Light detected from buildings varies depending on the satellite's viewing angle, not just due to moonlight or atmosphere, so looking straight down (nadir) versus obliquely changes what's visible, like missing a billboard's light from the side. Accounting for this angular signature of artificial light let researchers extract building heights from satellite data, and tracking these light patterns over decades reveals how cities grow, contrasting China's rapid horizontal urbanization that ran out of space with India's shift toward building vertically.
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The atmospheric correction method for nighttime light was adapted from daytime routines by substituting the moon's position for the sun's, an approximation that has held for 12 years.
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The current frontier in this research is modeling the angular structure of artificial light itself, which differs from the structure of natural light sources.
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A researcher named Eleanor Stokes, trained under Karen Seto at Yale, is cited as an expert using this data to advise cities on sustainable growth.
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18:20>> right? Okay. And so, okay, so back to the figure, you've got moonlight that >> that um that penetrates Earth's atmosphere, hits the ground, goes back. Sometimes it goes back into the ground and then comes back cuz there's like just photons are doing weird things. >> Um there's the the air glow from the atmosphere. Then there's clouds. There's all sorts of like random crap that that photons are hitting. Yes. >> Before it hits your sensor. >> Even before we did this, we didn't know how difficult it was. So, here's another problem. >> The lights from buildings also vary by angle. >> So, it matters a lot. And that's where we accounted for that in this paper.
19:01>> Oh, wow. Okay. >> If you are in New York City, Time Square and your spacecraft is looking obliquely at 45°, you're not seeing the lights, the billboard. >> The billboard. Ah okay. >> So you have to be looking from really at across the the the liio sites. So what we call nater and so we realized that this instrument had a lot of structure in the data if you understand the directional signature the multi-angular signature because you have natural variation but you also have anthropogenic radiation going on in the mirror. >> Wow. So the biggest breakthrough between this paper and this paper was the fact
19:41that we understood that the world the light in the world also vary a lot angularly >> and we couldn't we didn't even account for that when we did >> right here you have angle from the moon you've accounted for that >> yes that we accounted for that and we basically use atmospheric correction routines from daytime and we just basically plot the sun on the moon that's that's all we did >> okay yeah fair enough >> yes because the inherent optical properties of the atmosphere is really the Okay, you have aerosols, you have molecules, so you can make some approximations and those approximations have hold now for 12 years. The biggest state-of-the-art now is trying to figure out the angular structure of artificial light. And that is very fascinating because you could relate those different
20:24modes. So even though we don't have colors, we have a lot of understanding of the architecture of the likes. And that is how we started looking at the volatility of watch because the fact that the dark the it's dark at this angle and it's bright at this angle. What does it mean? I have something I have building height, >> right? >> So it's literally I can extract building heights from the lights data. >> Yeah. Yeah. Yeah. Yeah. That that's that's that's pretty cool. >> And if I can if I can track building likes over a 40year period, I know how your country is growing. China urbanized in 20 years. They built up and they ran out of space. Who's
21:06next? India. So India is going to be the next civilization that is still building horizontally and now they're building up. Then when you Elanar Stoke, he's our she's our expert in urbanization. She came out of Karen Cosbe Yale. They're the experts. They're the ones informing mayors on how to build cities sustainably where you don't end up in a situation where you're building so fast that you're not gaining benefits from building living in cities that are more accessible or those are the questions this needs. >> Yeah. Yeah. Hopefully Los Angeles also takes note because um I I would love to to have more housing in Los Angeles. So
21:48in order to do that you need to understand the makeup of transportation, commercial, you know, housing understanding how those functions change over time. For the first time we have data sets that can help you understand that variation and you can now understand the volatility of those sectors as a result of disasters. So that's another factor that that's very unique to this. >> Yeah. Yeah. Actually, so one of the
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