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Remote sensing

 

April 24, 1998: Sometimes, the best way to look for buried treasure is the same way you look at an oil painting: step back - or up into the sky or even space.

The first step up came in the American Civil War when some enterprising soul realized that balloons could give artillery spotters a view of the enemy's front yard. World War I fully demonstrated the value of aerial reconnaissance. As fixed-wing aviation exploded after the war, archaeologists, city planners, and others took to aerial photography. In the 1930s, aviation pioneer Charles Lindbergh gave archaeology in the American Southwest a boost. During their honeymoon, he and Anne Morrow Lindbergh were able to see from the air features that had eluded archaeologists on the ground.


To learn more, go to Goddard Space Flight Center's web site on the public use of remote sensing data.


Although their budgets could not always afford the latest technologies, archaeologists continued to take advantage of aerial reconnaissance.

Now the Space Age and the Electronics Revolution have brought number crunching to what had been one of the few sciences that required very little math. The digital era arrived in 1972 with the launch of Landsat 1, which carried electronic sensors that could make pictures with colors that Mother Nature never intended.

Most Earth observation satellites use electronic sensors to return images. Film is returned only from manned missions and military satellites. The sensors range from TV cameras to scanners that build images in dozens or hundreds of distinct, narrow wavelengths at a time.

Rather than just viewing what came out of the camera, archaeologists now can manipulate images with dozens of programs. Different wavelengths can be combined to make "false color" images. One wavelength can be subtracted from another - or added, or various combinations of equations applied - to produce an image that shows the relative intensity of one wavelength to another.

The variety is infinite, but years of research using satellites and ground truth teams have allowed scientists to focus on a number algorithms or computer rule. These are keyed to factors like crops reflecting light differently when they are parched or over-watered, as compared to healthy. While the farmer might see green the computer could extract shades of green that tell a different story.

The archaeologist, too, can extract images that reveal where vegetation is slightly discolored because it has grown over a manmade structure or an old road where the soil is compacted and thus the water flow is different.

And sometimes it's as simple as peering through a magnifying glass and seeing the tip of an ancient temple - just a tiny square of stone - poking through the treetops.

It's not an "X," but does just as well.

[Students explore 'ancient' site] [Remote sensing] [Navigation] [Geographic information systems]


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Author: Dave Dooling
Curator: Bryan Walls
NASA Official: John M. Horack