Publications

The requirement for additional automation in the air traffic control process has placed new emphasis on the need for high quality surveillance data and for a ground-to-aircraft data link. The ATCRBS beacon system has proven a valuable complement to radar because it provides the ground controller with position, identity, and altitude data that is not contaminated by ground and weather clutter. However, the growing number of beacon-equipped aircraft and ground interrogators and the inherent self-interference limitations of the ATCRBS beacon system have motivated the need for a more reliable and flexible beacon system. The 1969 the Air Traffic Control Advisory Committee recommended the development of such an improved system which they named the Discrete Address Beacon System (DABS), incorporating both surveillance and a data link. Since 1971, M.I.T. Lincoln Laboratory, under the sponsorship of the FAA, has been investigating various DABS design options.

The role of surveillance radar will change as the evolving ATC system relies more heavily upon cooperative beacons, but radars will still remain as an important system element. Today's radars have major limitations for an automated ATC environment because they report unwanted targets (ground, bird, and weather clutter) and because they are expensive to operate and maintain. In addition, to minimize ground clutter, radars are usually sited relatively close to the ground and consequently their performance is not adequate to detect small, distant, low-flying aircraft. By exploiting today's digital technology and by using a completely linear signal processing system, it is now possible to obtain a major improvement in MTI performance. The Lincoln Laboratory has demonstrated a 48-db clutter improvement factor on a 15-rpm scanning S-band ASR-type radar. This clutter rejection capability is about 20 db greater than exhibited by radars now in the field. By selection of more appropriate radar parameters, still greater fixed clutter and weather rejection can be achieved.

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.