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Spectra of ionospheric scintillation

Author:
Published in:
J. Geophys. Res., Vol. 81, No. 13, 1 May 1976, pp. 2041-2050.

Summary

Observation of amplitude and phase scintillation were made at the Millstone Hill radar facility by using phase coherent sources at 150 and 400 MHz on the U.S. Navy navigation system satellites. These observations have been processed to yield power spectra of the fluctuations in the logarithm of the received power (log power) at each frequency and the calculations in phase path length difference (differential phase) between the two frequencies. A theoretical analysis was performed to predict the log power and differential phase power spectra. The theoretical model was based upon weak scatter theory for a thick screen with a three-dimensional power law power spectrum representation for the electron density fluctuations. A -4 exponent for the power law best fit the observed spectra. For weak scintillation (rms fluctuations in log power less than 5 dB or S4 < 0.9) the theroretical calculations were in excellent agreement with the observations. For strong scintillation, saturation was observed, and the measured spectra were broader than those predicted on the basis of weak scatter theory. An increase in electron density fluctuations relative to the value predicted by the power law model was observed at scale sizes smaller than 0.8 km.This increase may be responsible for the anomalous scintillation observations at gigahertz frequencies.
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Summary

Observation of amplitude and phase scintillation were made at the Millstone Hill radar facility by using phase coherent sources at 150 and 400 MHz on the U.S. Navy navigation system satellites. These observations have been processed to yield power spectra of the fluctuations in the logarithm of the received power...

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Concept and plan for the development of a weather support subsystem for Air Traffic Control

Published in:
MIT Lincoln Laboratory Report ATC-64

Summary

This report summarizes the results of a study to: (1) investigate the primary needs of air traffic controllers, flow controllers, and central flow controllers for weather information, (2) define a cost effective system concept to meet these needs, and (3) lay out a plan for the development of the proposed weather subsystem to support Air Traffic Control. The recommended system will provide rapid geration and dissemination of reliable use oriented observations and very short range severe weather forecasts (up to 30 min.) to facilitate controller planning. This new capability will: 1) reduce weather induced controller work load peaks, 2) permit controllers to coordinate and preplan aircraft rerouting for weather avoidance, 3) achieve an improved balance between the inefficiency of overreaction and the essentials of safety, 4) facilitate controller response to pilot requests for weather data on a work load permitting basis, and 5) enable the issuance of accurate weather advisories. The system will also provide rapid generation and dissemination of reliable short range forecasts (up to 4 hours) to permit early introduction of necessary flow control procedures. This new capability will: 1) decrease problems for controllers, 2) increase acceptance of flow control, and 3) increase traffic flow efficiency without decreasing safety.
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Summary

This report summarizes the results of a study to: (1) investigate the primary needs of air traffic controllers, flow controllers, and central flow controllers for weather information, (2) define a cost effective system concept to meet these needs, and (3) lay out a plan for the development of the proposed...

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Beacon CAS (BCAS) an integrated air/ground collision avoidance system

Published in:
MIT Lincoln Laboratory Report ATC-62

Summary

BCAS is a DABS-based airborne collision avoidance system that exploits the feature of DABS discrete addressing and integral data link. This provides for a CAS with the unique capabilities of (1) cooperative threat resolution between BCAS and conflicting aircraft through the transmission of maneuver intent (to DABS-only aircraft) and tie breaking (with other BCAS aircraft) and (2) coordination of CAS activities with the ground ATC control function through the DABS air-ground-air data link. All beacon-equipped aircraft in the vicinity of the BCAS are detected. ATCRBS-equipped aircraft are interrogated using a special Mode C interrogation. DABS aircraft are detected passively through periodic squitters emitted by all DABS transponders. Squitter-detected aircraft are tracked on altitude and only those aircraft that represent a co-altitude threat are discretely interrogated to establish a range/altitude track. The use of discrete addressing eliminates synchronous garble for the BCAS in the same manner as for DABS. This document provides a general description of BCAS from the viewpoint of its operational features and then describes the avionics package required to achieve the capability.
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Summary

BCAS is a DABS-based airborne collision avoidance system that exploits the feature of DABS discrete addressing and integral data link. This provides for a CAS with the unique capabilities of (1) cooperative threat resolution between BCAS and conflicting aircraft through the transmission of maneuver intent (to DABS-only aircraft) and tie...

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DABS modulation and coding design - a summary

Published in:
MIT Lincoln Laboratory Report ATC-52

Summary

The Discrete Address Beacon System (DABS) has been designed as an evolutionary replacement for the Air Traffic Control Radar Beacon System (ATCRBS). As with ATCRBS, DABS is a cooperative Air Traffic Surveillance System utilizing ground based sensors (interrogators) and airborne transponders. In addition to its surveillance function, DABS integrally accommodates ground-to-air and air-to-ground data link communication within the interrogations and replies. In DABS, each aircraft transponder may be individually interrogated, using its unique 24-bit address, giving the ground based interrogators freedom to schedule interrogations and replies to make efficient use of the channels essentially independent of the aircraft traffic distribution. The evolutionary constraint on DABS, requiring the capability for one-for-one replacement of ATCRBS ground sensors and transponders, dictated the need to maximize commonality between the two systems. Thus, the ATCRBS interrogation and reply frequencies (1030 and 1090 MHz) were prime candidates for DABS operating frequencies. This report presents the rationale for the selection of the DABS signalling waveforms and error control techniques. The main issues in arriving at the final link design were (1) affordable transponder cost, (2) electromagnetic compatibility with ATCRBS and TACAN, and (3) adequate performance in the channel environment, which includes interference from ATCRBS transmissions. The resulting DABS that of ATCRBS, and transmits ground-to-air data link messages with high reliability. This is accomplished without noticeably affecting ATCRBS performance, with less channel occupancy per target report than ATCRBS, and with transponders projected to cost approximately 160% of the cost of ATCRBS transponders.
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Summary

The Discrete Address Beacon System (DABS) has been designed as an evolutionary replacement for the Air Traffic Control Radar Beacon System (ATCRBS). As with ATCRBS, DABS is a cooperative Air Traffic Surveillance System utilizing ground based sensors (interrogators) and airborne transponders. In addition to its surveillance function, DABS integrally accommodates...

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Discrete address beacon system (DABS) test plan for FY 1976

Published in:
MIT Lincoln Laboratory Report ATC-56

Summary

The major objectives of the continued DABS testing by Lincoln Laboratory are: (1) design validation and refinement, (2) performance assessment, and (3) the development of a data base of environmental characteristics. This document describes that portion of the test activities that will take place during FY 1976. Also included is a description of the special test facilities and teclmiques needed to collect and analyze the required data.
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Summary

The major objectives of the continued DABS testing by Lincoln Laboratory are: (1) design validation and refinement, (2) performance assessment, and (3) the development of a data base of environmental characteristics. This document describes that portion of the test activities that will take place during FY 1976. Also included is...

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DABS uplink coding

Author:
Published in:
MIT Lincoln Laboratory Report ATC-49

Summary

This report details the coding techniques incorporated into the DABS uplink design. Justification is given for the error control method selected in terms of the link characteristics and design constraints. Performance results, including extensive evaluation by simulation and bench test, are presented for the selected code. A binary shortened cyclic code having 24 redundant bits was selected. The overhead due to the code redundancy is minimized by a scheme in which the parity check bits are overlayed on the discrete address field in the encoded message. This code is shown to have the capability of protecting a DABS transponder from accepting an erroneous uplink message with an error probability of less than 10 to the -7 power in a severe interference environment. This same code will be used in the DABS downlink in a burst erasure correction mode. Results of the analysis of the downlink will appear in a separate report.
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Summary

This report details the coding techniques incorporated into the DABS uplink design. Justification is given for the error control method selected in terms of the link characteristics and design constraints. Performance results, including extensive evaluation by simulation and bench test, are presented for the selected code. A binary shortened cyclic...

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Impact of obstacle shadows on monopulse azimuth estimate [project report]

Author:
Published in:
MIT Lincoln Laboratory Report ATC-50

Summary

Obstacle shadows, within view of a sensor using monopulse azimuth estimate, cause an error in the azimuth estimate. This report discusses the azimuth error as a function of obstacle dimension and position, and the sensor antenna illumination.
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Summary

Obstacle shadows, within view of a sensor using monopulse azimuth estimate, cause an error in the azimuth estimate. This report discusses the azimuth error as a function of obstacle dimension and position, and the sensor antenna illumination.

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Plan for flight testing intermittent positive control

Published in:
MIT Lincoln Laboratory Report ATC-46

Summary

Intermittent Positive Control is an automated aircraft collision avoidance system requiring the participation of the aircraft pilots involved. The operational interface between pilots and the IPC system is being evaluated in a series of live flight tests. The Lincoln Laboratory DABS Experimental Facility, augmented to include the IPC function, is the test bed for these evaluation flights. This document described the objectives and methods of the IPC flight testing being conducted by Lincoln Laboratory.
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Summary

Intermittent Positive Control is an automated aircraft collision avoidance system requiring the participation of the aircraft pilots involved. The operational interface between pilots and the IPC system is being evaluated in a series of live flight tests. The Lincoln Laboratory DABS Experimental Facility, augmented to include the IPC function, is...

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DABS channel management

Author:
Published in:
MIT Lincoln Laboratory Report ATC-43

Summary

This report provides a full discussion of the design of the DABS channel management function. Channel management regulates all activity on the RF channel, scheduling ATCRBS interrogations and DABS roll-call interrogations and replies. Channel management arranges for multiple interrogations when required to satisfy both the surveillance and the communications functions of the sensor, and for reinterrogations in the event of link failure. The report consists of three major parts: Part I, Channel Control; Part II, Roll-Call Scheduling; and Part III, Transaction Preparation, Target List Update, and Transaction Update. Together they encompass the five basic subfunctions of channel management.
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Summary

This report provides a full discussion of the design of the DABS channel management function. Channel management regulates all activity on the RF channel, scheduling ATCRBS interrogations and DABS roll-call interrogations and replies. Channel management arranges for multiple interrogations when required to satisfy both the surveillance and the communications functions...

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Provisional Signal Formats for the Discrete Address Beacon System, Revision I

Published in:
MIT Lincoln Laboratory Report ATC-30,REV.1

Summary

This document specified provisional DABS signal formats, i.e., the characteristics of the "signals-in-space" which form the DABS interrogations and replies. Also included is a discussion of the utilization of the described formats to effect the surveillance and data link communication functions for which DABS has been designed. These signal formats will be used in the design and construction of engineering development model transponders and interrogators for prototype system test and evaluation at NAFEC during Phase II of the DABS Development Program; and, with modifications resulting from this test and evaluation effort, will form the basis for the operational implementation of DABS.
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Summary

This document specified provisional DABS signal formats, i.e., the characteristics of the "signals-in-space" which form the DABS interrogations and replies. Also included is a discussion of the utilization of the described formats to effect the surveillance and data link communication functions for which DABS has been designed. These signal formats...

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