Description: Shadows appear in the images as the result of light being shone, or blocked (e.g. by clouds) on part of the image over short periods of time. High levels of shadow appear during the sunrise and sunset periods each day; and may also appear during other parts of the day dependent on weather and visibility conditions.
Features / Attributes:
The shadows appear as building silhouettes in the background subtracted image. A feature we can use to distinguish shadows from plumes are the distinct edges and outlines of the buildings characteristic of the shadow when compared with the free-form characteristic of plumes.
Source of contamination: The shadows appear as a source of noise for detection of pollution plumes as they result in very dark spots and differences in the background subtracted images. This may appear like the originating source of a plume as typically the shadows are dense and can change a lot between images. The shadows can also move between images as the light or cloud moves across the image, although typically movements are horizontal across the image, rather than a rise into the air like plumes do.
Issues / challenges: Frequency and form of shadows can vary considerably across images. The objective of tagging shadows is to provide examples of inter-image motion that are not plumes to improve the model's precision.