2.3 The Xth International Congress in Lisbon, 1964 
In a paper entitled "The Application of Aerial Photo Interpretation 
in the Scientific Field of Ice met at Sea" by Ragnar V.A. Thorén, 
prepared as an Invited Paper to the ISP Commission VII at the 
World Congress in Lisbon, September 1964, the author stated: 
"Synoptic ice data, accurate ice charts, and reliable ice forecasts 
are of great value for the navigator." 
He further said: "In developing a true knowledge of the ice condi- 
tions, air photo interpretation generally offers the specialist 
an invaluable aid. Useful for the purpose are verticals as well 
as obliques (see for example the obliques in Fig 2 and 3), both in 
colour and black-and-white. 
The photos may be taken with ordinary air reconnaissance cameras, 
with a three-camera arrangement for trimetrogon photography, giving 
horizon-to-horizon coverage, or with precision-built high-resolution 
cameras, employing scanning principles to obtain successive 180° 
panoramic photographs. They may also be photographed from radar 
or TV-screens. Presumably, radar photography will be used more 
and more for collecting ice data, and the improvement of suitable 
radar sets, e.g. side-looking radar, may be expected." The remarkable 
evolution of the remote sensing technique during the last 14 years 
has confirmed the author^s presumption.