Empirical study of variation in lidar point density over different land covers

Point density in airborne lidar surveys is one of the key parameters that influence not only the accuracy of generated DSM/DEM but also processing and costs. Point density variations occur (independently of keeping constant flight parameters) throughout the survey depending on the topography, the land cover, and the laser scanning mechanism. In this article, variations in point density across different land covers are analysed with an airborne oscillating mirror laser scanner. A wide group of samples from the different land covers is taken from single flight strips over level ground in order to minimize the effect of topography. The influence of the oscillating mirror laser scanner system is also minimized considering points along the central swath area. Mean values for each land cover are established regarding ground point density and first pulse returns. Significant differences in both raw points as well as on-the-ground points are registered, mainly due to the presence of features over the ground and the degree of opacity thereof. Regarding ground points, the relative differences between the two software packages used are 5% approximately. Significant point density differences can be found among the six analysed land covers. Furthermore, extrapolated pulse rate increments are presented to fulfil lidar specifications that neglect land cover as an input parameter to satisfy ground point density values, namely in non-overlapping areas.