Sky Eyes Are Watching You
YOU may not know this, but you are being watched. No need to look over your shoulder, however. Your observer is overhead—920 km (570 miles) above you! The eyes watching you are not human, but electronic. They belong to a satellite called Landsat.
Actually, the satellite is more interested in the land around you than in you yourself. Are you a farmer? Landsat can tell what kind of crops you are growing and how well they are doing. Its data can be used to make estimates of your harvest, and these will often be 90 percent accurate. Could there be oil or uranium on your land? Landsat can detect subtle geological clues to help answer that question.
From Pole to Pole
Of course, you are not always being watched. Each Landsat (currently there are two) passes directly overhead about once every 18 days, taking electronic pictures from its polar orbit. Why a polar orbit? There is an important reason.
Suppose you were riding above the earth’s equator in a satellite. Things might get a little dull after the first few orbits, because you would always have the same view. All you would see below would be the tropics, orbit after orbit. Now imagine being in a polar orbit instead. As you traveled from north to south, the earth would slowly turn beneath you. No two orbits would be the same! If you just passed over Athens, Greece, your next orbit might put you over London, England. Eventually, you would get a bird’s-eye view of every place on earth, which is just what Landsat needs to do its job.
The polar orbit has another advantage as well. Because of it the sun angle in Landsat’s pictures is roughly constant, except for gradual changes with the seasons. This consistency is valuable for mapmaking.
Soon after Landsat was launched, scientists realized that it had great potential for finding minerals and identifying crops. During its very first week, Landsat I identified over 30 previously unknown geological features in one part of California. As early as 1977 it was estimated that Landsat had identified new oil reserves worth one billion dollars!
Meanwhile, an experimental program was under way to see if Landsat information could be used to identify crops and predict harvests. In a special study limited to wheat, harvest yields were predicted long in advance, and over nine tenths of those predictions turned out to be accurate within 90 percent of the actual figures. Soon private companies sprang up using Landsat data to give crop forecasts to private buyers.
Such crop forecasts are especially important to less developed countries, allowing them to anticipate possible famines and request aid early. But, ironically, much of Landsat’s valuable information is not being used by those countries. Why not?
Technology and Politics
Less developed countries simply do not have the computer complexes, the trained experts and the money needed to turn Landsat data into reliable crop forecasts. Techniques are being experimented with to allow such countries to get the same information out of Landsat pictures with man power instead of computer power. But while such techniques might work for crop estimates, computer analysis is still needed when Landsat pictures are used to find minerals. This is causing problems.
Although less developed countries do not have the technology and computer personnel to get the most out of Landsat pictures of their countries, others do—the big oil and mineral companies. “Many of these firms maintain well-equipped image analysis laboratories where Landsat scenes of LDC [less developed countries] land areas are routinely scrutinized,” observes the respected journal Technology Review. “These companies are then able to negotiate lease rights while possessing better information about the LDC resources than the LDC’s themselves.” What has resulted? “The mistrust generated by this unfortunate situation has led some LDC’s to take actions, such as the nationalization of the industry.”
Politics also enters the question of Landsat’s resolution—that is, how much detail can be obtained from its pictures.
Right now the “grains” on Landsat’s electronic “film” are about an acre in size. It is possible to improve the resolution greatly. Indeed, the next generation of Landsats is expected to have “grains” of less than 30 meters square (about 98 ft. square), or only about 1/4 acre. France is planning to launch a satellite with 10-meter (33-foot) resolution, which will yield a 1/40-acre “grain.”
But what if such high-resolution pictures are used, not by farmers and prospectors, but by intelligence agents of a hostile country? “The subject of what level of resolution civil survey satellites should be allowed to have has been heatedly debated in the United Nations,” says Technology Review. Some countries have used Landsat pictures “to monitor natural resources of their neighbors rather than to manage their own natural resources.”
Technology and Wisdom
It is an issue that goes back thousands of years in man’s history—his inability to use his achievements properly. Interestingly, the Bible comments on this very problem, which existed back at the time of the building of the tower of Babel some 4,000 years ago. Although it was the engineering marvel of its day, that tower was being misused, evidently for false religious purposes.—Gen. 11:5-9.
In the case of geological satellites such as Landsat, great potential exists for good, but also for harm. Will speculators use crop forecasts to attempt to manipulate commodities markets, or will those forecasts be used to help people needing food? Will mineral surveys open the door to wise national resource policies, or to international plunder by high-technology companies? Will fear of spying limit the usefulness of future satellites? Human nature may have more to do with the answers to those questions than human technology.
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The Short, Sad Story of Seasat
In June of 1978 the United States launched an ambitious experimental satellite called Seasat-A. It was like Landsat, except that it used high-resolution radar instead of light waves to see. So Seasat-A could observe ocean conditions day and night, regardless of cloud cover.
“Seasat-A’s primary mission is for one year,” announced NASA (the National Aeronautics and Space Administration), “but enough fuel and other consumables are being put aboard so the flight can be extended for another two years.” It did not work out that way.
On October 9, less than four months after being launched, the satellite went dead, the victim of a massive and progressive short circuit. What caused the loss of this multimillion-dollar, state-of-the-art satellite? A NASA review board concluded that Seasat’s engineers may have taken too much for granted.
The board found that “a test was waived without proper approval, important component failures were not reported to project management, compliance with specifications was weak, and flight controllers were inadequately prepared for their task.”
Technology works no better than the people who are responsible for making it work.
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Taking Pictures From Space
Although Landsat is equipped with a television camera, its high-resolution pictures are supplied, not by a camera, but by a device called a multispectral scanner. How does it work?
The satellite has a mirror that moves back and forth, “looking” at a strip of ground below. Light from the ground bounces off the mirror and goes into a telescope, where it is focused on four sets of light detectors, which are like the film for this electronic substitute for a camera. Each of the four sets of detectors is sensitive to a different kind of light. One looks at just green light, another looks at red light, and the other two look at different frequencies of infrared light.
Each of the four detectors is looking at light from the same small square of ground below, but since each detector is looking at a different type of light, the detectors respond differently. For example, water absorbs infrared light readily. So when Landsat looks at a little square of water down below, the infrared detectors don’t see much. The water appears black in infrared. Not so for the green-light detector! It sees plenty of green light being reflected from the water, so the water is very bright to it. In fact, the green detector can even be used to measure the depth of water down to about 20 meters (65 feet) with considerable accuracy.
These little squares below, about an acre in size, are the smallest things Landsat can see. They correspond to the grain in ordinary film. No matter how much a Landsat picture is enlarged, its resolution is limited by these little spots called “pixels.” Each pixel has a number showing how bright it appears to be for each wavelength in which it is viewed. These four numbers are like a fingerprint, allowing viewers to determine if they are looking at a pond of water, city streets, or an illegal marijuana patch.
So all Landsat really “sees” are numbers! From these far more can be learned than from an ordinary camera snapshot.