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Photographic Flights 
  
(a) Navigation 
Flights in already developed and mapped territories do not present partic- 
ular difficulties from the navigational point of view. By using various visual and 
instrumental navigational aids it is not too difficult to perform parallel flights 
with the required photographic side overlap. However, precise navigation becomes 
a serious problem when flights are carried out over featureless areas or over 
unmapped countries. 
Doppler, a device to continuously measure changes in the drift angle and 
the ground speed of the aircraft, is very helpful here. The accurate control of the 
drift angle is particularly useful in maintaining the parallelism of adjacent strips. 
The other component supplied by Doppler, the ground speed, could be used for the 
scale determination, but the accuracy as yet provided by the Doppler system is 
not sufficient for this purpose in regular topographical mapping projects. 
By reducing to a minimum the need for visual navigation and by increasing 
the navigational accuracy, Doppler may contribute greatly towards a more facile 
and more economical mapping of larger areas. 
As for the electronic means used for locating aircraft at the moment of 
exposure of survey photographs, the situation has not changed much during the 
past four years. The systems used are quite complex and expensive, but they 
offer some solutions under particularly difficult circumstances or when the rapid 
execution of provisional maps is required. 
The use of the radar profile method is becoming increasingly important. 
The operational range has been extended upto 9000 m above sea level by success- 
ful instrumental modifications. The radar profiles are being used in two different 
ways: as auxiliary data for the determination of distances and elevations in the 
aerial triangulation process, and as ameans for determining only spot elevations 
and profiles. In the latter case, the profiles can be flown at a lower altitude and 
without simultaneous survey photography. 
The performance and importance of the radar profile technique may be 
best characterized by the fact that the use of radar profiles has been considered 
in the larger geophysical surveying projects in connection with gravimetric 
determinations. 
(b) Survey photography 
Although a prototype of the superwide-angle camera was exhibited at the 
VIIIth International Congress in Stockholm, not much practicaluse has been made 
of this new and important element in photogrammetric mapping. This situation 
has been caused partly by successive changes in the originaldesign of the Super- 
Aviogon lens and by the limitation in the number of plotters that can use super- 
wide-angle photography.