'VIIRS serves so many disciplines, it's an absolutely critical set of measurements,' said Dr James Gleason, NASA project scientist for the Joint Polar Satellite System (JPSS) Flight Project. It also has what is known as a Day-Night Band, which captures images of lights at night, including city lights, lightning, auroras and lights from ships and fires. One of its most important uses is producing imagery over Alaska, Dr Kalluri added, because satellites like NOAA-21 orbit the Earth from the North Pole to the South Pole, so fly directly over the Arctic several times a day. It collects images in both the visible and infrared light spectra, allowing scientists to see details of Earth's surface. The instrument also provides analysis of snow and ice cover, clouds, fog, aerosols and dust, and the health of the world's crops. Over land, VIIRS can detect and measure wildfires, droughts and floods, and its data can be used to track the thickness and movement of wildfire smoke. 'The turquoise colour that's visible around Cuba and the Bahamas in the bottom-left image above comes from sediment in the shallow waters around the continental shelf,' said Dr Satya Kalluri, a program scientist at the National Oceanic and Atmospheric Administration. VIIRS measures sea surface temperature, a metric that's important for monitoring hurricane formation, while monitoring the colour of the ocean helps to keep tabs on phytoplankton activity - a key indicator of ocean ecology and marine health.

It snapped all manner of features, including the snow-capped Himalayas and the Tibetan plateau, to the haze and smog over northern India caused by agricultural burning.

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