  The 2021 Champlain Towers South Condominiums collapse in Surfside, Florida,
resulted 98 deaths. Nine people are thought to have survived the initial
collapse, and might have been rescued if rescue workers could have located
them. Perhaps, if rescue workers had been able to use robots to search the
interior of the rubble pile, outcomes might have been better. An improved
understanding of the environment in which a robot would have to operate to be
able to search the interior of a rubble pile would help roboticists develop
better suited robotic platforms and control strategies. To this end, this work
offers an approach to characterize and visualize the interior of a rubble pile
and conduct a preliminary analysis of the occurrence of voids. Specifically,
the analysis makes opportunistic use of four days of aerial imagery gathered
from responders at Surfside to create a 3D volumetric aggregated model of the
collapse in order to identify and characterize void spaces in the interior of
the rubble. The preliminary results confirm expectations of small number and
scale of these interior voids. The results can inform better selection and
control of existing robots for disaster response, aid in determining the design
specifications (specifically scale and form factor), and improve control of
future robotic platforms developed for search operations in rubble.
