THOR's most distinguishing feature is that its multiple wide field-of-views provide spatial and temporal information on multiple scattering processes that occur deep inside thick media such as thick clouds, snow, or sea ice. In contrast, most other lidars use a narrow field-of-view in order to reduce observational noise caused by background illumination, and consequently provide information only about a thin skin layer, because multiple scattering quickly spreads most photons outside their narrow field-of-view.

The initial focus of THOR data analysis has been retrieval of geometrical thickness. Such retrievals are possible because photons can reach distant parts of thick clouds, whereas they tend to leak out through the base of thin clouds (see figure below). As a result, THOR observes a larger bright halo for thicker clouds. In addition, the observed signal extends to longer times for thicker clouds, because photons spend more time traveling inside the cloud.

Details on THOR science areas: clouds, snow/sea ice