  3D object detection is a central task for applications such as autonomous
driving, in which the system needs to localize and classify surrounding traffic
agents, even in the presence of adverse weather. In this paper, we address the
problem of LiDAR-based 3D object detection under snowfall. Due to the
difficulty of collecting and annotating training data in this setting, we
propose a physically based method to simulate the effect of snowfall on real
clear-weather LiDAR point clouds. Our method samples snow particles in 2D space
for each LiDAR line and uses the induced geometry to modify the measurement for
each LiDAR beam accordingly. Moreover, as snowfall often causes wetness on the
ground, we also simulate ground wetness on LiDAR point clouds. We use our
simulation to generate partially synthetic snowy LiDAR data and leverage these
data for training 3D object detection models that are robust to snowfall. We
conduct an extensive evaluation using several state-of-the-art 3D object
detection methods and show that our simulation consistently yields significant
performance gains on the real snowy STF dataset compared to clear-weather
baselines and competing simulation approaches, while not sacrificing
performance in clear weather. Our code is available at
www.github.com/SysCV/LiDAR_snow_sim.
