Small-footprint Laser Scanning Simulator for System Validation, Error Assessment, and Algorithm Development

Airborne lidar systems have come to be extensively used in photogrammetry and mapping sciences. In this paper, a high-quality simulation approach and methods of small-footprint lidar processing are presented and discussed, validated for tree height estimation, and demonstrated for scanning geometry effects analysis and mobile mapping. The simulation method implemented combines both spatial and radiometric components to produce realistic waveform and point cloud data for system performance analysis and for algorithm development for lidar data processing and mapping purposes. Waveform data generated by the simulator were shown to demonstrate the possibilities of such an approach in system and data verification. As the related empirical data are insufficient for effective research and exploitation in mapping purposes at the moment, the simulated waveform data are needed.A tree location accuracy of 15 cm and tree height underestimation of 0.33 m was found using the simulation model for the TopEye Mk II laser scanner, compared to the artificial forest model reference data. Modeling of light interaction on object surfaces and characteristics of scanning systems provide an opportunity to simulate laser data acquisition of well-defined objects under controlled conditions. By eliminating different sources of error case-by-case, we can improve the knowledge obtained merely from the experimental studies.Data validation in the scanning geometry simulations was carried out by comparing the simulated first echo data to the environment model and, separately, to the first echo data from an independent TopoSys II flight strip that was not used for the environment model computation. The mean differences reveal that the simulator slightly overestimates the object elevations. Deviation between the real TopoSys point cloud and the environmental model was 2 to 3 times larger than that obtained for the simulated Optech and TopoSys data sets.We believe that the developed simulation and modeling is an efficient tool for determining the most reasonable set of flight parameters for any current mapping task, for analyzing change detection possibilities of repeated laser surveys, and for studying and verifying future lidar systems and concepts. However, this requires high-quality modeling of the system and extensive knowledge of the interaction between the laser beam and the object, which should be further developed in the coming years.