Abstract.
Dependences of reflectivity and transmissivity of the fluffy and
fine-grained
snow layer on the layer thickness were measured at frequencies of 22.2; 37.5: 60
and 94 GHz. The measurements were performed under indoor conditions using
artificial "cold" illumination of the investigated snow specimens. The snow
specimens were loaded into cylindrical metal containers with a diameter of 0.2 m
and a length of up to 1 m. Two structures of fluffy snow with average values of
a bulk density of 0.2 ... 0.3, one fine-grained structure and one structure of
medium-grained snow were investigated. The experimental dependences of the
reflectivity and transmissivity on the layer thickness were approximated by the
Kubelka-Munch equations. The frequency dependence of the Kubelka-Munch
scattering coefficient is analyzed. It has been established that clusters of ice
particles that make up snowflakes can strongly influence on the intensity of
scattering. The effect of clusters is appeared as the anomalous frequency
dependences of the reflectivity of a semi-infinite snow layer and the Kubelka-Munch
scattering coefficient.
The anomalous effect is that, firstly, the reflectivity of the semi-infinite
layer of fluffy snow at a frequency of 22.5 GHz is higher than at 37.5 and 60
GHz, and secondly, the exponent of the frequency dependence of the
Kubelka-Munch
scattering coefficient is higher the higher the frequency of radiation. In the
case of Rayleigh scattering, the exponent of the frequency dependence is known
to be 4,
whereas
in the case of the fluffy snow it does not exceed a value of 3 even in the 60 to
94 GHz range.
Key words:
dry
snow cover, thermal emission, microwaves,
backscattering, frequency dependence, clusters.
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