(0.49g/cm3), thickness of refrozen crust (increase from 1 to 6.5cm), volumetric liquid-water
content of the underlying layer (2.1%), and resulting heat loss of the snowpack (about
15W/m 2 ).
In a second example, which was observed in the evening of March 10, 1986, the 1.4m deep
snowpack was almost completely dry with the exception of a slightly humid layer at 2 to 10 cm
below the snow surface. We observed the decrease of the brightness temperatures due to the
refreeezing of the humid layer, which allowed the determination of the snowpack transmissivity
as a function of time. At 4.9 and at 10.4 GHz, the data indicated that the freezing rate was
0.12mm/h (or 120g water/m 2 /h) in agreement with the thermodynamic estimate based on
changes of the snow-temperature measurements. A larger value was estimated from the
21GHz data. A possible explanation for this discrepancy is an uncertainty of the frequency
dependence of the dielectric loss factor of slightly wet snow, especially if the density is low.
For a better quantification of the influence of structural and physical snow parameters we star
ted new work in cooperation with the Swiss Federal Snow and Avalanche Research Institute
on Weissfluhjoch in the snow season 1993-94. On the modelling side this work is supported by
a cooperation with Sylviane Surdyk, 'Laboratoire de Glaciologie et Géophysique de
l'Environnement' of the University of Grenoble. The experimental setup consists of portable
radiometers at frequencies of 11, 21, 35 and 48 GHz, and a further instrument at 94 GHz is
under construction. These radiometers are operated from a sledge-like platform, 1.5m above
the snow surface. In this way the snow samples to be investigated can be exactly positioned in
front of each sensor. First results were presented.
References
Màtzler C., E. Schanda and W. Good (1982) Towards the definition of optimum sensor specif-
cations for microwave remote sensing of snow, IEEE Trans. GE-20, 57-66.
Màtzler C. (1987) Applications of the interaction of microwaves with the natural snow cover,
Remote Sens. Reviews, 2, 259-391.
Màtzler C: (1994) Microwave signatures of landscapes in winter, Meteorology and Atmosphe
ric Physics, special issue on Physical Retrieval of Hydrological Variables from Space-Based
Microwave Measurements, in press.
