Declassified satellite images show how Himalayan glaciers have shrunk

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The researchers built 3D landscapes from spy satellite images like this one from the border between eastern Nepal and Sikkim, India, in 1975.

Enlarge / The researchers built 3D landscapes from spy satellite images like this one from the border between eastern Nepal and Sikkim, India, in 1975. (credit: Josh Maurer/LDEO)

The glaciers of the Himalayas are beautiful pieces of the unique landscape at the “roof of the world.” But they’re also water towers, filling rivers used by hundreds of millions of people in East and South Asia. The need to understand how climate change is altering these glaciers is obvious.

Data is not plentiful in this inhospitable part of the world, and the climate is particularly complex and variable from across the region. For example, the monsoon rains mean that the glaciers in the eastern portion of the range actually gain most of their snowfall in the summer. With such a huge and varied area, studies have generally only been able to focus on a small subset of glaciers, making it harder to draw broad conclusions across the region. A new study led by Josh Maurer at the Lamont-Doherty Earth Observatory relies on spy satellite photos from the 1970s to make that possible.

Spying on ice

Photos from the US KH-9 Hexagon satellite have been declassified, much to the delight of geoscientists. The trick is extracting precise information from the photos—and in this case, the trick is getting 3D information from 2D images. It’s one thing to mark a glacier’s extent, but the truly valuable thing is to work out their change in thickness and, therefore, volume.

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