• Login
  • Register

Work for a Member company and need a Member Portal account? Register here with your company email address.

Project

Bounce-Flash Lidar

Copyright

Connor Henley

Connor Henley

In photography, illuminating a subject directly using an on-camera flash can result in unflattering photos. To avoid this, photographers often choose to illuminate their subject indirectly by bouncing light off of a diffusely reflecting surface such as the ceiling or a nearby wall. This technique is known as bounce flash. Inspired by this technique, we introduce a new variation on flash lidar imaging that we refer to as bounce-flash lidar. In our method, we use a focused laser source to illuminate a spot on a diffusely reflecting surface. Light that scatters from this spot will subsequently illuminate other points in the scene. We ascertain the position of the laser spot using the time of flight of photons that are scattered directly backwards towards the camera. The first signal that returns from the indirectly illuminated points will have scattered exactly twice. We use the two-bounce travel-time, along with our knowledge of the laser spot's position, to compute the position of each indirectly illuminated point. In effect, a bounce-flash lidar is equivalent to a bistatic flash lidar that has a transmitter embedded within the scene itself, at the position of the laser spot. 

Copyright

Connor Henley

Bounce flash illumination is significantly more flexible than direct illumination.  With a bounce-flash system, any point in the scene that is visible to both the transmitter and the receiver can be turned into a light source.  This source might, for example, be placed very close to an object of interest in order to boost the intensity of the return signal.  Alternatively, the position of the source might be chosen to enable observation of a highly specular surface—such as a mirror or a window—that would be effectively unobservable if illuminated directly due to its weak retro-reflective return.  By scanning the laser beam, the position of the projected light source can also be rapidly re-positioned without physically moving the lidar system. The ability to introduce diverse scene illumination allows bounce flash systems to observe important cues for shape and material properties that might be invisible to typical lidar systems, and that could potentially aid target identification.                 

Copyright

Connor Henley

We develop the fundamental principles of using bounce-flash illumination for lidar imaging.  We demonstrate simple methods for deriving range and reflectance images of a scene using bounce-flash measurements, and for combining the information acquired using multiple projected light source positions.  We also demonstrate that the cast shadows that are observed in the two-bounce signal can be used to estimate the shape of hidden objects and occluded surfaces.  This capability is inaccessible to typical monostatic lidar systems, which cannot observe cast shadows when direct illumination is used.                   

Copyright

Connor Henley