The SLF Snow Sensor uses a capacitive sensor, which generates an electrical field that permeates the snow. Depending on the fractions of ice, air and water within the permeated snow volume, the measured capacitance changes, as ice, air and water have different dielectric properties.
For dry snow (absence of liquid water) the snow density can be directly deduced. To determine the LWC, the ice fraction (dry snow density) of the snow must be known.
The capacitive sensor forms an oscillator together with a quartz crystal. A change of the capacitance forces a frequency change in the oscillator. Measurements on materials with known dielectric properties (air, PTFE) provides the linear ε – Δf relation represented by the calibration factor k. Reference measurements (weighted volumes, LWC dilution method) on snow with varying densities and wetness give the ρ – ε relation function (Eq. 1) as well the LWC – Δε relation function (Eq. 2) expressing the increase of ε by liquid water within snow of a certain density.