Two Methods to Estimate the Spot Size of Terrestrial Laser Scanners

Abstract

This technical note presents the results of a study focused on the evaluation of laser beam divergence and its effect on the spot size of terrestrial laser scanners. For this purpose, experiments were accomplished using the Leica HDS3000 and HDS6000 laser scanners. Two methods for the evaluation of the spot size are compared: a direct method, based on the analysis of the capacity of the laser beam to go through small slots, and an analytical method that estimates the spot diameter based on the edge effect. Based on the performed experiments, the development of a conceptual model of the edge effect at sharp edges is described for each method and validated. The experiments proved that the methods are suitable to analyze the variation of the diameter of the spot as a function of the distance. The estimate of the spot size using slots of varying sizes is a direct and easy to use method, but the computation of the spot size using the sharp edge model is more stable in relation to the point density, and can be used to estimate the divergence of the laser beam and the expectable spot size before a survey is performed.