Steve Schear wrote: > At 06:33 PM 10/15/2002 +1300, [EMAIL PROTECTED] (Peter Gutmann) > wrote: > >> Scribe <[EMAIL PROTECTED]> writes: >> >> >"The technology 'sees' the shapes made when radio waves emitted by >> mobile >> >phone masts meet an obstruction. Signals bounced back by immobile >> objects, >> >such as walls or trees, are filtered out by the receiver. This allows >> >anything moving, such as cars or people, to be tracked. [snip]" >> >> Isn't this what CDMA already does using RAKE receivers (different fingers >> track multiple signals, so it uses multipath as a feature rather than a >> problem). [snip]
> Yes, this is very similar to a RAKE receiver. Its also similar to the > passive radar systems the U.S. recently accused a former Soviet republic > of selling to Iraq. Passive radars are particularly good at spotting > current generation stealth aircraft. Being passive, typically using > distant powerful shortwave broadcast signals, means its much harder to > spot the receiving sites. Nice explanatory picture at... http://www.pcquest.com/content/technology/101081001.asp The (over-a-year-old) article also states: "The downside is that you cant make out whether the plane is a spy plane or not. "However various companies are working on making it viable for detecting stealth aircraft. For instance, Roke Manor Research (www.roke.co.uk), UK-based has developed sensor technologies which can work with cellphone base stations to detect stealth aircraft." Detecting moving objects is one (simple) thing. Tracking them while identifying the type of object (stealth plane vs civilian, motorbike vs car, etc) is a different issue, naturally. What kind of resolution can be obtained from a few hundred meters (say, for mass-public-monitoring-services) if grounded base stations can make out high-altitude aircraft? Further, are there any known defenses against this kind of passive technology yet? Solitary surveillance aircrafts would surely have a harder time achieving countermeasures than a person on a cellphone amongst a crowd of bystanders. Intereference? Decoys?
