OCTOBER 20, 2003 
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 (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.
STRONG SIGNALS. Lockheed-Martin Corp. (LMT ) is perhaps the best-known 
passive-radar champion, but others include Avtec Systems, Dynetics, and 
ONERA, the French counterpart of NASA. Lockheed-Martin's system is 
dubbed Silent Sentry. Last fall, in a demo for the U.S. Air Force, a 
third-generation Silent Sentry radar tracked all the air traffic over 
Washington, D.C., by picking up FM and TV echoes. Because FM and TV 
transmissions are more powerful than their cell-phone cousins, Silent Sentry can 
detect planes as far away as 135 miles, roughly 10 times the reach of 
an individual cell-phone tower.
However, because cell-phone towers are scattered far and wide in many 
countries, an airborn Celldar system "could covertly monitor a whole 
country" by flying along its borders, says Lloyd. At the Seattle meeting, 
Roke Manor and British aerospace giant BAE Systems (BAESY ), which 
signed on as a Celldar partner in July, 2002, will reveal details on their 
progress toward systems for small robot spy planes as well as Airborne 
Warning & Control Systems (AWACS). With BAE on board, Lloyd declares, 
"we could field an AWACS model in two years."
That claim prompts some skeptical head-scratching by Benjamin J. 
Slocumb, a senior research engineer at Numerica Corp., a small Fort Collins 
(Colo.) defense contractor that develops advanced target-tracking 
algorithms. A receiving antenna that's moving, he says, "injects a whole 
bunch of difficult problems" in collecting and processing cell-phone echos. 
But Roke's Lloyd stands firm: "We'll show results in Seattle that are 
seven times better than [past studies] have said is possible."
Despite Celldar's military potential, Lloyd predicts the first 
applications will come in the civilian sector. He says transportation officials 
are eager to use Celldar to monitor road traffic because it would avoid 
the expense of installing either sensors in roads or TV cameras 
overhead. And police cars equipped with Celldar could follow a car driven by a 
suspected crook or terrorist from a safe distance, without danger of 
being seen.
TRACKING MADE CHEAP. Celldar might also provide an alternative to the 
global positioning satellite (GPS) systems now being explored by 
insurance companies and governments for monitoring vehicles. Their goal is to 
set premiums individually, based on how much and how fast each car or 
truck is driven -- or to levy a road-use toll determined by the distance 
a vehicle travels, over which types of roads, and at what times of day. 
In Ireland, AXA Insurance is testing a GPS gadget called Traksure. It 
continuously checks a car's speed and location, then compares that data 
with the local speed limit, obtained from digital maps. But Celldar 
might do the job more cheaply.
And it might support schemes by Oregon and other states regarding 
"pay-for-use" road taxes. Many transportation experts assert that taxing 
actual driving distances would be a more equitable way of funding highway 
upkeep than today's tax on gasoline and diesel fuels. That's why the 
European Commission wants every vehicle in Europe to be fitted by 2010 
with a black-box device that can be tracked by satellite. Germany is now 
testing such a system on trucks, and Britain plans to require it on 
trucks by 2006.
Once the passive-radar cat is out of the bag, there's even a chance it 
could evolve into a means of tracking people on the street. "But 
there'd be a lot of technical challenges," because the human body is a poor 
reflector of radio signals, says Shawn M. Herman, a researcher at 
Numerica whose 2001 PhD thesis was on passive radar. Still, classified 
research is under way in Europe to create a hybrid surveillance system, using 
both passive radar and images from the TV cameras that now monitor many 
urban intersections and streets, airports, and other public places. 
Suspected terrorists and other bad guys could then be watched more 
The Big Brother implications of all this might unleash a massive public 
backlash. But just as plausibly, people may decide to put up with 
technology's double-edged sword to regain a measure of the security they 
have lost. 
By Otis Port in New York
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