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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.

Water content, water distribution and variations with time of these quantities in the natural snow cover are important parameters for microwave remote-sensing studies, snow stability investigations and snow hydrology studies. The most promising method for snow wetness determination is the measurement of the dielectric constant at radio frequencies. Recent developments of electronic devices for long-term recording of snow wetness are reported. The measurement system consists of two parts: the tuning and display unit with the battery pack and the flat capacitive sensor. The system is controlled by a built-in low-power microcomputer, the operation frequency for the sensor is 20.00 MHz. Measurement data are displayed on an LCD and are also stored in a RAM; data transfer for a PC for further data processing is possible by a built-in V24 interface. Up to four individual sensors can be operated simultaneously. Field measurements of long-term variations in snow wetness during diurnal cycles and registrations of penetrating meltwater or rain-water waves with the formation of water shock fronts are presented.

No abstract

Water content, water distribution and variations with time of these quantities in the natural snow cover are important parameters for microwave remote-sensing studies, snow stability investigations and snow hydrology studies. The most promising method for snow wetness determination is the measurement of the dielectric constant at radio frequencies. Recent developments of electronic devices for long-term recording of snow wetness are reported. The measurement system consists of two parts: the tuning and display unit with the battery pack and the flat capacitive sensor. The system is controlled by a built-in low-power microcomputer, the operation frequency for the sensor is 20.00 MHz. Measurement data are displayed on an LCD and are also stored in a RAM; data transfer for a PC for further data processing is possible by a built-in V24 interface. Up to four individual sensors can be operated simultaneously. Field measurements of long-term variations in snow wetness during diurnal cycles and registrations of penetrating meltwater or rain-water waves with the formation of water shock fronts are presented.