require any ground stations. It controls flight on a pre- 
determined direction, overlap between flight lines and 
triggers the aerial camera, thus giving a fixed distance 
between exposures. 
As the name indicates, this equipment uses the 
Doppler principle. Four beams or pencils of radiation are e e 
directed downward from the aircraft. Two are transmitted 
forward and two backward in an X-shaped pattern. These 
pulses are reflected from the ground back to the aircraft 
and frequency changes are measured. Drift angle and ground 
speed are computed from these frequency changes. The data 
from the Doppler is computed and presented visually to the 
pilot. 
The Doppler navigation system includes a course e e 
and distance computer, compass and a specially designed 
computer to track the aircraft on a set course. 
MAPPING SYSTEM 
  
The mapping system which satisfies the requirements 
discussed in the foregoing paragraphs and which has a proven 
performance record on projects in Canada, Africa and South 
America consists of the following: