Abs sn 
CIONES GMEELLIEESAae 0 — 
  
more the roughness of the densely packed pancake ice (Figure 1d, Sor 
Situation B) are responsible for a large increase in backsattering, 
followed by a decline as discussed above. var 
; prc 
At smaller nadir angles, the backscattering of the thick and Phy 
rough pancake ice does not change noticeably. However, the back- 
scattering of open water, and of the very thin ice increases 
strongly, thus reducing the contrast between ice and water, and 
leading to an inversion of contrast at nadir. 
CONCLUSION 
Both passive and active microwave signatures show very strong 
changes when new ice is forming on the open ocean surface. Where- 
as the passive signatures show a monotonic variation with increa- 
sing ice thickness, active signatures undergo non monotonic 
changes; indeed, the most extreme backscattering coefficients 
among all ice types can be found within the young sea ice. This 
variation is helpful in increasing contrast at the ice edge and 
in other regions of young ice as long as individual ice floes can 
be geometrically resolved with high resolution radar imagery. Ice 
concentration and classification may then be deriveable from the 
geometrical structure, more than from the tone,,of the imagery. 
The comptutional effort for obtaining this information will be 
very large. 
On the other hand, the monotonic variation of emissivities allows 
the application of mixed signature algorithms to passive micro- 
wave data. Quantities like ice concentration, multiyear ice 
fraction and perhaps even energy exchange rate may be derived 
from imagery with large footprints such as the Nimbus-7 Scanning 
Multichannel Microwave Radiometer. A simple algorithm for re- 
trieving ice concentrations from such data is being prepared on 
the basis of NORSEX emissivity measurements by the NORSEX arctic 
working group, (see also Kloster and Svendsen, 1982). 
Further experiments in other arctic regions and during other 
seasons have to be added. The signatures of other ice types 
(e.g. nilas) have to be added before algorithms can be generalized 
in space and time. 
REFERENCES 
Kloster K. and Svendsen E., "A Nimbus-7 SMMR Algorithm for Ice 
Mapping and its Application to the NORSEX Marginal Ice Zone Ex- 
periment", Christian Michelsen Institute, Report 821153-1, 
Bergen (1982). 
  
Maykut G.A., "Energy Exchange Over Young Sea Ice in the Central 
Arctic" J. Geophys. Res. 83, p. 3646-3658 (1978). 
NORSEX arctic working group, "The Norwegian Remote Sensing Ex- 
periment (NORSEX) in a Marginal Ice Zone", Report l1, (1981), to 
be published in Science. 
Peake W.H., "Interaction of Electromagnetic Waves with Some 
Natural Surfaces", IRE Trans. Antennas and Propagation, AP-7, 
p.8324-S329 (1959) (Special Supplement). 
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