City lights viewed from space show cultural, tech differences

East-West divide persists in Berlin, US lighting similar to East Berlin’s.

In many areas of the US, it’s no longer possible to see more than a few hundred stars at night. Light pollution, the diffusion of things like street and stadium lights, is limiting our ability to see into space. However, while looking from space, lighting differences can be used to tell us things about the country where the light is originating. This includes both the technology behind the lights, as well as a bit about the cultural origin of the people using it.

A new paper in the journal Remote Sensing looks at two new sources of nighttime photos of the Earth. One is a relatively new NASA satellite, called Suomi NPP. Compared to previous instruments, its imaging has over twice the bit-depth and a spatial resolution that’s at least fifty times better.

The second is a growing archive of photographs taken by astronauts aboard the International Space Station. These are now taken with a high-end SLR called NightPod. These are accessible through a dedicated website and are used as part of a citizen science project called Cities at Night.

A group of European scientists has now gone through and analyzed the nighttime lighting of cities in Europe and the United States. One of the things that was possible to work out is the relative contribution of different sources of light to the overall light pollution. In Berlin, roughly a third of it comes from street lights. Another 16 percent comes from industrial areas, and another 10 percent from what the authors term “public service areas.” Everything else—urban housing, commercial centers, and airports—is less than 10 percent each.

The history of Berlin’s division is also apparent from space. Most of East Berlin emits an orange-hued light, which is typical of sodium lamps. The West, by contrast, has a glow that’s untinged white, which could be from mercury or LED lighting. The lighting in East Berlin is also more intense—there’s simply more light being produced in those areas that were once part of East Germany.

Part of that may simply be because some neighborhoods in Berlin still use gas lighting, and “these areas appear to be almost unlit in the composite image.” But another cause is a political decision. The Berlin Senate commissioned a study that found that accident rates were largely unaffected by the local lighting conditions. As a result, the city policy has been to only use “as much light as is sensible and necessary.”

But the area also hints that culture may be at play. Cities in Central Europe (with the exception of Warsaw) generally emit less light per capita than cities in Western Europe, such as London and Madrid. The US fits in with Western Europe, with its cities emitting far more light than equivalently sized cities in Germany. In fact, German cities, in terms of light per capita, trend downward as they get larger; in the US, the contrary is true.

The authors suspect that some of the contributors to this difference are due to the youth of American cities. They’ve got relatively broad streets compared to older European areas and probably have less mature tree coverage. Both of these factors would allow more light to escape to space.

In addition to providing a distinct window into energy use, the authors argue that the availability of this imaging can give insights into other areas related to human habitation on the Earth. For example, they suggest that the nighttime lighting can identify developments that are encroaching onto areas like wildlife corridors, thus helping planners to keep key habitat available.

Remote Sensing, 2014. DOI: 10.3390/rs70100001 (About DOIs)

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