The present disclosure relates to systems and methods for occlusion detection. One example method involves a light detection and ranging (LIDAR) device scanning at least a portion of an external structure within a field-of-view (FOV) of the LIDAR device. The LIDAR device is physically coupled to the external structure. The scanning comprises transmitting light pulses toward the external structure through an optical window, and receiving reflected light pulses through the optical window. The reflected light pulses comprise reflections of the transmitted light pulses returning back to the LIDAR device from the external structure. The method also involves detecting presence of an occlusion that at least partially occludes the LIDAR device from scanning the FOV based on at least the scan of the at least portion of the external structure.