information can not only be used for photographic scale determination but also for 
surveys which require topographic information, i.e. for road, railway and 
transmission line location, for hydrographic studies and for provision of vertical 
control for topographic mapping. The recording of the profiles on magnetic tape 
would provide a means for efficiently generating digital terrain models with a high 
density of data in the flight direction. This could be developed into an automated 
system for topographic mapping. 
2. The double trace capability of the system can generate a useable, general picture 
and measure of stand height. The forest profile from the radar altimeter is, 
however, subject to deviations along some stretches caused by the sampling and 
integration of readings. Other deviations can be attributed to large, dominant but 
open crowns which do not provide a sufficiently solid reflecting surface for the 
radar altimeter to react. This feature of the altimeter will be investigated further. 
On viewing Figure 6, one might ask: why not use the photogrammetric 
approach rather than the radar? In reply, first, the radar altimeter and tilt 
indicator were required in any event before the photogrammetric strip or "bridge" 
could be produced. Second, and more importantly, the radar record of the profile 
along the 1 km transect took 20 s to capture; the photogrammetric profile at least 
three hours. 
3. The species identification trial confirmed earlier findings (Sayn-Wittgenstein, 
de Milde and Inglis 1978) that a number of important species can be identified. It 
would be an interesting exercise to bring together, in the field, a sound knowledge 
of tropical tree species with a good background in photo interpretation. If quality 
of photography is good and photo scale right, there is little doubt that results 
obtained would satisfy most basic forest inventory requirements. 
Bibliography 
Aldred, A.H. and J.J. Lowe. 1978. Application of large-scale photos to a forest inven- 
tory in Alberta. For. Manage. Inst., Ottawa, Ont., Inf. Rep. FMR-X-107. 57 p. 
Nielsen, U. 1974. Description and performance of the forestry radar altimeter. For. 
Manage. Inst., Ottawa, Ont., Inf. Rep. FMR-X-59. 17 «vp. 
Nielsen, U. and A.H. Aldred. 1976. Can tropical forest inventories benefit from recent 
developments in aerial photography? Paper presented at the XVI IUFRO World 
Congress, Oslo, Norway. In Proc. published by Subject Group 56.05 Remote 
Sensing. 
Sayn-Wittgenstein, L. 1978. New developments in tropical forest inventories. Paper 
presented at the Twelfth Int. Symp. on Remote Sensing of Environ., Manila 
Philippines. 
Sayn-Wittgenstein, L., R. de Milde and C.J. Inglis. 1978. Identification of tropical trees 
on aerial photogrpahy. For. Manage. Inst., Can. For. Serv., Ottawa, Ont., Inf. Rep. 
FMR-X-113. 
Westby, R.L. 1967. A radar altimeter for forest inventory. Natl. Res. Counc. Can., 
Radio and Elec. Eng. Div., Bull. 17(1)146-49. 
Westby, R.L. 1975. Flight trials of the forestry penetrating radar altimeter in a tropical 
rain forest. Natl. Res. Counc. Can., Radio and Elec. Eng. Div., ERB-888. 9 p. 
      
  
  
  
  
   
   
   
  
    
  
   
  
   
     
   
   
   
  
   
   
  
   
   
   
   
  
   
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