Monday, September 2, 2019

New Zealand imaged by starlight

It's never really dark at night. Besides starlight, the Earth's atmosphere itself glows. Both airglow and starlight can be reflected from the surface of the Earth. Since plants, rock, soil, and snow have higher reflectance than water, in a nighttime image they should appear brighter.

However, there is only one satellite that images the entire Earth each night, and it's just barely sensitive enough to see this. For example, here is what a portion of the South Island of New Zealand looks like when the data from all the clear moon-free nights of October 2017 is averaged together:

This work by Christopher Kyba is licensed under a
Creative Commons Attribution 4.0 International License.

You can see the mountain ranges, and you can just barely see the separation between land and water. But the more data you add, the more the signal comes out from the noise. My colleague Helga Kuechly produced this image by combining the seven October moon-free composite images from the years 2012-2018:


"Aotearoa by starlight" by Helga Kuechly is licensed under
a Creative Commons Attribution 4.0 International License.

In addition to making a stunning image, it demonstrates that if we continue to work on increasing the sensitivity of night observing satellites, it is possible to extend traditional visible band remote sensing even to nights without moonlight!

4 comments:

  1. Awesome image! Might I ask if it is possible to get a high-res image so I can get printed off for my personal use, hang it in my office?

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    Replies
    1. Sure, it's CC licensed so that anyone can use it. Send me an email, and I'll send you a copy. My contact information is here: https://www.gfz-potsdam.de/staff/christopher-kyba/?

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  2. Very nice. What is the name of the satellite that the images came from?

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    Replies
    1. The Suomi NPP. The instrument is called VIIRS DNB.

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