期刊名称：ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences
印刷版ISSN：2194-9042
电子版ISSN：2194-9050
出版年度：2004
卷号：XXXVI-8/W2
出版社：Copernicus Publications
摘要：Structural characteristics of forest stands, e.g. in relation to carbon content and biodiversity, are of special interest. It has been stated in numerous publications that discrete return laser scanner data produce accurate information on a tree canopy since the quantiles of the height distribution of laser scanner data are related to the vertical structure of the tree canopy. Since some of the laser pulses will penetrate under the dominant tree layer, it is also possible to analyse multi-layered stands. In this study the existence and number of suppressed trees was examined. This was carried out by analysing the height distributions of reflected laser pulses. In this laser data (Toposys Falcon, survey May 2003 in Kalkkinen, flight altitude 400 m AGL) the average number of laser pulse hits per 1 m 2 was 12. The reference data consisted of 28 accurately measured field sample plots. These plots include highly heterogeneous boreal forest structures. The existence of lower canopy layers, i.e. suppressed trees, was analysed visually by viewing the plotwise 3D-images of laser scanner based canopy height point data and examining distributions of canopy densities which were computed as the proportions of laser hits above different height quantiles. Furthermore, a developed histogram thresholding method (HistMod) was applied to the height distribution of laser hits in order to separate different tree storeys. Finally, the number and mean height of suppressed trees were predicted with estimated regression models. The results showed that multi-layered stand structures can be recognised and quantified using quantiles of laser scanner height distribution data. However, the accuracy of the results is dependent on the density of the dominant tree layer
