SilviLaser 2011, Oct. 16-20, 2011 – Hobart, AU 1 Effect of scan coverage on stem diameter measurement using terrestrial lidar Akira Kato 1 , L.Monika Moskal 2 & Tatsuaki Kobayashi 3 1 GraduateSchool of Horticulture, Chiba University, Japan akiran@faculty.chiba-u.jp 2 Precision Forestry Cooperative, College of the Environment, School of Forest Resources, University of Washington, USA lmmoskal@u.washington.edu 3 GraduateSchool of Horticulture, Chiba University, Japan ktatsu@faculty.chiba-u.jp Abstract This paper presents a new approach to measure stem diameters based on the data acquired by multiple scanning by terrestrial lidar. Recent terrestrial lidar (Riegl VZ400) has wider coverage and is able to efficiently provide the highest point density data. Stem diameter derived from terrestrial lidar was compared with field measured diameter at breast height (d.b.h) of 42 sample trees. Stem returns of d.b.h were extracted and used to identify the approximated stem centre using principal component analysis. Various scan coverage of stem returns was used in the algorithm developed in this study to assess which is the most appropriate to measure stem diameter. The results show that more than 40% scan coverage of stem returns can produce stem diameter with the error of 5 cm or less using the algorithm. The applied technique can also assess the quality of wood by estimating straightness of stems from the alignment of stem centres at several heights. Furthermore, stem volume which is the most important variable to estimate the amount of carbon can also be measured directly using this technique. Keywords: Stem diameter, Scan angle, Stem volume, Terrestrial lidar, Principal component analysis 1. Introduction Above-ground carbon and woody biomass can be predicted using allometric equations with predictor variables such as diameter at breast height (d.b.h) and tree height. Tree parameters derived from remotely sensed data may be used as the inputs in the equations. The effectiveness of airborne Light Detection and Ranging (lidar) to acquire such tree parameters has been demonstrated across a wide range of forest types (Andersen et al., 2006, Hyyppä et al., 2001, Kato et al., 2009, and Næsset & Økland., 2002). The applicability of airborne lidar may however be limited by available facilities and cost, which depends on the distance from the airport and the flying time involved in data acquisition, among other things. For this reason airborne data collection is not always feasible in developing countries. Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (REDD) projects focus on the change in the amount of carbon sequestered in forests. Carbon change can be monitored using airborne lidar. But even if airborne lidar is the most promising technology to measure tree parameters (Patenaude et al., 2003), the airborne sensor itself may not be available in the developing countries. With the recent development of terrestrial lidar a more mobile sensor has become available to acquire high quality data for forest assessment. Even if terrestrial lidar does not offer the area coverage of airborne lidar and is less suitable for the measurement of total tree height, it is comparatively more suitable for the measurement of diameter, which is strongly correlated with biomass and carbon. To monitor the change in the amount of carbon in developing countries, terrestrial lidar is well suited since it can save and display the data in three dimensions, which