BBC Technology reported UK mulls 'radical' shake-up of air traffic control
. Technology reporter Jane Wakefield writes that Thales has received funding “to look into using existing TV signals to locate and track aircraft.” The system is called “multi-static primary surveillance radar” and uses the reflection of TV signals from TV transmitters around the United Kingdom to determine the location of aircraft. The reflected signal is compared with the signal from the transmitter to determine the distance to the aircraft, and reflections from multiple sites are used to determine its location.
The article did not mention the accuracy of the distance calculation, but with a digital TV signal I would expect it to be quite accurate, if enough transmitter signals are hitting the aircraft.
One of the reasons the United Kingdom is considering a move to this TV transmitter-based radar system is to free up the air traffic control radar frequency spectrum for use by new wireless broadband services. Another reason is that current air traffic control systems are facing interference from wind farms that springing up around the nation as an alternative energy source.
The BBC article quotes John Smith, head of Air Traffic Management strategy at Thales, saying that while these two issues make a compelling argument for change, he admits that not everyone is persuaded that the current system, in use since World War II, needs an overhaul.
“There are an awful lot of barriers to gaining acceptance in the market place,” said Smith. “In the air traffic control industry there is a belief that things have always been done a certain way and so there is reluctance to move to something that is radically different. We have to prove, first and foremost, that it is safe.”
This isn't the first time existing TV signals have been considered as a radar signal source. When I was working at a California television station more than 30 years ago, I got a call from an engineer, possibly at Raytheon or Hughes (I don't recall now), who was using our Channel 18 analog signal from Sunset Ridge as a radar source. He didn't provide any details, but it was easy to guess he was probably using it in combination with other transmitters on Mount Wilson as a way to identify targets without the need for a conventional radar system.