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Airplanes crash into each other. My colleague, George Zissis, and I were booked on one of the two airplanes that crashed over the Grand Canyon in 1958 before we switched to the redeye. If we had not done that, you wouldn't be reading this! The available air space is getting more crowded, especially near airports. A simple, cheap, effective device that has a high probability of detection and low false alarm rate would be advantageous. This chapter examines how it might be done.
The challenge is to design an infrared device that can detect the presence of an aircraft at a safe distance throughout the entire sphere that surrounds the host plane. That is easy to specify, but difficult to accomplish.
The field of regard must be the entire sphere that surrounds the aircraft, because collisions can be nose-on, from the sides, top and bottom, or even from the rear. The other craft must be detected anywhere in the sphere. However, it is unrealistic to assume that one sensor can do such a thing. Rather, there must be at least one in the nose and one in the tail, and perhaps one on each wing tip. This is illustrated in Fig. 6.1. Although each sensor is shown as having a 90-degree conical field of view, we might increase this by a few degrees to ensure complete coverage. The geometry includes the safe distance and the size of the aircraft involved. We assume that the planes are traveling at 500 mph. There are different closure rates (with many others that can be interpolated). The head-on case, the most difficult one, involves a closure rate of 1000 mph, i.e., 1600 kmph, 444 mâs. The flank approach is approximately half this, or 222 mâs. The tail chase for these assumptions is not a problem, but it is possible that the host plane has slowed to about 250 mph so that the closing velocity is 111 mâs. If we allow 10 s for reaction time, these distances are 4440 m, 2220 m, and 1110 m. Detection must be accomplished at ranges no less than these. Therefore I choose 5000, 2500, and 1250 meters.
There are several different potential sources of infrared radiation from these aircraft, so the target sizing is a little difficult. Three of the different views to consider are nose-on, side-on, and the rear view.
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