basically the military took fewer pictures and worse pictures.

So, scientists have observed Earth’s nightlights for more than four decades, first with astronaut photography and military satellites. Since the 1960s, the U.S. Air Force has operated the Defense Meteorological Satellite Program (DMSP), a series of 18 polar-orbiting satellites that observe clouds and other weather variables in key wavelengths of infrared and visible light. Starting in 1972, the DMSP satellites included the Operational Linescan System (OLS), which gives weather forecasters some ability to see in the dark.

While DMSP has been a source of nighttime images for decades, until fairly recently the data were classified, which meant that only a few civilian scientists could conveniently gain access to study the data. The atmospheric science community was eager to have a more accessible night-vision tool to better understand weather and climate patterns and phenomena. Finally, in 2011, a new source of unclassified satellite images of Earth at night became available—one that improved upon the capabilities of OLS. The new low-light sensor was called the Visible Infrared Imaging Radiometer Suite (VIIRS), and was launched in October 2011 onboard the Suomi National Polar-orbiting Partnership (NPP) satellite—a partnership between NASA, the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Department of Defense

-- Earth at Night