Simulation and modeling of return waveforms from a ladar beam footprint in USU LadarSIM

Abstract

Ladar systems are an emerging technology with applications in many fields. Consequently, simulations for these systems have become a valuable tool in the improvement of existing systems and the development of new ones. This paper discusses the theory and issues involved in reliably modeling the return waveform of a ladar beam footprint in the Utah State University LadarSIM simulation software. Emphasis is placed on modeling system-level effects that allow an investigation of engineering tradeoffs in preliminary designs, and validation of behaviors in fabricated designs. Efforts have been made to decrease the necessary computation time while still maintaining a usable model.A full waveform simulation is implemented that models optical signals received on detector followed by electronic signals and discriminators commonly encountered in contemporary direct-detection ladar systems. Waveforms are modeled using a novel hexagonal sampling process applied across the ladar beam footprint. Each sample is weighted using a Gaussian spatial profile for a well formed laser footprint. Model fidelity is also improved by using a bidirectional reflectance distribution function (BRDF) for target reflectance. Once photons are converted to electrons, waveform processing is used to detect first, last or multiple return pulses. The detection methods discussed in this paper are a threshold detection method, a constant fraction method, and a derivative zero-crossing method. Various detection phenomena, such as range error, walk error, drop outs and false alarms, can be studied using these detection methods.

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“…We model the emission of the light pulse P e (t) with a Gaussian of length τ and power I 0 as done in [15]…”

Simulation of a Doppler lidar system for autonomous navigation and hazard avoidance during planetary landing

“…To allow for multiple targets in the beam footprint, for non-uniform beam profiles, and for beams impinging on a sloped surface, the beam footprint is sampled and each "beamlet" is modelled individually. 5 The effect of this modelling for multiple returns or sloped surfaces is spread in the spectrum of f b .…”

The Development of a 3D LADAR Simulator Based on a Fast Target Impulse Response Generation Approach

“…More advanced and complex models [13,17,35,38,48,49], can be used to simulate the propagation of the laser beam, for example, from laser energy distribution to atmospheric effects and beam interaction models, to receiver optics and received signal processing electronics models. However, this study is focusses on evaluating the processing speed of the Fig.…”

“…This distribution is defined by the laser pulse energy E t in a unit of joules and pulse width s (full-width at halfmax power in a unit of seconds). The following equation [13,34] is used to model this distribution:…”

“…In consequence, simulations for LADAR systems have become a valuable tool for developing said systems and their data processing algorithms [13] because the simulator is able to produced LADAR images under different controlled effects, which enable the algorithms' developers to evaluate their algorithms under these effects individually. In order to simulate these systems, a target impulse response must be generated for each laser pulse transmitted to the components of the target.…”