It's simply Perspective: the distant view provides the big
Aerial archaeology is so effective for the simple reason that, paradoxical as it may seem, there are things that can be seen in a distant view that cannot be seen in a close one.
Examine a newspaper photograph under a strong magnifying glass. All you see are dots, right? Now imagine yourself about the size of an ant, standing on the surface of that paper. What chance would you have of seeing the picture then? At best you would see only clusters of dots. You'd be too close to the dot pattern to make any sense of it. However, if you could only get up off the surface a few feet, and get a vertical view, all the dots would once again merge into a picture.
An archaeologist standing on the ground is in much the same situation. There are patterns on the ground around him that he cannot see, simply because they are too large, he's right in the middle of them, and he is looking at them practically horizontally. Let's illustrate this with a real world example, and an almost literal one at that, if we substitute stones for dots.
In the first photo (20K) we see a person standing in the midst of what appear to be randomly scattered stones, or at best perhaps a few places where they seem to be piled in long rows. There is actually a large pattern of stone alignments all around that person, but it is not apparent to her because of its size. In the second photo (20K), an aerial view of the same location, the true arrangement of the stones is revealed.
Seen from above, it is obvious that someone has actually aligned these stones into big squares or grids (probably outlining food gardens, say archaeologists). Although it was done in prehistoric times, and weathering over the centuries has scattered the rocks somewhat, blurring the picture a bit, the overall arrangement is still clear in the aerial view
Thus, the archaeologist has the opposite problem from that of the astronomer. An astronomer wants to study things that are too distant for good viewing, so he must bring them closer and make them larger, optically, using a telescope. Some things the archaeologist wants to study, however, are too close for good viewing, and must be moved father away to gain a more distant and revealing perspective. Since he can't move his subject (the ground) away from himself, he accomplishes the same thing by moving himself away from the ground. He climbs a ladder, or goes up in an airplane, trading his practically horizontal view for a more vertical one.
And just as the astronomer focuses his telescope on a star by moving the lenses closer together or farther apart, the aerial archaeologist in an airplane focuses his view of the ground (and whatever he is looking at on it) by moving himself closer to or farther away from it (flying higher or lower). There are certain kinds of features (prehistoric roads, for example) that show up best from high altitudes. Details of a buried town, on the other hand, might best be seen at lower levels.
Another real-world example of what a more distant and vertical view can reveal is illustrated by the next two photographs. The remains of a buried city, which can look like a chaotic arrangement of mounds and hollows at ground level, will look far different when seen from above:
1. A ground view of a buried prehistoric Southwestern pueblo site (20K).
2. An aerial view of the same site (20K).
To summarize, it is simply a distant view of the ground, re-focusing our view in a larger perspective, that reveals things that are often undetectable at ground level. That is the secret of aerial archaeology.
Still to be discussed:
The above discussion covers the data acquisition side of aerial archaeology. In the next update of the site we will discuss the other half of the subject: the study and application of the data acquired (such as formulation of archaeological hypotheses, planning fieldwork, the making of maps from photographs, etc.), which is usually done on the ground.
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