Humvees No Match for Crude Bombs ( Report from the Humvee graveyard ~ Armor helps some )

FORWARD OPERATING BASE KALSU, Iraq — This is a graveyard for Humvees, the final resting place for the hulking vehicles felled by insurgents' roadside bombs.

In a parking lot, the U.S. military's most common personnel carriers lie flattened with noses down in the mud. Their metal carcasses are barely recognizable. Tires have been splayed to the sides or blown away entirely. Shrapnel has burst holes in unprotected parts of the vehicles, as if they were tinfoil.

The nine mangled Humvees here have been destroyed by what the military calls improvised explosive devices, or IEDs.

"Now this one here, you can see the IED tore the whole back end off the vehicle. It's just gone," said Sgt. Patrick Parchment of the 24th Marine Expeditionary Unit, which operates south of Baghdad.

"The front is sitting cock-eyed. And that's steel," he said, showing a visitor another severed vehicle.

The blasted remains do not inspire optimism about the fate of the Marines who had been riding in them. Sixteen Marines of the 24th have died since arriving here in July; 259 have been wounded. The majority of the casualties were caused by IEDs, as Marines must daily brave a gantlet of roadside bombs on highways and dirt roads that cut through farms.

The Marines and Army have almost 20,000 Humvees in Iraq, according to the Pentagon. But a quarter of the vehicles do not have proper armor.

The problem came into focus this week when a Tennessee National Guardsman told Defense Secretary Donald H. Rumsfeld that troops had to forage for scrap metal to weld to their vehicles for protection. The confrontation, at a U.S. base in Kuwait, triggered an uproar and raised questions about whether the Pentagon was doing enough to provide safety equipment ..........

8	“Dang George.......that's supposed to be a secret !”

Let me give you guys my 2¢ worth on this technology.

Beyond doubt, it works in the lab, and I would expect that it will one day find application in airport luggage screening, but I find it highly doubtful that it ever find a field application for IED detection. Let me explain why.

Photoluminescence is a process of producing light through stimulated emission. You stimulate (or excite) an appropriate material with light of a higher wavelength (bluer) and the material will fluoresce at a lower wavelength (redder). The wavelength (color) of the emitted light is characteristic of the material excited.

Virtually all explosive contain nitrogen in one or more NO₂ groups. All nitrogen based explosives are volatile, in that they will slowly out-gas these NO₂ groups which, if detected, can alert authorities to the presence of the explosives.

The photoluminescence detection being proposed, stimulates the NO₂ from the explosive with 532nm light (bluish-green) and the characteristic emitted light returning from the NO₂ will be 705nm (deep red). The light source for stimulating the NO₂ molecule is a laser. The wavelength is not critical as long as it is much "bluer" (shorter wavelength) than the stimulated emission from the explosive residue. The value of using a laser is only in (1.)being able to control the excitation wavelength, and (2.)to control directionality, and (3.)to provide enough power that the returning stimulated emission from the explosive is of sufficient intensity to be detected.

But here's the problem, if you are trying to detect IED's in the field, in the bright Iraqi afternoon sun, how are you going to separate the 705nm signal from the explosives, from the orders-of-magnitude brighter 705nm light from the sun?

Look at the graphic below to see the level of the problem. The dark blue line is what the energy the sun delivers at each wavelength. The light blue line is what the atmosphere lets get through. The two vertical orange lines demarcate the visible wavelengths. The 705nm signal is just a smidgen to the left of the right orange line.

Notice that the 705nm signal from the explosives occurs almost exactly at the same wavelength as the peak output from the sun.

One way to get around the problem would be to pulse the excitation source and have the detector look for the same pulsation occurring in the returning 705nm signal. But that technique has its limits when the "noise" (the sunlight) is very bright and you may therefore fail to detect actual explosives, even very "dirty" explosives.

But there is hope. George Smiley says: "this solution doesn't have the defusing part...", but there is something that can both detect and defuse simultaneously. The Israeli use what they jokingly refer to as "work accidents". They point a high powered transmitter at a suspected pali bomb factory which sets the bomb off by triggering the (usually) sensitive primer/triggering mechanism. All you would need would be something like the Hawk Missile battery 75kW CW Ku band Doppler radar. DOD has plenty of them, they come with their own set of wheels and a generator.

--Boot Hill

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