Flash Lidar: Monte Carlo Estimates of Ballistic, Diffuse, and Noise Photons as Recorded by Linear and Geiger Detector Arrays

Abstract

Abstract : A description is provided of a model that estimates the numbers of ballistic photons, diffuse photons, and arriving at the focal plane array of a lidar, resulting from a series of pulses of laser energy directed at a target, in the presence of obscurant. Inputs to the model include laser wavelength, pulse energy, number of pulses integrated, obscurant optical depth (number of scattering lengths) and forward scattering factor, target range, target structure and reflectivity, lidar aperture diameter and focal length, pixel pitch, time bin, defector noise level, and an efficiency factor related to such parameters as optics transmissivity, beam-spreading factor, defector fill factor, and defector quantum efficiency. Model outputs include three-dimensional plots of numbers of ballistic, diffuse, and noise photons versus focal plane array (FPA) x and y coordinate, and time delay after first ballistic photon arrival, for both linear and Geiger-mode defector arrays. The model can be useful for performance prediction of flash lidars in the presence of obscurants. A procedure is provided for remapping Geiger images, to improve their interpretability. The model is also shown to agree with diffusion theory in the limits of large optical depth and small forward scattering factor.