Sneak peeks: TSA to use standoff sensors in crowded train stations.

The Transportation Security Administration will begin using a recently unclassified remote sensor to scan rail and cruise line passengers as they walk by for explosives and other weapons, said an agency official.

Passive millimeter wave detectors are designed to peer under clothing to see guns, knives, ceramics and bombs. The system can be used covertly or overtly, according to its manufacturer, QinetiQ.

TSA sees the sensors as a solution to ferreting out possible terrorists seeking to infiltrate subway or commuter train stations. Because of the high volume of foot traffic and numerous entryways, such environments cannot accommodate individual searches similar to those carried out at airports.

The systems will first be tested on cruise line passengers at an as yet unspecified location in the Northeast, Bob Pryor, domain manager for surface transportation at TSA, said at a railway security conference.

The tests will be expanded to four sites at rail or subway stations on the: east and west coasts.

"It's harder to find threats in mass transit because it's more open," Pryor said. "You're dealing with dynamic situations because you don't have nearly as much control of the traveling public in those environments."

Pryor said remote sensors that scan passengers as they walk by are the "wave of the future." They can be fused with closed-circuit televisions, which are widely accepted by the public.

"A passenger need never know that they are being scanned," a QinetiQ fact sheet said.

The plan is certain to raise privacy issues. However, there will be a public information campaign to tell passengers about the tests, Pryor said.

Pryor quoted DHS Assistant Secretary Kip Hawley as saying the agency "will never go very far wrong as long as we keep the public informed as to what we're doing."

Passive millimeter wave detectors pick up radiation reflected off the body and can high light concealed metal non-metal objects.

It's yet another application for the rapidly growing field of millimeter wave technology. The millimeter wave band lies in the electromagnetic spectrum between microwave and infrared. The technology has been around for decades, but was considered prohibitively expensive. Costs are decreasing, and labs are developing numerous applications for the military and homeland security markets.

Active millimeter wave sensors, which resemble the walk-through metal detectors found at airports, have also been tested, said Doug Bauer, a program manager at the Department of Homeland Security science and technology directorate.

L-3 Communications security and detection systems division is marketing a walk-through portal.

Active millimeter wave devices can be weaponized. The Air Force has developed a non-lethal weapon designed for use in crowd and perimeter control. The Department of Energy is also considering their use to protect nuclear facilities.