2012 vs 2016: NASA images show how India looks like from space at night

NASA scientists on Thursday released new global maps of Earth at night, providing the clearest yet composite view of the patterns of human settlement across our planet.

Satellite images of Earth at night - often referred to as night lights - have been a source of curiosity for public and a tool for fundamental research for nearly 25 years.

And now, NASA has released broad, beautiful pictures of night lights as observed in 2016, as well as a revised version of the 2012 map of different countries including India showing how humans have shaped the planet and lit up the darkness.

This before-and-after comparison below shows composite nighttime views of India and surrounding areas in 2012 and 2016.

In 2012

India in 2012. (NASA Earth Observatory images by Joshua Stevens)

In 2016

India in 2016. (NASA Earth Observatory images by Joshua Stevens)

Produced every decade or so, such maps have spawned hundreds of pop-culture uses and dozens of economic, social science and environmental research projects.

In the years since the 2011 launch of the NASA-NOAA Suomi National Polar-orbiting Partnership (NPP) satellite, researchers have been analysing night lights data and developing new software and algorithms to make night lights imagery clearer, more accurate and readily available.

They are now on the verge of providing daily, high- definition views of Earth at night, and are targeting the release of such data to the science community later this year.

Composite image of continental US at night, 2016. (NASA Earth Observatory images by Joshua Stevens)

The principal challenge in nighttime satellite imaging is accounting for the phases of the moon, which constantly varies the amount of light shining on Earth, though in predictable ways.

Likewise, seasonal vegetation, clouds, aerosols, snow and ice cover, and even faint atmospheric emissions (such as airglow and auroras) change the way light is observed in different parts of the world.

The new maps were produced with data from all months of each year. The team wrote code that picked the clearest night views each month, ultimately combining moonlight-free and moonlight-corrected data.

Suomi NPP observes nearly every location on Earth at roughly 1:30 pm and 1:30 am (local time) each day, observing the planet in vertical 3,000-kilometre strips from pole to pole. Suomi NPP data is freely available to scientists within minutes to hours of acquisition.

These three composite images provide full-hemisphere views of Earth at night. The clouds and sun glint — added here for aesthetic effect — are derived from MODIS instrument land surface and cloud cover products. (NASA Earth Observatory images by Joshua Stevens)

Armed with more accurate nighttime environmental products, the NASA team is now automating the processing so that users will be able to view nighttime imagery within hours of acquisition.

This has the potential to aid short-term weather forecasting and disaster response.