1. An apparatus comprising: a lidar sensor that scans in two or more directions relative to the apparatus over a series of scanning cycles; and one or more computer processors in communication with the lidar sensor, wherein the one or more computer processors are programmed to: compute a correspondence between pulses from the lidar sensor and sensed returns from the pulses using a map of a surrounding environment of the apparatus; compute a time-varying pulse repetition rate (PRR) schedule for the lidar sensor for each of the two or more directions, wherein the one or more computer processors compute the PRR schedule based on information about surrounding terrain of the apparatus and a sensor pointing schedule for the lidar sensor that indicates directions that the lidar sensor is scheduled to point at times during the scanning cycles, wherein the lidar sensor is controlled according to the computed PRR schedule; and continuously update the map of the surrounding environment based on the sensed returns from the pulses.