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Leopard stalking Muscles tensed, a leopard prepares to pounce on a puku fawn that cannot see it in the pitch dark.

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The Camera that Caught a Leopard
by Rob Meyer

A leopard silently stalks its prey. Controlling every muscle in its body, it inches its way towards an antelope oblivious to impending doom. Any sound will give the leopard away, but this expert hunter is as careful as it is patient. Slowly, the leopard moves closer to the antelope, until it stands just feet away, ready to strike. The scene unfolds so slowly and dramatically it might seem to you a nightmarish fantasy—one of the most remarkable exchanges in nature. There is only one problem. You can't see a thing.

The leopard's enormous eyes are capable of vast dilation, which allows the predator to see in near-lightless conditions. Human eyes, like the eyes of the leopard's prey, become useless in low light. Until recently, this meant that we had no way of observing the night behavior of leopards. Today, infrared-sensitive cameras enable us to record on videotape what we are unable to see with our eyes.

Red - indigo
In order to understand how this is possible in total darkness, we must first understand light. Light travels in waves, much like ripples on a pool. Colors are simply light waves of different lengths. Very short light waves are violet in color; as the waves get longer, the light changes to indigo, blue, green, yellow, orange, and finally red. The waves can even be measured. From one peak to the next, an indigo-colored light wave is 400 nanometers (400 billionths of a meter) and a red wave is 700 nanometers. This range of colors is all that the human eye is capable of seeing—our "visible light spectrum." But what happens when waves get even longer or shorter?

Looking at a chart, one quickly realizes that the wavelengths we can see make up a very small portion of the total spectrum. As the waves get longer than red, they become so-called "near-infrared" waves, then infrared waves, microwaves, and lastly radio waves. As they get shorter than indigo, they become ultraviolet waves, X rays, and finally gamma waves. These waves surround us all the time, but we are unaware of their presence, since they are not in our visible light spectrum.

Electromagnetic spectrum

Near-infrared waves behave much like the light waves that we can see. They come in a range of lengths, and are absorbed and reflected by objects. But for our purposes there is one critical difference: They go undetected by humans, leopards, and antelopes. This is great news for producers who are looking to capture the behavior of wildlife at night.

For the NOVA film Leopards of the Night, producers Amanda Barrett and Owen Newman brought security cameras to Africa (see Behind the Scenes). They were not paranoid that their equipment would be stolen. Instead, they had their minds on stealing something for themselves: nighttime video images. While our eyes cannot see waves longer than 700 nanometers, certain security cameras are sensitive to waves well into the near-infrared range.

In order for these cameras to record dramatic wildlife scenes, near-infrared waves are needed to "illuminate" the subjects. Barrett and Newman relied on special lights as a source for these necessary waves. These lights, called infrared illuminators, use LEDs (light-emitting diodes) and are designed to produce light of particular wavelengths. In this case, they emit waves between 800 and 900 nanometers, right in the near-infrared range. While no visible light is emitted, the area is flooded with these invisible waves. The animals remain totally unaware of this illumination and go about their business in the dark. But as with visible light, their bodies absorb or reflect these near-infrared waves, depending on what part of the animal the waves bounce off.

Leopard and impala Focusing the infrared-sensitive camera, which had no viewfinder, was a constant challenge for cameraman Owen Newman.

While makers of infrared-sensitive cameras guard the secrets of their products, the basics behind the cameras are well understood. The infrared-sensitive camera picks up reflected light waves much like the human eye. The lens directs all of the incoming waves to a small internal chip that is sensitive to visible and near-infrared waves. The chip records the relative strength of the waves at each one of its 500,000-plus pixel points. It then changes this grid of energy levels into different shades of gray: the greater the strength of the near-infrared wave, the brighter the pixel. This information is then translated to the pixels on a black and white screen. These infrared-sensitive cameras give us just a first glimpse into night wildlife. With new technologies developing, we can only imagine what lies in store for us in the future. Dark, camera, action!


Rob Meyer is Production Assistant of NOVA Online.



Night Vision | Camera that Caught a Leopard
Behind the Scenes | Seeing through Camouflage
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