Most large-scale, global-level satellite maps and coverage have focused on the natural landscape or even the landscape as affected and evident in the daytime. However, NASA has recognized the importance of not only human impact on the globe but also the importance of seeing the world at night. Therefore, NASA introduced Black Marble in 2012, which complements its Blue Marble release of data that has become very popular with scientists and the public. The Black Marble data provide resolution up to 500m, giving a global perspective at night.[1]
Black Marble uses imagery from NASA’s Suomi satellite. Nearly every location on Earth is observed at 1:30 PM and 1:30 AM, giving a dual perspective on the area. The main instrument is the Visible Infrared Imaging Radiometer Suite (VIIRS), which detects light photons reflected from Earth’s surface and atmosphere at 22 different wavelengths. Data can be acquired for free within hours of initially being captured by the satellite. Overall, the resolution offered by the VIIRS system is about 250 times better than the older Operational Line Scan (OLS) system used previously for nighttime data acquisition. It also allows more quantitative distinguishing of light intensity, allowing for more accurate understanding of light emission from areas.[2] One problem that had been present before is noise from lights had not been accurately corrected for atmospheric conditions or other factors that might distort the effects of light pollution. The new version of Black Marble corrects for this better than earlier versions, giving a more accurate understanding of light pollution, development, conflict, and other indices which can use light as a measure or reflection of different human actions and circumstances.[3]
Since the release, other potential benefits have been looking at issues of development, such as urban sprawl. In fact, Black Marble allows urban geographers and others to more clearly define what might constitute areas we can classify as rural or urban, suburban, villages, towns, etc. Light intensity has been used in classification methods that allows researchers to measure percentages of population living in different types of urban or rural designated regions. The study showed that recently 40.26% of the world’s population lives in rural areas, 15.53% in what are rural-urban or mixed types spaces, 26.04% in suburban regions, and only 18.16% live in areas that central or metropolitan regions.[4]
The focus has been initially on light pollution but also light poverty as indicators of economic development or human conflict. To an extent, there is some contradictory nature in how Black Marble has been seen by researchers. While some see it as providing evidence for light pollution, others see the lack of light as negative in places as it indicates lack of basic services. There may need to be a balance in perception between environmentalists and those advocating for social justice. Other areas the satellite data from Black Marble could be used for includes understanding where to focus in disaster relief, as lights could be used as proxy for population distribution. Economic development and inequality within regional development plans have been a key research focus using light as proxy for different economic indices. [5]
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NASA’s Black Marble has shown itself to offer potential utility not only for nighttime observation, but this perspective allows new ways in which scientists can understand urban change, better plan for disaster relief, investigate global conflict, and understand human impact on the planet. Black Marble is still developing more powerful algorithms and in the future could offer even better resolution detail, allowing more focused views of planetary change.
References
[1] For more on NASA’s Black Marble, see: https://www.nasa.gov/topics/earth/earthmonth/earthmonth_2013_5.html.
[2] For more on the specification of Suomi, see: https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=90008.
[3] For more on recent corrections and utility for different measures NASA’s Black Marble can be used for, see: Román, M. O., Wang, Z., Sun, Q., Kalb, V., Miller, S. D., Molthan, A., … Masuoka, E. J. (2018). NASA’s Black Marble nighttime lights product suite. Remote Sensing of Environment, 210, 113–143. https://doi.org/10.1016/j.rse.2018.03.017.
[4] For more on classifying urban and rural regions using Black Marble, see: Roca, J., & Arellano, B. (2017). Defining urban and rural areas: a new approach. In W. Heldens, N. Chrysoulakis, T. Erbertseder, & Y. Zhang (Eds.) (p. 18). SPIE. https://doi.org/10.1117/12.2277902.
[5] For more on the use of Black Marble, see: Pritchard, S. B. (2017). The Trouble with Darkness: NASA’s Suomi Satellite Images of Earth at Night. Environmental History, 22(2), 312–330. https://doi.org/10.1093/envhis/emw102.
