Various instruments and techniques for the determination of snow wetness, for example calorimeters, centrifuges, chemical devices, dielectric devices and also tensiometers are in use. Problems in measuring the liquid water content with these techniques are discussed by Colbeck (1978). Dielectric measuring methods of liquid water content in snow make use of the large difference between the relative permittivity of ice (3.15) and of water (87.7) in the high-frequency regime. Various dielectric devices using air gap condensers and open resonators have been tested and compared recently (Denoth and others 1984). Here, new developments of dielectric sensors with operating frequencies in the range of 10 MHz to 1 GHz are presented: a plate condenser, a cylindrical condenser, a coaxial sample holder and a monopole antenna were used as sensors to measure the average dielectric constant in a snow volume of approximately 1000 cm³; a flat condenser in strip-line technique - which is the two-dimensional analogen of the plate condenser - was used as sensor for measuring the dielectric constant of thin snow layers. A sensor consisting of a combination of two flat condensers has also been developed. The geometry (spacing and width of the two coplanar conducting stripes) has been designed to allow the measurement of the vertical gradient in the dielectricl properties of a snow cover (Foglar 1983). The sensor is operated at 27 MHz. Neglecting the effects of snow texture and liquid water distribution, the dielectric constant of snow is a linear function of density and a quadratic function of the volumetric water content (Denoth and others 1984): snow wetness can, therefore, be calculated from the measured dielectric constant and the snow density.

The Austrian “Fonds zur Forderung der wissenschaftlichen Forschung” is thanked for supporting these developments through Grant nos 3888 and 4525.