SEA ICE CLASSIFICATION FROM INFRARED THERMOMETRY OVER 
THE NORTH WATER, WINTER 1980/81 
by 
KONRAD STEFFEN 
Departement of Geography 
Swiss Federal Institut of Technology (ETH) 
CH-8092 Ziirich Switzerland 
ABSTRACT 
This paper is a preliminary report on a sea ice remote sensing study 
carried out within the framework of a larger research project concerned with 
the so called North Water. The N.W. is a recurring polynya (an arctic sea ano- 
maly associated with a high percentage of young ice and open water) and one of 
the largest such phenomena in the Northern Hemisphere. The goal of the N.W. 
project is the study of the attributes of this polynya and of its modifying 
effects on the regional climate. 
To this end it is necessary to gather information on the spatial and 
temporal aspects of the sea ice distribution. So far such information has been 
available only for daylight conditions, i.e., for the Arctic summer. Presently 
there are no satellites in existence who produce high resolution imagery du- 
ring the dark season. Consequentely, data for the winter period were collected 
by low level altitude airborn remote sensing techniques. 
The author carried out six remote sensing flights at an altitude of 
300 m with a total profile length of 2300 km each. A Precision Radiation Ther- 
mometer (PRT-5) served to measure the thermal radiation emitted by the sea 
surface. To obtain additional pictorial information, the ground along the 
flight path was illuminated with a searchlight and filmed with a 16 mm movie 
camera. The brightness temperatures measured with the PRT-5 were subjected 
to a number of corrections to compensate for the emissivities of water, snow 
and ice surfaces, for the absorption by the atmospheric water vapour and for 
the multiple reflections of radiation between cloud bottoms and ground. The 
accuracy of the resulting data is estimated at +0.15°C. It was found that 
different sea ice types are associated with distinguishable surface tempe- 
rature levels and it is therefore possible to derive a sea ice classification 
from the thermal radiation measurements. 
A dominace of young ice and open water is observed along the Green- 
land coast at Wolstenholm Island, around Carey Islands,in Smith Sound and to 
the south of Coburg Island in Lady Ann Strait. In Lancaster Sound and Barrow 
Strait young ice occurs only in fractures. Water temperatures between 0 C and 
-] C were measured near Cape Alexander, around Wolstenholm Island and in Lady 
Ann Strait on different flight missions. In the northern Baffin Bay, the speed 
of ice movement is found to decrease from north to south. For the Lancaster 
Sound the relation between occurrence frequency of fractures (expressed in 
class percentages) and fracture width was investigated and found to be linear 
on a semi-logarithmic plot. 
Results of study of this nature may obtain a practical significance 
in view of the present developement of year-round arctic sea transport. 
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