Day/Night Band (DNB) is apart of 22 spectral channels on the VIIRS instrument, in which VIIRS is on-board S-NPP and NOAA-20 satellites. DNB can assist users in monitoring atmospheric and surface features via emitted and reflected light sources, during the nighttime. Features identified by DNB (but not limited to), span from observing cloud cover, snow cover, lightning, auroras, sea ice, ship lights, fires, gas flares, lights from volcanoes and city/town lights. But what DNB can also observe are other low-earth orbiting satellites placed lower in altitude than S-NPP and NOAA-20.
Two prime examples are seen in the DNB imagery below. Images are taken on 4 December 2018 @ ~15Z, and 5 December 2018 @ ~10Z and are courtesy of RAMMB Slider.
Low-earth orbiting satellites observed by DNB exhibit a ‘line of bright dots’ that are sequentially produced in a direction via VIIRS’ scan lines. The dots have bright signatures via sunlight reflecting off the satellite, that DNB observes. Notice in the two examples below that emitted city lights of Alert, Nunavut, Canada can be seen, along with sea ice (i.e. located along the coast of Canada and Greenland) and an aurora.
DNB –> 4 December 2018, @ ~15Z
DNB –> 5 December 2018, @ ~10Z