I n s t r u m e n t s

a n d

M e t h o d s

Fig.4. Experimental setup for reflection measurements (left) and a block diagram of the instrumentation for the microwave X and K- band. SO:
sweeper oscillator, VM: vector-volt-meter, r/t port: adapter forreflection/transmitting measurements, ref: reference signal, bus:IEEE bus, TH:
transmitting horn antenna, RH: receiving horn antenna, r: reflected signal.

Thedielectricfunction ofsnowwithdifferentstagesof
metamorphism, and different amounts of liquid water has
been measured in the frequency rangefrom 20 MHz up to
16GHz.Capacitiveflat-platesensorshave been usedin
theradio-frequencyrange of20-40MHz,themono-pole
sensor has been appliedin the rangefrom 100 MHz up to 3
GHz,andintheX/K-bandsreflectionmeasurementsof
electromagnetic waves on a smoothed snow surface have
been made using the free-space technique. Measurements
have beendoneinsitu on anatural snowcover in theStubai

Alps ([!]3000 ma.s.l.) and at the Hafelekar ([!]1900m a.s.l.)
near Inns-bruck, Austria. Snowwetnesshas beenmeasured
byfreezingcalorimetry;andsnowdensityhasbeen
measured simply by weighing a known volume ofsnow.
Snowporosityhasbeencalculated fromthevolumetric
liquid water content Wand snow density. The experimen-
tally found relation between snow mission.
Incremental permittivity E (real part),snow liquid wa-
tercontent W (volume basis),and frequency of sensorop-
eration is shown in Fig.5 as a 3-D wetness calibration plot

on a logarithmic frequency scale.E, the incremental per-
mittivity,is defined as:

E =e '(wet)e'(dry) e'(wet) is the(measured)dielectric functionof wet snow,

e'(dry) is the (calculated) dielectric function of snow with
the same porosityF:

e' (dry) = 1 + 1.76 (1-F) + 0.37 (1- F )2 For practicalreasons - and acceptinga slightly reduced

accuracyindeterminingsnowwetness-theveryweak
effect ofwatergeometry on the snow dielectric function
has been neglected, and it results a simple quadratic rela-
tion between snow wetness W (in % byvolume) and in-
cremental permittivity:E =a W +ßW² ,wherebythe pa-
rametersaandßdepend onthe actual frequencyf'of
sensoroperation:

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