rollout region was of poor quality due to low signal to noise ratio. The spatial region and time delay of specular multipath generally correlated well with expectations based on simple ray tracing. With the exception of Washington National, no significant (multipath to direct signal ratio (M/D >110 dB) multipath was encountered in operationally relevant areas which was not predicted. The quantitative predictions of the simple airport models agreed with the experimental data, although in some cases, (especially, near threshold) the measured M/D values were considerably higher than predictions.
Summary
This report presents the results of a short duration L band multipath measurement program at five major U.S. airports (St. Louis, Tulsa, Wright Patterson Air Force Base, Philadelphia and Washington National) and one smaller airport (Quonset, RI) to better quantify the expected multipath environment for the Microwave Landing System (MLS)...
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MLS Multipath Studies, Phase 3 Final Report, Volume III: Application of Models to MLS Assessment Issues, Part 2
June 8, 1981
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-88,III,PT-2
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Summary
This report presents work done during phase 3 of the US national Microwave Landing System (MLS) program toward developing a computer simulation model of the MLS multipath effects, the experimental validation ot the model, and the application of the model to investigate multipath performance of ICAO proposals for the new approach and landing guidance system. The first two volumes of the report presented an overview of the simulation effort as well as describing in detail the propagation and MLS technique mathematical models and their validation by comparison with experimental data. In this volume, we describe the results of comparative simulations for the various MLS techniques in various scenarios and analyze in detail certain multipath performance features which were found to be significant in the scenario simulations. Simulation results are presented for several scenarios, and shadowing of the MLS azimuth by taxiing and overflying aircraft is analyzed. The remainder of the report focuses onmultipath performance factors specific to various individual techniques. These include: (1) the effects of angle data outlier tests and filtering in the TRSB receivers, (2) the effects on the DMLS system due to receiver AGC, receiver motion-induced Doppler shifts, and the use of commutated reference systems, and (3) acquisition/validation algorithms for all three techniques. The report concludes with a summary and suggestions for future work. Part I of this volume consists of Chapters I through IV; Part II contains Chapters V through VIII and the Appendices.
Summary
This report presents work done during phase 3 of the US national Microwave Landing System (MLS) program toward developing a computer simulation model of the MLS multipath effects, the experimental validation ot the model, and the application of the model to investigate multipath performance of ICAO proposals for the new...
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MLS Multipath Studies, Phase 3 Final Report, Volume III: Application of Models to MLS Assessment Issues, Part 1
June 8, 1981
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-88,III,PT-1
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Summary
This report presents work done during phase 3 of the US national Microwave Landing System (MLS) program toward developing a computer simulation model of the MLS multipath effects, the experimental validation ot the model, and the application of the model to investigate multipath performance of ICAO proposals for the new approach and landing guidance system. The first two volumes of the report presented an overview of the simulation effort as well as describing in detail the propagation and MLS technique mathematical models and their validation by comparison with experimental data. In this volume, we describe the results of comparative simulations for the various MLS techniques in various scenarios and analyze in detail certain multipath performance features which were found to be significant in the scenario simulations. Simulation results are presented for several scenarios, and shadowing of the MLS azimuth by taxiing and overflying aircraft is analyzed. The remainder of the report focuses on multipath performance factors specific to various individual techniques. These include: (1) the effects of angle data outlier tests and filtering in the TRSB receivers, (2) the effects on the DMLS system due to receiver AGC, receiver motion-induced Doppler shifts, and the use of commutated reference systems, and (3) acquisition/validation algorithms for all three techniques. The report concludes with a summary and suggestions for future work. Part I of this volume consists of Chapters I through IV; Part II contains Chapters V through VIII and the Appendices.
Summary
This report presents work done during phase 3 of the US national Microwave Landing System (MLS) program toward developing a computer simulation model of the MLS multipath effects, the experimental validation ot the model, and the application of the model to investigate multipath performance of ICAO proposals for the new...
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Registration errors in a netted air surveillance system
September 2, 1980
Technical Report
Published in:
MIT Lincoln Laboratory Report TN-1980-40
Summary
Today's tactical military air surveillance radars generally operate in a stand-alone configuration. The many performance improvements that result when data from multiple radars of this type are merged have made such netted operations an attractive goal for many years. A major obstacle to achieving this goal has traditionally been the difficulty associated with the registration of multisensor data, the expression of the data in a common coordinate system free from errors due to site uncertainty, antenna orientation, and improper alignment. This report presents the results of a modest effort to develop a self-registration procedure by which multiple radar sensors operating in consort each calculate the errors In their data by comparing it with data from the remainder of the system and then uses the information to upgrade performance. The technique has been tested with experimental data and appears quite capable of improving system performance, measured in terms of residual inter-site bias errors, by almost a factor of one hundred.
Summary
Today's tactical military air surveillance radars generally operate in a stand-alone configuration. The many performance improvements that result when data from multiple radars of this type are merged have made such netted operations an attractive goal for many years. A major obstacle to achieving this goal has traditionally been the...
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Alternate waveforms for a low-cost civil GPS receiver
April 14, 1980
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-86
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Summary
This report examines the technical feasibility of alternate waveforms to perform the GPS functions and to result in less complex receivers than is possible with the GPS C/A waveform. The approach taken to accomplish this objective is (a) to identify, after a quick broad overview, a few promising waveforms, (b) to complete the architectural synthesis of a GPS system based on the new waveforms, (c) to analyze the performance of these systems in providing ranging and communication capability and (d) to assess the impact on receiver hardware and software. One conclusion is that the class of pulsed waveform, when combined with emerging matched filter technology, permits the use of a greatly simplified receiver design. Although very specific, the design was intended as a vehicle for performance analysis only and many refinements and alternatives within the same class are possible. Other classes of waveforms such as tome ranging and chirped FM waveforms, although adequate, do not seem superior to the present PN encoded CW waveform for GPS. Finally, if the "alternate" waveform is simply the present C/A waveform but with substantially increased power level, it is shown that with the present designs the performance will be greatly increased or, alternatively, performance margin can be traded for a simplified receiver implementation.
Summary
This report examines the technical feasibility of alternate waveforms to perform the GPS functions and to result in less complex receivers than is possible with the GPS C/A waveform. The approach taken to accomplish this objective is (a) to identify, after a quick broad overview, a few promising waveforms, (b)...
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Zoom antenna
February 12, 1980
Project Report
Published in:
Project Report ATC-90, MIT Lincoln Laboratory
Summary
In current ATC radars, high altitude targets are at a disadvantage when competing with low altitude undesired returns such as ground clutter and birds. The "zoom antenna" technique is proposed as a means of virtually eliminating this problem. An implementation based on control of multiple elevation beams during each range sweep interval is recommended as applicable to both S-band and L-band ATC radars.
Summary
In current ATC radars, high altitude targets are at a disadvantage when competing with low altitude undesired returns such as ground clutter and birds. The "zoom antenna" technique is proposed as a means of virtually eliminating this problem. An implementation based on control of multiple elevation beams during each range...
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Automated tracking for aircraft surveillance radar systems
January 1, 1979
Conference Paper
Published in:
IEEE Trans. Aerosp. Electron. Syst., Vol. AES-15, No. 4, July 1979, pp. 508-517.
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Summary
An improved moving target detector (MTD) (a digital signal processor) has been designed, constructed, and tested which successfully rejects all forms of radar clutter while providing reliable detection of all aircraft within the coverage of the radar. The MTD is being tested on both terminal and enroute surveillance radars for the FAA. This processor has been integrated with automatic tracking algorithms to give complete rejection of ground clutter, heavy precipitation, and angels (birds).
Summary
An improved moving target detector (MTD) (a digital signal processor) has been designed, constructed, and tested which successfully rejects all forms of radar clutter while providing reliable detection of all aircraft within the coverage of the radar. The MTD is being tested on both terminal and enroute surveillance radars for...
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