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Out of the Blue and Into the Black | New Views of the Earth at Night

Monday, December 10, 2012 14:21

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(Before It's News)

The night side of our planet twinkles with light, and the first thing to stand out is the cities. “Nothing tells us more about the spread of humans across the Earth than city lights,” asserts Chris Elvidge, who has studied them for 20 years.

“Nighttime light is the most interesting data that I’ve had a chance to work with,” says Elvidge, who leads the Earth Observation Group at NOAA’s National Geophysical Data Center. “I’m always amazed at what city light images show us about human activity.” His research group has been approached by scientists seeking to model the distribution of carbon dioxide emissions from fossil fuels and to monitor the activity of commercial fishing fleets. Biologists have examined how urban growth has fragmented animal habitat. Elvidge even learned once of a study of dictatorships in various parts of the world and how nighttime lights had a tendency to expand in the dictator’s hometown or province.

This image of the United States of America at night shows population distribution. – Image credit: NASA/NOAA /// CLICK IMAGE TO ENLARGE

“Night time imagery provides an intuitively graspable view of our planet,” says William Stefanov, senior remote sensing scientist for the International Space Station program office. “They provide a fairly straightforward means to map urban versus rural areas, and to show where the major population centers are and where they are not.”

This new global view and animation of Earth’s city lights is a composite assembled from data acquired by the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite. The data was acquired over nine days in April 2012 and thirteen days in October 2012. It took satellite 312 orbits and 2.5 terabytes of data to get a clear shot of every parcel of Earth’s land surface and islands. This new data was then mapped over existing Blue Marble imagery to provide a realistic view of the planet.

This animated globe shows the city lights of the world.

Away from human settlements, light still shines. Wildfires and volcanoes rage. Oil and gas wells burn like candles. Auroras dance across the polar skies. Moonlight and starlight reflect off the water, snow, clouds, and deserts. Even the air and ocean sometimes glow.

Marine layer clouds blanket the Pacific off the California coast. Higher clouds cast shadows on the low-lying fog below – Image credit: NASA/NOAA /// CLICK IMAGE TO ENLARGE

A handful of scientists have observed earthly night lights over the past four decades with military satellites and astronaut photography. But in 2012, the view became significantly clearer. The Suomi NPP satellite — launched in October 2011 by NASA, the National Oceanic and Atmospheric Administration (NOAA), and the Department of Defense — carries a low-light sensor that can distinguish night lights with six times better spatial resolution and 250 times better resolution of lighting levels (dynamic range) than before. Also, because Suomi NPP is a civilian science satellite, data is available to scientists within minutes to hours of acquisition.

This image of Europe, Africa and the Middle East is another example of population distribution. – Image credit: NASA/NOAA

The view was made possible by the “day-night band” of Suomi NPP’s Visible Infrared Imaging Radiometer Suite. VIIRS detects light in a range of wavelengths from green to near-infrared and uses “smart” light sensors to observe dim signals such as city lights, auroras, wildfires, and reflected moonlight. This low-light sensor can distinguish night lights tens to hundreds of times better than previous satellites.

The VIIRS on Suomi NPP can observe dim light down to the scale of an isolated highway lamp or fishing boat. It can even detect faint, nocturnal atmospheric light — known as airglow — and observe clouds lit by it. Through the use of its “day-night band,” VIIRS can make the first quantitative measurements of light emissions and reflections, distinguishing the intensity and the sources of night light. The sum of these measurements gives us a global view of the human footprint on the Earth.

Named for meteorology pioneer Verner Suomi, the polar-orbiting satellite flies over any given point on Earth’s surface twice each day at roughly 1:30 a.m. and 1:30 p.m. Suomi NPP orbits 824 kilometers (512 miles) above the surface as it circles the planet 14 times a day. Data is sent once per orbit to a ground station in Svalbard, Norway, and continuously to local direct broadcast users around the world. The mission is managed by NASA with operational support from NOAA and its Joint Polar Satellite System, which manages the satellite’s ground system.

Continents bordering the Atlantic ocean. – Image credit: NASA/NOAA /// CLICK IMAGE TO ENLARGE

“The night is nowhere near as dark as most of us think. In fact, the Earth is never really dark. And we don’t have to be in the dark about what is happening at night anymore either.” says Steven Miller, atmospheric scientist, Colorado State University. “These lights have always been there, but we’ve never had an ability to take full advantage of them. Now we finally have a way of doing that.”

To see more Earth at Night images visit this NASA Earth Observatory web page http://earthobservatory.nasa.gov/Features/NightLights/