Why was Australia lit up like Christmas tree?

Composite image of Australia at night

The apparent abundance of lights in this satellite image of Australia’s desolate outback, is easily explained – the image is made up of multiple images taken over many days and combined one on top of the other. So occasional fires or lightning bursts here and there have apparently joined up to produce large light shows in remote areas.

TWO WEEKS AGO, NASA’S Earth Observatory web site published a new map of the Earth at night, built by Earth Observatory designers together with colleagues at the US National Geophysical Data Center. That map—made possible by a new NASA and the National Oceanic and Atmospheric Administration (NOAA) satellite—showed the footprint of human civilisation on the planet, as revealed by the lights we use to brighten the darkness.

But it turns out the map showed something more. Astute readers noticed lights in areas that were thought to be uninhabited. Many of those readers pointed to Western Australia and asked: How can there be so much light there?

The image above shows the night-lights of Australia as observed by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite in April and October 2012. It is made up of multiple images that show both manmade light sources and the light of fires. The images were acquired over nine days in April 2012 and thirteen days in October 2012.

A closer view of Western Australia at night.

A closer view of Western Australia at night.

The extent of the lighting is a results of combining multiple images. Fires and other lights that were detected on one day were integrated into the composite, multi-day picture despite being temporary phenomena. Because different lands burned at different times that the satellite passed over, the cumulative result is the appearance of a massive blaze. But while the cities are fixed, the fires were temporary, moveable features.

Not every light in the night view matches up with a fire—partly because the fire map does not include fires from April and partly because not every fire leaves a scar that is detectable from space. Even simple cloud cover could prevent burn scars from being observed.

Aside from the fires, some of the night lights appearing in uninhabited areas can be attributed to natural gas flares, lightning, oil drilling or mining operations, and fishing boats—all of which can show up as points of light.

Adapted from information issued by NASA Earth Observatory. NASA Earth Observatory images by Robert Simmon, using Suomi NPP VIIRS data provided by Chris Elvidge (NOAA National Geophysical Data Center); MODIS Active Fire & Burned Area Products; and urban data from the University of Wisconsin-Madison Center for Sustainability and the Global Environment. Suomi NPP is the result of a partnership between NASA, NOAA, and the Department of Defense. Caption by Michael Carlowicz.

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