SOMMER SPA-2, Руководство пользователя

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6 How does the SPA-2 work?
A snowpack has strong spatial variability and transforms considerably over time. The evaluation of
snow properties and the assessment of snow conditions mostly relies on spot observations. The
snow pack analyzer SPA-2 breaks this limitation and provides information about the snow pack by
measuring the dielectric properties of a large snow volume. It provides all relevant snow properties
like snow depth, snow density, snow water equivalent as well as the contents of liquid water and
ice.
Snow consists of ice, water and air, which have distinctly different dielectric properties. By meas-
uring the complex impedance along a ribbon sensor (SPA-sensor) at two different frequencies, ice,
water and air can be distinguished and their relative volume contents can be determined.
Additionally, snow depth is measured with a USH-9, Sommer’s ultrasonic level sensor. With this
information, snow density and snow water equivalent (SWE) can be calculated. In
Figure 4 the cross
section of SPA-sensor and its surrounding electric field is illustrated.
Figure 4 Measurement principle of SPA-sensor
The SPA-sensors are 60 mm wide, reinforced rubber ribbons containing three parallel copper wires.
As soon as an alternating current flows through the wires, an electric field builds up that penetrates
up to 4 cm into the surrounding snowpack.
The 4.8-m long ribbons are stretched onto a supporting frame at different heights either hori-
zontally or in a sloping angle.
The USH-9 ultrasonic level sensor is mounted on the mast of the supporting frame to record the
snow height, which is required to determine the snow coverage of the tilted SPA-sensor and to cal-
culate the snow water equivalent.
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20 Manual