  The goal of non-line-of-sight (NLOS) imaging is to image objects occluded
from the camera's field of view using multiply scattered light. Recent works
have demonstrated the feasibility of two-bounce (2B) NLOS imaging by scanning a
laser and measuring cast shadows of occluded objects in scenes with two relay
surfaces. In this work, we study the role of time-of-flight (ToF) measurements,
\ie transients, in 2B-NLOS under multiplexed illumination. Specifically, we
study how ToF information can reduce the number of measurements and spatial
resolution needed for shape reconstruction. We present our findings with
respect to tradeoffs in (1) temporal resolution, (2) spatial resolution, and
(3) number of image captures by studying SNR and recoverability as functions of
system parameters. This leads to a formal definition of the mathematical
constraints for 2B lidar. We believe that our work lays an analytical
groundwork for design of future NLOS imaging systems, especially as ToF sensors
become increasingly ubiquitous.
