Seeing around corners using time of flight

The problem of seeing around corners, often referred in the broader "Non-Line-of-Sight" context, is to use sensed information from directly visible surfaces of an environment to infer properties of the scene not directly visible. For example, the geometry above presents a classic "around the corner" setting, where a flat wall is used as the visible surface, and the hidden scene is occluded by another wall. While many proposed sensing modalities have been proposed, including acoustic and RF signals, most approaches utilize photonic sensors in the visible spectrum due to the availability of hardware, and better temporal and spatial resolution. Approaches range from active time-resolved measurements, time-averaged continuous wave sources, and even to passive exploitation of ambient illumination.