RE A 
  
  
  
  
  
  
  
-19- 
OUTLOOK 
It is beyond any doubt that advanced navigation instrumentation can have 
great merits for aerial survey, in the near future. 
The major de-merit inherent to this type of instrumentation is the 
fact that it is subject to error propagation. 
. With doppler, this error propagation is a function of the distance 
and of the number of turns between photo flight lines. 
. With INS, this error propagation is a function of the time. 
Basic improvements can be obtained if the systems can be updated (0 
7 
N 
in short intervals by means of "fixes". 
This is possible by means of 
. visual fixes (only in case they are available) 
. DME (only where available) 
. VLF (limited in accuracy) 
. Satellite-doppler fixes (not yet available in flight) 
The most promising outlook, for precision survey navigation and 
airborne sensor orientation, is offered by the efforts to establish 
the NAVSTAR Global Positioning System (17) and to have this integrated 
with an advanced inertial photogrammetric system. 
(9 
A time schedule of this outlook is presented in figure 10.