Al Qaeda soldiers may know the terrain better and they may be able to
navigate hidden networks of underground tunnels. But once night falls,
any American troops in Afghanistan will have at least one advantage:



They can see in the dark

The U.S. Navy Commanding Officer watches aboard the USS Enterprise as aircraft prepare for a second day of night strikes in Afghanistan, as seen through the green filter of a camera's night vision lens on Oct. 8, 2001. [Reuters]

Taliban and al Qaeda forces may have access to some night vision
equipment, bought from other countries in the past. But experts believe
that any equipment al Qaeda forces may have is scarce, and inferior to
U.S. technology.

Night vision devices were invented during World War II for use by
American, British and Soviet soldiers and pilots. Since then, the
technology has evolved from bulky devices that amplify light about 1,000
times to compact equipment that can amplify any light source (including
faint starlight) up to 50,000 times, and eyewear that allows soldiers to
see in complete darkness (such as in caves) by detecting heat
differences.

Already, U.S. pilots have used night vision equipment to navigate and
find targets during night bombings of Afghanistan. Infrared lasers are
also used to illuminate targets with a light invisible to the naked eye,
but visible to those using infrared detection technology. Infrared
images are portrayed in shades of color onto a TV screen in the cockpit.

Amplifying Light, Seeing by Temperatures

Night vision equipment falls into two major categories: image
intensification systems and thermal devices.

Even when a night appears completely dark, near-infrared light is
emitted by the moon and stars. A night vision device amplifies this
light to visible levels. The light, which is made up of photons, is
converted into electrical energy and then accelerated through a thin
disk. As the converted photons strike a phosphorus screen as electrons,
they are perceived through an eyepiece in shades of green. The reason
it's in green is because when you put the unit down, you want your eyes
to remain dilated so you can see in dim light. Use most any other color
and your pupils will constrict when you take off the unit.

Infrared technology measures fraction of a degree differences of heat
given off by objects. All living things and many objects - people,
animals, recently used cars - emit heat in the form of infrared
radiation. Infrared devices read heat by absorbing infrared light,
converting it into a grid of video signals and creating a picture the
viewer can see.

Effective in Winter

While viewing through an infrared device, you'll see varying shades
of gray or black, with the whitest segments representing those giving
off the most heat. Some reports have suggested that infrared technology
will become more effective as winter arrives in Afghanistan, since
contrasts between body temperatures and the external temperatures will
increase. But the contrast doesn't necessarily enhance infrared images,
and once snow falls, the opposite is true.