The gauges, three of which are worn on a soldier's body, track the direction, pressure and speed of a blast wave as it overtakes a servicemember in the milliseconds after an improvised bomb detonates.

The bombs the Taliban buries along roads or pathways patrolled by Afghan and U.S. troops are among the deadliest weapons used against coalition forces.

Soldiers or Marines who step on them can be killed or lose arms and legs to the blast. Many comrades nearby are left unconscious or dazed from a brain injury scientists are still trying to understand — invisible damage long considered one of the signature wounds of wars in Iraq and Afghanistan.

More than 1,700 troops were diagnosed with brain injuries in the first six months of this year in Afghanistan, according to Pentagon data.

"What in the explosive blast ultimately causes the injury? That's what we really, really want to know," says Army Col. Geoffrey Ling, a scientist at the Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., where the sensor was invented.

At a NATO hospital in Kandahar, Lt. Cmdr. Josh Duckworth, a Navy neurologist, downloads information from the blast gauges. The data enable him to translate into an Excel spreadsheet a diagram of an explosion that causes mild brain damage.

"Because we have three gauges, we can also get the information from three different angles and we're able to then reconstruct the picture," Duckworth says in a telephone interview from Afghanistan.

The duration, pressure and speed of the blast wave are recorded, as is the acceleration of whatever portion of the body is affected, Duckworth says. The blast sensors are worn on the chest, the shoulder and a strap on the back of the helmet.

The gauges can be activated to produce a flashing light — yellow, green or red — indicating to corpsmen or medics the level of pressure from the blast, a preliminary sign of severity.

Duckworth, deployed since February, says he has gathered data from 24 explosions involving U.S. troops. DARPA says it has accumulated information on 250 cases so far.

Duckworth says he has diagramed the reverberation of blast waves inside a vehicle where a rocket-propelled grenade detonated. He also has seen the prolonged pressure wave from a "layered" improvised bomb in which several explosions occur in succession. Gauges also have recorded a blast wave bouncing off a wall so that a soldier or Marine is caught between two concussive waves.

Historically, doctors have diagnosed and treated brain injuries from such blasts based on the symptoms troops describe — dizziness, headaches, confusion and short-term memory loss. More than 300,000 troops may have suffered mild traumatic brain injury, research shows.

Most appear to recover. However, uncertainty remains about long-term effects or how the wounds complicate post-traumatic stress disorder.

As information from the sensors accumulates, Duckworth says, scientists could learn more.

The blast gauge, he says, "is really the first chance I have to have real data."