It looks like a Velodyne HDL-32 [1] LiDAR unit. Broadly speaking, it pulses a bunch of lasers (32 in this case) really fast and measures the response time of each beam; think hyper-focused radar. The resulting point cloud can be used to build a high res map of its surroundings essentially in realtime.

1. http://velodynelidar.com/lidar/hdlproducts/hdl32e.aspx