Different dielectric sensors for measuring the liquid water content of snow are compared and described in detail. The instruments make use of the significant difference in the dielectric properties of ice and liquid water at radio frequencies; they are operated with frequencies ranging from 1 MHz up to 1.3 GHz. Plate condensers in connection with ac bridges are used as sensors in the frequency range up to 100 MHz whereas open resonators are used in the GHz regime. Test measurements with the different sensors on homogeneous samples like dry sand and mixed and prepared snow showed the same results for the dielectric constant: the discrepancies are less than 1%. In the natural, inhomogeneous snow cover, the special properties of the different sensors appear. Snow wetness is calculated from the measured dielectric constant and the snow density using the model of Polder and van Santen. The comparative field measurements were made with Alpine snow in the Stubai Alps in Austria.
A flat condenser in strip-line technique has been developed to measure the gradient in liquid water content near the snow surface. This dielectric sensor is connected to a twin-T -bridge with an operating frequency of 27 MHz. The special design of the sensor allows the non-destructive measurement of the mean dielectric constant of underlying material at two different depths of 0 to 2 cm, and of 2 to 4 cm below the snow surface. Based on the model of Polder and van San ten, changes in the gradient of liquid water content can be calculated from measured changes in the dielectric constant in different depths; the density has to be measured separately . Results of measurements of wetness gradient with this flat capacitative sensor are given. Field measurements have been carried out in the Stubai Alps (3100 m a.s.l.) and at the Hafelekar (2256 m a.s.l.) near Innsbruck.
A flat condenser in strip-line technique has been developed to measure the gradient in liquid water content near the snow surface. This dielectric sensor is connected to a twin-T -bridge with an operating frequency of 27 MHz. The special design of the sensor allows the non-destructive measurement of the mean dielectric constant of underlying material at two different depths of 0 to 2 cm, and of 2 to 4 cm below the snow surface. Based on the model of Polder and van San ten, changes in the gradient of liquid water content can be calculated from measured changes in the dielectric constant in different depths; the density has to be measured separately . Results of measurements of wetness gradient with this flat capacitative sensor are given. Field measurements have been carried out in the Stubai Alps (3100 m a.s.l.) and at the Hafelekar (2256 m a.s.l.) near Innsbruck.
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