An improvement on accuracy of laser radar using a Geiger-mode avalanche photodiode by time-of-flight analysis with Poisson statistics

A new technique to improve the accuracy of direct detection time-of-flight (TOF) laser radar using a Geiger-mode avalanche photodiode (APD) by reducing range walk error is presented. The range walk error refers to the change of the measured distance as a function of the waveform and energy of the laser-return pulse scattered from the target. The technique is based on the theoretical model, established with Poisson statistics, of the system and it enables to overcome the inherent limitation of Geiger-mode APD so that the mean number of photons of the laser-return pulse is expectable within the range in which the target detection probability varies. The theoretical model for the detection probability of each time bin in a TOF histogram is derived after it is experimentally proved that the creation of primary electrons in the Geiger-mode APD is Poisson-distributed. It is shown that the range walk error depends on the energy of the laser-return pulse at the Geiger-mode APD with the theoretical model regarded as the TOF histogram of multiple laser pulses in a single-hit case. The method which reduces the range walk error with the center of mass detection in the TOF histogram is then proposed, and the experiment for its proof is carried out. The experimental results show that the theoretical model is appropriate and the range walk error is reducible within the range in which the detection probability varies.