MICROWAVE SIGNATURES OF YOUNG SEA ICE AND ITS 
INFLUENCE ON ICE CONCENTRATION ALGORITHMS 
Christian Mätzler 
Institute of Applied Physics 
University of Berne 
Switzerland 
ABSTRACT 
Passive and active microwave signatures show large variations when 
new sea ice is formed in the marginal ice zone. Whereas the 
emissivities increase monotonically with increasing ice thickness I 
as a result of decreasing surface wetness, no monotonic change is Td 
found for backscattering coefficients due to the strong influence I 
of the surface roughness. Therefore, passive sensors are prefer- 
able for ice concentration algorithms. The changes in signatures 
from open water to the typical first-year ice signature take 
place within the first few cm of ice thickness. These results are 
based on measurements of microwave signatures made from icebreaker 
based instruments during the Norwegian Remote Sensing Experiment 
in 1979. 
  
1. INTRODUCTION 
The microwave signatures are emissivities and backscattering co- | 
efficients as defined by Peake (1959). Both, passive and active MIU 
microwave remote sensing show high contrast between open and ice- | 
covered ocean surfaces. Together with the all weather and day and 
night capability of microwaves, this contrast makes the microwaves 
the most promising spectral band for remote sensing of sea ice. UM 
In order to assess the accuracy with which ice concentrations can Ii 
be retrieved, it is necessary to study the signatures of all types | 
of ice present, and to select those sensors which show a monotonic | 
transition of the signature when ice is growing in thickness from | 
open water to thick first year ice. I 
| 
  
  
In addition, the critical ice thickness at which a signature is 
half way between open water and thick ice should correspond to the Il 
critical thickness of the remote sensing application discipline. I 
For instance, in climatology sea ice is important for reducing the Il 
energy exchange between ocean and atmosphere; the thickness at ll 
which the energy exchange rate is reduced to one half is between ll 
5 and 10 cm (Maykut 1978). Therefore, an optimum heat exchange 
sensor should have a critical thickness in the cm range. 
  
  
Microwave signatures were measured mostly from aircraft, and also Il 
from sea ice platforms. In the first case, the investigation 
suffered from the lack of in situ observations, and in the latter 
case the investigation was limited to thick ice. During the Nor- 
wegian Marginal Ice Zone Experiment (NORSEX), Sept.-Oct. 1979, 
north of Svalbard, a multi-frequency (4.9, 10.4, 21, 36, 94 GHz) 
radiometer and a 10.4 GHz scatterometer installed on the Norwegian 
icebreaker "Polarsirkel" was used to obtain surface-based micro- 
wave signatures together with in situ observations of the objects. 
In addition to thick multi year ice, the experiment allowed to 
make measurements on open water and on freshly formed sea ice 
near the marginal ice zone. (NORSEX arctic working group, 1981). 
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