In the past 20 years, astronauts on the International Space Station (ISS) have taken millions of photos of the Earth. This series not only provides an extraordinary view of our home planet; it is a valuable tool for researchers. Christopher Small of Columbia University found night images to be particularly instructive. By analyzing the image of the earth at night, he is trying to gain insight into how the city develops and evolves.
Small has been dedicated to characterizing the different types of lighting used in various urban areas. Specifically, he wants to quantify the relative brightness, color, and area abundance of different types of city lights. He compiled hundreds of city photos taken from the International Space Station, specifically looking for cities with lights of various colors and spatial configurations.
The montage above shows 18 cities—from London to Singapore to Phoenix—with particularly diverse nighttime lighting landscapes. The resolution of these images is also relatively high: each image is shot with a 400mm lens capable of distinguishing a single light. Small then calibrates each image to have the same color temperature so that they can be compared directly. This montage is calibrated to 5500 Kelvin-roughly the same color temperature as sunlight.
Generally speaking, the warmer orange and yellow in the photo are likely to be high pressure sodium lamps. For example, Chicago has long been known for its extensive orange glow. (However, this situation has begun to change in recent years as cities replace more LEDs.) The cooler greens and blues are likely to be mercury vapor lamps. LEDs may also contribute to color.
A key part of Small’s research is trying to determine how much light comes from avenues (highways and city streets) compared to individual lights (parking lot lights, facade lights, and billboards). He found that "the light in the urban environment comes almost entirely from outdoor lighting, not from the light transmitted inside the building. Most of the light is on the streets and roads."
The photos of the International Space Station in Paris (above) and Kuwait City (below) have been calibrated to a color temperature of 2200 Kelvin, which is a typical color temperature for high-pressure sodium lamps. The two cities show very different colors and spatial configurations. The light in Paris comes almost entirely from street lamps-mainly yellow, but also blue and green. The Champs Elysées looks white, probably because the brightness of street lights and buildings saturates this part of the image. "Paris is probably the best example of the diversity of color and space configurations we are trying to quantify," Small said.
In Kuwait City and surrounding communities, the lighting of new developments such as Abdullah Mubarak Al-Sabah appears to be green-possibly mercury vapor street lights. Brighter lights, surrounded by darker, more evenly distributed lights, may be mosques.
The ability to resolve individual light sources and their colors—from high-resolution images of the International Space Station—and repeated observations of the brightness of night lights from low-resolution satellite sensors such as VIIRS—is helping scientists better understand urban development. "The brightness and color of different types of lighting can help us distinguish different types of infrastructure related to the form and function of urban development," Small said. "This allows us to understand how the spatial development network evolves in the process of urban development."
Small said that research has shown that the lights in most cities often show a common network structure and often "appear without centralized planning or design." This may mean that cities follow similar patterns no matter where they are. Growth process. "In cities around the world, the suggestion that the process of emergency behavior seems very similar is interesting in itself," Small said.
Astronaut photo ISS032-E-17635 (Kuwait City) was obtained on August 9, 2012, using a Nikon D4 digital camera with a 400mm lens. This photo was taken by a member of Expedition 32. The astronaut photo ISS043-E-93480 (Paris) was obtained on April 8, 2015, using a Nikon D4 digital camera with a 400mm lens. This photo was taken by a member of Expedition 43. These images have been cropped, calibrated to common hue and white balance, and corrected for atmospheric transmission loss related to wavelength. Both photos were provided by the Earth Observation Facility of the International Space Station crew and the Earth Science and Remote Sensing Department of Johnson Space Center. Astronauts and other images taken by astronauts can be viewed on the NASA/JSC Earth Astronaut Photography Portal. The story of Catherine Hanson.
Wherever it is, cities seem to follow a similar growth process.
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