A programme worth watching

摘要

A novel radar will soon be helping to keep an eye on aircraft flying over London. Conventional radar uses a rotating antenna to sweep the sky, sending out radio pulses and detecting those which are reflected back from aircraft. The experimental system that will begin operation in June does not send out any signals of its own, but instead relies on a network of receivers to pick up television programmes. It is hard to imagine British tv staples like "Cash in the Attic", "Downton Abbey" and endless repeats of "Top Gear" being used to detect aircraft. But that, in effect, is what will be happening. By measuring the slight differences between the original broadcast signal and the signals reflected from aircraft flying in the vicinity, it is possible to plot the position of aircraft on a screen, just as is done with conventional radar.