Antarctic and Arctic sea-ice revealed in 1964 satellite maps

The NSIDC project examined almost 40,000 images from the Nimbus-1 archive to produce the September 1964 maps of Arctic (L) and Antarctic (R) sea-ice extent.

The earliest satellite maps of Arctic and Antarctic sea-ice have been assembled by scientists.

They were made using data from Nasa's Nimbus-1 spacecraft, which was launched in 1964 to test new technologies for imaging weather systems from orbit.

The satellite's old pictures have now been re-analysed to determine the extent of the marine ice at the poles in the September of that year.

Regular Earth Observation mapping from space did not begin until 1978.

One key finding is that marine floes around the White Continent in the 1960s were probably just as extensive as they are today.

The new snapshot, published in The Cryosphere journal, therefore helps put current ice conditions into a longer-term context, say researchers at the US National Snow and Ice Data Centre (NSIDC).

It is also just a fascinating story of how old scientific data can be given a new lease of life.

Matching up
The Nimbus-1 satellite was a short-lived mission that observed the Earth's clouds in black and white video, which it transmitted to the ground as an analogue TV signal.

Those transmissions were then photographed on to 35mm film and archived. The NSIDC team had to pull the canisters containing the original film out of storage to perform the re-analysis.

NSIDC
"The canisters were kind of forgotten, almost lost in time, until about four years ago when they were found and it was realised they might contain some useful, interesting data," explained the NSIDC's Dr Walt Meier.

"We then got some funding to digitise the data and analyse it. I was sceptical at first; the quality of the data is nothing like what we can get now.

Dr Walt Meier

"But it turned out to be really good, especially in the Antarctic, where it was surprisingly easy to determine the ice edge. Don't get me wrong, it was certainly a challenge," he told reporters.

"One of the things you have to do is geo-locate the data - you have to know where you are looking. There was some information in there to help us, but we had to take care in matching up the images and locating them on the Earth as accurately as we could."

Although the satellite worked for just three weeks, it covered a period of key interest to polar scientists.

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