Schardt, Mathias 
  
   
local grid 
   
Figure 1: TopoSys laser scanner principles, scan pattern (left) and first and last pulse mode (right) 
1. The assessment of information on stand level is only possible in very large and homogeneous stands due to limitations 
in geometrical resolution of sensor types available at this time. 
2. The attained accuracy level is suitable for small scale inventories at a scale of 1 : 50.000 and less but not for detailed 
inventories on stand and district level (1:10.000 to 1:25.000). 
3. Not all inventory relevant parameters such as tree height, tree volume, vertical stand structure, under-storage, etc. 
can be derived directly from satellite remote sensing. 
Nevertheless, it can be expected that in future with the availability of very high resolution satellite systems such as 
IKONOS or SPOT V the assessment of information on stand and district level will be possible with the thematic accuracy 
depicted in table 2. 
3 APPLICATIONS OF LASER SCANNING FOR FOREST INVENTORY 
Measurement principle of a laser scanner 
Laser scanning allows the measurement of the distance between aircraft and the earth’s surface. The scanning mechanism 
sweeps the laser beam across the flight line. By knowing the position and orientation of the sensor in the aircraft, the 
measured distances can be converted into elevations (see figure 1). The position of the sensor can be measured with an 
accuracy of about 0.1 m with sensitive and noise suppressing kinematic DGPS receivers, additionally a corresponding 
reference station must be placed within or close to the surface area. Sensor’s orientation is obtained with a better accuracy 
than 0.2 mrad using a precise measurement device (INS)(Hyyppä et al., 1999, Samberg et al., 1999). 
All data presented in this study have been recorded for the EU-project High-Scan. Investigations are carried out in two 
Austrian test sites, a mountainous (Alpine) test site characterized by high relief energy and steep slopes (ranging from 
1200 - 1700 m) and a test site located at the south-eastern border of the Alps with typical small structured hilly terrain 
characterized by moderate height differences (ranging from 250 - 400 m) and small troughs and hillocks. Concerning tree 
species the Alpine test mainly consists of spruce (94 %), the main tree species within the hilly test site are beech (30 %), 
spruce (30 %) and pine (15 %). 
The laser scanner campaigns were carried out with the scanner from TopoSys because of its high measurement density, 
steep viewing angle and capability to provide both the first and last pulse mode, see figure 1. High measurement density 
was required in order to be able to have a good separation within individual trees. Steep viewing angle enable to have 
good number of ground points hitted (Hyyppä et al., 1999, Samberg et al., 1999). The two different modes - first pulse and 
last pulse - are necessary to get ground information (last pulse) on the one hand and information from the crown surface 
on the other hand 
Pre-processing of laser scanner data 
The original data from the laser scanner - last pulse and first pulse - is originally in a format (raw data) where corresponding 
X, y and z coordinates were listed in rows. The data was transformed into the local coordinate system. 
  
1318 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 
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