  One of the challenges of Unmanned Aircraft System (UAS) operations is to
operate an unmanned aircraft with minimal risk to people on the ground. The
purpose of this study is to define and measure such risks as population risk,
by incorporating spatiotemporal changes in population density. Unlike previous
studies, we use high-resolution de facto population data instead of residential
population data to reflect the spatiotemporal characteristics of population
distribution. Furthermore, we analyze the impact of mitigation measures based
on population risk in the context of airspace management. We set a restricted
airspace by using population risk and an acceptable level of safety. Scenario
analysis of the study area in Seoul, South Korea provides a richer set of
findings regarding spatiotemporal differences in restricted airspace. During
the daytime, there are many restricted airspaces around commercial areas, but
few around residential areas. Additionally, we observe the difference between
restricting airspace based on population risk derived from the residential
population and from the de facto population. These findings confirm the
importance of accurately considering population density when assessing and
mitigating the population risk associated with UAS operations. Sensitivity
analysis also reveals the need to precisely estimate population density when
estimating population risk with combinations of multiple parameter values. The
proposed approach captures spatiotemporal characteristics of population
distribution when assessing the population risk associated with UAS.
