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Forsensoroperationfrequencies exceeding [!]4GHz,the
sensitivity of snow dielectric functionto changes in liquid
watercontentdecreasessignificantly.So,forpractical
reasons, it is suggestedto operatedielectricwetnesssensors
at frequencies lower than approximately 3 GHz.
As a practical field application of these sensors a com-
parativemeasurementofaverticalwetnessprofileofa
naturalsnowcoverisshowninFig.6.:Alpinesnow
(Hafelekar near Innsbruck, [!]1900 m a.s.l, 03 96), 142 cm in
depth, and density ranging from 0.4 g/cm3on top to [!]0.54
g/cm3at the bottom. Due to the relative low spatial resolu-
tion of the monopole antenna, datapoints have been taken
only every 15cm (monopole probe and capacitivesensor)
and are compared to calorimetric wetness measurements.
Reflectionmeasurementsusingthe free-space technique
havebeenmadeat0ºincidenceangleandatafixed
frequencyof 8 GHz. Althoughhigh-gainhorn antennashave
been used,the spatialresolutionis low, so, data pointshave
been taken only with a 30 cm spacing.
The measurements of snow wetness with the capacitive
and monopole probes and the freezingcalorimeter show a
satisfying aggreement. The increase insnow wetness at the
87-cm level may be due to a high-density snow layer with
a thin icycrust.Due to the significantlylargersphere of
influence of the free-space technique, measurement with
thehornantennas giveameanvalueofsnowwetness,
averaged overanarea ofapproximately30x30cm2 .So,
measurements with the horn antennas may deviate from
measurementswith theother sensors; thisis especiallytrue
at regions with high variability in snow wetness.
REFERENCES
Achammer, Th. and A. Denoth, 1994. Snow dielectric proper-
ties: from DC to microwave X-band. Annals of Glaciology, 19,
pp 92
Colbeck,S.C., 1978.The difficulties of measuringthewater
saturationandporosityof snow.J. Glac.,20, pp 89
Denoth,A.,1994.Snowliquidwatermeasurements:Meth-
ods,Instrumentation,Results.
Proc.Symp.Snowand RelatedManifestations,Manali,H.P.,
India,pp 150
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