Abstract
Measurements of material moisture are essential in fields such as agriculture or civil engineering. Electromagnetic techniques, more precisely dielectric methods, have gained wide acceptance in the last decades. Frequency or Time Domain methods take advantage of the high dielectric permittivity of water compared to dry materials. This paper presents four new dielectric sensors for the determination of soil or snow water content. After a short introduction into the principles, both the hardware and operating mode of each sensor are described. Field test results show the advantages and potentials such as automatic measurement and profiling, state-of-ground detection or large-scale determination. From the results it follows that the presented sensors offer promising new tools for modern environmental research.
Highlights
In nature and in many industrial processes, soil or material moisture is an important criterion and has great influence on natural and production processes
Since the majority of the different SOG is mainly influenced by the moisture and show characteristic dielectric properties, we suggested to use the Frequency Domain (FD) techniques to design a measurement sensor and device that is capable to determine the different states by a capacitance measurement
Several access tubes of the LUMBRICUS system were installed in the barrier to monitor the change in water content within the different layers and several vertical moisture profiles were recorded
Summary
In nature and in many industrial processes, soil or material moisture is an important criterion and has great influence on natural and production processes. EM moisture measurement methods are so-called indirect methods that determine an electrical property which is closely related to the water content of the material, such as the electrical conductivity (EC) or the dielectric permittivity. TD methods, on the other hand, use signals with a transient character, confering a pulse-like time shape on the EM field. Both devices and analyzing techniques of these two methods differ significantly and are explained in more detail in the following. TDR estimates the bulk dielectric permittivity, b, of the soil mixture (soil matrix, soil water and air) by measuring the propagation time of an EM pulse, generated by a pulse generator and containing a broad range of different measurement frequencies.
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