2002. Generalized 
studies of species 
al Modeling, 157: 
| considerations in 
s to remote sensor 
approach, Swain P. 
-289. 
nage Processing-A 
on Education, Inc, 
xent modeling for 
1d endangered tree 
nia. Ecology and 
. Trees of Taiwan. 
culture, National 
sural networks as a 
uction. Ecological 
/. Chipman, 2008. 
5th Edition. John 
Generalized linear 
p. 512. 
3. Schapire, 2006. 
ecies — geographic 
-259. 
odeling of species 
tensions and a 
61-175. 
as mapped from a 
phical Information 
Lavergne and A. G, 
jecies distributions 
dron species in the 
09, 
  
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
DEVELOPING A 3D WAVEFORM LIDAR SIMULATOR FOR FOREST 
T. ENDO', Y. SAWADA, T. KOBAYASHI and H. SAWADA® 
" International Center for Urban Safety Engineering, Institute of Industrial Science, The University of Tokyo 
^ SE laboratory, Space Applications Mission Directorate, JAXA 
tendo@iis.u-tokyo.ac.jp 
Commission VIII, WG VIII/7 
KEY WORDS: Simulation, 3D full polygons, Echo signal, TEM, Visualization 
ABSTRACT: 
Waveform LiDAR systems is widely used in several fields such as terrain survey, disaster monitoring and forest monitoring. 
Especially, in forest research, using an echo signal is expected for understanding structural characteristics of the forest. However, an 
echo signal highly depends on the sensor configuration, the footprint size, the canopy structure, and terrain condition. Therefore, it is 
not easy to understand the forest attributes from the echo signal. In this paper, we describe the development and application of model 
which to simulate laser intersections within ideal forest environments and to visualize intersections. The developed model has three 
components. The first component was a creation of the forest environment as full polygon in 3DCG software. Characteristics of the 
forest was decided by individual trees which were generated by the plant growth model using species and planting years as the initial 
parameter. The second component was a simulation using a ray tracing to calculate intersections between the forest object and the 
modelled laser beam. In this study, a laser beam with a specific footprint and a pulse width was defined by spatiotemporal features. 
In point of view of spatial feature, numerous sub laser beams were generated within a specific footprint to make the laser beam hit 
the target uniformly. Each sub laser beam had the intensity which was calculated by both the distance from the center of laser beam 
and the TEMpp. On the other hand, in point of view of time feature, each sub laser beam was defined as several particles based on the 
sampling rate. Each particle had the intensity which was calculated by the pulse width and the sampling rate. The third component 
was a creation of an echo signal of a specific footprint using the calculated intersections and its intensity, reflectance of target at 
intersections and sampling rate. Moreover, the developed model had a view function that was able to show the calculated 
intersections on the surface of target object. As results of simulation of ideal forest environment scenarios, the developed model 
demonstrated that the model generated the echo signal of different environments well and the viewer function helped to understand 
the interactions between sub laser beams and target objects. 
1. INTRODUCTION 
Waveform data provides a valuable echo dataset for assessing 
forest structural attributes. However, it is not easy to interpret 
generation mechanisms of the echo signal of the forest. Because, 
the echo signal is dependent on the sensor configuration, the 
footprint size, the canopy structure and terrain condition. Many 
researchers have studied these influences using an actual data or 
a simulated data. Naeasset (2004) demonstrated that differences 
in footprint size affected echo signal. Clark et al, (2004) 
showed that slope and vegetation density have been identified 
as variables which influence the accuracy of Digital Elevation 
Model (DEM) . 
In order to understand the relationship between the echo 
signal and the sensor configuration and the target environment, 
à simulation model is useful. Sun and Randon (2000) developed 
the simulator for large footprint LiDAR that generated an echo 
signal using a forest 3D model and a radiative transfer model. 
Also, Goodwin et al. (2007) developed a simulator that 
generates an echo signal using the LITE model and a ray tracing 
approach. Overall, a definition of the forest structure is quite 
Important in order to simulate an echo signal. 
In this study, the development of new LiDAR waveform 
Simulator using targets defined as full polygons discussed. The 
simulator used full polygons as the target environment to avoid 
an effect of gap probability. Intersections between the laser 
cam and the target was simulated by a ray tracing approach. 
An echo signal was calculated by intersections, reflectance at 
intersections, the pulse width, the sampling rate, and the 
Intensity. In this paper, firstly, a detailed description about the 
developed model is given, and secondly, results of several 
scenarios are described. 
2. FEATURES OF THE DEVELOPED MODEL 
The developed model has several features. Firstly, targets 
such as the forest and terrain dataset are defined as full 
polygons in a 3DCG space. Secondly, phenology of the forest in 
the developed model is variable, since the plant growth model is 
used to generate the forest data. Thirdly, the illumination angle 
and the footprint size are variable. Fourthly, a laser beam is 
defined as sub laser beams with the intensity based on TEM, in 
point of view of spatial feature. Also, sub laser beams are 
defined as particles in point of view of time feature. Numbers of 
particles are based on the sampling rate and the pulse width. 
Finally, intersections are visualized in 3DCG space to help 
understand an echo signal generation procedure. 
3. DEVELOPMENT ENVIRONMENT 
The development environment in this study shows as Table 1. 
Commercial 3DCG software was used to generate intersections 
using full polygons and a ray tracing approach. Matlab was used 
to generate an echo signal. Merits of using 3DCG software are 
the followings: using the commercial plant growth model 
software as add in for the 3DCG software, handling a large 
amount of polygons easily, calculating the angle between leaf 
inclination and the direction of laser beam easily and the 
availability of an external DEM dataset.