MLA Citation: Bloomfield, Louis A. "Question 1316"
How Everything Works 18 Oct 2017. 18 Oct 2017 <http://howeverythingworks.org/print1.php?QNum=1316>.
1316. Is there any equipment that can track people in a large, dense forest? — BRAR, India
To track someone in a forest, he must be emitting or reflecting something toward you and doing it in a way that is different from his surroundings. For example, if he is talking in a quiet forest, you can track him by his sound emissions. Or if he is exposed to sunlight in green surroundings, you can track him by his reflections of light.

But while both of these techniques work fine at short distances, they aren't so good at large distances in a dense forest. A better scheme is to look for his thermal radiation. All objects emit thermal radiation to some extent and the spectral character of this thermal radiation depends principally on the temperatures of the objects. If the person is hotter than his surroundings, as is almost always the case, he will emit a different spectrum of thermal radiation than his surrounds. Light sensors that operate in the deep infrared can detect a person's thermal radiation and distinguish it from that of his cooler surroundings. Still, viewing that thermal radiation requires a direct line-of-sight from the person to the infrared sensor, so if the forest is too dense, the person is untrackable.


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