According to a report on "IR-scanner results" by Erik Fagerlund 
and Gunnar Lundholm (at the Research Institute of National Defence), 
Stockholm 1976, the field experiment "SEA ICE 75" has shown that 
thermal infrared sensing can be used to differentiate ice from 
water and new ice from old, thicker ice. The thermal imagery has a 
much better capability than visual imagery in differentiating new 
ice and open water. Special features, such as rafting patterns, 
ridges and cracks, are correlated to thermal variations and can be 
detected and identified in the thermal image. Tape recordings are very 
useful for studying the objects in detail. 
Whenever weather and light conditions permit, it is of great value 
if aerial photographs could be taken simultaneously with the thermal 
recordings. The thermal sensing technique itself is, however, in- 
dependent of illumination and can be used day or night. The weather 
dependence is less than for the visual and photographic techniques, 
but clouds or heavy fog cannot be penetrated. 
The SEA ICE 75 clearly demonstrated that a future ice mapping 
system will have to include a combination of sensors if all the 
required ice parameters are to be mapped. 
The choice of sensors and carriers will depend on the actual 
requirements and the general layout of the total ice mapping and 
ice surveillance system. The two major requirements are: 
l. To provide the ice-breaker units with real-time information on 
the ice situation within say 20-50 km ahead of the ice-breaker. 
This is required in order to find the immediate safest and most 
economic route through the ice. 
2. To provide an overall picture of the situation in the whole 
Baltic area. This is required for the preparation of reliable ice 
maps and ice forecasts, which are needed by the Ice-breaking 
Service when planning the operations of ships and ice-breakers for 
the next days. 
For the short range operations of ice-breakers, the ship's radar 
is an obvious component. In addition the helicopters stationed on 
board the ice-breakers could profitably be equipped with suitable