Change Over Time—Chicago, Illinois

These images show the area surrounding Chicago, Illinois, using nightlight data from the Operational Linescan System(OLS) onboard a Defense Meteorological Satellite Program (DMSP) satellite released in 2003 (left), the Visible Infrared Imaging Radiometer Suite “Day/Night Band,” or VIIRS DNB, in 2012 (middle), and the VIIRS DNB in 2016 (right). When you look at the images side by side, the OLS image appears coarse and blurry compared to the high-precision VIIRS images from 2012 and 2016. The most readily noticeable difference in these nighttime composite views of Chicago and surrounding areas in 2012 and 2016 is lighting along a recently expanded section of Interstate 90. This part of the highway, the Jane Addams Memorial Tollway, links Chicago with Rockford, Illinois, to the northwest.

Since the 1960s, the U.S. Air Force has operated the DMSP, a series of 18 polar-orbiting satellites. Starting in 1972, the DMSP satellites included the OLS, which gives weather forecasters some ability to see in the dark. In 2011, a new source of satellite images of Earth at night became available from the VIIRS “Day/Night Band,” or DNB, onboard the Suomi National Polar-orbiting Partnership (NPP) satellite. The VIIRS DNB can observe dim light down to the scale of an isolated highway lamp or fishing boat. It can even detect faint, nocturnal atmospheric light—known as airglow—and observe clouds lit by it.

Thanks to advancements in sensor technology and improved optics, the VIIRS DNB is ten-to-fifteen times better than the OLS sensor at resolving the relatively dim lights of human settlements and reflected moonlight. Each VIIRS pixel covers a distance of roughly 0.46 miles (742 meters) across, compared to the 1.86-mile (3-kilometer) footprint of OLS.