The high frequency radiometer, on the other hand, has a much better 
  
; 2 ; o ; 
resolution but it requires surface temperatures below -10 C if 
ice thicker than about 40 cm is to be measured. 
The passive microwave radiometer also gave certain indications of 
its capabilities for ice roughness mapping. 
5.1.5 IR-scanner 
The use of infrared thermography was tested by means of an airborne 
infrared line scanner. The thermal radiation from the ice surface 
was recorded in the 8-14 yum region simultaneously on photographic 
film and magnetic tape. 
The IR-scanner showed clear distinction between thick ice (bare 
or snow-covered) and thin new ice/open water. With appropriate 
processing also thin new ice could be differentiated from open 
water. The ice concentration therefore can be obtained from IR- 
scanner registrations with a high degree of accuracy. 
The IR-scanner gave some indications as to the areal distribution 
of deformed ice. The radiance temperature of the ridges differed 
from the surrounding level ice. The differences, however, will 
depend on the weather and the temperature history. 
The IR-scanner may give rough information on the relative thickness 
of the bare level ice. 
As regards the state of the ice surface, the IR-scanner could 
distinguish snow-covered ice from bare ice, and that is of interest 
both for navigation and for ice forecasting. 
The area coverage of the IR-scanner depends on the scanning angle. 
At an altitude of 5,000 m, a maximum coverage of 17.5 km was 
obtained with a resolution of better than 10 m.