Performance Requirements

Abstract

Stone et al. -Advances in Primary-Radar Technology Fig. I-Detection of aircraft flying in rain. (a) Output of a conventional MTI radar taken with a 5-min exposure. The aircraft flying within the rain echoes is obscured. (b) Output of moving target detector (MTD). The screen is free of rainclutter and the overall track of the aircraft is clearly delineated. Because only one display was available, the photographs were made sequentially.[9, 101. Figure 1 gives a qualitative illustration of the superiority of MTD over MTI in detecting aircraft flying in rain.MTD and the weather channel used in ASR-9 represent a significant improvement in primary-radar technology. The FAA is installing ASR-9 systems at more than 100 major airports in the United States (Fig. 2). This article first delineates the primary-radar requirements for aircraft and weather surveillance. Next, MTD is described and the system's test results are discussed. Finally, we comment on possible future enhancements to the MTD concept. Table 1 gives the performance requirements of a n airport primary radar. The requirements, which are embodied in our current MTD model, place extreme demands on primary-radar performance. It is essential that a primary radar reject ground clutter by at least 40 dB, continue to perform in the presence of rain, adapt to limit the false-target reports generated by birds and vehicular traffic such as automobiles and trucks, and eliminate any additional clutter breakthrough by means of scan-to-scan processing. Performance Requirements for Airport Primary Radars Moving Target DetectorThe main improvements of MTD over its predecessor, MTI, are that MTD performs clutter mitigation by means of digital Doppler filter processing and the use of false-alarm-rate thresholds. Other adaptive features of MTD eliminate bird echoes and vehicular traffic. The overall processing reduces the output to telephone-line bandwidth. Figure 3 shows a block diagram of the MTD system, which includes a dual fan-beam elevation antenna (Fig. 4). Transmission takes place through the lower beam. The upper beam receives echoes at close range, which reduces the strength of the echoes that result from ground clutter. The lower beam is used for distant targets; its minus 3-dB point is typically di- rected toward the horizon.to circular polarization. By doing so, the sensor Although the antenna normally both radiates achieves an additional 12 to 20 dB of precipitaand receives vertical polarization, whenever tion-echo rejection. During the time that circuthere is heavy precipitation over a significant lar polarization is used, weather signals are portion of the coverage area, the radar switches derived from the orthogonal-polarization ports -'2.. !:-'2-,-',? Maximum range ='60 nmi. Altitude coverage = 0 ft to 25,000 ft. Update rate = 4.8 s.Probability of detecting a small aircraft = 0.9. False-alarm rate at the output of a tracking filter = 1 per scan. False-alarm rate at the output of the correlation and interpolation filter = 20 per scan. Range accuracy = 1/32 ...