Nasa has released a new high-resolution map of Earth at night – and New Zealand shows up as mostly dark.
The map provides the clearest composite view of human settlement around the globe, the space agency says.
Both our country and Australia are almost shrouded in darkness, with points of light showing the main settlements and infrastructure.
Satellite images of Earth night lights have been used in research for decades.
Nasa updates satellite imagery every few years and the map is the first new composite image of the planet at night since 2012.
Night maps can be used to study energy use, light pollution, human settlement changes, and urbanisation.
A research team at the Nasa Goddard Space Flight Centre in Maryland, USA, plan to investigate whether night maps can be updated annually, or even daily, with new technology instead of every five or 10 years.
Earth scientist Miguel Roman and colleagues have been developing software to make night map imagery clearer, more accurate, and accessible to the scientific community.
The team have been working to integrate satellite data from the Earth in darkness with the Nasa global browser, a near real-time searchable satellite map of Earth.
Roman said satellite imagery was used to monitor short-term power outages, the effects of conflict, storms, earthquakes, and brownouts – partial power network outages.
“We can monitor cyclical changes driven by re-occurring human activities such as holiday lighting and seasonal migrations.
“We can also monitor gradual changes driven by urbanisation, out-migration, economic changes, and electrification. The fact that we can track all these different aspects at the heart of what defines a city is simply mind-boggling.”
The new map shows the planet at night in 2016. Scientists had to account for the varying qualities of light depending on how it is reflected by, for example, the ocean, land, and the atmosphere.
The biggest challenge, Nasa says, was accounting for the phases of the moon, which constantly varies the amount of light shining on the planet.
“Likewise, seasonal vegetation, clouds, aerosols, snow and ice cover, and even faint atmospheric emissions (such as 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.”
Data were gathered by a satellite launched in 2011 in partnership with the National Oceanic and Atmospheric Administration, known as Suomi NPP.
The satellite observes almost the entire planet twice each day, recording 3000-kilometre wide strips from pole to pole. A low-light sensor distinguishes night from day.
The team plans to automate data gathering and processing, making night imagery of Earth available within hours of a satellite pass.
By the end of 2017, they hope to make daily high-resolution night light maps available to the public.
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