Bounce-Flash Lidar

We introduce a new mode of lidar imaging called bounce-flash lidar . In bounce-flash lidar, most surfaces in the scene are illuminated indirectly by light that has scattered off of a nearby surface. We exploit the fact that a laser spot projected onto a diffusely reflecting surface can be treated as a point source. We use single-bounce time-of-flight measurements to determine the position of this point source, and then use a bi-static range equation to compute the position of indirectly illuminated points from two-bounce time-of-flight measurements. We propose and then experimentally demonstrate simple methods for estimating scene range and reflectance using the time-of-flight and intensity of one- and two-bounce returns. We also demonstrate two important advantages of using bounce-flash illumination in lidar imaging. First, two-bounce light carries information that the single-bounce returns do not. In particular, cast shadows can be used to estimate the geometry of occluded surfaces. Second, bounce-flash lidar systems enable strategic positioning of the illumination source. This source can be placed arbitrarily close to a target of interest, or positioned to enable observation of specular surfaces that would otherwise reflect very little light back towards the receiver.