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identified. One problem here was the fact that the beam of the non-prism infra-red laser- 
ranger used had a diameter of 20cm from a distance of 100m. Dowels with differing diameters 
(25, 19, 10mm) were used as the subjects during the identifying precision tests, and the 
measurement distance was alternated at variable distances between 60m and 120m. With the 
fact that the beam has a diameter of 20cm ata distance of 100m as a basis, we obtained the 
relationship between varying distances and the ratio of the beam (surface area ratio) on the 
surface of the dowels. The results of these tests are indicated in fig.2. 
  
  
  
   
  
  
  
  
  
  
  
  
   
    
  
  
  
  
Dowel (25mm) 
50 
& 40 
8 3) 
= Ratio of area 
= 2 ! 
Unable to detect 
9 10 160 
A x 
= 0 
0 40 a) 120 
Distance(m) 
Dowel (19mm) Dowel (10mm) 
50 50 
S 40 S 40 
8 S 
- D = X 
1 Ci- 
o 2 Ratio of area o 20 Ratio of area 
2 10 Unable to detect 2 in 
= T: / Unable to detect 
S 0 7 d 0 RE ] 
0 40 60 120 160 0 40 860 120 16) 
Distance(m) Distance(m) 
  
  
  
Figure 2. Relationship Between Varying Distance and The Ratio of The Beam 
on The Surface of The Dowels 
2-5 Summary of Test Results 
Ye confirmed the fact that measurement values taken with a non-prism laser-ranger did not 
change even though the types of the objects measured differed and the measurement distances 
were alternated in laboratory and field tests. This led us to believe that we could rely on 
the measurement values obtained in the following stage by measuring the ground surface with 
a non-prism laser-ranger from a helicopter. In further detail, this meant that we could 
measure distances with an accuracy level of 3:50mm from an aerial position 100m and 150m up 
in the continual mode with precision levels set at--20mm. We also discovered that we could 
measure all objects with a size of 10% or more of the beam s surface area (approximately 
31. 4c nf at 100m - a circle with a diameter of 3.2cm or an object of the same area). Having 
obtained these results, we prepared a bridge over a pond and continually measured the 
distance between the parapet and the ground surface. The conditions below the bridge are 
indicated in fig.3., and the cross-sectional profile we obtained is indicated in fig. 4. The 
plants on the slope of the pond and the railings of the scenic path were clearly captured. 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences", Zurich, March 22-24 1995