NPP's Ozone Mapping and Profiler Suite (OMPS) Limb instrument first observed the dust plume from the explosion about 1,100 kilometers east of Chelyabinsk, due to the location of the satellite's orbit. NPP's second observation was farther west, close to Chelyabinsk, because the spacecraft's orbit moves from east to west. The third observation of the plume occurred the day following the event. The OMPS instrument could only see the plume during the daytime, and the NPP orbit had progressed westward away from the plume and into night by the time it was again over the plume.
The OMPS Limb instrument observations are made by looking backward (relative to NPP's orbit) toward the Earth's limb. The instrument makes measurements through three separate slits. Early on, some of the plume observations where only made in one or two of the slits, but later observations tended to include all three slits as the plume stretched out.