If the pixel is very dark, the signal is amplified. If it is very bright, a low-gain mode prevents the pixel from oversaturating. Then, the day-night band reviews the amount of light in each pixel. Unlike a camera that captures a picture in one exposure, the day-night band produces an image by repeatedly scanning a scene and resolving it as millions of individual pixels. The Black Marble> Click to view more images and animations of the Earth at night The sensor, called "VIIRS" (short for Visible Infrared Imaging Radiometer Suite), is sensitive enough to detect the light from a single ship in the sea. With a new sensor aboard the NASA-NOAA Suomi National Polar-orbiting Partnership (NPP) satellite launched last year, scientists now can observe Earth's atmosphere and surface during nighttime hours. Many satellites are equipped to look at Earth during the day, when they can observe our planet fully illuminated by the sun. Credit: NASA Earth Observatory/NOAA NGDC > High-resolution download and more information The image was made possible by the satellite's "day-night band" of the Visible Infrared Imaging Radiometer Suite (VIIRS), which detects light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe dim signals such as city lights, gas flares, auroras, wildfires and reflected moonlight. This image of the continental United States at night is a composite assembled from data acquired by the Suomi NPP satellite in April and October 2012.
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