There’s no denying that our planet looks absolutely stunning when wrapped in ‘night lights’ from human colonies, wildfires, oil wells, auroras, or even the reflection of the stars and the moon off the oceans and ice sheets. But the nighttime images captured by earth-observing satellites serve a purpose beyond beauty. They are a testament of not just where we live, but how.
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As China came to terms with the gravity of the COVID-19 pandemic outbreak with the dawn of the New Year, the government suspended air, road, and rail travel in the Hubei province and placed restrictions on other activities in the region in late January 2020. This pronounced change in human activity reflects clearly in the nighttime images captured by NASA’s satellites around the city of Wuhan, China, between January 19 and February 4, 2020.
In the side-by-side comparison above, the labels marked with ‘G’ or ‘S’ indicate the highways with most prominent changes. For a more detailed view of the changes in nighttime lights, check out the satellite view of the Jianghan District, a commercial area of Wuhan, and nearby residential areas below:
These image pairs were captured by the NOAA–NASA Suomi NPP satellite precisely from the same angle 16 nights apart – which is the satellite’s orbital pattern. The raw images were then calibrated to account for changes in moonlight, clouds, pollution, the landscape, atmosphere, and even the Moon phase.
Also see: Better air quality over China due to anti-corona actions
Precision is critical for studies with night lights and the last few years have seen NASA’s ‘Black Marble’ research team build tools and techniques to gather a better, more consistent signal from nighttime images. Miguel Román, a principal investigator of the team, says, “We have been studying cities around the world and how they grow and change. Are they becoming more or less sustainable and livable? How do they consume energy? When, where, and how do people move and why?”
Monitoring night lights gives scientists new insights not just about cities, their infrastructure development, and their growth patterns, but also about the pulse of human activities that make up urban life. After all, urbanization is not just about a place; it is a socioeconomic, demographic, and land-use phenomenon.
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The anti-corona measures that were implemented by many European countries in the course of March led to a lockdown of cities, regions and even countries. With the nomination to an exclusion area by 10 March 2020 the territory of Italy became the first country to be locked. Others followed soon thereafter. Meanwhile almost every country in Europe is affected by measures to curb the spread of the corona infection. The implemented actions led to a significant reduction of transport (on the road and in the air), an extensive ban of trade and a shut down of industries resulting in a hefty diminished demand for energy and fossil fuels.
Similar to China, new data based on observations from the Copernicus Sentinel-5P satellite, operated by ESA, have shown significant reductions of nitrogen dioxide concentrations over several urban regions across Europe, among them the metropolitan areas of Paris, Milan and Madrid. The maps at hand compare the average nitrogen dioxide concentration of March 2019 with the NO2 concentration from 14-25 March 2020 for the mentioned agglomeration areas. The 10 days time frame in March 2020 is necessary to average out meteorological variability and see the human induced changes in the atmosphere. Hence, the substantial decrease of NO2 concentration can be explained by the anti-corona actions. Considering that the range of anti-corona measures was realized gradually starting around mid March, the atmospheric response to the decreasing emissions is quick.
Nitrogen dioxide concentrations over Italy in March 2019 (averaged) in the left panel and from 14 – 25 March 2020 in the right panel. Source: ESA
Nitrogen dioxide concentrations over France in March 2019 (averaged) in the left panel and from 14 – 25 March 2020 in the right panel. Source: ESA
Nitrogen dioxide concentrations over Spain in March 2019 (averaged) and from 14 – 25 March 2020. Source: ESA
The reduced burning of fossil fuels in China has cut carbon dioxine emissions by 25% over a four-week-period resulting in cleaner air at relatively low economic costs (The Guardian). Considering the drop of CO2 emissions in Europe, the United States and other parts of the world might be possible that 2020 will register the first fall of CO2 emissions after the financial crisis in 2008. However, in the course of the corona pandemic political and corporate authorities have been taking radical emergency measures on the advice of scientists to protect human beings. It will be crucial that related to global heating politics act with similar decisiveness and purposefulness on behalf of the human population.
Articles: Guardian, Carbon Brief, Euractiv (German)
