Air Traffic Control Radar Research Articles

Beacon Splits in Air Traffic Control Radar Beacon System (ATCRBS)

The ATC radar beacon system is today's primary source of surveillance ance data for air traffic control. For en route traffic control, radar and beacon data are collected at numerous long range radar (LRR) facilities and typically sent by remote control to the air traffic control center (ARTCC) by a radar microwave link (RML). Selfsupporting or guyed RML towers are installed at some LRR sites adjacent to the LRR antenna to establish a line-of-sight microwave path to the first repeater site. For these LRR sites, beacon splits and pulse-stretching effects have been observed particularly in the direction of the RML tower. This paper relates to the determination ion of the magnitude of the beacon split problem for such sites and the extent to which this problem is caused by the RML tower. It has been shown that the RML tower causes distortion in the patterns of both the directional and omnidirectional antenna. The nature and extent of these distortions are such that they tend to nullify the advantages achievable by the SLS and ISLS techniques. Consequently, the beacon split phenomenon may be referred to more specifically by the well-known "ring-around" effect. Finally, the paper makes a few recommendations for eliminating or reducing this problem.

Troposcatter signal enhancement due to aircraft

Aircraft enhancement of troposcatter signal intensity on two troposcatter paths in the State of Washington has been experimentally verified by monitoring aircraft in the common volumes with an air traffic control radar. Observed enhancements usually lasted for several minutes, but occurred only if the aircraft was within a few kilometers of the great-circle path.

ATC Beacon Interference Characteristics in the New York Area

An experimental program is described that had the objective of measuring the effects of the time-dependent structure of downlink (air craft to ground) interference generated by the Air Traffic Control Radar Beacon System (ATCRBS) in an active air traffic terminal area that are relevant to system and ground controller response time. The results of this program indicate a number of interesting details concerning the correlation of the level of the downlink interference with changes in the arrival and departure rates of aircraft at the local terminal sites.

The Effects of Defruiting on the ATCRBS

The defruiter that is employed in the Air Traffic Control Radar Beacon System (ATCRBS) to prefilter asynchronous replies has a complex impact on the detection, estimation and validation properties of the detection subsystem. Its positive and negative effects are quantitatively enumerated via a simulation of the beacon processing subsystem of the Automated Radar Terminal System (ARTS III). It is concluded that the disadvantages of using the present-day defruiter in the ARTS III digital processing channel outweigh the advantages when fruit rates are below several thousand per scan. As an alternative to the total elimination of the defruiter a more general class of preprocessors is defined and their input-output relationships are derived using a Markov Chain formulation. These are found to represent an improvement over the current defruiter in that the positive effects of defruiting are retained while some of the negative effects are reduced.

New techniques applied to air-traffic control radars

During the past two years a program has been carried out to show how new techniques can greatly improve the performance of radars used for air-traffic control. A survey of problems associated with presently used radars was undertaken. This survey indicates that primary radar in an automated air-traffic control system can be made significantly more effective by the use of new techniques. The radar's handling of extraneous reflections (clutter) is critical to its performance. Three types of interfering clutter were found to predominate: ground clutter, weather clutter, and angels. Angels are generally accepted to be radar returns from flocks of birds. In addition, second-time-around clutter is often troublesome. For each type of clutter, all known remedies for improving the signal-to-clutter ratio were studied and radar systems were configured using appropriate sets of remedies. Some specific solutions incorporated in the resulting radar systems are: a) the use of linear large dynamic range, near-optimum digital signal processors to filter signals from clutter, b) the use of electronically step-scanned antennas to improve the correlation of aircraft and clutter returns from pulse to pulse, c) the use of multiple PRF's instead of staggered PRF's together with coherent transmitters to keep second-time-around clutter returns well correlated while still overcoming blind speeds, d) the use of a fine grained ground clutter map to give superclutter visibility on tangential targets, and e) the use of lower operating frequencies to greatly reduce weather and angel returns. Two demonstration radar systems have been implemented, an S-band radar using a mechanically rotating antenna and a UHF radar using an electronically step-scanned cylindrical antenna. Experimental results are described.

Radar Technology Applied to Air Traffic Control

Use of primary radars for air traffic control (ATC) is discussed. The location and the parameters of various ATC radars are described. The clutter environment (land clutter, birds, automobiles, and weather) has had a major impact on the configuration of these radars. Signal-processing techniques and antenna techniques utilized to cope with the clutter are described. Future signal-processing techniques for the ATC radars are postulated.

PPL - an extensible language that failed

PPL, a conversational extensible language, has been running on the DEC PDP-10 for over a year now. Its applications have included: matrix, vector, polynomial, rational and complex arithmetic; formula, list, string, tree and graph manipulation; significant programs in real-time radar air traffic control simulation and parser generation for context-free languages; and a host of useful conversational tasks in population biology, algebra word problems and optimization of programs. Indeed, the parser for another extensible language(ECL) was generated in PPL(using the De Remer algorithm). PPL is now used by over 450 students in Harvard's introductory programming course. Needless to say, for me and a number of others, PPL is the preferred medium for writing programs and serves as an important and enjoyable tool of thought. To me, PPL is rich, highly versatile and easy to use As is the case for most other languages, PPL evokes both adoring remarks from its proponents and the usual scorn from its detractors. In analogy to the process of stellar evolution, if there is such a thing as a “main sequence” for the life of programming languages, PPL seems well launched on it (though programming languages probably die by fizzling out, not by exploding). Yet PPL is a failure. A few years ago, the vision of extensible languages held by some was that users could rapidly and cheaply extend the base of an extensible language to encompass the data, the operations, the notation and the control natural to many diverse application areas. In short, one was supposed to be able to manufacture personalized languages of reasonable efficiency and substantial utility with great ease just by applying some easily learned extension techniques. It was thought that just as programmers decree the organization of processes (by defining and calling subroutines),they should also decree appropriate organizations for data and for notation, in order to attain more clarity and efficiency.

Automatic Height Transmission is One Step Closer

Use of automatic height transmission, the essential ?third dimension? for use in the control of aircraft, has been brought closer by action taken recently at the Seventh Session of the International Civil Aviation Organization. The Session recommended adoption of technical standards that will: 1) update and improve the existing international standards for SSR, better known in the U. S. as the Air Traffic Control Radar Beacon System (ATCRBS); 2) provide specifications for 3-pulse sidelobe suppression (SLS); 3) provide standards for introduction of automatic height transmission; and 4) specify conditions under which SSR is to be implemented. It was agreed further that the sensing element of the system should use a standard pressure setting of 1013.2 millibars and that it would be necessary to refer to the system as height transmission rather than altitude reporting. Although a separate data link for height transmission is a possibility, the probable implementation data was considered too uncertain. Since air traffic is a heterogeneous mixture of civil and military aircraft, the existing SSR used by both civil and military aircraft was expanded to accommodate automatic height transmission features. It was agreed that SSR is needed to supplement the use of primary radar in air traffic control, but that each country would determine whether or not its use is required. The system specifications are appended to the paper.

Altitude Processing in the ATCRBS

Equipment to process and display beacon-derived altitude information is being developed to enhance the operational capability of the Air Traffic Control Radar Beacon System (ATCRBS). Beacon identity and altitude information assists the air traffic controller to establish positive identification quickly and reliably; radar handoff procedures are completed more efficiently. The principle altitude functions of the beacon video processor under development are 1) To provide a digital display, in decimal form, of altitude data received from aircraft equipped with modified transponders which reply to a ground-to-air altitude interrogation. 2) To provide simultaneous altitude zone filtering of the altitude reply codes and tri-coordinate (3-D) radar data. 3) To provide altitude information to associated beacon video tracking units for aircraft tracking. The fully transistorized processor converts beacon video code trains from serial to parallel form. Leading edge decoding, pulse regeneration, pulse standardization, and destructive readout techniques are used to detect and eliminate spurious or garbled codes and to correctly process closely interleaved replies. Aircraft spaced as close as 344 feet in slant range are correctly read out. The equipment is designed for operation in either a computerizedor noncomputerized environment.

ATCRBS Experimental Altitude Reporting Subsystem and Developments

FAA's Aviation Research and Development Service (ARDS), has recently embarked on an active program of establishing an altitude reporting subsystem for the Air Traffic Control Radar Beacon System (ATCRBS), internationally known as Secondary Surveillance Radar (SSR). This action is in response to a long-standing requirement for the provision of altitude information to the Air Traffic Control System by a means other than flight plan and voice transmission of altitude information from the cockpit. The use of the ATCRBS for altitude reporting utilizes precisely the same techniques used for the identification function on Mode A. The major difference is that while codes are manually selected for identification, they would be automatically selected for altitude through an automatic encoding system from a source of barometric altitude. The essential characteristics of the experimental subsystem are detailed, and the Federal Aviation Agency's (FAA) progress to date is described.

A Mathematical Analysis of the Performance of the ATC Radar Beacon System

The capacity of the Air Traffic Control Radar Beacon System can be evaluated by extensive high-density flight testing, simulation, or mathematical synthesis. Actual flight testing, although desirable, is costly and inflexible. Simulation techniques would be an effective approach to analyzing the system problems, were it not for the cost of the simulator required for this type of work and the delay incurred waiting for the construction and test of the simulator. Use of a mathematical model makes numerous variations of system parameters and equipments feasible at low cost while providing sufficient environmental flexibility. A previous paper described the development and application of such a model for evaluation of traffic-handling capacity in the dense environment of the New York area. Applications of the model and conclusions and recommendations based on the results of its use are presented in this paper.

The Air Traffic Control Radar Beacon System

This paper outlines the major advantages and limitations of the Air Traffic Control Radar Beacon System under evaluation at the Civil Aeronautics Administration Technical Development Center. It discusses the advantages and disadvantages of compatibility, the system traffic capacity problems, and the need for an operational doctrine to restrict the use of interrogators. System coverage, ground antenna, reply-code garbling, and reflection problems also are discussed. The paper points out specific applications of the beacon system, including its ability to improve the reliability of aircraft position information, to provide identity for specific aircraft targets in a traffic situation, and to furnish the information required for a filtered air traffic control display with a very rapid and flexible cross-reference between aircraft identification, plan position, and altitude.