surface. 
Recently, the Radio and Electrical Engineering 
Division of the National Research Council of Canada has 
developed a modified APR instrumentation which appears to 
have considerable potential for use in heavily forested 
areas. In this instrument, the time measurement is made 
at the peak of the return pulse which would correspond to 
the energy reflected by the ground. Experiments are being 
conducted at the present time to evaluate the potential of 
this new instrumentation as a possible tool for establish- 
ing vertical control in forested areas. 
AERIAL TRIANGULATION 
  
The mapping system described in the foregoing para- 
graphs includes instrumentation (horizon camera and Statoscope) d - 
which determine the tip and tilt of the aerial camera at the 
moment of exposure and give differences in elevation between 
exposure stations. This auxiliary data minimizes the require- 
ment for vertical control and permits the use of simple 
instruments such as the Wild B.8 for aerial triangulation. 
The application of horizon camera data and Statoscope 
to aerial triangulation has been described by the author in 
(9). 
It would appear that aerial triangulation by the method