Description: Lights appear in the skyline at different time periods, most frequently before sunrise and after sunset. Lights are also observed on the tops of buildings and tall structures as collision avoidance measures for aircraft which may fly overhead.
Features / Attributes: The lights appear again as small, round objects in the skyline and present as bright areas in the original image. The lights may appear in single images such as flashing warning lights atop building, or consecutive images when they are switched on, or off.
Source of noise: Lights are a densely concentrated object in the differenced image. They appear very similarly to when smoke clouds initiate, although they are stationary and do not dissipate in subsequent images like the pollution clouds do.
Issues / challenges: The lights comparably easy to identify for tagging, relative to clouds and shadow. They appear as a very pronounced difference in the background subtracted images, with a static shape over time.
Ambiguous identifier