A weather eye turns 40

Posted by Francis Reddy
on Wednesday, December 27, 2006

Satellite images have become such a staple of nightly TV weather segments, it's difficult to imagine a time when they didn't exist. Yet, the first full-disk images of a cloudy Earth turned 40 earlier this month.

It's not much to look at by modern standards. But images like this from ATS-1's
spin-scan cloud camera revolutionized meteorology. NASA

An innovative device called a spin-scan camera made these first images possible. The first one roared into a 22,200-mile-high (35,800 kilometers) geosynchronous orbit aboard Applications Technology Satellite-1 (ATS-1) December 6, 1966. In less than a decade, its descendants would return the first spacecraft images of Jupiter, Saturn, and Venus.

"It was a milestone," says Hank Revercomb, who directs the Space Science and Engineering Center (SSEC) at the University of Wisconsin in Madison. "It was up there before Apollo went to the Moon, and it spawned a continual commitment to monitoring severe weather from space." The camera "gave us the first pictures of the full disk of the Earth from space and would become a cornerstone of the remote sensing we take for granted today," he adds.

Wisconsin meteorologist Verner Suomi and his collaborator, engineering professor Robert Parent, invented the imaging system — and founded the SSEC — in 1965.

Sanjay Limaye, an SSEC planetary scientist, credits Suomi as the first person to demonstrate that Earth observation from space had real value. In a 1957 proposal to the National Science Foundation, Suomi showed that a satellite would be an ideal place to measure Earth's radiation budget — the balance between incoming solar energy and what the planet reflects or radiates away as heat. "Prior to that, everybody was looking out, to astronomy," Limaye explains. "Nobody paid any attention to the fact we might learn something by looking at the Earth because there was no stable platform to do so."

The device worked by scanning Earth as it spun and building up an image one line at a time. "What the camera did was look perpendicular to the spin axis, change its orientation slightly for each rotation of the satellite, and build up an image," says Lawrence Sromovsky, an SSEC planetary scientist who worked with Suomi. "From that vantage point with that camera, you could see cloud patterns over half of the Earth. As Suomi said, 'You could see the clouds move, not the satellite.'" It took ATS-1's camera 20 minutes to make a full picture of Earth.

For meteorologists used to gathering data with high-altitude weather balloons and airplanes, the view from space changed everything, Sromovsky notes.

A later Earth-observing satellite, ATS-3, used spin-scan technology to make the first full-color image of Earth from space in 1967 — before the famous view of earthrise taken by Apollo 8 astronauts circling the Moon.

Technology has since surpassed Suomi's invention, but not its legacy. "It's how we watch hurricanes and severe weather. It's how we know storms are coming," Revercomb says. "Vern Suomi deserves his title as 'father of satellite meteorology.'"

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