LiDAR-SPD: Improving Adversarial Robustness of 3D Object Detection via Spherical Projection and Diffusion

The advancements in light detection and ranging (LiDAR) sensors and 3D object detection techniques have boosted their deployment in a wide range of applications, autonomous driving, in particular. However, it has been demonstrated that 3D object detection models based on deep neural networks exhibit vulnerabilities and tend to be susceptible to adversarial attacks. Nonetheless, there exists a scarcity of defensive strategies explicitly tailored for mitigating adversarial attacks on 3D object detection. In this paper, we introduce LiDAR-SPD, a novel approach to defend against adversarial attacks targeting LiDAR-based 3D object detectors. Specifically, a spherical purification unit is designed, which encompasses two pivotal processes: spherical projection and spherical diffusion. The former leverages a spatial projection strategy to eliminate adversarial point clouds inserted in occluded regions, while the latter employs a diffusion model to regenerate points, rendering it closer to a pristine LiDAR scene. Comprehensive experiments conducted on the KITTI dataset demonstrate that our proposed LiDAR-SPD method effectively thwarts various types of adversarial attacks, decreasing the attack success rates against 3D object detectors by 60%.