ISPRS Commission III, Vol.34, Part 3A „Photogrammetric Computer Vision“, Graz, 2002 
  
ASSESSMENT OF FOREST PARAMETERS BY MEANS OF LASER SCANNING 
* Mathias Schardt, * Michaela Ziegler, ^ Andreas Wimmer, * Roland Wack & " Juha Hyyppä 
* Institute of Digital Image Processing, Joanneum Research, Austria - (mathias.schardt@joanneum.ac.at) 
? Finnish Geodetic Institute, Finnland 
Commission III, WG III/3 
Key words: Forest Inventory, Laser Scanning Data, Segmentation 
ABSTRACT: 
This paper deals with forest inventory methods based on laser scanning and satellite remote sensing. It will be demonstrated to what 
extent forest inventories can benefit from the synergistic use of both sensor types. The forest inventory parameters to be assessed are: 
tree height, timber volume, tree species, tree age, stand boundary, and basal area. The results presented are derived from the 
"HIGHSCAN"' project (Assessing forest stand attributes by integrated use of high-resolution satellite imagery and laser scanner) 
which is coordinated by the Helsinki University of Technology and financed by the EU, DG XII. Developments have been carried 
out in close co-operation with forest management authorities, in particular with private forest owners. In this paper the results derived 
from the Austrian test sites will be presented. 
1. BACKGROUND 
In the Austrian Federal Forests and those belonging to large 
forest owners, forest inventories are performed every ten years 
on a stand-wise basis using cost-intensive field surveys in com- 
bination with yield tables. Inventory data for small forest own- 
ers are collected on the basis of questionnaires (Wood Felling 
Reports). Inventories of a similar intensity to those taken for the 
national forests and large forestry companies are carried out 
only for those small forest owners which have combined into 
agricultural associations. The proportion of small forest owners 
participating in agricultural associations is very small, therefore 
field inventories are only carried out to a limited extent. It may 
therefore be concluded that small forest owners, which actually 
own 65 % of the total area of Austrian forests, lack optimal 
planning data. 
The investigation concentrates on private forest owners since 
the lack of reliable forest inventory data is far more critical in 
this sector than is the case for federal forests or large forest 
owners. In order to overcome these shortcomings inventory 
methods are required which are capable of gathering inventory 
data in an effective manner. 
2. APPROACH 
Laser scanner data have the potential to assess forest parame- 
ters. The most important parameters required by forest owners 
is timber volume and tree height, which can be indirectly de- 
rived at stand or tree level. To classify these parameters the 
following approaches were tested in this study. 
Statistical stand-wise approach 
One approach to be used in this investigation is to determine the 
mean tree height of stands using merely statistical techniques 
(Naesset et al., 1997). This method demands the availability of 
digitized stand boundaries stored in a GIS system. Using this 
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method, noise reduction with different mean value calculation is 
first applied to the tree surface model. In a second step the tree 
height is determined by calculating the differences of the sur- 
face model derived from the last pulse data and the crown 
model derived from the first pulse data. Since laser scanner data 
systematically underestimate tree height, empirically derived 
correction offsets must be introduced to correct the data. Naes- 
set et al. (1997) found out that the accuracy of a stand-wise 
estimation of tree height outperformed traditional estimates for 
their test areas. In a next step timber volume can be derived 
from the average tree height using yield tables available for 
most of the forest regions in Austria. One restriction of the 
statistical stand wise approach is that this method can only be 
used in pure stands. 
Tree-wise approach 
Although the statistical methods are very simple, the full poten- 
tial of the high resolution laser scanner data cannot be utilized. 
In addition to the statistical stand-wise approach, this investiga- 
tion was therefore also aimed at classifying the inventory pa- 
rameters on the basis of single trees. The tree-wise approach 
assesses the following basic parameters directly from laser 
scanner: 
- Tops of trees 
- Segmented tree crowns or groups of crowns 
- Forest floor model 
In a second step timber volume can be derived on the basis of 
increment models using the above listed basic parameters: 
- Breast height diameter derived from tree height and crown 
diameter 
- Timber volume of single trees: 
" derived from the basic parameters tree spe- 
cies, tree height and crown diameter 
- Timber volume on a stand basis: 
" derived from the basic parameters tree spe- 
cies, tree height, crown diameter and num- 
ber of trees in a stand