Lidar based distance measurements with tiered power control

Methods and systems for controlling illumination power of a LIDAR based, three dimensional imaging system based on discrete illumination power tiers are described herein. In one aspect, the illumination intensity of a pulsed beam of illumination light emitted from a LIDAR system is varied in accordance with a set of illumination power tiers based on the difference between a desired and a measured return pulse. In a further aspect, the illumination power tier is selected based on whether an intensity difference exceeds one of a sequence of predetermined, tiered threshold values. In this manner, the intensity of measured return pulses is maintained within a linear range of the analog to digital converter for objects detected over a wide range of distances from the LIDAR system and a wide range of environmental conditions in the optical path between the LIDAR system and the detected object.