A group of climate scientists has brought satellite imagery from the 1960s back from the dead, not only extending the record of Arctic and Antarctic sea ice by at least another decade compared to what researchers had previously known, but also providing new opportunities for studying the planet to a wide range of researchers.

The restoration of imagery from the Nimbus satellite program, which ended in the 1970s, is an example of an experiment in obtaining access to so-called “dark data,” which refers to data that exists in some form, such as a ship’s logbook or old satellite data tapes, but is not currently accessible to present-day researchers.

In this case, the 35-millimeter data tapes from the satellites were lost in the bowels of facilities at the National Oceanic and Atmospheric Administration (NOAA).

The Nimbus data provides the earliest known view of Antarctica’s sea ice, which has made headlines recently for setting a record for the largest ice extent, and spotted large breaks in Arctic sea ice where none were thought to have occurred. The modern satellite record of sea ice in the Arctic and Antarctic starts in 1979, so the added data gives scientists a longer-term view that informs their understanding of present-day events.

Antarctic sea ice extent (marked in red) in 1969, as observed by a Nimbus satellite. Image: NSIDC

There are also photos of Hurricane Camille, one of the most powerful hurricanes ever to strike the U.S., which devastated the northeast Gulf Coast in 1969.

In their quest to unlock the secrets of the planet’s climate system and better understand the consequences of manmade global warming, scientists are increasingly turning to dark data projects to provide new insight.

David Gallaher, a researcher at the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado, said he and his colleagues had to overcome numerous obstacles, including technical and bureaucratic hurdles, to read data tapes from the Nimbus satellites. There were a total of seven Nimbus satellites launched between 1964 and 1978, and machines to read the 35-millimeter data reels hadn’t been made since the 1970s, Gallaher said.

Once his team gained access to them and borrowed a machine capable of reading the tapes, they scanned all 250,000 images. However, there were still more challenges to overcome, such as figuring out what spot on Earth the pictures were showing, since the images lacked location data. Simply guessing the location wouldn't have worked, considering how disorienting some of the data was.

A lead in Arctic sea ice, outlined in purple, observed in 1969 from a Nimbus satellite. Image: NSIDC

Gallaher and his colleagues managed to find an old Air Force file of satellite navigation data that enabled them to create a cross-referencing system for undergraduate students to use when cataloging the images.

The only records we have of Antarctic sea ice in the 1960s

The Nimbus satellites had visible light sensors that were considered state of the art for the time, as well as infrared light sensors. This data allows researchers to spot sea ice extent, among other things. The new record of Antarctic sea ice that has resulted is intriguing, Gallaher says. “We actually found the ice edges and it’s been kind of fascinating.”

According to the recovered data, 1964 was largest sea ice year in the Antarctic, until 2014, that is. Yet just two years later, sea ice declined by 20%, to the smallest extent on record there. “There was wild variability going on,” Gallaher said.

“The Arctic was colder, but in the Antarctic, strange things were going on,” he said. Scientists are still trying to determine why Antarctic sea ice has been growing in recent years even while the land-based ice has been melting at an increasing rate, adding to global sea level rise.

The high variability in the 1960s, based on the Nimbus satellite data, suggests that scientists may not yet have a full understanding of what governs sea ice dynamics in the Southern Hemisphere. The Nimbus data is the only direct data of 1960s-era Antarctic sea ice that scientists have from that time period, Gallaher says.

Hurricane Camille, as viewed by a Nimbus satellite. Image: NSIDC

Sea ice extents in the Arctic were much larger in the 1960s than they are now, Gallaher said, which is consistent with the global warming-induced decline in Arctic sea ice. Still, even in years with higher volume’s of sea ice, the satellite spotted ice-free areas near the North Pole that were 200 to 300 miles across. “We found holes in ice at North Pole that we didn’t expect to find,” he said.

“It’s a big hole,” said Garrett Campbell, who also works on the Nimbus project from the NSIDC.

“We basically opened a window into the past… this data was truly dark.”

The data recovered from the old satellites, which have long since burned up in the Earth’s atmosphere, extend beyond climate science and might include studying deforestation, sea surface temperatures, human development patterns such as highways and cities, and more. “We haven’t even scratched the surface of what people might be able to do with it,” Gallaher said.

Another term for the dark data project, Gallaher says, is “techno-archeology.” He said there is talk of starting a foundation dedicated to funding such projects, because traditional sources of science research funding, such as the National Science Foundation, don’t have specific programs geared toward such activities.

“This is not a terribly expensive process to get this stuff back, but it does take some money to do it,” he said. The entire project, which NASA funded, cost only $450,000, compared to the many millions it cost to put the satellites into orbit in the first place, Gallaher said.

“It looks like a new satellite but it’s fifty years old."