Shedding Light on Earth: How Nighttime Lights Have Revolutionized the Way We Understand Our World

By Ran Goldblatt, Steven Rubinyi, Hogeun Park

Published in GIM Magazine

Images of Earth taken at night are revolutionizing our ability to measure and understand nearly every dimension related to human activity on Earth and allow us to get a glimpse into human/Earth interactions in near real time. The recent COVID-19 outbreak exemplifies how nighttime lights can help us understand the impacts of shocks on populations, economies and markets. Given the interdisciplinary nature of remote sensing-based socioeconomic research, a special issue of ‘Remote Sensing’ journal will bring together original and novel studies demonstrating innovative applications of nighttime lights-based analysis to broaden our understanding of human society and its further implications.

Seeing the Impacts of COVID-19 at Night  

In mid-December 2019, COVID-19 began emerging in Wuhan, China and in just 30 days rapidly spread to the entire country, causing significant impacts not only on the health of people in China, but on the entire economy, the job market and the daily life of the population. Within several weeks the disease started spreading globally, with millions of confirmed cases recorded around the world, together with significant implications to global economies.

The need to track and predict outbreaks, and understand the impacts of COVID-19 on economies, have led to the utilization of unique sources of data that could help track the spread of the pandemic in close to real time. Satellite observations – including those taken at night – are becoming a primary source of data for tracking the progress of the pandemic and its impacts on energy consumption, transportation, social interactions, the functionality of critical infrastructure, tourism, trade emissions, etc. They provide a compelling and striking picture of the large-scale impacts of COVID-19 on Earth, from the impacts of the pandemic on businesses and transportation networks to monitoring the gradual recovery of cities around the world. The idea of using nighttime lights to understand pandemics is not new, and previous studies have already shown, for example, how nighttime lights can be used to estimate seasonal measles epidemics, which are directly linked to spatiotemporal changes in population density as measured by anthropogenic light emissions.

Changes in activity around the city of Wuhan, China, between 19 January and 4 February 2020, as retrieved by the Visible Infrared Imaging Radiometer Suite (VIIRS) using NASA’s Black Marble product suite: https://blackmarble.gsfc.nasa.gov/. Source: NASA’s Goddard Space Flight Center (GSFC) and Universities Space Research Association (USRA)
Changes in activity around the city of Wuhan, China, between 19 January and 4 February 2020, as retrieved by the Visible Infrared Imaging Radiometer Suite (VIIRS) using NASA’s Black Marble product suite: https://blackmarble.gsfc.nasa.gov/. Source: NASA’s Goddard Space Flight Center (GSFC) and Universities Space Research Association (USRA)

Shedding Light on Earth

The use of nighttime lights observations to monitor pandemics is only one example of how satellite observations can be used to help us better understand processes on Earth. Since the early 1990s, with the launch of DMSP-OLS, remotely sensed observations of nighttime lights have been a key instrument for understanding almost every aspect related to human activity on Earth; particularly in the data-scarce region, without being filtered through national data agencies that are potentially inefficient or biased. Today, newer sensors, such as VIIRS/DNB, provide nighttime light data even at a higher spatial resolution and granularity. With advances in the availability and the quality of nighttime light data, together with improvements in data storage capabilities and the development of new analytical methods and workflows for analyzing the data, there is an ongoing increase in the number of scientific applications that exploit remotely sensed nighttime lights to measure our world.

Nighttime lights observations – or the measurements of the intensity of light emitted from Earth at night – provide a unique glimpse into human behavior and socio-economic patterns and into the nature of human-Earth interactions.  Nighttime light observations are especially vital in countries where timely, accurate and reliable statistical or administrative data is poor. In these countries, nighttime light measurements can provide important insights into where people are, how people move, understand patterns of economic development or evaluate the economic impacts of investments in infrastructure. While in some cases nighttime light observations may prove to be noisy and carry inherent measurement errors especially when compared across space and time, there is a general consensus that nighttime lights are able to represent many dimensions related to human presence and activity on Earth. 

Changes in the intensity of nighttime lights can be used to illustrate pace of recovery. These images show changes in nighttime lights between March 2020 and February 2020. Cyan = lighting brightened, Red = lighting dimmed.  Source: Elvidge et al., 2020. The Payne Institute for Public Policy
Changes in the intensity of nighttime lights can be used to illustrate pace of recovery. These images show changes in nighttime lights between March 2020 and February 2020. Cyan = lighting brightened, Red = lighting dimmed. Source: Elvidge et al., 2020. The Payne Institute for Public Policy

Today, nighttime lights are being used to measure the extent and characteristics of urbanization processes, estimate economic growth at a national and sub-national level, map global poverty, track local household wealth, education and health, map population density,  migration and mobility patterns, understand armed conflicts, measure accessibility to electricity and electrificationcommunity resiliencefishing activitycoral reef health and more. Recently, researchers have also shown that nighttime lights can explain brain development and human behavior.

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