Remote sensing of nighttime light emissions offers a unique perspective for investigations into human behaviors, such as tracking the expansion of urban areas or assessing power outages caused by natural disasters like hurricanes. Unlike daytime remote sensing, there are multiple sources of nighttime illumination. These sources include moonlight, light directly emitted by objects (e.g., streetlights, buildings, ships, etc.), and light reflected by the ground (also known as surface albedo). Snow, especially fresh snow, has a high surface albedo and reflects a high percentage of light hitting it. On the other hand, surfaces with low albedo, such as water bodies and forest canopies, reflect far less light.
The Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP), NOAA-20, and NOAA-21 platforms acquires global daily measurements of nocturnal visible and near-infrared (NIR) light that can be used for Earth system science and applications studies. VIIRS Day/Night Band (DNB) data are used for estimating population, assessing electrification of remote areas, monitoring disasters and conflict, and understanding biological impacts of increased light pollution.
VIIRS DNB operates in the visible to near-infrared portion of the spectrum: 400-900 nanometers (nm). This spectral range is ideal for exploring nighttime lights as many human-made light sources, including metal halide lamps and light-emitting diode (LED) lights, have spectral responses in this range.
To enable the use of nighttime lights data for scientific investigations, NASA developed a series of products known as the Black Marble. NASA’s Black Marble product suite for Suomi NPP (VNP46) improves nighttime lights data in several ways:
Nighttime lights contribute to a variety of Earth science studies and applications. By "subtracting" moonlight and other extraneous sources, researchers can systematically monitor artificial lights like street and building lighting, fishing boats, gas flares, fires, aurora, and many human activities. Below are three use cases that are changing the way we "see" our world at all hours.
Natural events like hurricanes, winter storms, earthquakes, and volcanic eruptions affect millions of people every year. These events often are followed by power outages and blackouts. The high spatial and temporal resolution of VIIRS DNB images provide information on where outages are occurring and the progressive restoration of the electric grid.
For example, Hurricane Maria swept across the Caribbean in September 2017, devastating many islands. In Puerto Rico, the hurricane caused power outages across the island. This disaster was the first time nighttime lights data were routinely used by emergency management agencies to aid in disaster mitigation and recovery efforts. The near real-time data informed federal and local government authorities, construction and utility crews, and relief organizations so that they could visualize the extent of outages and prioritize areas for recovery.
Houston, TX, experienced a major winter storm in February 2021 that shattered low-temperature records and knocked out power to 1.4 million customers. Natural gas shortages were already impacting demand, which only intensified over time. Controlled outages and downed power lines left parts of the state in the dark. NASA Black Marble data clearly showed the extent of power outages during this event.
Additional natural event use case stories:
As population grows and urbanization increases, cities and humans encroach on natural environments. Wildlife in or close to these urban centers face new stressors that can have behavioral and ecological effects, including artificial nighttime lights. For wildlife, light influences navigation, activity, and reproduction. For example, turtle hatchlings follow the brightest light source, which naturally is moonlight reflected off the ocean surface; artificial lights can cause disorientation and prevent their movement toward the ocean, often resulting in mortality. In addition, a study by researchers at Northeastern Illinois University using nighttime photography images acquired by astronauts aboard the International Space Station found that increases in artificial light led to behavioral changes in nocturnal animals, causing them to become less active and roam less. In another study, researchers looked at predator-prey interactions between pea aphids and two species of ladybugs. They found that for those species of ladybugs that foraged effectively in darkness, light pollution did not change the suppression of aphids; for more visual predators, however, light pollution aided their predation, leading to much lower aphid abundances.
While most research exploring the impacts of NTL on ecological systems has focused on terrestrial environments, there are several studies of aquatic environments. Most of the studies have focused on coastal and offshore fishing activities. The improving spatial resolution of nighttime images facilitates more studies in aquatic environments.
Additional biological use case stories:
Nighttime lights data provide insight into the social, economic, and cultural patterns and behaviors within urban environments, from electrification, conflict-induced migration, holidays, and more. In one investigation, a research team used Black Marble products to illustrate different types of changes in social, economic, and cultural behaviors depicted in nighttime lights patterns between 2012 and 2020 in the Middle East.
In Aleppo, Syria, the impact of conflict and population displacement that began in early 2013 was seen as a dramatic decrease in nighttime lights. In the El Zaatari refugee camp in Jordan, an influx of refugees from Syria during this time made the camp one of the largest in Jordan, with a corresponding increase in nighttime lights.
As Dubai, UAE, expanded to became a global Middle East business hub, this also led to an increase in nighttime lights from increased road networks and industrial units. While the steady increase in Dubai's nighttime lights pattern over the decade suggests a growing economy in the country, impacts on economic activities due to lockdowns and business closures during the COVID-19 pandemic are also observed in a dip in lights starting in 2020.
Additional socioeconomic and cultural use case stories:
Levin, N., Kyba, C.C.M., Zhang, Q., Sánchez de Miguel, A., Román, M.O., Li, X., Portnov, B.A., Molthan, A.L., Jechow, A., Miller, S.D., Wang, Z., Shrestha, R.M. & Elvidge, C.D. (2020). “Remote sensing of night lights: A review and an outlook for the future.” Remote Sensing of Environment, 237(111443). doi:10.1016/j.rse.2019.111443
Román, M.O. & Stokes, E.C. (2015). “Holidays in lights: Tracking cultural patterns in demand for energy services.” Earth's Future, 3 (6), 182-205. doi:10.1002/2014EF000285
Román M.O., Stokes E.C., Shrestha R., Wang Z., Schultz L., Carlo E.A.S., et al. (2019). “Satellite-based assessment of electricity restoration efforts in Puerto Rico after Hurricane Maria.” PLoS ONE, 14(6):e0218883. doi:10.1371/journal.pone.0218883
Stokes, E.C., Román, M.O., Wang, Z., Shrestha, R.M., Yao, T. & Kalb, V. (2019). “Urban Applications of NASA’s Black Marble Product Suite.” Joint Urban Remote Sensing Event (JURSE), 1-4. doi:10.1109/JURSE.2019.8809074
Stokes, E.C. & Seto, K. (2019). “Characterizing urban infrastructural transitions for the Sustainable Development Goals using multi-temporal land, population, and nighttime light data.” Remote Sensing of Environment, 234 (111430). doi:10.1016/j.rse.2019.111430
Wang, Z., Román, M., Sun, Q., Molthan, A. & Kalb, V. (2018). “Monitoring Disaster-related Power Outages Using NASA Black Marble Nighttime Light Product.” The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, XLII-3, 1853–1856. doi:10.5194/isprs-archives-XLII-3-1853-2018
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