I recently saw two pictures of southern Saskatchewan taken one year apart, in the summers of 1983 and 1984. The photographs are primarily green and pink. In the first photo there’s plenty of green, but also plenty of pink. In the second photo, the green has just about overwhelmed the pink.

That might sound like a good sign–green being associated in our minds with growing things–but in fact, it was just the opposite. The green in those images was artificially supplied by a computer to identify soil dried out by drought, and the photographs clearly show how the drought worsened over that 12-month period.

Those two photographs, taken right over our heads by passing satellites, bring home the importance of the science of teledetection–the study of Earth from a distance. To achieve the same kind of understanding of the extent of the drought from the ground, you’d have to travel to dozens of sites, take all kinds of measurements, and then collate the date. The satellite precisely mapped the worst-hit area in a single pass.

Of all the benefits of space exploration we enjoy daily, from modern computer technology to freeze-dried foods, none are more important than the ones that arise from the use of artificial satellites.

Until we sent satellites into space, we had no way of seeing the Earth as a whole: we could only study it piecemeal. Yet the Earth is really a single, vast system. A coffee blight in Brazil may cause suffering in Africa, if growers there decide to grow coffee for cash rather than food. The carbon dioxide produced by our cars in Saskatchewan may be contributing to global warming, which could eventually result in higher sea levels that flood the Netherlands.

The first images of the Earth from space had a great impact on many people’s understanding of the planet as a habitable island in an unfriendly sea–an island which must be kept habitable, because there aren’t any other likely looking islands in sight. Seeing our planet from orbit still has that impact: one of the regrets astronauts regularly express is that they were so busy on their space flight they never had enough time to just sit and look out the window at the Earth passing beneath them. One of the most striking images I have recently seen, which appeared in a recent issue of the science magazine Discover, is a collage of carefully chosen satellite photos that creates an almost cloud-free image of the entire planet.

But aesthetic and philosophical considerations aside, satellite images have a great many purely practical applications, from weather forecasting to resource location and management.

Weather satellites are probably the best-known kind of satellite of all, because we see images of the clouds swirling over western Canada on the news every night. The improved forecasts made possible by satellites have saved lives and millions of dollars’ worth of property by providing better warning of catastrophic storms.

Teledetection also plays an important political and military role. “Spy” satellites help verify arms treaties, warn of troop build-ups, and provide accurate battlefield information to military planners–something we’ve seen most recently in the Persian Gulf War.

But satellites do a lot more than just photograph clouds and military sites. Using select wavelengths of light, both visible and infrared, satellites can build up pictures of rocks, soil, water, vegetation and land use that provide far more information than just an ordinary photograph.

In infrared photographs, for instance, unhealthy trees have a different colour than healthy ones–important in the study of the effect of pollution or other factors on forests.

Satellites have been used to detect the colours of coastal waters and the amount of key gases in the stratosphere and to generate data on wind, waves and currents in the sea. Some satellites generate images using radar, which is unaffected by darkness, cloud cover or atmospheric conditions. Just as the spacecraft Magellan is currently using radar to map the hidden surface of Venus, permanently shrouded in clouds, radar has allowed scientists to map the bottom of this planet’s ocean and to detect the course of ancient rivers long since buried under the shifting sands of the Sahara Desert.

Canada is a leader in the field of teledetection. It has the largest library of satellite and aerial photographs of any country in the world, and has pioneered several technical innovations and applications. In the near future a Canadian satellite, RADARSAT, will be launched by the U.S. space shuttle, and is expected to expand the bounds of remote sensing with its high-resolution radar images of Earth; images that can be used, for example, to monitor ice conditions in the Arctic sea lanes, or for precise mapping of Canada’s vast territory. RADARSAT images will be available to the rest of the world, as well, as Canada expands its presence the growing market for satellite images, expected to be worth $20 billion by 2000.

The reason that market is growing is because the value and applications of satellite images are really only just beginning to be understood. It’s been only slightly more than 30 years since the very first artificial satellite, Sputnik, was launched by the Soviet Union. It’s been only 18 years since the first Landsat was launched. As with any other technology, it’s taken a little time for its full impact to be appreciated; but now, with growing concern over the health of the Earth’s environment, a growing appreciation for the interrelationship among all living things and the Earth’s own natural processes, and a growing need for a way to accurately assess mankind’s impact on the planet, teledetection is really taking off.

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