Passive Radar Ready for Prime Time

[Dave Farber <dave () farber net>]

Delivered-To: dfarber+ () ux13 sp cs cmu edu
Date: Tue, 14 Oct 2003 15:08:11 -0400
From: Alex Salkever <alex_salkever () businessweek com>
Subject: Passive Radar Ready for Prime Time
To: dave () farber net

Hi, Dave:

My colleague Otis Port has put together an excellent overview of the 
current status of passive radar.It's eye-oepning and  alot further along 
than many may think. Here's the URL and an extended excerpt. Cheers.

<http://www.businessweek.com/magazine/content/03_42/b3854113.htm>http://www.businessweek.com/magazine/content/03_42/b3854113.htm

Super-Radar, Done Dirt Cheap
A radar system that uses ubiquitous cell-phone signals is on its way

Any technology can be a two-edged sword. Cell phones are a good example. 
They're clearly a great convenience, even a life-saving tool during natural 
disasters and medical emergencies. And they should save many more lives 
under the Federal Communications Commission's enhanced 911 mandate, which 
requires that cell phones relay their precise locations to 911 operators.

Yet some people are appalled that their cell phone will always give away 
where they are. That makes it possible to compile a "road map" of a user's 
movements. So imagine the outcry when privacy worriers learn that 
cell-phone systems can be used to locate and track a car, boat, or plane -- 
even if no one inside is carrying a wireless phone. But outcry or not, the 
technology seems certain to be deployed, given its myriad civilian and 
military applications.

The technology is called Celldar, from "cellular" plus "radar." Under 
development since 1997 at Roke Manor Research Ltd (<javascript: void 
showTicker('SI')>SI ). in Romsey, England, it differs from conventional 
radar in several key respects. When radar tracks planes for air traffic 
controllers -- or maps the surface of Venus from a space probe -- the same 
set of equipment both sends out radio signals and picks up the returning 
echoes. So computers can easily calculate an object's distance and relative 
size based on how long it takes the returning signals to bounce back and 
how strong they are.

In contrast, Celldar takes a so-called passive approach: It watches and 
interprets how signals from cell-phone base stations interact with objects 
such as cars, trucks or planes. The hardware required for this is much 
simpler than existing radar systems. A Celldar prototype built in 1999 
consisted of a PC and the insides of two cell phones, and cost just $3,000, 
says Peter Lloyd, head of Roke Manor's Celldar program. The flip side is, 
the signal-processing software is complex: It must allow for the varying 
travel times for signals between two or more cellular base stations and a 
Celldar receiver, as well as the times from the different base stations to 
the target. Lloyd says Roke's clever program is based on "$10 million worth 
of expertise in writing software" for cellular systems and military radars. 
One big plus to the military: passive radar systems are invisible to 
anti-radar weapons because they don't have their own transmitters.

Celldar's implications are exciting -- but also troubling to some. Even 
though the technology can't be used to identify cell-phone users, since it 
"sees" only radio waves echoing off hard surfaces, it and similar 
approaches are evolving quickly. In addition to Celldar, which is sopping 
up $1.5 million a year for development, a dozen other passive-radar 
projects are under way in the U.S., Europe, and Asia. As the technology 
bears fruit, it should give the world's police and homeland security 
agencies new tools for monitoring shipments of illegal weapons and drug 
smuggling operations. Highway officials could gain a detailed window on 
traffic flows, helping them to minimize congestion. But because 
passive-radar systems could be cheap enough for hobbyists to buy -- or 
cobble together themselves -- the technology could also become the next fad 
among people who own police-radio scanners or who enjoy snooping on their 
neighbors' comings and goings.

This month marks something of a passive-radar milestone. In late October, 
Roke will show off the latest Celldar system to officials of Britain's 
Defense Ministry at an army exercise on the Salisbury Plain. During the 
field maneuvers, Celldar will detect the movement of ground vehicles and 
determine whether cell-phone signals are bouncing off a tank, truck, or 
armored personnel carrier.

Also in late October, radar researchers from around the world will gather 
in Seattle to discuss recent advances, including passive systems that use 
FM radio or TV broadcasts instead of cell-phone signals. The 
invitation-only meeting will be hosted by John D. Sahr, a University of 
Washington electrical engineer. Since 1997 he has operated a passive-radar 
system unshrouded by military secrecy. It harnesses an FM station's signals 
to study particles in the ionosphere -- the top layer of the atmosphere, 
over 300 miles up. Sahr decided to go with passive radar, he says, "because 
it's incredibly cheap" -- $20,000 vs. $25 million for a comparable active 
system. "You could probably do an amateur system for under $5,000," Sahr 
adds. A system for small airports might cost as little as $15,000. That's 
important because of the 5,280 public airports in the U.S., only about 300 
currently have radar.





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