  Image degradation impedes our ability to extract information from
astronomical observations. One factor contributing to this degradation is
``dome seeing", the reduction in image quality due to variations in the index
of refraction within the observatory dome. Addressing this challenge, we
introduce a novel setup-DIMSUM (Differential Image Motion Sensor Using
Multisources)-which offers a simple installation and provides direct
characterization of local index of refraction variations. This is achieved by
measuring differential image motion using strobed imaging that
effectively``freezes" the atmosphere, aligning our captured images with the
timescale of thermal fluctuations, thereby giving a more accurate
representation of dome seeing effects. Our apparatus has been situated within
the Auxiliary Telescope of the Vera C. Rubin Observatory. Early results from
our setup are encouraging. Not only do we observe a correlation between the
characteristic differential image motion (DIM) values and local temperature
fluctuations (a leading cause of variations in index of refraction), but also
hint at the potential of DIM measures to characterize dome seeing with greater
precision in subsequent tests. Our preliminary findings underscore the
potential of DIMSUM as a powerful tool for enhancing image quality in
ground-based astronomical observations. Further refinement and data collection
will likely solidify its place as a useful component for managing dome seeing
in major observatories like the Vera C. Rubin Observatory.
