>>>>>>>>>>>>http://www.bbc.co.uk/news/technology-21373771
>>>>>>>>>>>
>>>>>>>>>>>Basically a passive-radar system, same idea as passive sonar on submarines using ambient noise. But, potentially using it for ATC is interesting.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>In a disaster, TV stations likely will be off the air before aircraft are out of it. But at least people on the airliners will be able to be twits on the way down.
>>>>>>>>>
>>>>>>>>>Wouldn't that depend on the type of the disaster? If it was an enemy attack then existing radar ground stations (of which there are comparatively few) would be most likely to be disabled. In this country at least, there is a TV relay mast about every 30 miles - most of those, regardless of the disaster, would be more likely to remain functional.
>>>>>>>>
>>>>>>>>Until their fuel supplies ran out.
>>>>>>>>
>>>>>>>>In case of enemy attack, most electronics will be fried (enhanced EMP bursts) and this country, being as dependant as it is to high tech, will simply fail.
>>>>>>>
>>>>>>>I guess that if we were considering a disaster on that scale it's a bit academic whether conventional radar or the TV mast system was being used. In the case of a localized disaster or problem the TV mast solution might well be more resilient.
>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>>Also, loss of radar contact is not the end of the world. Most position reporting is done via transponders anyway.
>>>>>>>>
>>>>>>>>Transponders reply to Radar.
>>>>>>>
>>>>>>>True. Wasn't thinking straight there. Don't know the state-of-play with GPS Transponders though.
>>>>>>>
>>>>>>>>>I'd also hazard a guess that the TV mast approach would also catch low flying aircraft operating below the normal radar horizon.
>>>>>>>>
>>>>>>>>Not nearly as well as conventional (especially military) radar. Frequency is much too low.
>>>>>>>
>>>>>>>But conventional radar as used by ATC does not have 'over the horizon' capability. I thought there were very few of those (early-warning stuff)
>>>>>>
>>>>>>It (real radar) works much better seeing through weather and smoke, among other things.
>>>>>
>>>>>Not very good at seeing thru mountains tho :-}
>>>>>IIRC, over the horizon radar has to rely on bouncing of the Ionosphere
>>>>
>>>>or via ground scatter. Neither way is very reliable.
>>>>
>>>>The TV mast approach still requires line of site to the tracking radar. You really don't gain anything as far as what you will detect. you do make your standard radar transmitter less of a glaring target though.
>>>
>>>As I understood the article it would be a *complete* replacement for conventional radar ?
>>
>>That doesn't make sense to me unless they want to invest in some type of receiving capability to be able to track reflections.
>
>I think when they talked of TV Transmitters they were referring to relay masts - so they do have receiving capability. So the intention is to measure variations in the time that different masts receive the same signal. Snip:
>
>"Each will receive the same TV signal but at a slightly different time because of the reflections and interactions with aircraft flying in their vicinity. The received signals are then compared to the original broadcast, and the difference is used to locate the position of the aircraft."
>
>Must admit that it seems like they will be looking at very small differences....

and a mighty complicated system...

>
>
>
>>Otherwise, if a tree falls in the forest and nobody is there to hear it... (yeah yeah - someone will blame global warming).
>>>
>>>Not too many off-shore TV transmitters about tho :-}
>>>
>>>>
>>>>One option is to use airborne surveillance (AWACS) aircraft to pick up reflections from broadcast signals. The AWACS would then not have the massive homing beacon lit up on its back. I wouldn't be suprised if that isn't already in their bag of tricks.
>>>>
>>>>That doesn't do much for standard air traffic - just for defense.
>>>>
>>>>>
>>>>>Anyway if will be interesting to know how the research pans out.....
>>>>>>
>>>>>>>
>>>>>>>>>
>>>>>>>>>>Who needs safety when we can tweet?
>>>>>>>>>>
>>>>>>>>>>Kinda like the deal Public Safety got about 10 years ago in this country where they were given a "deal" where cellular carriers would get a lot of public safety spectrum and the carriers were supposed to cover the costs to move public safety to new spectrum.
>>>>>>>>>>
>>>>>>>>>>Odd how the police seem to be stuck using cell phones for a lot of their work now. That will cost lives in a disaster. But hey - people have cooler cell phones now.