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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
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| 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.
(Agencies)
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戰爭中，阿爾-凱達恐怖組織的武裝分子也許比美軍更熟悉阿富汗的地形，也許他們在暗藏在地下的四通八達的通道中行走如履平地。，但是每當夜幕降臨，就該是美軍的夜視技術大顯身手的時:
夜視儀，讓黑夜中作戰成為可能
塔利班和阿爾-凱達恐怖組織軍隊過去可能從別的國家購買過一些夜視設備，但是專家認為阿爾-凱達目前的夜視設備非常匱乏，而且在技術上也要比美軍落后得多。
夜視儀是在二戰期間發明的，供美國、英國和前蘇聯的士兵和飛行員使用。這項技術發展至今，已經由當初僅可以將光源增強1000倍的大型儀器改進成為現在可將任何光源（包括微弱的星光）增強5萬倍的小巧的精密儀器了。戴上可以感應熱量的夜視目鏡，士兵們即使在完全黑暗的環境里（例如山洞里）也可以將周圍的物體看得清清楚楚。
在這次對阿富汗的夜間轟炸中，美軍戰機就是使用了夜視技術進行導航和確定轟炸目標。美軍還使用了紅外線激光儀對轟炸目標進行照明，這種紅外線肉眼是看不到的，但是紅外線探測技術卻可以感應得到，并且可以在戰機駕駛艙中的電視屏幕上形成彩色的影像。
夜視儀，放大光源和感應溫度
夜視儀主要分為兩種：影像清晰化系統和熱感應儀器。
在漆黑的夜里，月亮和星星所發的光與紅外線很接近。夜視儀將這種光增強到可視的程度，并把這種由光子構成的光轉變為電子能量，然后通過一種很薄的磁盤增加電子能量的強度。這樣，戴上一種綠色的目鏡就可以看到由這種電子在磷屏幕上形成的影像。這種目鏡之所以是綠色的，是因為當使用目鏡者摘下目鏡時，瞳孔可以繼續保持放大狀態，這樣就可以微弱的光線中保持"夜光眼"。但是如果使用其他顏色，當摘下目鏡時，瞳孔就會縮小，也就不再能看見黑暗中的東西了。
紅外線技術可以探測到物體散發熱量的輕微變化。所有生物和其它一些沒有生命的物體，包括人類、動物、使用過不久的汽車，他們都是以紅外線輻射的方式散熱。紅外線探測儀通過吸收紅外線感應熱度，將紅外線轉變為一系列視頻信號，然后形成可視的圖像。
夜視技術，數九寒冬也適用？
在使用紅外線探測儀的時候，你眼前的景象是灰色或黑色的，其中散熱最多的物體呈白色。有報道說，當冬季到來的時候，紅外線技術在阿富汗戰場上會更加有威力，因為人體和外界之間的溫差變大了。但是，這種溫差并不能使紅外線影像更加清晰，事實上如果下雪的話，紅外線技術的功效反而會下降。
(中國日報網站譯)
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Updated: 2001-10-19 01:00
