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Hong Kong, China, aglow with night light

Q&A: New light pollution tracking tool is a physicist’s bright idea

Think it’s getting harder to see the stars above your home? Now, you can check whether the night sky is getting brighter on a new website that displays changes in nighttime illumination across Earth since 1992.

The Radiance Light Trends website, launched today, is the brainchild of physicist Christopher Kyba of the German Research Centre for Geosciences in Potsdam. For years, Kyba has been analyzing data collected by satellites that peer down at the planet, measuring the glow from street lamps, neon signs, and other forms of night lighting. But traditionally, it has taken up to a day to download, polish, and comb through the numbers.

On the new site, which is updated constantly, users can select areas of up to 5000 square kilometers anywhere on the globe and, in just seconds, produce a graph of nighttime radiance over any period in the past 25 years. Select parts of Puerto Rico, for instance, and you’ll see how Hurricane Maria knock out the island’s power grid in 2017. Or pick a rapidly growing city in Africa or Asia and witness how urban sprawl is brightening the night sky.

Users can also download the data and will eventually have access to the underlying software code, produced under the European Union–funded GEOEssential project, which can be used to perform similar analyses of other kinds of environmental data.

The tool could be useful to a wide array of users. Kyba and other researchers, for example, have been documenting the spread of nighttime illumination around the globe, with one study concluding light pollution now affects nearly 80% of the planet. Scientists are also examining how that artificial glow affects human health and the natural world; studies have already suggested it can alter underwater ecosystems and even promote the spread of infectious diseases. Economists have begun to use nightlight data to study economic development and the impact of government policies and natural disasters. Municipal officials and dark sky advocates concerned about night lighting could use the tool to analyze the impact of new development, and amateur astronomers could locate promising viewing locations.

Kyba recently spoke with ScienceInsider about the tool’s origins and some intriguing observations. The interview has been edited for clarity and brevity.

Q: Where did this idea come from?

A: I’ve been working on light pollution for a long time. In general, I’m interested in how light emissions are changing. But analyzing the data sets was a tricky business. You needed a lot of special knowledge, and it took a long time. So, we began to think about how to make it easier and faster. Last September, we hired an external firm to begin the programming, which took about 3 months. [The resulting tool] is really amazing for me as a researcher. In less than a minute, I can do an analysis that used to take a half-hour or more. I think others will find it useful, too.

Q: Where do you get the data?

A: Two satellites. One was operated by the U.S. military, and that data covers 1992 to 2013. But it was never intended for research purposes, so it has taken a lot of work to process. But there is a newer U.S. satellite [the Suomi National Polar-orbiting Partnership satellite] that is amazing for researchers. Starting in 2012, we have night light data from a Suomi instrument [the Visible Infrared Imaging Radiometer Suite], which is incredibly sensitive. You can see something down to as small as about a dozen street lights.

Q: Did you come across any surprises when you started to play with the tool?

A: Well, the website does allow you to really see … the [light emitted by commercial] greenhouses, which seem to be becoming more common. They emit more light than you would imagine—they are something like 10 times brighter than Times Square in New York City, which is really bright. I recently saw a greenhouse near Salt Lake City that was responsible for a significant fraction of the light coming from that region. [Search for this coordinate on the map: -111.893241, 39.815426] Another is a large greenhouse complex in Russia. [Coordinate: 34.522524, 53.810438]

And that is one of the nice things about the application: You can very quickly compare how much light is coming from something like a greenhouse compared to the rest of the surrounding area. That can be very useful to city administrators and other people who are concerned about light pollution and want to understand where the light is coming from and how it is changing.

Q: Do you have any cautions for users?

A: Night light data can be complex. For example, a few years ago we published a study that suggested night light in the United States has been pretty flat in recent years. Actually, it is likely the case that the U.S. has gotten brighter, but we aren’t seeing that in the satellite data because many [communities] are switching over to LED [streetlights], and the satellite is less sensitive to LEDs.

Also, you have to be a little cautious because these are monthly data sets, so when you have transient events—such as a fire—the total amount of light you see can be a little off. For example, there are these ferries that cross the Baltic Sea and the Mediterranean regularly at night, so they tend to be at the same locations every night and they can show up in the composite data. But there is not really a continuous light there, just a transient light source that is regular enough that it shows up.

But in general, the application will make it much easier for people to use this kind of data without needing a lot of very specialized knowledge.